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Circum-Caribbean Granitoids: Characteristics and Origin
International Geology Review
Abstract
Caribbean granitoids occur among a series of widespread magmatic arcs that developed during a period of major oceanic plate convergence and subduction that began in Late Cretaceous time. Evaluation of Caribbean granitoids reveals that two main suites of granitoids are widespread. Low-K granitoids, including gabbro, diorite, quartz diorite, tonalite, and trondhjemite, comprise one of these suites. The second main type is distinctly more potassic and consists primarily of quartz monzodiorite and granodiorite, but also includes monzodiorite, quartz monzonite, and granite. Both groups contain rocks that are transitional to the other group. The granitoids are part of an extensive Caribbean calc-alkaline assemblage that includes low-K, medium-K, and high-K rocks. Island-arc tholeiitic and normal-K calc-alkalic compositions reflect geochemical continua within the orogenic granitoids. The granitoids (including low-K rocks) lie within the calc-alkaline field on FeOT/MgO and AFM diagrams. Alkali-lime indices generally correlate with potassium content, the low-K varieties being calcic (tholeiitic) and the higher K rocks being calc-alkalic.
... Whole rock geochemical data for the associated Late Cretaceous calc-alkaline intrusive rocks of the Greater Antilles exhibit low-K, medium-K and high-K signatures even in a single intrusive complex (Kesler et al., 1975;Lidiak and Jolly, 1996). Most radiometric dates published for plutonic rocks associated with porphyry copper mineralization in the Greater Antilles (Hollister, 1978;Kesler, 1978) are K-Ar dates from the 1970's. ...
... The Memé and Casseus copper-gold skarn deposits of Haiti (Fig. 3A) are found in limestone pendants within the Terre Neuve intrusion, a composite calc-alkaline pluton of medium to high potassium content (Lidiak and Jolly, 1996) with quartz monzonite, granodiorite and quartz diorite phases (Kesler, 1968;Harnish and Brown, 1986). Production dates back to the early 1700's; neither mine is currently active. ...
... Terre Neuve intrusive rocks lie along a northwest trending structure in the Terre Neuve Massif separate from the Massif du Nord to the north. These intrusive rocks are distinctly more K-rich and have a higher content of largeion lithophile elements (LILE) than those of the western Cordillera Central and Massif du Nord (Lidiak and Jolly, 1996). Their compositions are similar to plutonic rocks from central and eastern Jamaica, central Cuba and the Nicaraguan Rise (Lewis et al., this volume (1980)(1981)(1982)(1983)(1984)(1985)(1986)(1987)(1988)(1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999) 70.6 Mt at 3 g/t Au, 15.8 g/t Ag, 0.06 % Cu High sulfidation, under construction Ruiz (1997), Smith et al. (2008), Nelson (2000a, b) Grand Bois, Haiti none 4.5 Mt at 2.3 g/t Au High sulfidation Louca (1990), Sillitoe et al. (1996) Morne Bossa, Haiti none 2.0 Mt at 2.25 g/t Au High sulfidation Louca (1990), Sillitoe et al. (1996) Candelones intrusions (Kesler and Fleck, 1967), younger than most K/Ar and Ar/Ar dates for intrusive rocks in the Massif du Nord and Cordillera Central Escuder-Viruete et al., 2006). ...
The Greater Antilles host some of the world’s most important deposits of bauxite and lateritic nickel as well as significant resources of gold and silver, copper, zinc, manganese, cobalt and chromium. Beginning in Jurassic time, sedimentary exhalative base metal deposits accumulated in marine sedimentary rift basins as North and South America drifted apart. With the onset of intraoceanic subduction during the Early Cretaceous, a primitive (tholeiitic) island arc formed above a southwesterly-dipping subduction zone. Podiform chromite deposits formed in the mantle portion of the supra-subduction zone, directly above subducted Proto-Caribbean oceanic lithosphere. Within the nascent island arc, bimodal-mafic volcanogenic massive sulfide (VMS) deposits formed in a fore-arc setting; mafic VMS deposits formed later in mature back-arc basins. The Pueblo Viejo gold district, with five million ounces in production and twenty million ounces in mineable reserves, formed at 108-112 Ma, in an apical rift or back-arc setting. By Late Cretaceous time, calc-alkaline volcanism was well established along the entire length of the Greater Antilles. Volcanogenic massive sulfide and shallow submarine VMS deposits characteristic of the primitive island arc gave way to porphyry copper and epithermal precious metal deposits typical of the mature island arc. Oblique collision of the Greater Antilles with North America began in the Late Cretaceous in Cuba and migrated eastward. Orogenic gold and tungsten deposits that formed during the collision event are preserved in ophiolites and in metamorphic core complexes. Since the Eocene, regional tectonism has been dominated by strike-slip motion as the North American continent pushes westward relative to the Caribbean Plate. Large deposits of lateritic nickel-cobalt formed during Eocene and younger weathering and supergene enrichment of ultramafic rocks. Bauxite deposits formed by mobilization and precipitation of aluminium derived from volcanic intervals within a carbonate platform of Eocene to Miocene age.
... The three Nicaraguan rocks fall into the category of calc-alkaline granitoids according to the alkali-lime index the most widely used criterion for classifying granitoid rocks (e.g.,Brown, 1982;Brown et al., 1984). With their relatively high K content they are similar to the Above Rocks and Terre Neuve intrusions, and lie in the high-K field in a K 2 O-SiO 2 plot for Caribbean granitoids (Lidiak and Jolly, 1996). In this way they contrast strongly with the low-K calcic group of granitoids as found in the Cordillera Central-Massif du Nord of Hispaniola and the intrusive rocks of Paleogene age from the Sierra Maestra of Cuba (Lidiak and Jolly, 1996;Kysar Mattietti, 2001;RojasAgramonte, 2004). ...
... With their relatively high K content they are similar to the Above Rocks and Terre Neuve intrusions, and lie in the high-K field in a K 2 O-SiO 2 plot for Caribbean granitoids (Lidiak and Jolly, 1996). In this way they contrast strongly with the low-K calcic group of granitoids as found in the Cordillera Central-Massif du Nord of Hispaniola and the intrusive rocks of Paleogene age from the Sierra Maestra of Cuba (Lidiak and Jolly, 1996;Kysar Mattietti, 2001;RojasAgramonte, 2004). Trace elements for the Nicaraguan Rise samples together with the available data for the Above Rocks, Terre Neuve and Sierra Maestra intrusions have been plotted on an N-MORB normalized multi-element diagram (Fig. 3). ...
... The Nicaraguan rocks show enrichment of the LREE compared with average chondrite (Fig. 4). La/Yb in the three Nicaraguan Rise rocks ranges from 5.9 to 11, typical of the calc-alkaline group of Caribbean granitoids (Lidiak and Jolly, 1996)Further insight is gained by plotting the data on a multi-element mantle normalized diagram (Fig. 5) andcomparing these data with two large groupings of arcrelated rocks taken from the study ofBrown et al. (1984). AsFig. ...
The Nicaraguan Rise is a major submarine structure of poorly known origin. Its lithologies have been studied from dredge hauls and land outcrops on the Greater Antilles and Central America and its structure from geophysical data. In this paper we present the first geochemical analyses for granitoids that were recovered during the 1970s from cores drilled on the Nicaragua Rise for oil prospecting. The three Nicaraguan Rise rocks are calk-alkaline granitoids, and lie in the high-K field for Caribbean granitoids similar to the Above Rocks, Jamaica and Terre Neuve, Haiti intrusions. All of these intrusions are considered to be of Late Cretaceous - Paleocene age. Key elements abundances - K, La, Ce, Nd, Hf, Zr and Sm - indicate that the three Nicaraguan Rise rocks present more affinity with mature oceanic arc rocks similar to other granitoids from the Greater Antilles rather than mature continental arcs. The Pb, Nd and Sr isotope data show no evidence of a continental component, thus indicating that the more eastern and northern submarine area of the Northern Nicaraguan Rise is not underlain by continental crust of the Chortis block. Although of similar age, the Nicaraguan Rise samples are different from the more depleted Cuban granitoids of the Sierra Maestra, though both show strong similarities in their 207Pb/204Pb composition. We postulate that the Northern Nicaraguan Rise was most likely a Caribbean oceanic arc system that may have interacted only at its margin with the continental blocks bounding the region to the west in the area of the Northern Honduran borderland.
... The published data for Palaeogene granitoid suites of the northern Caribbean realm were compiled and). summarized by Lidiak and Jolly (1996), and previous dating efforts in Cuba, based mainly on the K–Ar system, were summarized by Itturalde-Vinent et al. (1996) . The former authors described hornblendebearing granitoids from Puerto Rico (Fig. 1a), emplaced between 49 and 39 Ma, and normative minerals of these rocks plot in the fields of quartz diorite, tonalite, and granodiorite. ...
... The granitoid rocks in the Virgin Islands (Fig. 1a) constitute a medium-K suite, and Ar–Ar ages indicate emplacement between 37 and 42 Ma (Smith et al., 1998). The main rock types are gabbro, diorite, tonalite, trondhjemite and granodiorite (Lidiak and Jolly, 1996). The mineralogical composition is similar to granitoids in Puerto Rico and the Sierra Maestra. ...
... The mineralogical composition is similar to granitoids in Puerto Rico and the Sierra Maestra. The intrusive rocks on St. Martin (Fig. 1a ) are mainly mediumgrained quartz diorite stocks and plugs (Lidiak and Jolly, 1996). Normative compositions include tonalite, trondhjemite, quartz monzodiorite, granodiorite and granite, and K–Ar ages range from 37 to 28 Ma. ...
The Palaeogene volcanic arc successions of the Sierra Maestra, southeastern Cuba, were intruded by calc-alkaline, low-to medium-K tonalites and trondhjemites during the final stages of subduction and subsequent collision of the Caribbean oceanic plate with the North American continental plate. U–Pb SHRIMP zircon dating of five granitoids yielded 206 Pb/ 238 U emplacement ages between 60.5F2.2 and 48.3F0.5 Ma. The granitoids are the result of subduction-related magmatism and have geochemical characteristics similar to those of magmas from intra-oceanic island-arcs such as the Izu Bonin–Mariana arc and the New Britain island arc, Lesser Antilles. Major and trace element patterns suggest evolution of these rocks from a single magmatic source. Geochemical features characterize these rocks as typical subduction-related granitoids as found worldwide in intra-oceanic arcs, and they probably formed through fractional crystallization of mantle-derived low-to medium-K basalt. D 2004 Elsevier B.V. All rights reserved.
... Volcanic stratigraphy in the Virgin Islands concludes with predominantly fine-grained, felsic tuff of the Necker Fm, which was locally strongly metamorphosed by contact effects associated with the final major magmatic event in the northeast Antilles, intrusion of the calcalkaline Virgin Gorda Batholith. The plutonic rocks, ranging widely in composition from gabbro to adamellite and segregations of granitic pegmatite (Helsley, 1960;Donnelly and Rogers, 1980;Lidiak and Jolly, 1996), have Late Eocene radiometric ages ranging from 39 to 35 Ma (K/Ar, Cox et al. 1977 andVila et al., 1986;40 Ar/ 39 Ar, Rankin (2002), consistent with an Eocene age for the Necker Fm (Helsley, 1960). ...
... MORB-normalized incompatible trace element spectra reveal that Puerto Rican volcanic rocks, like Cretaceous lavas and associated plutonic rocks from other islands of the Greater Antilles (Donnelly, 1989;Lebron and Perfit, 1994;Lidiak and Jolly, 1996), are uniformly over enriched in LILE with respect to LREE, moderately enriched in LREE and Th, and strongly depleted in HFSE, all fundamental features of island arc associations (Fig. 9). The most depleted rocks in the northeast Antilles include the Water Island and Louisenhoj Fms in the Virgin Islands, which have normalized slopes ranging from slightly enriched to moderately depleted (Fig. 9). ...
Island arc basalts (IAB) in the Greater Antilles, dating between Albian and mid-Eocene time (~112 to 45 Ma), consist of an early low-K, primitive island arc (PIA) basalt series and a later, predominantly intermediate calcal-kaline (CA) series. The rocks resemble modern sediment-poor, low-light rare earth element (LREE)/heavy rare earth element (HREE) arc basalts from intra-oceanic tectonic settings and sediment-rich, high-LREE/HREE types from continental margin arcs, respectively. Isotope and incompatible trace element distribution along a 450 km segment of the arc in the northeast Antilles demonstrates that low-LREE/HREE basalts predominate in Albian to Santonian (~85 Ma) stratigraphic sequences in the Virgin Islands (VI) and northeast Puerto Rico (NEPR), while there is a gradual but spectacular increase in both LREE/HREE and absolute abundances of incompatible elements in central Puerto Rico (CPR). Northeastern Antilles basalts have consistently elevated La/Nb and relatively low Nb/Zr, both inconsistent with the presence of a significant ocean island basalt component. Hence, observed differences are interpreted to reflect variation in proportions of pelagic sediment subducted by the south-dipping Antilles arc system as it swept north-eastward across the Caribbean region and eventually approached the Bahama Banks along the south-eastern fringes of the North American Plate. Trace element mixing models indicate sediment proportions in VI and NEPR were limited, averaging considerably below 1.0%. In comparison sediment content in CPR increased from an average slightly above 1.0% in Albian (~112 Ma) basalts to as high as 8% in Cenomanian (100-94 Ma) types. Hypothetical pre-arc pelagic sedimentary facies in the subducted proto-Atlantic (or proto-Caribbean) basin, included 1) a young, centrally located longitudinal ridge-crest facies, with a thin sediment cover, eventually subducted by VI and NEPR, 2) a slightly older basin-margin facies of variable width and moderate sediment thickness, subducted by CPR during Albian time, and 3) a thick, pre-arc continental margin facies in the vicinity of Central America, subducted by CPR during Cenomanian time. Following collision of neighboring Hispaniola with the Bahamas sediment budgets in the northeast Antilles stabilized at moderate levels from 2 to 3%, reflecting widespread subduction of North Atlantic Cretaceous pelagic sediment (AKPS).
... High heatflow is observed in the Aves ridge, the Grenada Basin and the active Lesser Antilles volcanic arc (Clark et al., 1978;Epp et al., 1970;Manga et al., 2012;Nason & Lee, 1964;Vacquier & von Herzen, 1964). High heat-flow is associated to the volcanic arc, up to 250 mW/m 2 (Clark et al., 1978) Along the Greater Antilles arc, arc magmatism was only active until early to middle Eocene in eastern Cuba and Hispaniola and middle Eocene in Puerto Rico (Lidiak & Jolly, 1996). In Cuba and Puerto Rico, the average heat-flow is low, 30-50 mW/m 2 (Anderson & Larue, 1991;Cermak et al., 1984Cermak et al., , 1991. ...
Heat‐flow in the Caribbean is poorly known and generally low in the major basins and the Greater Antilles arc, but with some high values in active zones, like in the Cayman trough or in the Lesser Antilles Arc. Here we present new heat‐flow data for offshore Haiti, which is part of the Greater Antilles arc. We obtain new heat‐flow estimates from in situ measurements and Bottom Simulating Reflector (BSR). Both methods suggest a regionally low heat‐flow, respectively 46±7 mWm‐2 and 44±12 mWm‐2, with locally high values exceeding 80 mWm‐2. The high heat‐flow values are generally located near faults, and could be related to fluid circulations. Our study confirms a low heat‐flow pattern at the scale of the Caribbean but points out the existence of local‐scale variability with high heat‐flow along the northern faults of the Caribbean region.
... However, the tectono-magmatic record in the Western Cordillera has been barely studied (Kerr et al., 1997;Montes et al., 2015;Villagómez et al., 2011), with most of the discussions limited to the temporal similarities with the coeval Panamanian rocks. There, a more extensive geochronological and geochemical database is available, which has been recently discussed in terms of long-term arc evolution (Buchs et al., 2010;Farris et al., 2017;Lidiak and Jolly, 1996;Lissinna, 2005;Montes et al., 2012aMontes et al., , 2012bRamírez et al., 2016;Wegner et al., 2011;Whattam et al., 2012;Wörner et al., 2009). Moreover, the geodynamic significance and origin of coeval arc-related rocks exposed in the Western Cordillera of Ecuador (e.g. ...
The northern Andes of Colombia comprise two non-cogenetic Paleogene arcs formed in contrasting geodynamic settings including continental and oceanic domains. New whole-rock geochemistry and isotopic constraints, together with a review of 332 geochemical, 76 isotopic and 204 geochronological data from Paleocene to Eocene volcanic and plutonic rocks exposed in central and western Colombia and Panama, are used to evaluate cause-effect relations between regional plate kinematics and the spatio-temporal distribution of the circum-Caribbean magmatic arcs. Short-lived, ~60–45 Ma arc-like magmatism in the Central Cordillera of Colombia was emplaced in a thickened continental crust due to the oblique subduction of the Caribbean oceanic plate underneath South America, as suggested by the high Sr/Y ratios. Conversely, the Panama Arc, and its poorly explored extension in the northwestern segment of the Western Cordillera of Colombia document a major phase of tholeiitic to calc-alkaline arc magmatism between ~71 Ma and ~34 Ma, mostly derived from a hydrated mantle wedge, and emplaced in an oceanic plateau crust. This arc record a major phase of magmatic activity between 40 Ma and 50 Ma that can be associated to changes in the convergence direction and subduction rates of the Farallon plate. Farther to the south, in the Pacific region of Colombia, Eocene arc-related rocks from the Timbiqui Complex show a geochemical signature that suggests a magmatic origin from melting of both a subduction-modified mantle and lower tectonically thickened crust. A possible interpretation for the Pacific and Western Colombia-Panama Arc systems, and its analogous in Ecuador, recall an Aleutian-type convergent margin in which the continental arc laterally switches to a purely oceanic system along the trailing edge of the Caribbean plate as consequence of eastward subduction of the Farallon plate.
... Within the circum-Caribbean realm, similar trondhjemitic rocks found in Sierra del Convento, Cuba, have been interpreted by Garcia-Casco et al. (2008) as the product of partial melting of amphibolite lithologies in a young oceanic slab during the initial phases of subduction. Further, intrusive rocks with TTG characteristics, mostly associated with subduction complexes, are common all around the Caribbean, including in the Sierra Maestra (Cuba), Hispaniola, Puerto Rico, Virgin Islands, Margarita, Aruba, Tobago, Parashi, Santa Marta, Antioquia, and Buga (Fig. 7.31) (Lidiak and Jolly 1996;Maresch et al. 2009;Pindell and Kennan 2009;Cardona et al. 2011aCardona et al. , 2014. These intrusives are found on both margins of the Caribbean Plateau with ages becoming younger to the east, a feature that has been used to track the "tectonic escape" of the Caribbean Plate during the Cenozoic (Müller et al. 1999). ...
One of the main northern South American geological conundrums has been to establish the tectonic relationship between Caribbean and South American plates during Mesozoic and Cenozoic times. Based on the petrogenetic interpretation of magmatic bodies within the Maracaibo block, we suggest an interplay between subduction and overthrusting tectonics in the northern part of South America during the Cenozoic. Our data show that the subduction of the Caribbean Plate beneath the South American Plate started around 65 million years ago, as is evidenced by the presence of trondhjemitic intrusions in the Santa Marta Province. Then, after a ca. 5-million-year magmatic gap, the evolution of this subduction system allowed the formation of a magmatic arc represented by the calc-alkaline Santa Marta Batholith (~56–49 Ma) and Parashi Pluton (51–47 Ma). For the interval between 50 and 25 million years, our data and compiled data point to a reduction in the tectonic activity, which is supported by relatively slow rates of cooling and uplifting in the Maracaibo block. Finally, for the period since the early Miocene, the reported uplift data, subsidence rates, and stratigraphic discordances indicate a differential uplift of the Maracaibo block, decreasing from the northwestern tip (Sierra Nevada de Santa Marta) toward the southeast (Merida Andes) and suggesting that this tectonic “reactivation” is the result of dominant overthrusting tectonics.
... The CCOP consists of anomalously thick oceanic crust, which is commonly considered to have formed as an oceanic plateau between the Early and Late Cretaceous, and that part of this plateau Lidiak and Jolly (1996). (Nivia, 1996;Lapierre et al., 2000;Revillon et al., 2000;Spikings et al., 2001;Kerr and Tarney, 2005). ...
Plateau related rocks accreted to the Caribbean plate margins provide insights into the understanding of the intra-oceanic evolution of the Caribbean plate and its interaction with the continental margins of the Americas.
Petrologic, geochemical and isotope (Sr and Nd) data were obtained in rocks from the Santa Fé Gabbro-Tonalite and Buriticá Tonalite in the Western Cordillera of Colombia.
Field relations and whole rock–mineral geochemistry combined with juvenile isotope signatures of the different rocks present in the area, suggest that initial melts, represented by the Buriticá Tonalite, formed due to asthenospheric upwelling at ∼100 Ma, which intrude the Colombian-Caribbean Oceanic Plateau (CCOP) basalts, and subsequent migration of the Caribbean plate towards the northeast resulted in subduction initiation and the formation of the Santa Fé tonalitic units at ∼90 Ma on the CCOP.
The relation of the Santa Fé Batholith with other units from the Caribbean, such as Aruba and the Buga Batholiths suggests the existence of an immature arc constructed on the Caribbean Plateau, which partially accreted onto a continental margin of South American in pre-Eocene times, or migrated to the present day position in the Lesser Antilles.
... This middle Eocene cooling age is confirmed by hornblende and biotite K/Ar ages in the range 45 -47 Ma reported in Cardona et al. (2007). This pluton probably belongs to a Paleogene magmatic event recorded at the boundary betweentheCaribbeanplateandtheSouthAmericanplate.Forexample,intrusives oftholeiticaffinity,andinterpretedasrelatedtoislandarctectonicsetting,havebeen reported at the south end of the Caribbean plate in Venezuela, Tobago, Talamana andVirginIslands (LidiakandJolly,1996).Similarbodiesofdioritictogranodioritic composition and Tertiary age have also been recognized in Panama, Costa Rica, Jamaica, Haití, Puerto Rico and Virgin Islands (Lidiak and Jolly, 1996). The rocksof the Etpana Metamorphic Suite were accretioned to South America and partially exhumed during Late Cretaceous -early Tertiary Caribbean plate convergence with the South American plate in a tectonic event known as the Caribbean episode (James, 2000). ...
In the northernmost portion of the Serrania de Jarara (Alta Guajira, Colombia), low - medium grade metamorphic rocks from the Etpana Metamorphic Suite were thermally affected by emplacement of a small calc-alkaline intrusion (Parashi Stock). Detailed petrographic analysis in collected rock samples across the NE and NW plutonic contacts show occurrences of textural and mineralogical changes in the country rock fabric that evidence contact metamorphism overprinting regional metamorphism of the Etpana Suite. These changes include growth of andalusite (chiastolite), calcic clinopyroxene and amphibole porphyroblast crosscutting Sn+1 metamorphic foliation. Hornblende-plagioclase barometry (ca. 3.1 kbar) and cooling models for the stock show maximum time temperature evolution in the country rock at the interpreted depth of intrusion (ca. 11 km) and help to evaluate the behavior of the country rock with the changing local geotherm.
... Only the Camarones pebbles show some deviating patterns, suggesting either significant fractionation or a different magma source. SiO 2 plotted against (Na 2 O+K 2 O) displays the subalkaline nature, and SiO 2 plotted against K 2 O exhibits the low to medium-K character, typical of intra-oceanic island-arc plutonic rocks, also known as M-type granites (Pitcher, 1983) such as in Puerto Rico, The Virgin Islands (Lidiak and Jolly, 1996 ), the Aleutians (Kay and Kay, 1994), the Izu-Bonin-Mariana arc (Kawate and Arima, 1998), and the New Britain island arc (Whalen, 1985). ...
We summarize the available geological information on the Sierra Maestra Mountains in southeastern Cuba and report new zircon fission track and biotite Ar-Ar ages for this region. Two different and genetically unrelated volcanic arc sequences occur in the Sierra Maestra, one Cretaceous in age (pre-Maastrichtian) and restricted to a few outcrops on the southern coast, and the other Palaeogene in age, forming the main expression of the mountain range. These two sequences are overlain by middle to late Eocene siliciclastic, carbonatic and terrigenous rocks as well as by late Miocene to Quaternary deposits exposed on the southern flank of the mountain range. These rocks are britle deformed and contain extension gashes filled with calcite and karst material. The Palaeogene volcanic arc successions were intruded by calc-alkaline, low- to medium-K tonalites and trondhjemites during the final stages of subduction and subsequent collision of the Caribbean oceanic plate with the North American continental plate. U-Pb SHRIMP single zircon dating of five granitoid plutons yielded Pb-206/U-238 emplacement ages between 60.5 +/- 2.2 and 48.3 +/- 0.5 Ma. These granitoids were emplaced at pressures ranging from 1.8 to 3.0 kbar, corresponding to depths of ca. 4.5-8 km. Ar-40/Ar-39 dating of two biotite concentrates yielded ages of 50 2 and 54 4 Ma, indicating cooling through ca. 300 degrees C. Zircon and apatite fission track ages range from 32 3 to 46 4 Ma and 31 10 to 44 13 Ma, respectively, and date cooling through 250 +/- 50 degrees C and 110 +/- 20 degrees C. The granitoids are the result of subduction-related magmatism and have geochemical characteristics similar to those of magmas from intra.-oceanic island-arcs such as the Izu Bonin-Mariana arc and the New Britain island arc. Major and trace element patterns suggest evolution of these rocks from a magmatic source. Geochemical features characterize these rocks as typical subduction-related granitoids as found worldwide in intra-oceanic arcs, and they probably formed through fractional crystallization of mantle-derived low- to medium-K basalts. Several distinct phases of deformation were recognized in the Sierra Maestra, labelled D-1 to D-6, which define the transition from collision of the Palaeogene island arc to the formation of the Oriente Transform Wrench Corridor south of Cuba and later movement of the Caribbean plate against the North American plate. The first phase (D-1) is related to the intrusion of a set of extensive subparallel, N-trending subvertical basalt-andesite dykes, probably during the early to middle Eocene. Between the late-middle Eocene and early Oligocene (D-2), rocks of the Sierra Maestra were deformed by approximately east-west trending folds and north-vergent thrust faults. This deformation (D-2) was linked to a shift in the stress regime of the Caribbean plate from mainly NNE-SSW to E-W. This shift in plate motion caused the abandonment of the Nipe-Guacanayabo fault system in the early Oligocene and initiation of a deformation front to the south where the Oriente Transform Wrench corridor is now located. Compressive structures were overprinted by widespread extensional structures (D-3), mainly faults with southward-directed normal displacement in the Oligocene to early Miocene. During this period the plate boundary jumped to the Oriente fault. This event was followed by transpressive and transtensive structures (D-4-D-6) due to further develpment of the sinistral E-trending Oriente Transform wrench corridor. These structures are consistent with oblique convergence in a wide zone of left-lateral shear along an E-W-oriented transform fault.
... (Escalona and Mann, 2011;Lugo and Mann, 1995), as part of a single Great Caribbean oceanic arc (Burke, 1988) or as multiple oceanic arcs (Wright and Wyld, 2011). Paleogene arc related magmatism within the Great Caribbean arc has been reported in different granitoid units from the Greater and Leeward Antilles (Lidiak and Jolly, 1996). ...
Recognition of magmatic events in polyphase arc–continent collision margin is critical for proper tectonic reconstructions that trace the short and changing nature of the configuration of the continental margin. Additionally, the recognition of the origin of detrital volcanic zircons within continental basins becomes a challenge if only distant oceanic and continental magmatic arcs are considered as the only possible source. In this study we report U/Pb zircon ages in isolated plutons that support an early Paleogene magmatic arc that extended ca 700 km along the northern Andean continental margin. Additional detrital zircon Paleogene ages (45–65 Ma), from Paleocene–lower Eocene continental sandstones and volcaniclastic rocks in 19 localities from Colombian and Venezuela Andean basins, indicate that volcanic detritus were supplied from a magmatic arc striking parallel to the subduction zone and also show the existence of intraplate magmatism extending more than 400 km inland.The wide distribution of this Early Paleogene magmatism along the northern South America margin is related to subduction of the buoyant Caribbean plate; the relative short period of magmatism (< 10 myr) and sudden stop in early middle Eocene time may be related to the difficulty of the thick plateau to subduct and the relative strike–slip movement of the South America and Caribbean plates since middle Eocene due to northward migration of those plates.
... 2a). Both series are characterized by homogenous and coarseto medium-grained rocks; textures near contacts are porphyritic to fine-grained holocrystalline (Lidiak and Jolly 1996) The most reliable ages for the Cretaceous volcanic rocks in central Cuba have been inferred from fossiliferous carbonate interlayers and stratigraphic positions (e.g., García-Delgado et al. 1998). Despite some uncertainty, the K-Ar age data for the Cretaceous Arc in Cuba range from to 100.1 ע 3.8 Ma, reflecting both magmatic and tec-49.5 ע 3.5 tonic events (Iturralde-Vinent et al. 1996). ...
SHRIMP and conventional zircon dating place temporal constraints on the evolution of the Cretaceous Volcanic Arc system in central Cuba. The arc has a consistent stratigraphy across strike, with the oldest and deepest rocks in the south (in tectonic contact with the ∼5–10-km-wide Mabujina Amphibolite Complex [MAC]) and younger rocks in the north. The MAC is thought to represent the deepest exposed section of the Cretaceous Volcanic Arc and its oceanic basement in Cuba. We undertook a single zircon geochronological study of five gneisses and two amphibolites from the MAC and seven rocks from the Manicaragua Batholith, which intrudes both the MAC and the Cretaceous Volcanic Arc. A SHRIMP zircon age of Ma for a trondhjemitic orthogneiss (MAC) from the Jicaya River dates the oldest phase of granitoid magmatism in this area and the entire Caribbean (Antillean) region. A tonalitic gneiss collected near the previous sample yielded an age of Ma, and a further tonalitic gneiss had an age of Ma, with one inherited zircon at Ma. Two trondhjemitic orthogneisses from the central part of the MAC yielded ages of and Ma, whereas two amphibolites from the eastern part of the complex provided similar ages of ca. 93 Ma and zircon inheritance at 315, 471, 903, and 1059 Ma. Two weakly foliated Manicaragua granitoids from the eastern part of the massif provided ages of and Ma, whereas five unfoliated granitoid samples from the central and eastern part of the massif yielded ages of , , , , and Ma. Our age data support the view that the Mabujina Protholiths are exotic and formed somewhere NNW along strike of the nonmetamorphosed Cuban arc since pre–Middle Hauterivian time (before ∼133 Ma). The MAC became part of the Cuban Volcanic Arc during the Turonian (ca. 90–93 Ma), when it was intruded by plutonic rocks of the Manicaragua Batholith (Turonian-Campanian; ca. 89–83 Ma). The geology and geochronology of central Cuba do not support the idea of a polarity reversal event at any stage of the Cretaceous Arc–building process. Because most of our dated samples come from the narrow Mabujina Belt, the polarity reversal model would imply that the axis of a newly developing arc (with opposite polarity) would spatially coincide with the older arc, which appears unlikely. Inherited Precambrian and Palaeozoic zircons in the MAC granitic rocks (similar to inherited zircon populations in the Guerrero terrane from central-western Mexico) suggest a Neocomian proximal setting close to a cratonic area (probably SW Mexico/Maya Block) for the protolith of the MAC relative to the synchronous Primitive Island Arc of central Cuba.
... Only the Camarones pebbles show some deviating patterns, suggesting either significant fractionation or a different magma source. SiO 2 plotted against (Na 2 O+K 2 O) displays the subalkaline nature, and SiO 2 plotted against K 2 O exhibits the low to medium-K character, typical of intra-oceanic island-arc plutonic rocks, also known as M-type granites (Pitcher, 1983) such as in Puerto Rico, The Virgin Islands (Lidiak and Jolly, 1996 ), the Aleutians (Kay and Kay, 1994), the Izu-Bonin-Mariana arc (Kawate and Arima, 1998), and the New Britain island arc (Whalen, 1985). ...
The Sierra Maestra in southeastern Cuba comprises Paleogene intraoceanic volcanic arc sequences which have been accreted to the North American continental margin during the late Middle Eocene, during the final stages of collision with the Caribbean plate. Geochronological analysis and geobarometric investigations on samples from Eocene granitoids constrain the cooling history and tectonic evolution of the region. Granitoids intruded at pressures ranging from 1.8 to 3.0 kbar, corresponding to depths of approx. 4.5-8 km. 40Ar/39Ar dating of biotite yielded ages of 50+/-2 to 54+/-4 Ma (2-sigma errors), indicating cooling through ca. 300 oC. Zircon and apatite fission track ages range from 32+/-3 to 46+/-4 Ma and 31+/-10 to 44+/-13 Ma, respectively, and date cooling through 250+/-50 oC and 110+/-20 oC. These data suggest fast cooling and exhumation of the granitoids during collisional processes in the Eocene. Apatite track length measurements show a bimodal frequency distribution suggesting initial very fast cooling between 45 and 40 Ma, down to 120 oC, followed by a period of 30 Ma where almost no variation occurred in the temperature. Final cooling occurred since 12 Ma and is probably related to transform faulting along the southern margin of the Sierra Maestra. We propose that slab breakoff of the subducting North American plate occurred during the final stages of collision between the North American and Caribbean plates, and we argue, therefore, that the granitoids cooled and were exhumed as a consequence of this process and eastward migration of the slab-tear. Several lines of evidence support this model: (1) Published cooling and exhumation ages of the granitoids are younging from west to east, with old ages (ca. 56 Ma) in the west and young ones in the east (ca. 49 Ma). (2) Subsequent rapid cooling through 300 to 110 °C occurred also partly in the Middle to early Late Eocene, suggesting rapid uplift and cooling of the entire crust as granitoids intruded at a depths of ca. 8 km. (3) Eastward migration of depocenters with coarse-grained clastic rocks now exposed to the north of the Sierra Maestra argue for earlier surface uplift and denudation in the west than in the east. Oligocene to Neogene tectonic processes such as strike-slip faulting contributed little to exhumation.
... Mantle melting processes, recycling of weathered exogenous sediments (McCarthy & Patiño-Douce, 1997), and repeated melting-solidification cycles (igneous distillation), have all been invoked to produce the high potassium content in lower crustal settings. The high potassium in melts in settings such as Costa Rica (Lidiak & Jolly, 1996;Hannah et al., 2002) and the Philippines (T. Vogel, personal communication, 2004) where a thick crust of meta-sediments is absent, appears to imply that in some settings incorporation of weathered material is not necessary for the production of high-K suites. ...
We present a quantitative assessment of the thermal and dynamic response of an amphibolitic lower crust to the intrusion of basaltic dike swarms in an arc setting. We consider the effect of variable intrusion geometry, depth of intrusion, and basalt flux on the pro- duction, persistence, and interaction of basaltic and crustal melt in a stochastic computational framework. Distinct melting and mixing environments are predicted as a result of the crustal thickness and age of the arc system. Shallow crustal (� 30km) environments and arc settings with low fluxes of mantle-derived basalt are likely reposit- ories of isolated pods of mantle and crustal melts in the lower crust, both converging on dacitic to rhyodacitic composition. These may be preferentially rejuvenated in subsequent intrusive episodes. Mature arc systems with thicker crust (� 50km) produce higher crustal and residual basaltic melt fractions, reaching � 0� 4 for geologically reasonable basalt fluxes. The basaltic to basaltic andesite composi- tion of both crustal and mantle melts will facilitate mixing as the network of dikes collapses, and Reynolds numbers reach 10� 4-1� 0 in the interiors of dikes that have been breached by ascending crustal melts. This may provide one mechanism for melting, assimilation, storage and homogenization (MASH)-like processes. Residual min- eral assemblages of crust thickened by repeated intrusion are predicted to be garnet pyroxenitic, which are denser than mantle peridotite and also generate convective instabilities where some of the crustal mater- ial is lost to the mantle. This reconciles the thinner than predicted crust in regions that have undergone a large flux of mantle basalt for a prolonged period of time, and helps explain the enrichment of incompatible elements such as K2O, typical of mature arc settings, without the associated mass balance problem.
... Also shown is the Guiana Massif, part of the Amazon Craton. Adapted from Lidiak and Jolly (1996). Lockwood (1965) and Gómez et al. (2007). ...
Mesozoic metamorphic units exposed along the northern margin of the South American plate record the different stages of subduction evolution or arc-continent collision between the margins of the Caribbean plate and the South American continent. U–Pb detrital zircon geochronology for provenance analysis was carried out on meta-sedimentary rocks of the Etpana formation and metamorphic boulders found within a nearby Tertiary conglomerate, including high-pressure rocks in the Colombian Caribbean. All samples have similar age populations, suggesting that they share a relatively common source and paleogeography. Prominent age peaks include Meso and Paleoproterozoic ages of ca. 1624 Ma and 1315 Ma, Cambrian to Neoproterozoic ages of ca. 630 Ma, 580 Ma and 547 Ma, and less abundant Jurassic and Permian ages of ca. 270 Ma and 160 Ma, which indicate that the South American margin is a major source for the sedimentary protoliths. There are also remnants of younger Cretaceous allocthonous Caribbean arc input at ca. 90–70 Ma. The deposition and metamorphism of these units records the ongoing Late Cretaceous continental subduction of the South American margin within the Caribbean intra-oceanic arc-subduction zone. This gave way to an arc-continent collision between the Caribbean and the South American plates, and sediments with continental signatures were incorporated into the subduction channel and the accretionary wedge. As convergence continued, sediments derived from a mix of South American and arc sources were deposited and included in the collisional wedge up until <71 Ma.
... All the samples are low in titanium (TiO 2 ≤ 0.47 wt%), potassium (K 2 O ≤0.63 wt%), Y (≤15 ppm), Yb (≤1.5 ppm), and Nb (≤1.6 ppm). On the Nb vs Y discrimination diagram (Pearce et al., 1984), the Téneme intrusive rocks plot within the volcanic-arc and syn-collisional granites field (no shown), while the K- Na-Ca plot (Fig. 13A) shows that Río Grande plutonics fall into the fields of Aruba batholith (Aruba, Dutch Caribbean; White et al., 1999) and granitoid rocks of the Cordillera Central (Dominican Republic; Lidiak and Jolly, 1996; Lewis et al., 2002). As regards the REE contents of the Río Grande diorites , all samples exhibit low incompatible element values and patterns characterized by a slight LREE enrichment with flat MREE and HREE segments (Fig. 13B). ...
The Téneme Formation is located in the Mayarí-Cristal ophiolitic massif and represents one of the three Cretaceous volcanic Formations established in northeastern Cuba. Téneme volcanics are cut by small bodies of 89.70 ± 0.50 Ma quarz-diorite rocks (Río Grande intrusive), and are overthrusted by serpentinized ultramafics. Téneme volcanic rocks are mainly basalts, basaltic andesites, andesites, and minor dacites, and their geochemical signature varies between low-Ti island arc tholeiites (IAT) with boninitic affinity (TiO2 < 0.4 %; high field strength elements
... All the samples are low in titanium (TiO 2 ≤ 0.47 wt%), potassium (K 2 O ≤0.63 wt%), Y (≤15 ppm), Yb (≤1.5 ppm), and Nb (≤1.6 ppm). On the Nb vs Y discrimination diagram (Pearce et al., 1984), the Téneme intrusive rocks plot within the volcanic-arc and syn-collisional granites field (no shown), while the K- Na-Ca plot (Fig. 13A) shows that Río Grande plutonics fall into the fields of Aruba batholith (Aruba, Dutch Caribbean; White et al., 1999) and granitoid rocks of the Cordillera Central (Dominican Republic; Lidiak and Jolly, 1996; Lewis et al., 2002). As regards the REE contents of the Río Grande diorites , all samples exhibit low incompatible element values and patterns characterized by a slight LREE enrichment with flat MREE and HREE segments (Fig. 13B). ...
The Téneme Formation is located in the Mayarí-Cristal ophiolitic massif and represents one of the three Cretaceous volcanic Formations established in northeastern Cuba. Téneme volcanics are cut by small bodies of 89.70 ± 0.50 Ma quarz-diorite rocks (Río Grande intrusive), and are overthrusted by serpentinized ultramafics. Téneme volcanic rocks are mainly basalts, basaltic andesites, andesites, and minor dacites, and their geochemical signature varies between low-Ti island arc tholeiites (IAT) with boninitic affinity (TiO2 < 0.4 %; high field strength elements << N-type MORB) and typical oceanic arc tholeiites (TiO2 = 0.5-0.8 %). Basaltic rocks exhibit low light REE/Yb ratios (La/Yb < 5), typical of intraoceanic arcs and are comparable to Maimón Formation in Dominican Republic (IAT, pre Albian) and Puerto Rican lavas of volcanic phase I (island arc tholeiites, Aptian to Early Albian). The mantle wedge signature of the Téneme Formation indicates a highly depleted MORB-type mantle source, without any contribution of E-MORB or OIB components. Our results suggest that Téneme volcanism represents a primitive oceanic island arc environment. If the Late Cretaceous age (Turonian or early Coniacian) proposed for Téneme Formation is correct, our results indicate that the Cretaceous volcanic rocks of eastern Cuba and the Dominican Republic are not segments of a single arc system, and that in Late Cretaceous (Albian-Campanian) Caribbean island arc development is not represented only by calc-alkaline (CA) volcanic rocks as has been suggested in previous works.
... Only the Camarones pebbles show some deviating patterns, suggesting either significant fractionation or a different magma source. SiO 2 plotted against (Na 2 O+K 2 O) displays the subalkaline nature, and SiO 2 plotted against K 2 O exhibits the low to medium-K character, typical of intra-oceanic island-arc plutonic rocks, also known as M-type granites (Pitcher, 1983) such as in Puerto Rico, The Virgin Islands ( Lidiak and Jolly, 1996), the Aleutians ( Mahlburg-Kay and Kay, 1994), the Izu-Bonin-Mariana arc (Kawate and Arima, 1998), and the New Britain island arc (Whalen, 1985). ...
We summarize the available geological information on the Sierra Maestra Mountains in southeastern Cuba and report new zircon fission track and biotite Ar-Ar ages for this region. Two different and genetically unrelated volcanic arc sequences occur in the Sierra Maestra, one Cretaceous in age (pre-Maastrichtian) and restricted to a few outcrops on the southern coast, and the other Palaeogene in age, forming the main expression of the mountain range. These two sequences are overlain by middle to late Eocene siliciclastic, carbonatic and terrigenous rocks as well as by late Miocene to Quaternary deposits exposed on the southern flank of the mountain range. These rocks are britle deformed and contain extension gashes filled with calcite and karst material. The Palaeogene volcanic arc successions were intruded by calc-alkaline, low-to medium-K tonalites and trondhjemites during the final stages of subduction and subsequent collision of the Caribbean oceanic plate with the North American continental plate. U-Pb SHRIMP single zircon dating of five granitoid plutons yielded 206Pb/ 238U emplacement ages between 60.5 ± 2.2 and 48.3 ± 0.5 Ma. These granitoids were emplaced at pressures ranging from 1.8 to 3.0 kbar, corresponding to depths of ca. 4.5-8 km. 40Ar/ 39Ar dating of two biotite concentrates yielded ages of 50 ± 2 and 54 ± 4 Ma, indicating cooling through ca. 300 °C. Zircon and apatite fission track ages range from 32 ± 3 to 46 ± 4 Ma and 31 ± 10 to 44 ± 13 Ma, respectively, and date cooling through 250 ± 50 °C and 110 ± 20 °C. The granitoids are the result of subduction-related magmatism and have geochemical characteristics similar to those of magmas from intra-oceanic island-arcs such as the Izu Bonin-Mariana arc and the New Britain island arc. Major and trace element patterns suggest evolution of these rocks from a single.
... Succeeding, also conformable, volcanic sandstone, shale, and conglomerate of the Tutu Fm, of Santonian to Campanian age (Donnelly, 1966), are restricted to a narrow belt on the north side of the islands (Fig. 2). Strata in northern St. John were metamorphosed to hornblende-garnet amphibolite by the calcalkaline Virgin Islands Batholith and satellite plutons (Fig. 2;Helsley, 1960;Donnelly and Rogers, 1980;Donnelly et al., 1990;Lidiak and Jolly, 1996). The intrusive rocks, representing the final major magmatic event in the northeast Antilles, have Oligocene K/Ar ( Cox et al., 1977) and 40 Ar/ 39 Ar (Rankin, 2002) radiometric ages ranging from 35 to 39 Ma. ...
The latest Aptian to earliest Albian (~115 Ma) Water Island Fm in the Virgin Islands contains some of the oldest known arc-related strata in the Greater Antilles Island Arc. Hence, the unit is of considerable significance in tectonic reconstructions of initial subduction parameters along the long-lived destructive plate margin separating the North American and Caribbean Plates. Exposed Water Island strata are bimodal, consisting predominantly of altered dacite and rhyolite (originally called keratophyre; 65-85% SiO2) and subordinate degraded (spilite; 46-57% SiO2). TiO2 content of Water Island basalt averages approximately 0.5%, resembling borderline intermediate-Ti boninite basalts, consistent with low incompatible element abundances and low normalized light rare earth elements (LREE) with respect to Sm. Trace element patterns of the felsic suite, characterized by pronounced negative normalized anomalies for high field-strength elements (HFSE), low Sr/Y, and low absolute rare earth element (REE) abundances, and relatively flat normalized REE patterns, have analogues in plagiorhyolite suites from bimodal Cenozoic arcs, including the western Aleutians, Izu-Bonin, the Kermadecs, and South Sandwich. Relatively low incompatible element concentrations in plagiorhyolites and contrasting normalized incompatible trace element patterns in basalts preclude an origin of Water Island plagiorhyolite through MORB-type fractional crystallization. Compositions are consistent instead with melting models involving partial fusion of amphibole-bearing gabbro at low pressures (within the stability range of plagioclase) in response to introduction of heat and aqueous flux by arc-related basalt melts and associated hydrothermal fluids during transmission to the surface. Truncation of the basalt fractional crystallization trend at SiO2 = 57% indicates evolved island arc basalt (IAB) crystal fractionates were gradually displaced from crustal magma conduits by more buoyant plagiorhyolite melt, and trapped in underplated, sub-crustal magma chambers. Basalts have low (Ce/Ce*)N (average ¿0.78), indicating the presence of significant pelagic sediment (0.5 to 1.5% Atlantic Cretaceous pelagic sediment, AKPS). One subunit of relatively high-HFSE plagiorhyolite has (Ce/Ce*)N near-expected values, but another with low-HFSE has slightly lower than expected (Ce/Ce*)N, consistent with a small sediment component. Absence of intermediate andesite from the Water Island Fm is inconsistent, however, with basaltrhyolite magma mixing processes. Consequently, incorporation of sediment by low-HFSE plagiorhyolite is inferred to have resulted from re-melting of arc-related gabbro.
Siliciclastic sandstone composition on the island of Puerto Rico, part of the Greater Antilles, was influenced by both tectonic setting and climate. Cretaceous through Eocene volcanic and plutonic rocks on Puerto Rico formed in an oceanic-arc setting. Sandstones deposited during arc volcanism are quartz-poor lithic and feldspatholithic arenites, whose geochemistry largely matches that of the oceanic-arc volcanic and plutonic rocks on Puerto Rico. After cessation of volcanism on Puerto Rico during collision of the Greater Antilles island arc with the Bahamas Bank, an Oligocene through Holocene overlap assemblage was deposited unconformably above the arc deposits in the North Coast and South Coast basins of Puerto Rico. The overlap assemblage consists of some siliciclastic material, but largely shallow-water carbonate deposits. Siliciclastic deposition in the overlap assemblage reflects the volcanic-arc source, plus quartz derived from plutons exposed during uplift. In the Pleistocene and Holocene (and possibly earlier), poorly consolidated quartz-arenitic sands with SiO2 values from 92 to 98% were deposited in the overlap assemblage.
On geochemical tectonic-affinity diagrams, the lithic sandstones plot, as expected, in or near the fields for oceanic-arc provenance. However, the quartz-arenitic sands plot incorrectly in the passive-margin field when considering major elements, and correctly in or near the oceanic-arc field when considering trace elements. Trace elements in the quartz-arenitic sands are largely found in refractory minerals, whereas major elements in feldspars and lithic fragments are effectively removed by intense tropical weathering. Hence, future use of tectonic-affinity diagrams should rely on trace-element geochemistry.
Sandstones derived from the Sierra Nevada continental arc in California have QFL quartz fractions below 60%, even though the source magmatic arc has significant modal quartz. This observation suggests a “climate cap,” which does not “allow” formation of more quartzose sediments. In contrast, tropical weathering on Puerto Rico removes this climate cap allowing the creation of quartz-arenitic sands from a source rock containing limited quartz. It is remarkable that quartz-arenitic sands occur on Puerto Rico, sourced from a provenance area containing extremely limited quantities of modal quartz (estimated at less than 5%) in an oceanic-arc environment bounded by two active subduction zones. Quartz-arenitic sands and sandstones are not uniquely continental or of cratonal origin; chemical weathering is fundamentally important for the origin of first-cycle quartz-arenitic sands.
The Greater Antilles islands of Cuba, Hispaniola, Puerto Rico and Jamaica plus the Virgin Islands host fragments of the fossil convergent margin that records Cretaceous subduction (operated for about 90 m.y.) of the American plates beneath the Caribbean plate and ensuing arc-continent collision in Late Cretaceous-Eocene time. The “soft” collision between the Greater Antilles Arc (GAA) and the Bahamas platform (and the margin of the Maya Block in western Cuba) preserved much of the convergent margin. This fossil geosystem represents an excellent natural laboratory for studying the formation and evolution of an intra-oceanic convergent margin. We compiled geochronologic (664 ages) and geochemical data (more than 1,500 analyses) for GAA igneous and metamorphic rocks. The data was classified with a simple fourfold subdivision: fore-arc mélange, fore-arc ophiolite, magmatic arc, and retro-arc to inspect the evolution of GAA through its entire lifespan. The onset of subduction recorded by fore-arc units, together with the oldest magmatic arc sequence shows that the GAA started in Early Cretaceous time and ceased in Paleogene time. The arc was locally affected (retro-arc region in Hispaniola) by the Caribbean Large Igneous Province (CLIP) in Early Cretaceous and strongly in Late Cretaceous time. Despite multiple biases in the database presented here, this work is intended to help overcome some of the obstacles and motivate systematic study of the GAA. Our results encourage exploration of offshore regions, especially in the east where the forearc is submerged. Offshore explorations are also encouraged in the south, to investigate relations with the CLIP.
Al norte de la serranía de Jarara se encuentra el valle de Parashi, el cual esta establecido principalmente por rocas del Stock de Parashi y sus diques asociados en una dirección predominante NE-SW, los cuales sobresalen en montículos en el valle en forma de Thor al igual que las partes menos meteorizadas del stock. El cuerpo se encuentra limitado casi completamente por las rocas metasedimentarias de la Formación Etpana y rocas ultramáficas asociadas, que han sido afectadas térmicamente por la intrusión del stock. La composición del stock varía de cuarzodiorita a granodiorita con moderada cantidad de enclaves que representan segregaciones de minerales o xenolitos de pórfidos; los diques son de carácter porfídico, principalmente dacítico con algunas variaciones en el contenido de cuarzo, hornblenda o plagioclasa. La petrografía del stock revela un zonamiento abundante de las plagioclasas y en menor proporción en los anfíboles, en una textura idiomórfica equigranular con cristales de plagioclasa aglomerados y maclados (maclas tipo albita, carlsbad y periclina), cristales incompletos de hornblenda y biotitas. Los diques presentan una textura claramente porfídica con fenocristales de cuarzo bipiramidales, hornblenda y plagioclasas zonadas, macladas y a veces muy sausuritizadas o epidotizadas.
Constraints on the polarity of Cretaceous subduction in the Greater Antilles are provided through geochemical comparison between the erupted island arc lavas in central Puerto Rico and potential pelagic sediment reservoirs in the flanking ocean basins. Early Jurassic to mid-Cretaceous (185- to 65-Ma) sediment from the open Pacific on the southwest is dominated by pelagic chert, which is highly refractory and depleted with respect,to incompatible elements. In comparison, mid- to Late Cretaceous (ca. 112- to 65-Ma) sediment from the younger Atlantic basin on the northeast was dominated by mixtures of two end members. These include (1) biogenic clay and carbonates with elevated light rare-earth element (LREE) abundances, negative MORB-normalized, high field-strength element (HFSE) anomalies, and low Zr/Sm; and (2) turbiditic detritus of upper continental crust composition with high LREE, comparatively shallow HFSE anomalies, and high Zr/Sm. Compositions of Puerto Rican arc basalts are inconsistent with incorporation of Pacific pelagic chert. Instead, patterns characteristic of high-Fe island arc tholeiites are reproduced by incorporation of up to 4% of a low-Zr/Sm biogenic sediment component of Atlantic origin, whereas patterns of low-Fe lavas require, in addition to biogenic sediment, introduction of up to 2% of a high-Zr/ Sm crustal turbidite component. The Allantic origin of all the subducted sediments indicates the polarity of subduction throughout the Cretaceous in the northeast Antilles was persistently southwest dipping. This conclusion is supported by the presence of a low-Zr/Sm suprasubduction zone component of Atlantic origin in Caribbean plateau basalts (91-88 Ma) from southwest Puerto Rico, which were erupted within the broad back-arc region of the Greater Antilles during intermediate stages of arc development.
Island arc volcanism in the Greater Antilles persisted for >70 m.y. from Middle Cretaceous to Late Eocene time. During the initial 50 m.y., lavas in central Puerto Rico shifted from predominantly island arc tholeiites (volcanic phase I, Aptian to Early Albian, 120-105 Ma), to calc-alkaline basalts (phase II, Late Albian, 105-97 Ma), and finally to high-K, incompatible-element-enriched basalts (phases III and IV, Cenomanian-Maastrichtian, 97-70 Ma). Following an island-wide eruptive hiatus, geochemical trends were reversed in the Eocene with renewed eruption of calc-alkaline basalts (phase V, 60-45 Ma). Progressive increases in large-ion lithophile elements (LILE)/light rare earth elements (LREE), LILE/high field strength elements (HFSE), LREE/ HFSE, and HFSE/heavy rare earth elements (HREE) characterize the compositional evolution of the first four volcanic phases. The shift in trace element compositions is mirrored by increasing radiogenic content of the lavas. PbΔ8/4 values, representing deviations of 208Pb/204Pb from the Northern Hemisphere Reference Line (NHRL), range from - 20 to almost + 2.0 in phases I and II, and up to + 25 in phase III. Similarly, εNd values decrease slightly from + 8 to almost + 6 between volcanic phases I and III. Finally, initial (i) 87Sr/86Sr values in phase I basalts have a narrow range from 0.7033 to 0.7040, near the upper limit of altered mid-ocean ridge basalt (MORB), whereas values from phases III and IV basalts have a broader range from 0.7034 to 0.7044. N-MORB-normalized incompatible element distribution patterns of Puerto Rican volcanic rocks have uniformly flat HREE segments and γ/γb is - 1, indicating that garnet and amphibole were insignificant as residual phases and that melting occurred predominantly within relatively dry spinel lherzolite. γb concentrations, which provide constraints on degree of melting, are consistent with a narrow range from 30 to 35% melting in volcanic phase I, but with a much broader range from 25 to 40% melting during phase III. It seems likely that such high degrees of melting were attained through a combination of flux-related melting and buoyancy-driven pressure-release fusion. Nb abundances, which reflect degree of incompatible element enrichment compared with fertile MORB mantle (FMM), are low in volcanic phase I, consistent with - 2% low-degree pressure release melting of source material in the back-arc region before entry into the arc melting zone. Subsequent lavas from phases II and III have N-MORB-like or higher Nb abundances, indicating that (1) back-arc processes peaked in intensity during the first 10-20 m.y. and later declined in significance, and/or (2) the degree of incompatible element enrichment gradually increased as a result of subduction of a thickening accumulation of pelagic sediment. Isotope mixing models indicate that the proportion of authigenic pelagic sediment incorporated into Puerto Rican basalts increased from negligible levels in phase I to as high as 2% in phases III and IV. Although the absolute magnitude of the sediment component increased progressively, a narrow range of Th/La in mafic end-members indicates that the terrigenous contribution remained uniform throughout volcanism, consistent with the insular setting of the eastern Greater Antilles Arc.
Abstract The initial volcanic phase of Cretaceous island arc strata in central Puerto Rico, at the eastern end of the extinct Greater Antilles Arc, comprises a 6-km thick pile of lava and volcanic breccia (Río Majada Group). Preserved within the sequence is a conspicuous shift in absolute abundances of the more incompatible elements, including Th, Nb, and the light rare earth elements (LREE: La, Ce, Pr and Nd). The compositional shift is marked by a decrease in La/Sm from averages of 2.11 in the lowest third of the pile (Formation A) to 1.48 at the top (Formation C), and by a distinctive flattening of LREE segments of chondrite-normalized REE patterns. i87Sr/86Sr and ɛNd average about 0.7035 and 8.2, respectively, in early Formation A basalts. These ranges normally overlap samples from later Formations B and C. Isotope compositions of the latter group are more variable, however, and several samples are considerably more radiogenic than Formation A basalts, such that i87Sr/86Sr averages almost 0.7042 while ɛNd-values decrease to 7.5 in Formation B and C basalts. Theoretical models of non-modal melting processes in both amphibole peridotite and spinel lherzolite sources provide insight into the origin of depleted Th, Nb, and LREE abundances in Puerto Rican basalts. Low Nb concentrations less than normal mid-oceanic ridge basalts in Formation A basalts indicate the wedge was slightly depleted by low-volume decompression fusion due to induced convection in the back-arc region prior to entry of the source into the arc melting zone. However, depleted patterns in Formation C basalts cannot be generated by relatively greater degrees of decompression fusion in the back-arc, because addition of the La-enriched slab-derived component to more depleted source material invariably produces elevated rather than decreased La/Sm. Refluxing of Formation A harzburgitic residua is similarly precluded. In contrast, the observed patterns are readily reproduced by multistage melting models involving hybridized sources containing normal Formation A lherzolite source material blended with recycled, unrefluxed harzburgite residua. Successful models require hybrid sources containing large volumes of recycled harzburgite (up to 50%) during generation of Formation C basalts. Slightly elevated radiometric Sr and Nd isotopes in a few flows from Formation C are attributed to partial refluxing of the hybrid sources within the wedge.
Bimodal extrusive volcanic rocks in the northeast Greater Antilles Arc consist of two interlayered suites, including (1) a predominantly basaltic suite, dominated by island arc basalts with small proportions of andesite, and (2) a silicic suite, similar in composition to small volume intrusive veins of oceanic plagiogranite commonly recognized in oceanic crustal sequences. The basaltic suite is geochemically characterized by variable enrichment in the more incompatible elements and negative chondrite-normalized HFSE anomalies. Trace element melting and mixing models indicate the magnitude of the subducted sediment component in Antilles arc basalts is highly variable and decreases dramatically from east to west along the arc. In the Virgin Islands, the sediment component ranges between< 0.5 to ∼ 1% in Albian rocks, and between ∼ 1 and 2% in succeeding Cenomanian to Campanian strata. In comparison, sediment proportions in central Puerto Rico range between 0.5 to 1.5% in the Albian to 2 to > 4% during the Cenomanian-Campanian interval. The silicic suite, consisting predominantly of rhyolites, is characterized by depleted Al2O3 (average < 16%), low Mg-number (molar Mg/Mg + Fe < 0.5), TiO2 (< 1.0%), and Sr/Y (< 10), oceanic or arc-like Sr, Nd, and Pb isotope signatures, and by the presence of plagioclase. All of these features are consistent with an anatexic origin in gabbroic sources, of both oceanic and arc-related origin, within the sub-arc basement. The abundance of silicic lavas varies widely along the length of the arc platform. In the Virgin Islands on the east, rhyolites comprise up to 80% of Lower Albian strata (112 to 105 Ma), and about 20% in post-Albian strata (105 to 100 Ma). Farther west, in Puerto Rico, more limited proportions (< 20%) of silicic lavas were erupted. The systematic variation of both sediment flux and abundance of crustally derived silicic lavas are consistent with current tectonic models of Caribbean evolution involving approximately perpendicular subduction of the Caribbean spur of the mid-Atlantic Ridge, which was located approximately midway between North and South America until Campanian times. Within this hypothetical setting the centrally positioned Virgin Islands terrain remained approximately fixed above the subducting ridge as the Antilles arc platform swept northeastward into the slot between the Americas. Accordingly, heat flow in the Virgin Islands was elevated throughout the Cretaceous, giving rise to widespread crustal melting, whereas the subducted sediment flux was limited. Conversely, toward the west in central Puerto Rico, which was consistently more remote from the subducting ridge, heat flow was relatively low and produced limited crustal melting, while the sediment flux was comparatively elevated.
Two-pyroxene-bearing high-Mg andesite, hornblende basalt and andesite, and high-Fe augite basalt were erupted simultaneously in southwest Puerto Rico between 85 and 65 Ma. An analogy with geologic settings in Cenozoic arcs indicates that hornblende-bearing lavas and high-Mg andesites, restricted to the southwestern-most corner of Puerto Rico, represent the forearc assemblage, whereas high-Fe basalts, concentrated in an adjacent volcanic belt toward the northeast, represent the arc-axis suite. This arrangement implies northeast-dipping subduction of refractory Jurassic chert from the Caribbean Basin, and is, therefore, consistent with relatively low Sr-isotope ratios in all three lava suites compared with correlative strata in Eastern Puerto Rico. Moreover, Pb- and Nd-isotope ratios and trace element melting models for both high-Mg andesites and hornblende-bearing lavas are consistent with the presence of a slab melt component generated by high-pressure fusion of incompatible element-enriched plateau basalts. The most likely source for such a basaltic component is the Caribbean basalt plateau, which is represented in southwest Puerto Rico by the Upper Cajul Formation. The models indicate that up to 5% slab melt was added to the source of hornblende-bearing lavas, but higher proportions, as much as 10%, are required to generate high-Mg andesites. The elevated buoyancy of the more enriched and siliceous high-Mg andesite source apparently destabilized the mantle wedge and induced combined mantle-mass assimilation and fractional crystallization of orthopyroxene (AFC ≈ 1), which ultimately produced elevated MgO and low Al2O3 concentrations characteristic of the high-Mg andesites. The tectonic setting in southwest Puerto Rico was unlike Cenozoic analogues, because the pre-arc basement was already old (Early Jurassic, 185–155 Ma) at the time of initial island arc volcanism (∼ 85 Ma). However, geothermal gradients in the region were increased again immediately preceding arc volcanism by emplacement of the Caribbean mantle plume (92–88 Ma), during which the original N-MORB-type upper mantle in the region was replaced by incompatible element-enriched material. The elevated heat flow produced by plume emplacement, supplemented by ascent of plume basalts from depth and associated gabbroic underplating, is inferred to have promoted slab melting. The presence of a low Zr/Sm component in both plateau basalts and arc lavas in southwest Puerto Rico is consistent with the incorporation of a small biogenic supra-subduction zone component of Atlantic origin, introduced into the back-arc region of an older (from 115 Ma) southwest-dipping subduction zone in eastern Puerto Rico.
A major change in volcanic associations and their tectonic settings occurred in much of the Western United States during late Cenozoic time. Where this volcano-tectonic transition can be documented, an earlier orogenic and post-orogenic association of predominantly calc-alkalic andesitic rocks typical of circum-Pacific continental margin and island arcs was succeeded by fundamentally basaltic volcanism which accompanied regional normal and strike-slip faulting. The igneous fields regarded here as fundamentally basaltic include: (1) basaltic fields, (2) alkalic fields in which differentiated igneous series commonly can be related to alkali-basaltic parent magmas, and (3) bimodal associations of mafic and silicic rocks, generally basalts and high-silica rhyolites. Similar igneous fields occur in other regions of the world characterized by tectonic extension. The nature and timing of the late Cenozoic volcano-tectonic transition in various areas of the Western United States are documented from published references. The transition began in the south-eastern part of the region in latest Oligocene time and moved northwestward through Miocene, Pliocene, and Quaternary time. The inception of basaltic, alkalic, or bimodal volcanism and associated regional extension of inland areas appears to date the times at which plate-tectonic boundaries between North America and two Pacific plates underwent drastic changes. These changes resulted from collision of the East Pacific Rise with a mid-Tertiary continental-margin trench and resulting direct contact of the American and western Pacific plates along a right-lateral transform fault system. These plate-tectonic interactions have evolved continuously and have determined the volcanic and tectonic evolution of the Western United States for the last 30 million years.
Blueschists and associated low-grade greenschists and amphibolites occur in the Blue Mountains of E Jamaica and are found in proximity to volcanic-arc-generated rocks. In the blueschist and greenschist rocks, known as the 'Mount Hibernia Schists', metamorphosed basalts, gabbro, and peridotites are found in a structurally disrupted region along with meta-cherts, marbles, meta-conglomerates, and meta-epiclastic rocks. A model for the genesis of the Jamaican Schist terrane describes the formation and subsequent erosion of these rocks in a pre-Campanian, accretionary complex. -from Author
The pressure-temperature-time-deformation evolution for the crust of Margarita Island (Venezuela) has been established to allow comparison with current plate-tectonic models for the Caribbean region. On Margarita, the 12 recognizable stages of development can be summarized in terms of the following evolving tectonic settings: Protolith evolution as Aptian-Albian or older oceanic crust, as well as continental crust with Paleozoic basement (stages 1 and 2); accretion and high-pressure metamorphism (500 600 °C, 10 14 kbar) as the Margarita Complex in the deep level of a fore arc at 100 90 Ma (stage 3); ascent, cooling, and emplacement into the intermediate crustal level of a volcanic arc at 90 80 Ma (stage 4); transform plate-margin setting at a comparable level at 80 50 Ma (stage 5); second episode of rapid uplift and cooling (stages 6 and 7); and shallow crustal level close to transform plate margin from 50 Ma to present (stages 8 to 12). This complex sequence is in excellent agreement with plate-tectonic scenarios that require a Pacific origin for the Caribbean plate and eastward migration of the Margarita Complex and its correlatives along northern South America since the Cretaceous.
Trace-element data for mid-ocean ridge basalts (MORBs) and ocean island basalts (OIB) are used to formulate chemical systematics for oceanic basalts. The data suggest that the order of trace-element incompatibility in oceanic basalts is Cs ≃ Rb ≃ (≃ Tl) ≃ Ba(≃ W) > Th > U ≃ Nb = Ta ≃ K > La > Ce ≃ Pb > Pr(≃ Mo) ≃ Sr > P ≃ Nd (> F) > Zr = Hf ≃ Sm > Eu ≃ Sn (≃ Sb) ≃ Ti > Dy ≃ (Li) > Ho = Y > Yb. This rule works in general and suggests that the overall fractionation processes operating during magma generation and evolution are relatively simple, involving no significant change in the environment of formation for MORBs and OIBs. In detail, minor differences in element ratios correlate with the istopic characteristics of different types of OIB components (HIMU, EM, MORB). These systematics are interpreted in terms of partial-melting conditions, variations in residual mineralogy, involvement of subducted sediment, recycling of oceanic lithosphere and processes within the low velocity zone. -from Authors
Arguments are made in favor of using variation diagrams to plot analyses of igneous rocks and their derivatives and modeling differentiation processes by least-squares mixing procedures. These methods permit study of magmatic differentiation and related processes in terms ofall of the chemical data available. Data are presented as they are reported by the chemist and specific processes may be modeled and either quantitatively described or rejected as inappropriate or too simple.
Examples are given of the differing interpretations that can arise when data are plotted on an AEM ternary vs. the same data on a full set of MgO variation diagrams. Mixing procedures are illustrated with reference to basaltic lavas from the Columbia Plateau.
Based on extensive seismic profiling it is postulated that the Caribbean is a relict of Mesozoic Pacific crust that was emplaced between North and South America during separation from Europe and Africa. The interaction of the Caribbean plate with the circumCaribbean lands resulted in the formation of geosynclines. The Caribbean plate subsequently has decoupled from the parent Pacific spreading system and is protected from being assimilated into the mantle by the presence of crustal sinks on both the east and west margins.
The island of Hispaniola is one of the largest land masses straddling the North American-Caribbean plate boundary and is a critical area for testing ideas about the development of the plate boundary. The aims of this volume include establishing a systematic geologic database and stratigraphic nomenclature for the island; testing recent models for the tectonic evolution of Hispaniola; and studying a variety of plate boundary zone processes including evolution of island arcs, the transition between arc and strike-slip tectonics, and terrane accretion. The 18 chapters (abstracted separately) are organized into two sections: the first section describes and interprets the composition and structure of early Cretaceous to middle Eocene rocks of the Hispaniola volcanic arc, the second section describes and interprets late Eocene to Recent sedimentary rocks which postdate arc activity and were formed in a collisional or strike-slip environment. A set of regional geologic maps of the Dominican Republic are included. -A.W.Hall
Potassium-argon ages of hornblende, biotite, and whole rocks in Puerto Rico include the following: 126 m. y. for amphibolites in the southwest part of the island; 109 m. y. for the oldest known quartz diorite plutons; 88 to 65 m. y. for emplacement of various quartz diorite and granodiorite batholiths and stocks; 38 to 46 m. y. for intrusions of quartz diorite porphyry stocks and their hydrothermal alteration and mineralization. These intrusions are the youngest known igneous rocks in Puerto Rico. In addition, a 35-m. y. age was determined for hornblende and biotite from the Virgin Gorda batholith. Although widespread hydrothermal alteration as old as 75 m. y. is known in Puerto Rico, all important copper deposits are related to the 38- to 46-m. y. old intrusions.
This chapter presents a synthesis of the most relevant geological and tectonic features of the land and continental margin that borders the Pacific Ocean from southern Mexico to northwestern Colombia (Fig. 1). The objectives are to emphasize the variations in geological constitution of different segments of the region and to review briefly the major problems in understanding the geological history and the tectonic processes that resulted in its present configuration.
The Late Miocene Talamanca Intrusive Suite (TIS) represents one of the youngest and most extensively exposed plutonic suites associated with orogenesis in the world. Rapid uplift associated with subduction of the Cocos Ridge (approx 5 Ma) is primarily responsible for exposing this plutonic core. In addition, a combination of Pleistocene glacial and recent rain forest conditions provided an efficient erosional mechanism for unroofing the Cordillera de Talamanca and generating an eclectric mix of geomorphological features. Four major lithologic groupings are made on igneous rocks of the Cordillera de Talamanca, which include mid-Oligocene tholeiitic gabbros, mid-Oligocene El Baru plutonic rocks, Late Miocene calc-alkaline TIS, and a Plio-Pleistocene volcanic group. -from Authors
Twenty-four piston core sediment samples and 13 sediments and 3 basalts from DSDP Leg 78 Site 543 were analyzed for Sr, Nd and Pb isotopic compositions. The results show sediment with highly radiogenic Pb up to 19.8) and rather radiogenic Sr and unradiogenic Nd has been deposited in the region since the Cretaceous. The source of this sediment is probably the Archean Guiana Highland, which is drained by the Orinoco River. Pb and Sr isotopic compositions and sediment thickness decrease and increases northward due to a decrease in turbiditic component. This decrease is partly due to the damming action of basement ridges. Rare earth concentrations in the sediments are somewhat low, due to the abundance of detrital and biogenic components in the sediment and rapid sedimentation rates. Both positive and negative Ce anomalies occur in the surface sediments, but only positive Ce anomalies occur in the Site 543 sediments. It is unlikely that sediment subducted to the source region of Lesser Antilles arc magmas could be the cause of negative Ce anomalies in those magmas.Isotopic compositions of Site 543 basalts show some effect of contamination by seawater-basalt reaction products and sediments. Beyond this, however, they are typical of “normal” depleted MORB.
The occurrences of arc tholeiites in the two active subduction zones
involving the Caribbean plate, Central America and the Lesser Antilles,
are quite restricted. Volcanic rock suites exhibiting strong iron
enrichment are limited to five volcanoes, all in Central America. Three
of the five occur along the Nicaraguan portion of the volcanic front
beneath which the arc crust is thinnest. On the other hand, volcanic
rock suites with low absolute concentrations of large ion lithophile
elements and light rare earth elements are largely confined to two
northern islands in the Lesser Antilles, St. Kitts and St. Eustatius,
and solely confined to the Nejapa-Granada cinder cone alignments of
Nicaragua in Central America. These tholeiitic characteristics, strong
iron enrichment and low concentrations of certain incompatible elements,
are produced by dissimilar processes. Strong iron enrichment results
from extensive fractional crystallization at low pressure or with low
water contents, perhaps in shallow magma bodies, whereas low absolute
concentrations of specific incompatible elements are governed by
relatively high degrees of source melting. The high degree of melting is
made possible by a greater flux of material from the subducted plate.
Crustal contamination exerts only a secondary and local control on
incompatible element concentrations, at least in Central America.
The Eastern Loma de Cabrera Batholith, located in the NW Cordillera Central, Dominican Republic, is a heterogeneous intrusive complex composed of a zoned ultramafic-mafic core surrounded by tonalite and diorite. The batholith intrudes metasbasaltic rocks of the Duarte Complex of early Cretaceous age. The ultramafic-mafic core consists of peridotite, olivine-pyroxenite, pyroxenite, and augite-hypersthene gabbro-norite. Pyroxenites and gabbro-norites exhibit large scale interlayering and small scale layering involving a regular variation in the proportions of ortho- and clinopyroxene. Tonalities and diorites are mafic to leucocratic, some being porphyritic. Petrographic types include hornblende, hornblende-pyroxene, hornblende-biotite, and muscovite-biotite types. Aplites are abundant. Intrusive relations suggest that ultramafic-mafic complex is the oldest intrusive phase, and was partially amphibolitized during later intrusion of the felsic rocks. Ultramafic-mafic rocks contain 43-54% SiOâ and MgO ranges from 8-45%. Trace and REE in these rocks are relatively depleted. Tonalitic rocks range in SiOâ from 53-76%, with KâO varying from 0.15-2.9%. In addition, they are LREE enriched. A small Eu anomaly is best explained by fractionation of plagioclase and hornblende. Trends shown by Rb-Sr data suggest that fractional crystallization of hornblende and plagioclase, that is high level fractionation, is the important factor in controlling chemical variation in the tonalites.
A volcanic suite of olivine-rich alkali picrites, basanites and alkali basalts, rich in normative nepheline, occur on the island of Grenada and are Late Tertiary to Recent in age. They appear to be near-contemporaneous with subalkaline basalts and the more usual calc-alkaline andesites which, with dacites, characterize the other volcanic islands of this Lesser Antilles island arc. Major and trace element data suggest a sequence of primary, hydrous, mantle-derived melts from picritic to basanitic compositions. The alkali olivine basalts (rich in alumina) constitute a link between the undersaturated suite and the high-alumina, subalkaline basalts, andesites and dacites with saturated and oversaturated compositions. Experimental work is needed to establish the conditions for this critical association of magmas, particularly in regard to the role played by fractionation of nepheline-normative amphibole from alkalic magmas, at moderately low pressures. This paper is concerned more with the evidence for undersaturated nephelinic magmas derived by partial melting of Upper Mantle material in an island-arc environment.
A series of pelagic clays and nannofossil oozes from the Nazca plate have been analysed for REE and other trace elements. A calculated average - Pacific Authigenic Weighted Mean Sediment (PAWMS) - shows light REE-enrichment (La n/Yb n approx 4.5), high contents of Ba and Sr, but low abundances of Rb, Nb and Ta; large negative Ce anomalies (Ce/Ce* approx 0.2) are also found. An attempt is made to model the contributions of PAWMS-type material to the source of the magmas of the Mariana island arc, an intra-oceanic arc far from the effect of continent-derived detritus. Only small amounts of pelagic sediment (0.3-0.5%) are needed to develop the negative Ce anomalies, high Ba/La ratios, and high LIL/HFS-element ratios which characterize these lavas, though a small fluid contribution from the dehydrating subducted oceanic crust is needed to give the high Rb/Ba found in several Mariana suites. Volumetrically it would appear that much of the sediment approaching the Mariana trench may be recycled into the deeper mantle, but incorporation of such material alone cannot account for the trace-element and isotope chemistry of ocean islands. -R.A.H.
Geochemical variations in modern subduction-related igneous suites with respect to arc maturity in time and space are illustrated using data for extrusive (basalt, andesite and dacite) and intrusive suites (diorite, tonalite, granodiorite, granite) from circum-Pacific arcs. Two groups of processes are believed to control the variation in the parental magmas: 1) subduction-zone enrichment of lithospheric mantle, locally coupled with crustal assimilation allied with fractional crystallization in zones of thickened crust, all of which yield magmas with enhanced concentrations of LIL elements; and 2) with increasing distance from the active trench, contributions from within-plate sub-continental lithosphere producing mantle-derived magmas with enhanced levels of high field strength (HFS) elements, among which Nb, Ta, Hf and Y are distinctive. Even for the evolved granitic rocks of intrusive arc series, the ratios of HFS/LIL elements not significantly affected by crystal fractionation, e.g. (Ta,Nb)/(K,Rb,La), may throw some light on the origin of mafic-intermediate precursor magmas. The following criteria are suggested: 1) primitive calcic arc granitic rocks have low LIL- and HFS- element abundances, 2) normal calc-alkaline continental arc granitic rocks have enhanced LIL-element abundances and low HFS/LIL ratios, 3) mature alkali-calcic arc granitic rocks have high levels of LIL and HFS elements and higher HFS/LIL ratios and 4) back-arc anorogenic alkaline granitic rocks have the highest levels of HFS elements.-R.A.H.
Goldschmidt's definition (1916) of the rock name “trondhjemite,” unfortunately, was not quantitative. Furthermore, the trondhjemite intrusives of the type area, south of Trondheim, Norway, have had much of their original mineralogy obliterated by metamorphism to greenschist facies. The author suggests that the IUGS definition of trondhjemite as leucotonalite be followed, except that andesine-bearing leucotonalite be termed calcic trondhjemite, and that albite-bearing leucotonalite, as well as the oligoclase variety, be termed trondhjemite.
K-Ar age determinations, mainly whole rock, with some corroboration from mineral separates, are presented for lava flows, domes, minor intrusives and blocks in tuffs from 95 localities in the Lesser Antilles. Together with the much smaller number of previously published data, these show a distinction between a range 38-10 million years (Ma) in the outer arc (Limestone Caribbees) and less than 7.7 Ma in the inner arc (Volcanic Caribbees). From southern Martinique southwards, the two arcs are superposed, and the whole range is fragmentarily represented. The observed age ranges in the outer and inner arcs fit between discontinuities in sea floor spreading in the North Atlantic at ca. 38 and ca. 9 Ma and a causal connection between spreading change and relocation of arc volcanicity is suggested. Palaeomagnetic directions at 108 localities in ten of the islands fall into normal ( N = 56, k = 13.8, D = 359°, I = + 22°, pole position 229° E, 89° N with drjr = 3°, d X = 6°) and reversed groups ( N = 41, k = 14.1, D = 178°, I = -22°, pole position 18° E, 88° S with d xjr = 3°, dx = 6°) plus six sites of intermediate polarity and five sites indeterminate. The mean dipole axis is within 2° of the present rotation axis and is likely to be identical with it with a probability of 99%. The data are generally in accord with the established geomagnetic polarity time scale, but there is some suggestion of a normal polarity event at ca. 1.18 Ma within the Matuyama Reversed Epoch. The palaeomagnetic data relate mainly to be past 10 Ma and suggest that within that time the Lesser Antilles have not changed their latitude or geographic orientation, and that the geomagnetic field has averaged that of a centred axial dipole. The few older palaeomagnetic data are consistent with these same conclusions (though with less certainty) back to ca. 20 Ma ago. There is no evidence for oroclinal bending of the arc since then.
A comparison of the trace-element abundances and radiogenic isotope
ratios in oceanic basalts and the primordial mantle suggests that the
present suboceanic upper mantle has undergone depletion and, in some
places, recent re-enrichment events. The following model is proposed:
Incipient partial melts were removed from much of the Archean mantle;
this caused a depletion in the hygromagmatophile (incompatible) trace
elements. At the same time, higher levels of the mantle were veined with
these melts and were thus enriched. Trace-elements and radiogenic
isotope data indicate that mantle sources of basalts which erupted at
oceanic hot spots have had a complex, multistage evolution from the
primordial mantle and consist of more than one component. A mixing
process involving the veining of parts of the mantle on a centimetre
scale by an undersaturated mafic magma is preferred to the mantle-plume
model. Some quantitative mixing models show that the trace-element
chemistry of hot-spot mantle sources can be generated by introducing
about 5% of an undersaturated mafic magma into a mantle source for a
normal mid-ocean ridge.
143Nd/144Nd, 87Sr/86Sr and REE results are reported on volcanic rocks from the islands of Dominica and St. Kitts in the Lesser Antilles. Particular attention is given to the lavas and xenoliths of the Foundland (basalt-andesite) and the Plat Pays (andesite-dacite) volcanic centres on Dominica. Combined major and trace element [2] and isotope results suggest that the bulk of the andesites and dacites on Dominica, and by analogy in the rest of the arc, are produced by fractional crystallisation of basaltic magma. The differences in the erupted products of the two volcanoes do not appear to be related to any significant differences in the source rocks of the magmas. Along the arc 87Sr/86Sr ratios range from 0.7037 on St. Kitts, to 0.7041-0.7047 on Dominica, and 0.7039-0.7058 on Grenada [5], and these are accompanied by a parallel increase in K, Sr, Ba and the light REE's. Moreover, compared with LIL-element-enriched and -depleted rocks from MOR and intraplate environments, the basic rocks from the Lesser Antilles are preferentially enriched in alkaline elements (K, Ba, Rb, Sr) relative to less mobile elements such as the rare earths. 143Nd/144Nd varies from 0.51308 on St. Kitts, to 0.51286 on Dominica, and 0.51264-0.51308 on Grenada [5], and all these samples have relatively high 87Sr/86Sr ratios compared with the main trend of Nd and Sr isotopes for most mantle-derived volcanic rocks. Alkaline elements and 87Sr appear to have been introduced from the subducted ocean crust, but the results on other, less mobile elements are more ambiguous - island arc tholeiites (as on St. Kitts) do not appear to contain significant amounts of REE's, Zr, Y, etc., from the subducted oceanic crust, but such a contribution may be present in more LIL-element-enriched calc-alkaline rock types.
87Sr/86Sr and 143Nd/144Nd ratios, REE, K2O, Rb and Sr are presented for a variety of basanitoids, alkalic and subalkalic basalts, and calc-alkalic rocks from the island of Grenada, Lesser Antilles. The 87Sr/86Sr ratios vary from 0.7039 to 0.7058 whereas, with one exception, the 143Nd/144Nd ratios cover a small range from 0.51282 to 0.51308. There is a reasonable correlation between Sm/Nd and 143Nd/144Nd, but not between Rb/Sr and 87Sr/86Sr. The ankaramites tend to have higher K2O and Sr contents, but lower 87Sr/86Sr ratios than the microphyric basalts.A broad negative correlation between Nd and Sr isotopes is observed but it is both displaced to relatively higher 87Sr/86Sr ratios and has a flatter slope than most of the available results on mid-ocean ridge and ocean island basalts. The high 87Sr/86Sr ratios are thought to reflect a contribution from seawater affected material in the subducted ocean crust and yet they are observed in SiO2-undersaturated rocks which are most unlikely to have been derived by melting of subducted ocean crust. This is reconciled in a model whereby the alkalic elements are preferentially released during dehydration of the subducted lithosphere and contaminate the overlying mantle source region of the arc magmas.
Granodiorite intrusions in Jamaica were assigned by early workers to various ages from Pre-Cambrian to late Tertiary. Recent surveys have shown that the granodiorite intrudes Maestrichtian sediments and has provided material for pebbles in an Eocene conglomerate. Its age is therefore very late Cretaceous or very early Tertiary. Radio-metric determinations using Potassium/Argon; Rubidium/Strontium and isotopic lead methods suggest an age of 65 ± 5 million years.
Subduction related basalts display wide ranges in large ion lithophile element ratios (e.g., Rb/Ba and Rb/ Sr) which are unlikely to result from mixing, but suggest a role for small degree partial melting of a relatively Rb-poor mantle wedge source. However, these variations do not correlate with other trace element criteria, such as the depletions of high field strength elements (HFSE) and light rare earth elements (LREE) relative to the LILE, which characterise subduction related magmatism. Integration of radiogenic isotope and trace element data demonstrates that the elemental enrichment cannot be simply related to two component mixtures inferred from isotopic variations. Thus a minimum of three components is required to describe the geochemistry of subduction zone basalts. Two are subduction related: high Sr/Nd material is derived from the dehydration of subducted basaltic ocean crust, and a low Sr/Nd component is thought to be from subducted terrigenous sediment. The third component is in the mantle wedge, it is usually similar to the source of MORB, particularly in its isotopic composition. However, in some cases, notably continental areas, more enriched mantle wedge material with relatively high 87Sr/86Sr, low 143Nd/144Nd and elevated incompatible trace element contents may be involved Mixing of these three components is capable of producing both the entire range of Sr, Nd and Pb isotope signatures observed in destructive margin basalts, and their distinctive trace element compositions. The isotope differences between Atlantic and Pacific island arc basalts are attributed to the isotope compositions of sediments in the two oceans.
New Pb-, Sr-, and Nd-isotopic data have been obtained for the rocks of volcanoes overlying a wide range of depths (100–580 km) to the Wadati-Benioff Zone (WBZ) in the New Britain island arc, Papua New Guinea. Well-defined trends consistent with two-component mixing are observed in combined Pb-isotope/trace-element plots. One of the components is believed to represent a slab contribution whose isotopic signature, unlike those noted for several other arcs, appears to be dominated by subducted, altered, oceanic crust rather than by sediment. This conclusion is consistent with the results of a recent Be–B study of New Britain rocks. The influence of the slab component is considered to decrease as depth to the WBZ increases. Higher abundances of high-field-strength elements correlate with increasing depths to the WBZ, and may be indicative of smaller degrees of partial melting of the mantle wedge as WBZ depths increase. Abundances of other incompatible elements appear to reflect a complex interplay between the slab-derived flux and melting process.
At head of title: Rice University. Thesis--Rice University. Photocopy.
The development of the Caribbean is discussed in terms of modern tectonic theory. The nature of the site on which the Caribbean formed is examined, and the development of the rifted margins of the Caribbean is described. Constraints on Caribbean evolution from the relative motions of North and South America are briefly examined, and the Caribbean Oceanic Plateau is discussed. The great island-arc system of the Caribbean is addressed in detail, emphasizing the way the Great Arc of the Caribbean was segmented. The role of Central America in Caribbean history is briefly considered.
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