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Petrographical images (plane polarized light) of the main garnet types defined in sample 2. A: Type 1 garnet shows a large inclusion-free core and scattered quartz inclusions in the rim. B: Type 2 garnet shows a core with abundant euhedral inclusions of quartz and a thick inclusion-free rim. C: Type 3 garnet contains large lobular inclusions of quartz in the core and smaller quartz inclusions toward the rim. D: Type 4 garnet shows a core rich in small apatite and quartz inclusions, which increase in size in the outer zones, and an inclusion-free rim. E and F: Type 5 garnet shows a rutile-rich core and an inclusion-free rim (E). The zoning is not clear in the strongly corroded porphyroblasts (F). Red arrows mark the position of the chemical profiles shown in Fig. 6.
Source publication
Garnet from diamondiferous granulites of Ceuta (Betic-Rif cordillera,
Spain and Morocco) contains a variety of inclusion types. To better
understand the evolution of these rocks during the ultrahigh pressure
event, two samples (1 and 2) were selected for the detailed study of
garnet. Primary inclusions of apatite, quartz, coesite, rutile and
retrog...
Contexts in source publication
Context 1
... from sample 2 contains, except for type 1, abundant inclu- sions of different nature (Fig. 5). Although locally coexisting, the several inclusion types appear concentrated in different porphyroblasts, follow- ing a common pattern: An inclusion-rich core is surrounded by an inclusion-free ...
Context 2
... quartz inclusions show anomalous morphology and birefrin- gence ( Fig. 9C and D). The inclusions are surrounded by anomalous birefringent fields indicating a strong strain of garnet around them (Fig. 9D). In some cases, the strain results in mechanical disturbances in the host garnet to form small microfractures (Fig. 9E). The anomalous morphology can be better observed in the BSE images, in the case of the numerous hollows produced as a consequence of the inclusion loss during polishing (Fig. 9F). This behavior is suggestive of the presence of a silica polymorph with hardness higher than garnet. Very similar quartz inclusions in shape and morphology have been interpreted as formed from coesite (Tomilenko et al., 2009, Fig. 3). The Raman spectra are dominated by the bands of quartz although small bands (at 269 and 521 cm −1 ) that can be interpreted as due to coesite (Boyer et al., 1985) are frequently present (Fig. 9G). The spectrum with the most intense coesite bands, obtained from the inclusion labeled as Qz + Coe in Fig. 9A, is shown in Fig. 9H. Despite coesite shows in most cases weak bands (e.g. Fig. 9I-a), the 521 cm −1 one cannot be ascribed to garnet ( Type 3 garnet contains large (~200 μm) quartz inclusions with a lobular shape in the core, and rounded inclusions toward the rim (Fig. 5C). The large quartz inclusions display morphologies (Fig. 10A) sim- ilar to the melt-derived quartz inclusions trapped by garnet during exper- imental melting of metapelites ( Spandler et al., 2010, Fig. 1B). We have also identified similar quartz inclusions coexisting with "granitic" inclu- sions unambiguously derived from trapped melt in other zones of the Betic belt (unpublished data). Quartz includes, in turn, phengite, clusters of aluminosilicate (Fig. 10B) and minute inclusions of moissanite (Fig. 10C). Whereas moissanite is easily identified by Raman spectroscopy (Fig. 10D), the aluminosilicate phase shows bands suggesting the current coexistence of several phases (Fig. 10E). In type 4 garnet the dominant inclusion type is apatite. The garnet cores show high density of apatite inclusions, which are seen either as short prisms (b10 μm in length) and rods (Fig. 11A), as needles ( Fig. 11B), and as rarer hexagonal crystals (~ 30 μm) from which needles emerge (Fig. 11C). Apatite coexists with quartz, kyanite and with needles of a silica phase interpreted as coesite (Fig. 11D) on the basis of the lack of quartz bands and of the presence of bands at 178 and 521 cm −1 in the Raman spectra (Fig. 11F), Zircon, xenotime, rutile and graphite are frequent phases associated with apatite (Fig. 11E). Small transparent inclusions in zircon and xenotime are diamonds, according to the Raman spectra (Fig. 11G), which are sim- ilar to those provided by diamond from type 1 garnet in sample 1. The geometrical pattern defined by prismatic apatite is difficult to be de- duced from the petrographical images (Fig. 11A) given the size variations, the high density of inclusions located at different depths and the presence of inclusions of other phases. Despite apatite and garnet show similar contrast in the BSE images, these indicate that apatite needles and prisms define equilateral triangles, whereas coesite needles show an orthogonal pattern. Both phases seem to share, however, one of the directions (Fig. ...
Context 3
... sample 2 five garnet types can be distinguished on the basis of the dominant inclusion types and location ( Fig. 5): Type 1 garnet (the most abundant) shows very variable size and appears located both in biotite-rich and in quartz-feldspar-rich domains. It consists of a thick inclusion-free core and a rim containing scarce quartz inclu- sions (Fig. 5A); type 2 garnet, also showing variable size, consists of a core with abundant oriented euhedral quartz inclusions and a thick inclusion-free rim (Fig. 5B); diamond has been identified in the quartz-rich core; type 3 garnet is scarce and appears in quartz-rich domains, as large porphyroblasts containing quartz inclusions with a lobular shape in the core and scarce rounded quartz inclusions in the rim (Fig. 5C); type 4 garnet was only found in two of the studied thin-sections. It appears located in the biotite + sillimanite-rich domains and consists of a core with abundant inclusions of apatite and minor quartz and an inclusion-free rim (Fig. 5D); small diamonds are present as inclusions in phases associated with apatite; type 5 garnet only appears in the biotite + sillimanite-rich domains as small, strongly corroded porphyroblasts. It contains high concentration of rutile inclusions in the core, which increase in size toward the rim, and incomplete inclusion-free rims ( Fig. 5E and ...
Context 4
... sample 2 five garnet types can be distinguished on the basis of the dominant inclusion types and location ( Fig. 5): Type 1 garnet (the most abundant) shows very variable size and appears located both in biotite-rich and in quartz-feldspar-rich domains. It consists of a thick inclusion-free core and a rim containing scarce quartz inclu- sions (Fig. 5A); type 2 garnet, also showing variable size, consists of a core with abundant oriented euhedral quartz inclusions and a thick inclusion-free rim (Fig. 5B); diamond has been identified in the quartz-rich core; type 3 garnet is scarce and appears in quartz-rich domains, as large porphyroblasts containing quartz inclusions with a lobular shape in the core and scarce rounded quartz inclusions in the rim (Fig. 5C); type 4 garnet was only found in two of the studied thin-sections. It appears located in the biotite + sillimanite-rich domains and consists of a core with abundant inclusions of apatite and minor quartz and an inclusion-free rim (Fig. 5D); small diamonds are present as inclusions in phases associated with apatite; type 5 garnet only appears in the biotite + sillimanite-rich domains as small, strongly corroded porphyroblasts. It contains high concentration of rutile inclusions in the core, which increase in size toward the rim, and incomplete inclusion-free rims ( Fig. 5E and ...
Context 5
... sample 2 five garnet types can be distinguished on the basis of the dominant inclusion types and location ( Fig. 5): Type 1 garnet (the most abundant) shows very variable size and appears located both in biotite-rich and in quartz-feldspar-rich domains. It consists of a thick inclusion-free core and a rim containing scarce quartz inclu- sions (Fig. 5A); type 2 garnet, also showing variable size, consists of a core with abundant oriented euhedral quartz inclusions and a thick inclusion-free rim (Fig. 5B); diamond has been identified in the quartz-rich core; type 3 garnet is scarce and appears in quartz-rich domains, as large porphyroblasts containing quartz inclusions with a lobular shape in the core and scarce rounded quartz inclusions in the rim (Fig. 5C); type 4 garnet was only found in two of the studied thin-sections. It appears located in the biotite + sillimanite-rich domains and consists of a core with abundant inclusions of apatite and minor quartz and an inclusion-free rim (Fig. 5D); small diamonds are present as inclusions in phases associated with apatite; type 5 garnet only appears in the biotite + sillimanite-rich domains as small, strongly corroded porphyroblasts. It contains high concentration of rutile inclusions in the core, which increase in size toward the rim, and incomplete inclusion-free rims ( Fig. 5E and ...
Context 6
... sample 2 five garnet types can be distinguished on the basis of the dominant inclusion types and location ( Fig. 5): Type 1 garnet (the most abundant) shows very variable size and appears located both in biotite-rich and in quartz-feldspar-rich domains. It consists of a thick inclusion-free core and a rim containing scarce quartz inclu- sions (Fig. 5A); type 2 garnet, also showing variable size, consists of a core with abundant oriented euhedral quartz inclusions and a thick inclusion-free rim (Fig. 5B); diamond has been identified in the quartz-rich core; type 3 garnet is scarce and appears in quartz-rich domains, as large porphyroblasts containing quartz inclusions with a lobular shape in the core and scarce rounded quartz inclusions in the rim (Fig. 5C); type 4 garnet was only found in two of the studied thin-sections. It appears located in the biotite + sillimanite-rich domains and consists of a core with abundant inclusions of apatite and minor quartz and an inclusion-free rim (Fig. 5D); small diamonds are present as inclusions in phases associated with apatite; type 5 garnet only appears in the biotite + sillimanite-rich domains as small, strongly corroded porphyroblasts. It contains high concentration of rutile inclusions in the core, which increase in size toward the rim, and incomplete inclusion-free rims ( Fig. 5E and ...
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... sample 2 five garnet types can be distinguished on the basis of the dominant inclusion types and location ( Fig. 5): Type 1 garnet (the most abundant) shows very variable size and appears located both in biotite-rich and in quartz-feldspar-rich domains. It consists of a thick inclusion-free core and a rim containing scarce quartz inclu- sions (Fig. 5A); type 2 garnet, also showing variable size, consists of a core with abundant oriented euhedral quartz inclusions and a thick inclusion-free rim (Fig. 5B); diamond has been identified in the quartz-rich core; type 3 garnet is scarce and appears in quartz-rich domains, as large porphyroblasts containing quartz inclusions with a lobular shape in the core and scarce rounded quartz inclusions in the rim (Fig. 5C); type 4 garnet was only found in two of the studied thin-sections. It appears located in the biotite + sillimanite-rich domains and consists of a core with abundant inclusions of apatite and minor quartz and an inclusion-free rim (Fig. 5D); small diamonds are present as inclusions in phases associated with apatite; type 5 garnet only appears in the biotite + sillimanite-rich domains as small, strongly corroded porphyroblasts. It contains high concentration of rutile inclusions in the core, which increase in size toward the rim, and incomplete inclusion-free rims ( Fig. 5E and ...
Context 8
... sample 2 five garnet types can be distinguished on the basis of the dominant inclusion types and location ( Fig. 5): Type 1 garnet (the most abundant) shows very variable size and appears located both in biotite-rich and in quartz-feldspar-rich domains. It consists of a thick inclusion-free core and a rim containing scarce quartz inclu- sions (Fig. 5A); type 2 garnet, also showing variable size, consists of a core with abundant oriented euhedral quartz inclusions and a thick inclusion-free rim (Fig. 5B); diamond has been identified in the quartz-rich core; type 3 garnet is scarce and appears in quartz-rich domains, as large porphyroblasts containing quartz inclusions with a lobular shape in the core and scarce rounded quartz inclusions in the rim (Fig. 5C); type 4 garnet was only found in two of the studied thin-sections. It appears located in the biotite + sillimanite-rich domains and consists of a core with abundant inclusions of apatite and minor quartz and an inclusion-free rim (Fig. 5D); small diamonds are present as inclusions in phases associated with apatite; type 5 garnet only appears in the biotite + sillimanite-rich domains as small, strongly corroded porphyroblasts. It contains high concentration of rutile inclusions in the core, which increase in size toward the rim, and incomplete inclusion-free rims ( Fig. 5E and ...
Context 9
... results indicate, despite the complex orientation relation- ships, that most apatite, coesite and rutile (in type 4 and 5 garnet), and the small quartz ± coesite inclusions (in type 2 garnet) have all characteristics of true exsolution microstructures ( Liu et al., 2009), including the idiomorphic shape (Figs. 9, 11 and 12), the dense and homogeneous distribution in the garnet core (Fig. 5B, D and E) and the crystallographic control by garnet (Figs. 13 and ...
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... Consequently, there are large uncertainties in the tectonic reconstructions used to frame the geodynamic environment responsible for orogeny and crustal thickening in the region. This is clearly evident in the Western Mediterranean (Figure 1), where a widespread early Miocene thermal event is documented across the metamorphic hinterland of the Betic-Rif orogen (the so-called Alboran Domain; see Bessière et al., 2021 for a recent review) and debate continues in relation to the Alpine tectonometamorphic evolution of the Alboran Domain, with regard to: (a) the geodynamic scenario during consumption of the Neotethys ocean and formation of the Apennine-Maghrebian-Betic orogen, with models involving either double or single subduction scenarios (see e.g., Bessière et al., 2021;Carminati et al., 2012;Daudet et al., 2020;Faccenna et al., 2004;Handy et al., 2010;Lacombe & Jolivet, 2005;Leprêtre et al., 2018;Malusà et al., 2015;Molli & Malavieille, 2011;Pedrera et al., 2020;Platt et al., 2006;Romagny et al., 2020;Rosenbaum et al., 2002;van Hinsbergen et al., 2020;Vergés & Fernàndez, 2012;Williams & Platt, 2018); (b) the age of crustal thickening and thinning, including the role of structural inheritance (e.g., Acosta-Vigil et al., 2014;Augier et al., 2005;Gueydan et al., 2015;Homonnay et al., 2018;Li & Massonne, 2018;Massonne, 2014;Michard et al., 1997;Montel et al., 2000;Platt & Vissers, 1989;Platt & Whitehouse, 1999;Platt et al., 1998Platt et al., , 2005Platt et al., , 2006Rossetti et al., 2010Rossetti et al., , 2020Ruiz Cruz & Sanz De Galdeano, 2013;Sánchez-Navas et al., 2014Sánchez-Rodríguez & Gebauer et al., 2000;Zeck & Whitehouse, 2002;Zeck & Williams, 2001); (c) the metamorphic conditions prevailing during late-orogenic extension (e.g., Azañón et al., 1998;Michard et al., 2006;Platt et al., 1998Platt et al., , 2003aPlatt et al., , 2003bVidal et al., 1999); and (d) the tectonic evolution of the back-arc regions, with models showing continuous extension, pulses of shortening or transpressional shearing (e.g., Azañón & Crespo-Blanc, 2000;Balanyá et al., 1997;Booth-Rea et al., 2007;Frasca et al., 2017;Hidas et al., 2013;Garrido et al., 2011;Gueydan et al., 2019;Mazzoli & Martín-Algarra, 2011;Platt & Vissers, 1989;Platt et al., 2003aPlatt et al., , 2003bRossetti et al., 2005). ...
The variety of temporal and structural constraints on the Alpine tectonometamorphic signature of the metamorphic core of the Betic‐Rif orogen (Alboran Domain) has supported a long‐lasting debate regarding the Alpine tectonic and geodynamic evolution of the Western Mediterranean region. Uncertainty still exists on the timing and tectonic significance of (a) the Alpine orogenic construction; (b) exhumation of the deep roots of the orogen; and (c) transition from orogenic shortening to crustal extension. In this study, we address these major geological issues by focusing on the lower‐grade units of the Alboran Domain (Upper Sebtides and Ghomarides) exposed in the Rif belt of northern Morocco. Through a multidisciplinary approach that integrates mesostructural and microstructural investigations with X‐ray diffraction, quantitative mineral chemistry, and ⁴⁰Ar/³⁹Ar geochronology, a 20 Ma long tectonic history is reconstructed, which involves burial of the tectonic units at depth (late Eocene) and postorogenic exhumation under brittle conditions in the upper crust (early Miocene). We document a Priabonian (∼37‐34 Ma) D1/M1 progressive compressional deformation, during the formation of a SW‐verging orogenic wedge (present coordinates), accreted toward the Africa plate. Brittle extensional detachment tectonics operated during the Burdigalian (∼18‐17 Ma), controlling the thinning of the previously structured Alboran Domain nappe stack and the final exhumation of the Alpine orogenic units. We propose that transition from orogenic build‐up to collapse in the hinterland of the Betic‐Rif orogen occurred when the retreat of the Apennine‐Maghrebian subduction was efficient to drive transition from shortening to extension in the back‐arc domain of the western termination of the Apennine‐Maghrebian subduction zone.
... The Filali units underwent a poly-phased metamorphic E. Homonnay et al. Tectonophysics 722 (2018) 507-535 evolution recording a Variscan ultra-high pressure/high temperature event (4.3 to 7 GPa and 1100 °C), superimposed with Alpine highpressure/high-temperature (750-870 °C and 9-13 kbar) then lowpressure/high-temperature (650-750 °C and 3-5 kbar) conditions (El Maz and Guiraud, 2001;Haissen et al., 2004; Ruiz Cruz and Sanz de Galdeano, 2012ade Galdeano, , 2012bde Galdeano, , 2013Gueydan et al., 2015). The Upper Sebtides (Federico units) is affected by an Alpine high-pressure/lowtemperature blueschist and eclogite facies metamorphism typical of subduction zone conditions ( Bouybaouène et al., 1995;Goffe et al., 1996). ...
... sliver of serpentinized peridotite;-the Ceuta paragneisses: mostly constituted of granulitic and migmatitic paragneisses in which relictual ultra-high pressure and temperature metamorphic minerals (i.e. diamond and coesite) have been recently identified in garnet inclusions (Ruiz Cruz and Sanz de Galdeano, 2012ade Galdeano, , 2012bde Galdeano, , 2013). Seldom geochronological data is available in all these units. ...
... Samples M10-32 and CEU13-16 are MHLU orthogneisses. See Table 1 de Galdeano (2012ade Galdeano ( , 2012bde Galdeano ( , 2013) are indicated in blue circles. CUU P-T path is represented in brown arrow. ...
In Western Mediterranean, the Rif belt in Morocco is part of the Gibraltar Arc built during the Tertiary in the framework of Eurasia-Africa convergence. The structural and metamorphic evolution of the internal units of this belt as well as their timing, crucial to constrain the geodynamic evolution of the Alboran Sea, is still largely debated. Our study on the Ceuta Peninsula (Northern Rif) provides new structural, petrological and geochronological data (U-Th-Pb, Ar-Ar), which allow to precise the tectono-metamorphic evolution of the Lower Sebtides metamorphic units with: (1) a syn-metamorphic thrusting event developed under granulite facies conditions (7–10 kbar and 780–820 °C). A major thrust zone, the Ceuta Shear Zone, drove the emplacement of metapelites and peridotitic lenses from the Ceuta Upper Unit over the orthogneisses of the Monte Hacho Lower Unit. This compressional event ended during the Upper Oligocene. (2) an extensional event developed at the boundary between amphibolite and greenschist facies conditions (400–550 °C and 1–3 kbar). During this event, the Ceuta Shear Zone has been reactivated as a normal fault. Normal ductile shear zones contributed to the final exhumation of the metamorphic units during the Early Miocene. We propose that the compressional event is related to the formation of an orogenic wedge located in the upper plate, in a backward position, of the subduction zone driving the geodynamic evolution of the Alboran domain. In this context, the episode of lithospheric thinning could be related to the opening of the Alboran basin in a back-arc position. Furthermore, unlike the previous models proposed for the Rif belt, the tectonic coupling between mantle peridotites and crustal metamorphic rocks occurred in Ceuta Peninsula at a depth of 20–30 km under high temperature conditions, before the extensional event, and thus cannot be related to the back-arc extension.
... In the Western Mediterranean Orogen (WMO), evidence for crustal rocks affected by UHP metamorphism are restricted to only few areas in the Betic-Rif orocline (Ruiz-Cruz and Sanz de Galdeano, 2013aGaldeano, , 2013b and more recently in the Maghrebides . The timing of UHP metamorphism in the WMO is however still the matter of controversy, with two alternatives corresponding to the two last main orogenic events that have affected this area, i.e. ...
Diamond-bearing UHP metamorphic rocks witness for subduction of lithospheric slabs into the mantle and their return to shallow levels. In this study we present U–Pb and trace elements analyses of zircon and rutile inclusions from a diamond-bearing garnet megacryst collected in a mélange unit exposed on the northern margin of Africa (Edough Massif, NE Algeria). Large rutile crystals (up to 300 μm in size) analyzed in situ provide a U–Pb age of interpreted as dating the prograde to peak subduction stage of the mafic protolith. Trace element analyses of minute zircons (≤30 μm) indicate that they formed in equilibrium with the garnet megacryst at a temperature of 740–810 °C, most likely during HP retrograde metamorphism. U–Pb analyses provide a significantly younger age of attributed to exhumation of the UHP units. This study allows bracketing the age of UHP metamorphism in the Western Mediterranean Orogen to the Oligocene/early Miocene, thus unambiguously relating UHP metamorphism to the Alpine history. Exhumation of these UHP units is coeval with the counterclockwise rotation of the Corsica–Sardinia block and most likely resulted from subduction rollback that was driven by slab pull.
... A later Variscan event is recorded by mineral assemblages (e.g. Ruiz Cruz and Sanz de Galdeano, 2013) and by the presence of late Variscan (280-265 Ma) granites. In contrast, possible pre-Alpine metamorphic events have been overprinted extensively by the Alpine assemblages in the Nevado-Filábride Complex (Puga et al., 2002). ...
Zircon from two types of orthogneisses (inheritance-rich and inheritance-poor) from Sierra Nevada (Betic Cordillera, Spain) was investigated by integrating U-Pb geochronology, cathodoluminescence and backscattered SEM imaging, laser-ablation inductively coupled plasma mass spectrometry analyses and Raman spectroscopy to examine the conditions of magmatic zircon growth and the variable extent and mechanisms of the Alpine modifications. Zircon from inheritance-rich gneiss consists of two main domains: inherited (Neoproterozoic-to-Early Paleozoic and Devonian) cores and magpper intercept with the Concordia at 287 + 21 -22 Ma and a lower intercept at 20.8 + 48.6 -20.8 Ma. Magmatic domains of zircon from inheritance-rich gneiss have lower rare-earth element (REE) contents than magmatic domains from inheritance-poor gneiss, reflecting the less evolved nature of the melt. Altered domains in zircon from inheritance-poor gneiss show greater U concentrations, lower REE concentrations and lower Th/U ratios relative to the cores, interpreted as representing Pb loss from the U-rich magmatic domains during the Alpine event. Morphological changes within single grains and between populations reflects the evolution during magmatic cooling.We show that, whereas classic methods allow two different interpretations for the geodynamic setting of the two types of gneisses, a complete study of composition, morphology and structure of zircon can help to decide that a model based on a common source for the granitic melt better fits the zircon characteristics than a model based on melts generated in two different geotectonic settings.
... The unusual P content of the garnet megacrysts in this study (up to at least 0.22 wt% P 2 O 5 ), together with their abundant internal precipitates of apatite and rutile, invite close comparison with similar features reported in garnet from ultrahigh-pressure (UHP) and mantle settings (Haggerty et al. 1994;Ye et al. 2000;Mposkos and Kostopoulos 2001;Ruiz Cruz and Sanz de Galdeano 2013). However, in the present example, the phosphatic garnet does not contain free SiO 2 inclusions, as might be expected for typical garnet in metapelites, nor has any free C yet been found either in the garnet or in matrix, so detection of conventional UHP minerals remains problematic at this locality. ...
Highly restitic garnet-kyanite-phlogopite metapelitic schists from the Goshen Dome of western Massachusetts contain: a population of prograde monocrystalline, megacrystic garnet, some with significant P in substitution for Si; precipitates of hydroxylapatite and rutile; and <1 μm zircon crystals of undetermined origin and abundance on the order of 10⁵/mm³. The unusual P content and the abundant internal precipitate suite are similar to features reported in garnet from ultrahigh-pressure (UHP) and mantle settings, suggesting a potential (U)HP origin for the garnet megacrysts. Zircon included in megacrysts is surrounded by radial fractures, indicating in situ volumetric expansion or new growth. Cores display rare earth element (REE) profiles and cathodoluminescence (CL) zoning consistent with magmatic growth, and yield only Paleozoic dates (447-404 Ma). The embayed core-rim boundary is marked by a several micrometers wide band of CL-dark zircon enriched in Y, P, U, and Th that is interpreted as the accumulation of redistributed xenotime component from the original zircon rim during metamorphism. Outside of this band, the rim has elevated Hf, Th/U << 1, and steep heavy REE profiles. The metamorphic rims yield concordant dates from 400 to 381 Ma. Matrix zircon grains have magmatic cores (1726-415 Ma) with similar core-rim boundaries enriched in Y, P, U, and Th. Metamorphic rims on matrix zircon yield slightly younger dates (393-365 Ma) and are compositionally heterogeneous. The difference between the youngest core and oldest rim indicates a short interval (ca. 4 Ma) between deposition of detrital zircon and the onset of metamorphism in the earliest Acadian. The oldest zircon rim dates are found within phosphatic garnet megacrysts of possible very high-pressure origin. The compositional uniformity of these rims indicates equilibrium with a single source; the anomalous composition suggests a combination of dissolution-reprecipitation and new growth of zircon that is derived from garnet. The range in both composition and dates indicates that matrix zircon rims formed in response to local changes in mineralogy and fluid/melt composition and/or availability. New growth of zircon on these grains cannot be confirmed, suggesting that dissolution-reprecipitation reactions during continued metamorphism may be the dominant mechanism that formed these rims. The data collectively suggest that dissolution-reprecipitation may be a common mechanism for producing metamorphic rims on zircon that does not require additional Zr and Hf, which are limited within most metamorphic settings.
... In the Alpujárride/Sebtide Complex, Permian (280-265 Ma) granitic magmatism consists of S-type granites whose source rocks, locally exposed on the surface, record an early Hercynian UHP metamorphic event as inclusions of diamond and coesite in garnet and apatite and as a variety of exsolution microstructures of apatite, rutile, and composite rutile1 silicate in garnet (Ruiz Cruz et al. 2011;Sanz de Galdeano 2013, 2014). In the Nevado-Filábride Complex treated here, the pre-Alpine metamorphic events have been extensively overprinted by the Alpine assemblages (Puga et al. 2002). ...
... It is interpreted that diamond precipitated from the FIs once they reached the stability field of diamond. Indeed, water-rich FIs, in some cases containing diamond, are common in UHP garnet (Frezzotti and Ferrando 2007;Frezzotti et al. 2011;Ruiz-Cruz and Sanz de Galdeano 2014). In the inclusions described by Frezzotti et al. (2011), the Raman spectra indicate, as in our case, the presence of graphite-like, poorly organized carbonaceous material intergrown with or coating diamonds. ...
Diamond inclusions have been found in apatite from a specific type of orthogneiss of a volcanosedimentary sequence from the deepest tectonic complex (Nevado-Filábride) of the Alpine Betic-Rif belt (Spain). This unusual finding led us to make a detailed petrographical and geochemical study, with the aim of characterizing ultrahigh-pressure (UHP) apatite and comparing it with the younger and widespread magmatic and/or metamorphic generations. The UHP apatite is abundant in biotite-rich orthogneisses, whereas it is lacking in the most common biotite-poor orthogneisses, which instead contain abundant magmatic apatite. In addition to diamond, UHP apatite contains abundant biphased inclusions consisting of chlorides and hydrocarbons. The late alteration of fluid inclusions caused oligomerization of hydrocarbons and graphitization of diamond, leading to a characteristic irregular outer brownish zone. The UHP apatite shows bell-shaped rare earth element (REE) profiles, with weak Eu anomalies and Sr and Th contents higher than those of magmatic apatite. The variable degree of modification of REE (mainly increase of light-REE contents) and trace-element composition (mainly decrease in Sr contents) of UHP apatite may be related to alteration during exhumation and partial reequilibration with the melt during the subsequent anatexis. This discovery suggests that apatite preserves some UHP geochemical signatures during anatexis and that it can help in the recognition of UHP events.
... These include the Dabie-Sulu, Qinling, and North Qaidam terranes in China ( Song et al., 2005;Xu et al., 1992;Yang et al., 2003), the Western Gneiss Region, Norway ( Dobrzhinetskaya et al., 1995;Vrijmoed et al., 2008), Sulawesi, Indonesia ( Parkinson and Katayama, 1999), the Saxonian Erzgebirge, Germany ( Dobrzhinetskaya et al., 2006;Hwang et al., 2001;Massonne, 1999;Nasdala and Massonne, 2000), the Rhodopes, northern Greece ( Mposkos and Kostopoulos, 2001;Perraki et al., 2006;Schmidt et al., 2010), the Maksyutov Complex, South Ural Mountains, Russia ( Bostick et al., 2003;see also Leech and Ernst, 1998), the Kontum Massif, central Vietnam ( Nakano et al., 2006), and the Jack Hills, Western Australia ( Menneken et al., 2007;Nemchin et al., 2008). More recently, UHP microdiamond was described from the Bohemian Massif, Czech Republic ( Kotková et al., 2011;Naemura et al., 2011), the western Alps, Italy ( Frezzotti et al., 2011), the Betic-Rif Cordillera in southeast Spain and northwest Africa (Ruiz Cruz and Sanz de Galdeano, 2012de Galdeano, , 2013), the Scandinavian Caledonides ( Janák et al., 2013;Majka et al., 2014), the Edough Massif, northeastern Algeria ( Caby et al., 2014), the Pohorje Mountains, Slovenia ( Janák et al., 2015), and the Massif central, France ( Thiéry et al., 2015). Microdiamond also occurs in chromitites in the Polar Ural Mountains and Tibet ( Robinson et al., 2004;Yang et al., 2007Yang et al., , 2015). ...
Raman spectral characteristics of a range of diamond-based abrasives (powders and sprays) and drilling and cutting tools, originating from preparation laboratories worldwide, are presented. Some abrasives show strong broadening of the main diamond band [FWHM (full width at half band-maximum) > 5 cm− 1] accompanied by strong band-downshift (image = 1316–1330 cm− 1). Others are characterised by moderate band broadening (FWHM = 1.8–5 cm− 1) at rather regular band position (image = 1331–1333 cm− 1). In addition we found that a “fresh” abrasive and its used analogue may in some cases show vast differences in their Raman spectra. The Raman parameters of diamond-based abrasives overlap widely with Raman parameters of UHP (ultra-high pressure) microdiamond. It is hence impossible to assign diamond detected in a geological specimen to either an introduced artefact or a genuine UHP relict, from the Raman spectrum alone. Raman is an excellent technique for the detection of minute amounts of diamond; however it does not provide conclusive evidence for the identification of UHP microdiamond. The latter requires thorough verification, for instance by optical microscopy or, if doubts cannot be dispelled, transmission electron microscopy.
... Before this last age, the continental crust underwent a process of subduction. This is demonstrated by the presence of relict UHP phases (mainly diamond and coesite) as inclusions in several phases (garnet, apatite and zircon) from the deepest crustal rocks (migmatitic granulites and gneisses) of Jubrique unit (Ruiz Cruz & Sanz de Galdeano, 2014) and from the Sarchal area in Ceuta the (Rif Cordillera) (Ruiz Cruz et al., 2011;Ruiz Cruz & Sanz de Galdeano, 2013). The age of this subduction event is uncertain, although our most recent data (e.g. ...
... The peridotite body probably reached the subducted crust and then formed the metamorphic aureole (that existing in the proximities of Jubrique and in other sectors, Fig. 2, and Fig. 1 of Tubía et al. 2013 for a more complete location). During the exhumation of the UHP rocks a melting stage seems to have occurred, recorded by granitic inclusions in garnets from several zones (Ruiz Cruz & Sanz de Galdeano, 2013, and by the Carboniferous (>300 Ma) zircon domains with oscillatory zoning (Fig. 11C-C' and D-D'), which appear as fractured cores, reflecting their origin inherited from the feeder in the granitic rock studied here. ...
The age of the emplacement of the Ronda Peridotites has been widely debated during recent decades, and ages ranging from the Palaeozoic to the early Miocene have been proposed, although most of the current interpretations suggest an Oligocene-Miocene age. In this article, we describe two meta-sedimentary formations (the lower one formed by detrital sediments and the upper one by marbles) that were unconformably deposited over the Ronda peridotites and now record low-grade metamorphism. The detrital formation contains layers of acidic rocks with an age of 269±9 Ma and the overlying marbles are assumed to be Triassic. The existence of these unconformable formations over the peridotites is crucial for the dating of the exhumation of the latter. The presence of peridotite clasts in the detrital formation indicates that peridotites were exposed during the Permian and other data suggest that peridotites were exhumed during the late Carboniferous. During the Alpine cycle, the peridotites operated as an element situated at the bottom of the tectonically higher Alpujarride/Sebtide unit (the Jubrique unit) and forming part of it, then being incorporated to the Alpine thrusts of this unit.
... GPa has been also proposed for the garnet-phengite gneiss from the German Erzgebirge (Massonne, 1999(Massonne, , 2003. A P-T path more comparable with our reconstructed path has been recently described for the UHP-UHT diamond-and coesite-bearing granulites from the Betic-Rif cordillera (Spain/Morocco), with a peak temperature of about 1100°C at a pressure of at least 4.5 GPa followed by HT granulite-facies overprint at about 900°C and 1 GPa (Ruiz-Cruz and de Galdeano, 2012Galdeano, , 2013. ...
Intermediate garnet–clinopyroxene rocks from the Eger Crystalline Complex, North Bohemian Massif, contain microdiamonds enclosed in garnet and zircon. The variable mineral assemblage of these rocks allows for an evaluation of the P–T evolution using numerous univariant equilibria and thermodynamic modelling, in addition to the ternary feldspar solvus, Ti-in-garnet, Zr-in-rutile and Ti-in-zircon thermometry. Zircon mantle domains with diamond inclusions contain 111–189 ppm Ti, reflecting temperatures of 1037–1117 °C. The peak pressure consistent with diamond stability corresponds to c. 4.5–5.0 GPa. Ti-in-garnet thermometry using the Ti content of diamond-bearing garnet core yielded temperatures of 993–1039 °C at c. 5.0 GPa. An omphacite inclusion in garnet (reflecting c. 2.3–2.4 GPa at c. 1050°C) and metastably preserved kyanite represent relics of eclogite-facies conditions. The dominant high-pressure granulite-facies mineral assemblage of low-Ca garnet, diopsidic clinopyroxene, antiperthitic feldspar and quartz equilibrated at 1.8–2.1 GPa and c. 1050 °C, based on the XGrs isopleth of the garnet mantle, garnet–feldspar–kyanite–quartz univariant equilibria and ternary feldspar solvus. Our thermodynamic modelling shows that a steep decrease of XGrs from a maximum core value of 0.32 to 0.17 at the rim as well as a rimward XMg increase (from 0.42 to 0.50) are consistent with significant decompression without heating. The latter is related to omphacite and kyanite breakdown reactions producing garnet and plagioclase. The Ti content in the rim zone of zircon (13–42 ppm), exsolved plagioclase and K-feldspar associated with matrix diopside and garnet rim, and late biotite reflect temperatures of c. 830–900°C at c. 1.4 GPa. A similar temperature is recorded by matrix rutile grains, containing 2028–4390 ppm Zr and representing a relatively homogeneous population in contrast to rutile enclosed in garnet with variable Zr content. Our results show that the garnet–clinopyroxene rocks from North Bohemia are UHP–UHT rocks which were extensively overprinted under HP granulite-facies conditions during rapid exhumation along a near-adiabatic P–T path. The UHT peak and UHT–HT exhumation distinguish this area from the other UHP terrains worldwide. We demonstrate that Ti-in-zircon thermometry can provide robust temperature estimates in the rocks exhumed at HT, where the UHP–UHT mineral assemblage has not been preserved. In addition, the calculated UHP–UHT conditions are similar to those determined for the associated garnet peridotites, providing evidence for juxtaposition of these crustal and mantle rocks during deep Variscan subduction.
... Exsolution of SiO 2 polymorphs in form of quartz or coesite was observed in clinopyroxenes (e.g. Katayama et al., 2000) and garnets (Ague and Eckert, 2012;Mposkos and Kostopoulos, 2001;Ruiz-Cruz and Sanz de Galdeano, 2013) of UHP metamorphic eclogites and pelitic rocks. Alpha-quartz inclusions together with rutile were described in garnets of sanidine-orthopyroxene eclogite xenolith from South Africa (Schmickler et al., 2004). ...
... The research was supported by the Russian Foundation of Basic Research (grant Nos. 12-05-31411 and 12-05-00508), by the grant of the President of Russia (MD-1260(MD- .2013) and by the Ministry of education and science of Russian Federation (project No. 14.B25.31.0032). ...
Eclogite mantle xenoliths from the central part of Siberian craton (Udachnaya and Zarnitsa kimberlite pipes) as well as from the northeastern edge of the craton (Obnazhennaya kimberlite) were studied in detail. Garnet and clinopyroxene show evident exsolution textures. Garnet comprises rutile, ilmenite, apatite, and quartz/coesite oriented inclusions. Clinopyroxene contains rutile (± ilmenite) and apatite precipitates. Granular inclusions of quartz in kyanite and garnet usually retain features of their high-pressure origin. According to thermobarometric calculations, studied eclogitic suite was equilibrated within lithospheric mantle at 3.2–4.9 GPa and 813–1080 °C. The precursor composition of garnets from Udachnaya and Zarnitsa eclogites suggests their stability at depths 210–260 km. Apatite precipitation in clinopyroxenes of Udachnaya and Zarnitsa allows us to declare that original pyroxenes could have been indicative of their high P–T stability. Raman spectroscopic study of quartz and coesite precipitates in garnet porphyroblasts confirms our hypothesis on the origin of the exsolution textures during pressure-temperature decrease. With respect to mineralogical data, we suppose the rocks to be subjected to stepwise decompression and cooling within mantle reservoir.
