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Geological map of eastern Serbia showing the Proterozoic to Mesozoic basement and Cretaceous magmatic rocks of the Timok Magmatic Complex (TMC) and Ridanj^Krepoljin Zone (RKZ) (modified after Kra « utner & Krstic, 2003). The white dotted line separates the eastern from the western Timok Magmatic Complex.
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New age and whole-rock Sr-87/Sr-86 and Nd-143/Nd-144 isotopic data are used to assess petrogenetic and regional geodynamic processes associated with Late Cretaceous subvolcanic intrusions within the sparsely studied Timok Magmatic Complex (TMC) and Ridanj-Krepoljin Zone (RKZ) of eastern Serbia. The TMC and RKZ form part of the Apuseni-Banat-Timok-S...
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Context 1
... characteristic low Y and high Sr concentrations of adakites and adakite-like rocks are generally interpreted in terms of amphibole, garnet, and plagioclase stability. Amphibole or garnet fractionation leads to Y depletion because Y is highly compatible in amphibole and garnet (Kay et al ., 1991). Where plagioclase is not stable, Sr becomes enriched in the melt because Sr is compatible in plagioclase. However, the specific nature of the associated petrogenetic processes is debated. Proposed processes include eclogite slab melting and interaction of slab melts with the mantle (Kay, 1978; Defant & Drummond, 1990; Kay et al ., 1993; Y ogodzinski et al ., 1995; Abratis & Wo « rner, 2001; Kay & Kay, 2002; Jego et al ., 2005), melting of thickened mafic lower crust (Atherton & Petford, 1993; Petford & Gallagher, 2001; Bourdon et al ., 2002; Kay & Kay, 2002; Chung et al ., 2003), and high-pressure fractionation of hydrous magmas with or without melting of the lower crust (Castillo et al ., 1999; Rohrlach & Loucks, 2005; Macpherson et al ., 2006; Davidson et al ., 2007; Chiaradia, 2009; Chiaradia et al ., 2009). This last hypothesis may provide a plausible explanation for the relationship between adakite-like magmas and ore deposits, although there is little consensus regarding this topic as yet (Oyarzun et al ., 2001; Rabbia et al ., 2002; Richards, 2002). High-pressure fractionation of amphibole in the lower crust may be indi- cative of volatile-enriched parental magmas enhancing the generation of volatile-rich magmas that efficiently transport water, sulfur and ore metals to the upper crust (Hedenquist & Lowenstern, 1994; Burnham, 1979). In this study, we investigate the origin and evolution of calc-alkaline adakite-like and normal arc magmas that overlap in space and time within the Late Cretaceous Timok Magmatic Complex (TMC) and Ridanj^ Krepoljin Zone (RKZ) of eastern Serbia. The TMC and RKZ belong to the 30^70 km wide, 4 1000 km long Late Cretaceous Apuseni^Banat^Timok^Srednogorie (ABTS) belt that extends across southeastern Europe. The largest porphyry-style and high-sulfidation epithermal Cu^Au deposits of the ABTS belt are spatially and temporally associated with the TMC and RKZ (Mitchell, 1996). Previous geochemical studies on the ABTS magmas have revealed a wide variation (Downes et al ., 1995; Jankovic, 1997; Karamata et al ., 1997; Banjesevic, 2001; von Quadt et al ., 2001, 2005; Ciobanu et al ., 2002; Chambefort et al ., 2007; Georgiev, 2008; Zimmerman et al ., 2008; Georgiev et al ., 2009). However, there is little geochemical or petrogenetic information related to the Serbian segment of the ABTS belt. Here we present new geochronological, whole-rock, major and trace element, and Sr and Nd isotope data for TMC and RKZ subvolcanic rocks. We then focus on modeling the trace element and isotope data using the energy-constrained assimilation^fractional crystallization (EC-AFC) model of Spera & Bohrson (2001). We demonstrate that the adakite-like and normal arc magmas may have been generated from a common source prior to evolution via distinct combinations of lower- and upper-crustal assimilation and fractional crystallization. Variations in age and crustal assimilation processes across the arc form the basis for the development of a new interpretation of the tectonomagmatic evolution of this locally ore-mineralized belt. The central Balkan Peninsula of southeastern Europe (Fig. 1) consists of continental fragments that collided prior to the Late Cretaceous closure of the Vardar Ocean (a branch of the former T ethys Ocean): the Dacia Mega-Unit and Tisza Domain European microcontinents, along with the Moesian platform, a promontory of the stable Eurasian plate (Schmid et al ., 2008, and references therein; Figs 1 and 2). Vardar subduction occurred beneath the Dacia Mega-Unit, which is subdivided into the Supragetic Unit containing the Serbo-Macedonian Massif, the Getic Unit including the Srednogorie Zone, and the Danubian Unit as part of the Balkan Unit (Schmid et al ., 2008; Fig. 2). Associated widespread calc- alkaline magmatism collectively forms the ABTS magmatic belt in eastern Serbia (the target of the present study), the southern Carpathians, Romania, and the Srednogorie zone, Bulgaria (Popov et al ., 2002; Figs 1 and 2). Subduction ceased shortly after the end of the Cretaceous ( $ 60 Ma; Karamata & Krstic, 1996; Fu « genschuh & Schmid, 2005; Schmid et al ., 2008). However, subduction continued throughout the Cenozoic in the Aegean region (Fig. 1) and in the neighboring Alps, leading to dextral translation of the Dacia Mega-Unit (Wilson & Bianchini, 1999) and alternating transpressive and extensional episodes (Marovic et al ., 1998; Krstic, 2001) along strike-slip fault zones. Plate reconstructions and paleomagnetic data show that the Vardar subduction zone was oriented WNW^ESE to east^west in the Late Cretaceous (Patrascu et al ., 1994; Neubauer, 2002; Fu « genschuh & Schmid, 2005; Schmid et al ., 2008). Differential Cenozoic subduction led to clockwise rotation (80 8 ) of the Tisza Domain into the Pannonian Basin, deforming the ABTS belt into its present-day L-shape (Fu « genschuh & Schmid, 2005; Ustaszewski et al ., 2008; Fig. 1). Rotation acted on the TMC and RKZ segment of eastern Serbia ( $ 30 8 clockwise), but not on the Srednogorie region in Bulgaria, which remained in an east^west orientation. In Serbia, the Late Cretaceous magmatic complexes are bordered on the west and east by the Eastern Serbo-Macedonian Strike-Slip Zone and the Timok Fault Zone. The Timok Fault Zone shows a north^south dextral offset of $ 25^50 km related to ...
Context 2
... 1. Schematic overview map of the Alpine^Carpathian arc. Main structural features are shown with dashed lines; the ophiolitic Vardar suture zone of the former T ethys ocean is indicated with a dotted line (modified after de Jonge et al ., 1994). Rectangle shows the location of Fig. 2. ABTS belt: Apuseni^Banat^Timok^Srednogorie belt (thick dashed line).
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... As discussed above, early Carboniferous rocks in the western segment crystallized from magmas that originated from partial melting of a juvenile lower crust. External heat sources are necessary to initiate partial melting of the lower crust; these heat sources may be related to the underplating of asthenospheric magma that upwelled in response to delamination of the lithosphere or thickened lower crust (Chung et al. 2003;Wang et al. 2007), ridge subduction (Geng et al. 2009), or slab rollback (Kolb et al. 2012). Delamination of thickened lower crust typically occurs in post-collisional Supplementary Table S7. ...
The tectonic regime is an important factor controlling the formation of ore deposits, and magmatic rocks generated in different tectonic regimes are characterized by contrasting ore affinities and mineralization styles. A series of early Carboniferous volcanogenic massive sulphide (VMS) deposits occur in the western segment of the Dananhu Arc in the Central Asian Orogenic Belt. In contrast, coeval magmatic rocks in the middle segment are devoid of VMS copper mineralization but host porphyry copper deposits. However, the relationship between tectonic setting and mineralization still needs to be clarified. Herein, we synthesize the new and existing geochemical data of the Carboniferous arc rocks of the Dananhu Arc, showing diverse arc magmatism and contrasting Cu mineralization styles in the western and middle segments. Magmatic rocks in the western segment are consistent with normal island arc origin. In contrast, magmatic rocks in the middle segment of the Dananhu Arc have adakite-like affinities. The magmatic rocks in the western segment were derived from the partial melting of the juvenile lower crust triggered by slab rollback in an extension setting.
In contrast, the rocks in the middle segment originated from partial melting of the subducted slab that was triggered by flat subduction. The extension setting coupled with high temperature magmatic activity induced the circulation of the hydrothermal fluids, which were critical to the development of the Xiaorequanzi VMS deposit. Copper would become progressively enriched in the fractionating melt under the high–fO2 condition, and the compressional regime caused by flat subduction reduces the ‘leakage’ of hydrothermal fluids, which are favourable for the formation of the porphyry mineralization in the middle segment. It is, therefore, evident that variations in the tectono-magmatic setting across the Dananhu Arc played an important role in generating the diversity of Cu deposit types and variable ore affinities throughout the Eastern Tianshan.
... The Timok ore distract is the largest area of preserved volcanic rocks in the Apuseni-Banat-Timok-Srednogorie belt (ABTS, Fig. 1A). This magmatic arc originated from the subduction of an oceanic plate beneath the continental margin and remained active during the Late Cretaceous period (Gallhofer et al., 2015;Knaak et al., 2016;Kolb et al., 2012). Current tectonic models broadly propose that ore formation is associated with either rifting or collisional processes (Gallhofer et al., 2015;Zimmerman et al., 2008). ...
... Amphibole is widely considered to have a strong potential to generate high Sr/Y adakitic rocks (Castillo et al., 1999;Foley et al., 2002;Moyen, 2009;Kolb et al., 2013). It has a standard for- ...
... where A is a monovalent cation or vacant in the A site, B is monovalent/divalent cations in the M4 site, C is divalent/trivalent/tetravalent cations in the M1, M2 and M3 sites, and T is Si and Al in the tetrahedral site (Leake et al., 1997;Shimizu et al., 2017). Amphibole is more enriched in middle REE relative to heavy REE and has relatively light Fe isotopes due to its low Fe 3+ contents and Fe 3+ / Fe ratios (Kolb et al., 2013;Li et al., 2020;Ye et al., 2020). Thus, an amphibole residue would lead to partial melts with low Dy/Yb ratios and Fe contents, and mildly heavy Fe isotopes. ...
Available online xxxx Editor: R. Hickey-Vargas Keywords: Sr-Nd-Hf-Fe isotopes Gangdese adakitic intrusion amphibole effect Nd-Hf decoupling crustal reworking Rocks with "adakitic" affinities are widespread in continental collision zones, recording important information about crustal thickening. Residual garnet during partial melting of the lower crust is traditionally considered to be responsible for heavy rare earth element and Y depletion, which is a key characteristic feature of these rocks. However, magmatic garnet is rarely observed in such adakitic igneous rocks and associated protolithic eclogite is also rarely reported. Instead, amphibole is a proposed abundant phase in lower arc crust. Whilst both garnet-and amphibole-rich assemblages can act as potential sources for intracrustal intermediate-silicic melts, their distinctive fractionation of f Sm/Nd and f Lu/Hf should, with time, lead to different Nd-Hf isotopic compositions in high Sr/Y rocks. Here we report whole-rock radiogenic Sr-Nd-Hf and stable Fe isotope compositions of well-characterized Oligocene to Miocene (33-14 Ma), post-collisional high-K adakitic intrusions from the Gangdese belt, South Tibet. The plutons have a low alumina saturation index and depleted Dy/Yb, pointing to negligible amounts of sediment contribution. They are characterized by variable initial 87 Sr/ 86 Sr ratios (0.7048 to 0.7078), mostly negative εNd (−4.9 to +0.3), positive εHf values (+1.5 to +8.3), and variable but heavy δ 57 Fe values ranging from +0.04 ± 0.08 to +0.35 ± 0.08. Modeling of Fe isotopes and fractionation factors of f Sm/Nd and f Lu/Hf indicate an amphibolite source. A Nd-Hf isotope correlation that is quasi-parallel to the mantle array can be best explained by the evolution of amphibolitic lower crust with a residence time of ca. 400 Myrs. Although these adakitic rocks have depleted, mantle-like Hf isotope compositions, they are part of an existing, older crustal foundation and thus represent a process of crustal reworking, instead of crustal growth. Therefore, proportions of mantle-derived materials that contributed to the Phanerozoic crustal growth based on Hf-in-zircon signatures alone may be overestimated. Combined mineral and whole-rock radiogenic and stable isotopes are required to address this issue in the future.
... Keskin and Tüysüz 2018;Karsli et al. 2018). Kolb et al. (2013) describe Late Cretaceous arc and adakite-like magmas from the Timok segment of ABTS, which overlap in space and time, similar to those from the Çangaza Volcanic Member. They explain the formation of adakite magmas by high-pressure amphibole differentiation in the lower crust, whereas normal arc magmas have evolved through upper crustal differentiation. ...
During the Late Cretaceous, a magmatic arc extended from the Lesser Caucasus through the northern margin of the Pontides into Srednogorie, Timok, Banat, and Apuseni (ABTS) in the Balkans for a distance of 2700 km. We studied the arc volcanic rocks in three regions in the Western Pontides and reviewed the geological data on the Lesser Caucasus-Pontide-ABTS magmatic arc, which shows several common features. Prior to the start of the arc magmatism, the region underwent uplift and erosion. New and published geochronologic and biostratigraphic data show that magmatism in the Lesser Caucasus-Pontide-ABTS arc started in the Turonian (ca. 93 Ma) peaked in the middle Campanian (80–78 Ma) and became rare and sporadic after the late Campanian (ca. 75 Ma). Magmatism was dominantly calc-alkaline to high-K calc-alkaline and shows typical subduction geochemical signatures. Late Cretaceous volcanism took place in a submarine and extensional environment. In the Lesser Caucasus-Pontide-ABTS belt, the arc volcanic rocks are overlain by Maastrichtian to Palaeocene marine limestones and sandstones, marking the end of the main phase of arc magmatism. However, in the Kefken region in the Western Pontides, Maastrichtian limestone sequence includes a volcanic horizon with a U-Pb zircon age of ca. 71 Ma. The Maastrichtian volcanic rocks show a more varied geochemistry than the older arc volcanic rocks, and include alkaline basalts, calc-alkaline basalts, and adakites. The coeval start of arc magmatism in the 2700-km-long Lesser Caucasus-Pontide-ABTS belt is related to the inception of the Africa-Eurasia convergence at ca. 96 Ma, which is also independently indicated by the beginning of intra-oceanic subduction, inferred from the ages of sub-ophiolite metamorphic rocks in Anatolia. The end of magmatism is linked to a marked decrease in the convergence rate during the Campanian, which was also partitioned between the northern and southern Tethyan subduction zones.
... Considering these facts, they argued that the magmatic intrusive was probably formed by direct partial melting of the mafic protolith. KOLB et al. (2013) have argued that the rocks with adakitic affinity in the Timok magmatic complex were probably formed by high-pressure intense amphibole fractionation in lower crustal conditions. On the other hand, rocks with the affinity of normal-arc andesites were formed in upper crustal processes of combined fractionation and assimilation of crustal rocks. ...
... We have chosen siginifanctly more samples from Čukaru Peki to analyze different types of andesites and diorite dykes. also, bulk rock analysis of rocks from Bor is already known from previous research (e.g., KOLB et al., 2013). Four samples from Čukaru Peki porphyry intrusions and five samples from Bor were selected for zircon dating and trace element measurements. ...
... These samples are the same three samples that contain low hree concentrations (Fig. 6a). Table 3. O n -L i n e similar to the previous bulk rock measurements of rocks from the Timok magmatic complex (KOLB et al., 2013;GaLLhOFer et al., 2015), some selected samples exhibit adakitic affinities. riCharDs & Ker-riCh (2007) define adakite-like rocks by the following composition: ≥ 56 wt. ...
Bor and Cukaru Peki are world-class porphyry deposits spatially and genetically associated with the Cretaceous Timok magmatic complex. This research was conducted to determine the age and geochemical affinity of the magmatic rocks that formed these ore deposits. Our new geochemical analyses of magmatic rocks from Bor and Cukaru Peki deposits imply they comprise adakite-like compositions that have undergone the amphibole fractionation and sulphide saturation processes. The zircon ages indicate that the Bor system was formed in the age span between 84.5-82 Ma, while the Cukaru Peki system was created in the age span between 86.5-85 Ma.
... The studied trondhjemite samples have similar characters, such as high Sr/Y and La/Yb ratios, to those of Cenozoic adakites or adakitic granites (Fig. 8A-B), which are considered to be formed by fractional crystallization of garnet/amphibole from basaltic magma (Castillo, 2012;Kolb et al., 2013;Macpherson et al., 2006;Xu et al., 2022d), partial melting of subducted oceanic crust Drummond and Defant, 1990;Hastie et al., 2010) or continental crust (Petford and Gallagher, 2001;Wang et al., 2005;Wang et al., 2008a;Xu et al., 2022a) under relatively high pressure. ...
... Adakitic melts formed by fractional crystallization of a garnetbearing assemblage under high pressure or a hornblende-bearing assemblage at a shallow depth both have positive Sr/Y and La/Yb versus SiO 2 correlations (Castillo, 2012;Kolb et al., 2013;Macpherson et al., 2006;Xu et al., 2022d). However, in this study, the trondhjemite samples show compositional trends of partial melting (e.g., positive La/ Sm vs La correlation), inconsistent with fractional crystallization of garnet or amphibole ( Fig. 11A and inset, and 11B). ...
The Neoproterozoic magmatic and tectonic history of the South China Craton (SCC) is critical for the reconstruction of Rodinia break-up and subsequent Gondwana assembly. Nonetheless, the tectonic attribution of the Neoproterozoic igneous rocks in the southwestern Yangtze is contentious, and the mechanism for crustal anatexis remains unclear. Here, we report mineralogical, whole-rock geochemical and Sr-Nd isotope data, and zircon U-Pb-Hf-O isotope data from the newly found Neoproterozoic trondhjemites and granites in the Diancangshan-Ailaoshan (DCS-ALS) fold belt along the southwestern Yangtze. Both the trondhjemites (ca. 771-762 Ma) and granites (ca. 767 Ma) have high SiO 2 and low MgO contents. The trondhjemites have relatively high CaO, Na 2 O and Sr contents, but low K 2 O contents and Rb/Sr ratios, and show positive to slightly negative Eu anomalies and heavy rare earth elements (HREEs) depletions, resulting in high Sr/Y and La/Yb ratios. In contrast, the granites have lower CaO, Na 2 O, and Sr contents, but higher K 2 O and Rb/Sr, and display negative Eu anomalies and flat HREEs patterns. The trondhjemites have negative εNd(t) (-4.12 to − 3.85), positive to negative εHf(t) (-2.50 to + 5.28) and low δ 18 O (4.37 ‰-7.27 ‰) values. In comparison, the granites have positive εNd(t) (0.09 to 0.26), εHf (t) (+1.24 to + 9.86) and higher δ 18 O (6.50 ‰-7.24 ‰) values. The distinct elemental and isotopic compositions between the trondhjemite and granite samples reflect two different types of crustal anataxis within different crustal levels. The trondhjemites were formed by water-fluxed melting of the juvenile mafic lower continental arc crust (with addition of ancient Yangtze basement). The granites were derived from dehydration melting of juvenile felsic middle crust. Our results imply that the trondhjemites and granites were formed in a continental arc setting. The melting processes revealed here should be applicable to decipher the widespread Neoproterozoic crustal melting along the southwestern Yangtze, which was most likely fluid-controlled via subduction-induced asthenosphere upwelling. Combined with available regional geological data, we suggest that a long-lived Neo-proterozoic (~880-730 Ma) subduction zone may have extended from the Panxi-Hanna region in the northern/ western Yangtze Block to the DCS-ALS fold belt in the southwestern Yangtze. Thus, the SCC may have located on the northwestern margin of Rodinia.
... Existing geochronological data ( Figure 3) differentiate all of Timok's magmatic events into three stages [13][14][15][16][17][18][19][20][21]. ...
... A dacite sample from the vicinity of Bor is dated at 84.28 ± 0.86 Ma [23], and the termination of Phase I is defined at 84.66 ± 0.5 Ma [22]. New ages obtained by [24] from the Nikolicevo area nearby Cukaru Peki encompass an interval from 90.97 ± 0.39 Ma to 89. 49 [15,18,20,22,[24][25][26]. Start and end of Phase I, as well as end of Phase II are based on U/Pb zircon analysis and field relationships; start of Phase II cannot be constrained [20,22] [18]. ...
... A dacite sample from the vicinity of Bor is dated at 84.28 ± 0.86 Ma [23], and the termination of Phase I is defined at 84.66 ± 0.5 Ma [22]. New ages obtained by [24] from the Nikolicevo area nearby Cukaru Peki encompass an interval from 90.97 ± 0.39 Ma to 89. 49 [15,18,20,22,[24][25][26]. Start and end of Phase I, as well as end of Phase II are based on U/Pb zircon analysis and field relationships; start of Phase II cannot be constrained [20,22] [18]. These ages reflect the ore-forming events and may not reflect the age of the host rock. ...
The deposits of Bor and Cukaru Peki are important contributors to the Apuseni–Banat–Timok–Srednogorie (ABTS) belt’s metallogenic endowment. We use decision tree and random forest algorithms applied to zircon geochemistry data from Bor, Cukaru Peki and a selection of other localities within the ABTS. The resulting predictions, supported by high scores on the test set predictions for the random forest algorithm, suggest that it is possible to fingerprint the studied deposits and localities from the ABTS belt based on zircon geochemistry. These results take into account the multivariate geochemical patterns and can be used in combination with a widely accepted Eu anomaly indicator or assist in finding more subtle geochemical differences for systems where applying a single cut-off value does not result in a good separation between barren and mineralized rocks.
... The Čukaru Peki hydrothermal system is part of the Bor metallogenic zone, which is hosted by the Timok magmatic complex (JANKOVIĆ, 1990;KOLB et al., 2013). This complex is considered to be the eastern segment of the large magmatic and metallogenic arc known as the Apuseni-Balkan-Timok-Srednogorje belt (ABTS belt, which is located in Romania, Serbia and Bulgaria (NEUBAUER, 2002). ...
... The magmatic activity in the Timok magmatic complex was manifested in two or three volcanic phases (DROVENIK, 1961;JANKOVIĆ, 1990), which altogether lasted around 10 Ma (VON QUADT et al., 2002). It is generally accepted that most of the significant ore deposits in this complex were formed during the first volcanic phase (JANKOVIĆ, 1990;KOLB et al.,2013;JELENKOVIĆ et al., 2016), which lasted from 89 to 84 Ма (VON genetically classified the Čukaru Peki system as a porphyry Cu-Au deposit with high-sulfidation epithermal (Cu-As-Au) massive sulfides. ...
Čukaru Peki is a recently discovered porphyry- high-sulfidation Cu-Au deposit located 5km south of the mining town of Bor in east Serbia. Three styles of mineralization are distinguished in the Čukaru Peki system: a high-sulfidation type with massive sulfides (named the Upper zone), a porphyry type (named the Lower zone) and a transition type (between porphyries and massive sulfides). This study investigates the concentration and distribution of trace elements in pyrite from these three mineralization zones of Čukaru Peki. The high-sulfidation pyrite contains elevated concentrations of V, Mn, Ni, Cu, As, Mo, Ag, Cd, In, Sn, Sb, Au, Hg, Tl, Pb and Bi, compared to pyrite from the porphyry zone. The porphyry zone pyrite contains elevated concentrations of Co and Se. The sample from the transition zone contains concentrations between the two other zones, with the exception of the relative enrichment of Co and Ag. This research also aims to separate different stages of ore deposition. The porphyry stage contains several types of veins: quartz A veins, quartz B veins, pyrite D veins, magnetite veins, purple anhydrite veins, sulfide veins and orange anhydrite veins. The high sulfidation stage also formed in several stages: pyrite1, pyrite-enargite veins, pyrite-covellite veins, pyrite2 veins and calcite-anhydrite veins. There are distinct differences between various vein generations found within each zone, notable examples are the enrichment of Se in quartz B veins pyrite and Cu in sulfide veins, compared to other veins from porphyry zone veins and the enrichment of several trace elements (Cu, Mo, Ag, Cd, In, Sn, Sb, Au, Hg, Tl, Pb and Bi) in pyrite from the Py-cov veins in comparison to the other high-sulfidation veins. The trace element data also indicates a change in fluid compositions; the earlier fluids responsible for the porphyry zone mineralization showing a slightly more magmatic fluid signature (higher Co/Sb and Se/As values) and the later high-sulfidation fluids bearing a more typical epithermal trace element signature, which indicates cooling and diluting of fluids. Some of the porphyry zone pyrite crystals (from B-type veins and Purple anhydrite-veins) contain elevated concentrations of elements attributed to the high-sulfidation zone (e.g. Cu, Ag, Cd, In, Sn, Pb and Bi), which suggests that these veins were affected by later high-sulfidation fluids.
... The saturation of the magmatic system by volatiles stabilises amphiboles instead of its consumption via dehydratation-melting (Weinberg & Hasalová 2015;Johnson et al. 2021). Peritectic hornblende usually forms along with plagioclase, which buffers the Sr content of melt (Moyen 2009); however, the high-water content under HP conditions suppresses crystallisation of plagioclase (Alonso-Perez et al. 2009;Kolb et al. 2013). More pronounced "adakitic" signature and lower Dy/Yb ratios (Davidson et al. 2012) observed in the Prašivá granite types along with its more felsic character in comparison to the Ďumbier type can reflect the lower incorporation of peritectic amphibole into partial melt products due to lower temperatures or higher pressures of melting (Alonso-Perez et al. 2009). ...
... Calc-alkaline arc rocks generally can be divided into two groups based on their different trace-element compositions, while some rocks show normal arc-type trace-element compositions with low La/Yb (<20) and Sr/Y (<20) ratios, some others are characterized by adakite-like high La/Yb (>20) and Sr/Y (>20) ratios and low Y (∼18 ppm) and Yb (∼1.9 ppm) contents Drummond and Defant, 1990;Castillo et al., 1999;Castillo, 2006Castillo, , 2012Macpherson et al., 2006;Kolb et al., 2013), which are closely related to their magma formation conditions under the garnet or amphibole stability field (Kay et al., 1991). Garnet and amphibole fractionation or their occurrence in the residue can lead to depletions of Y and Yb in the melt, because both minerals preferentially incorporate heavy rare earth elements (HREEs) over light rare earth elements (LREEs) (Johnson, 1994;Tiepolo et al., 2007). ...
... (2) partial melting of thickened or delaminated mafic lower continental crust (Petford et al., 2000;Xu et al., 2002;Chung et al., 2003;Wang et al., 2004Wang et al., , 2005Wang et al., , 2007b; (3) melting of subducted continental crust (Wang et al., 2008a); and (4) high-pressure fractionation of garnet or amphibole in hydrous mafic magmas with/without crustal assimilation (Castillo et al., 1999;Macpherson et al., 2006;Chiaradia et al., 2009;Castillo, 2012;Kolb et al., 2013;Xu et al., 2015;Jaoutz and Klein, 2018). ...
... Petrogenesis of group 1 granites is also difficult to explain by partial melting of the thickened or delaminated mafic lower continental crust (model B). Previous studies suggested that an important feature of high-pressure crystallization is that some elemental ratios (e.g., Sr/Y and La/Yb) should increase with increasing SiO 2 contents (e.g., Kolb et al., 2013;Lee and Bachmann, 2014;Macpherson et al., 2006). Melting of lower crust within the garnet stability field gives rise to high Sr/Y and La/Yb ratios, yet it cannot generate positive SiO 2 versus Sr/Y and La/Yb correlations (Fig. S2). ...
Geochemical similarities between the continental crust and arc magmas have led to the inference that subduction zones may be the primary sites of crustal growth. Thus, it is necessary to unravel the petrogenetic mechanism(s) of granitoid generation in subduction-related settings to understand crustal growth through magmatic differentiation processes. In this study, we focused on granitoid generation in oceanic-continental subduction zones. We analyzed the whole-rock geochemistry and Sr-Nd isotopes, together with zircon U-Pb-Hf-O isotopes, of the newly identified Middle Triassic granitoids in the Ailaoshan high-grade metamorphic complex (Yunnan, SW China). All the studied granite samples were characterized by large ion lithophile element (e.g., Rb, Sr, and Ba) enrichments and high field strength element (e.g., Nb, Ta, and Ti) depletions, similar to arc-type rocks. They also showed a range of whole-rock Sr-Nd, (87Sr/86Sr)i = 0.7020−0.7048, εNd(t) = +0.6 to +4.2, and zircon Hf-O, εHf(t) = +10.3 to +18.1, δ18Ozircon = 5.09‰−6.65‰, isotope compositions, which overlap with those of previously reported coeval (ca. 237−235 Ma) hornblende diorite and granodiorite, the formation of which was interpreted to have originated from a mantle wedge metasomatized by a sediment-derived melt. Furthermore, the fractionation trends of some of the granitic samples and diorite-granodiorite suite overlap. They can be divided into two geochemical groups: Group 1 has intermediate to high SiO2 (66.9−73.8 wt%) and K2O (3.40−5.42 wt%) and low MgO (0.19−1.09 wt%) contents and shows depletion in heavy rare earth elements (HREEs; e.g., Yb and Y), resulting in adakite-like high Sr/Y (61−183) and La/Yb (47−90) ratios. Group 1 shows positive SiO2 versus Sr/Y and La/Yb correlations and negative SiO2 versus HREE and Y correlations, implying fractionation of a garnet-bearing assemblage. The negative correlations between SiO2 and εNd(t) and Nb/La reveal a crustal assimilation trend. Group 2 has relatively high SiO2 (72.6−76.5 wt%) and low K2O (1.93−3.82 wt%) and MgO (0.05−0.83 wt%) contents and shows depletion in middle REEs (MREEs; e.g., Gd and Dy) with low Sr/Y (1−10) and La/Yb (4−11) ratios. Group 2 granites show negative Gd/Yb versus SiO2 correlation, which indicates significant fractionation of an amphibole-bearing assemblage.
Our results suggest that both group 1 and 2 granites were formed in a subduction setting from a common mantle-derived parental dioritic magma, but they experienced two distinct fractionation processes. While group 1 granites were likely formed by crustal assimilation and high-pressure (lower-crustal) garnet-dominated fractionation, group 2 granites were generated through low-pressure (middle-/upper-crustal) amphibole-/plagioclase-dominated fractionation. We suggest that these two fractionation trends are critical to crustal growth and the development of a more fractionated (felsic) upper crust.
