I-type Granites Research Articles

Late Mesozoic tectonic affinity of the Tengchong Block and southward extension of the Bangong-Nujiang Suture: constraints from Early Cretaceous granitic rocks in western Yunnan, SW China

ABSTRACT The southward extension of the Bangong-Nujiang Suture and the late Mesozoic tectonic affinity of the Tengchong Block have been subject to debate, and the Early Cretaceous magmatism in the eastern Tengchong Block provides a crucial window to address these issues. This paper reports comprehensive petrographic, geochemical, geochronological, and isotopic data of Early Cretaceous granitic rocks from the eastern Tengchong Block. Results show that these granitic rocks consist of monzogranites and granodiorites, with zircon U-Pb ages of 120.4–113.9 Ma. These granitic rocks are characterized by enrichments in large ion lithophile elements (e.g. Rb, U, K) and light rare earth elements, but depleted in high field strength elements (e.g. Nb, Ta, P, Ti), and have negative apatite εNd(t) values (−10.4 to −6.7) and negative zircon εHf(t) values (−11.7 to −1.2). The molar [Al2O3/(CaO + K2O + Na2O)] (A/CNK) values and whole-rock zircon saturated temperatures of the studied monzogranites of 1.04–1.09 and 714–799°C, respectively, indicate that they have I-type granite affinity. The presence of biotite indicative of I-type granite and the observation that P2O5 decrease with increasing SiO2 further indicated that the monzogranites have affinities of I-type granites. The petrography, geochemical and isotopic signatures of the studied monzogranites indicate that they originated from partial melting of mafic lower crustal rocks. The Na-rich granodiorites have elevated Na2O/K2O ratios and Na2O contents of 1.19–2.04 and 3.12–3.47 wt.%, respectively. These granodiorites also have relatively high Mg# values and the transition metal element Cr of 53.3–54.5 and up to 100 ppm, respectively. According to these isotopic and geochemical features and the occurrence of magnesiohornblende, we propose that the Na-rich granodiorites were derived from partial melting of ancient basaltic lower crust, with certain inputs of mantle materials in the magma source. Considering these results as well as published data, we finally propose that the Tengchong Block was likely the southeastern extension of the Lhasa Block and that these Early Cretaceous granitic rocks were formed in the setting of the volcanic arc due to westward subduction of the Bangong-Nujiang Tethys oceanic lithosphere beneath the Tengchong Block.

Mesozoic crustal reworking at different depths in the North China Craton: Insight from the coexisting Early Cretaceous high and low Sr/Y granitoids

Crustal reworking, an important part of continental evolution, can occur in cratons even though they are generally rigid and stable. However, the reworking mechanisms are still debated. Here, we present detailed zircon UPb ages, mineral compositions, major and trace elements, and Sr–Nd–Pb–Hf isotopic data for the coexisting high and low Sr/Y granitoids in the Liaodong Peninsula to decipher the reworking mechanism in the eastern North China Craton (NCC). Mafic microgranular enclaves (MMEs) are common in the studied granitoids, and both the granitoids and their MMEs have consistent emplacement ages of 128–126 Ma. The low and high Sr/Y granitoids are characterized by high-K calc-alkaline I-type granites. They are enriched in light rare earth elements (REEs) and large ion lithophile elements (e.g., Rb, K, and Pb), with depletions in high field strength elements (e.g., Nb, Ta, P, and Ti). The low Sr/Y granitoids have homogeneous Sr–Nd–Pb-Hf isotopic compositions, indistinguishable from those of their MMEs, indicating that they are of cognate origin. Their high (87Sr/86Sr)i (0.713759–0.715341), low εNd(t) and εHf(t) values (−19.2 to −18.1 and − 20.9 to −15.0, respectively), and old two-stage Nd and Hf model ages (ca. 2.50 Ga) suggest that they are derived from partial melting of the ancient lower crust at a normal crustal depth. In contrast, the high Sr/Y granitoids show more depleted heavy REEs and higher Sr/Y (21.1–80.2) and (La/Yb)N (19.2–50.2) ratios, with very low Y (≤ 12.5 ppm) and Yb (≤ 1.11 ppm) contents and negligible Eu anomalies. Their enriched and variable Sr–Nd–Pb-Hf isotopes (e.g., εNd(t) = −20.8 to −14.9, εHf(t) = −24.3 to −9.2) are distinctly different from those of their MMEs (e.g., εNd(t) = −17.6 to −13.2, εHf(t) = −20.8 to −0.3), implying a magma mixing process. These features suggest that the high Sr/Y granitoids and their MMEs are formed by mixing of the thickened ancient lower crustal and lithospheric mantle-derived magmas, with minor contributions of the asthenospheric mantle. Combined with the coeval (129–114 Ma) high-Mg adakitic and A-type granitoids, the coexisting high and low Sr/Y granitoids may indicate intensive crustal reworking at variable depths in the NCC. The reworking is attributed to the asthenosphere upwelling and lithospheric delamination induced by the rollback of the subducting Paleo-Pacific plate.

Middle Permian granitoids in the western section of the northern Qaidam Block, NW China: Petrogenesis and tectonic implications

Origin and tectonic setting of late Late Paleozoic to Early Mesozoic igneous rocks in the northern Qaidam Block (NQ) have long been a matter of debate. In this paper, we report new zircon U-Pb ages and Hf isotopic compositions and bulk rock major and trace elemental compositions for granitoids of the Yanchangbeishan area in the NQ. The granodiorite, tonalite, granodiorite, and syenogranite yielded zircon U-Pb ages of 271.9 Ma, 262.0 Ma, 272.4 Ma and 261.3 Ma, respectively, corresponding to εHf(t) values are 13.04–14.32, 8.14–10.77, 8.66–11.88, and 8.22–10.43, respectively. These granitoids are compositionally I-type granites and exhibit varying degrees of enrichment in Rb, Th, U, and K, and depletion in Nb, Ta, and Ti. According to field relationships, petrology, geochronology, and geochemistry, the granitoid types can be divided into three groups: (1) ca. 272 Ma granodiorites, which are formed through partial melting of metagreywackes and amphibolites derived from depleted mantle; (2) ca. 262 Ma tonalite, which represents a typical high-silica adakite derived from partial melting of subducted oceanic crust during the evolution of depleted mantle; and (3) ca. 261 Ma syenogranite, which is formed by the partial melting and high-degree fractional crystallization of mixed crustal materials. Considering our findings and the regional geological background, we propose a five-stage tectonic evolution model of subduction slab roll-back and subduction zone retreat for the late Late Paleozoic to Early Mesozoic of NQ.

Munabulake ophiolitic mélange: Implication for the evolution history of the north branch of the Proto-Tethys ocean

One of the ophiolites that record the Proto-Tethys Ocean’s episodic closure is the Munabulake ophiolitic mélange, which is situated in the middle of the Kunlun–Qaidam and Altun–Qilian blocks. Detailed field mapping revealed that the Munabulake ophiolitic mélange comprises local (ultramafic rocks, basalts, andesites, gabbros, diorites, and plagiogranites) and exotic (marble, gneiss, schist, and amphibolite) blocks, many of which are in the schist matrix (Qimantage Group). Based on geochronological, geochemical, and petrological observations, the mafic rocks in the Munabulake ophiolitic mélange can be categorized into three categories: 498-Ma OIB-like gabbros, 468-Ma Hawaiian alkaline basalt-like dolerite and pillow basaltic slices, and 428 Ma massive SSZ-like ultramafic rocks. The 501–452 Ma I-type granites exhibit arc affinities due to the oceanic crust subduction. These findings, along with spatial relationships, suggest that the Early Paleozoic ophiolite complex, island arc rocks, and accretionary complex generated as an intra-oceanic arc system as a result of obduction of the south Altun Ocean’s onto the Central Altun block within a north-directed subduction event. A dextral strike–slip was evident throughout the Early Paleozoic oceanic crust subduction based on the whole set of planar and linear structural data, and the subduction polarity was likely to the north. According to the ophiolitic mélange’s youngest rocks and the existence of 413 Ma granite dykes that are widely exposed in the Munabulake ophiolitic mélange, the Munabulake ophiolitic mélange was most likely emplaced during the Middle Silurian. This Munabulake ophiolitic mélange is similar in age and petrochemical characteristics to the other ophiolites in the South Altun subduction–collision belt, indicating that the Manabulak ophiolite mélange is a westward extension of the Apa–Mangya subduction–collision belt, which formed during the northward subduction of the South Altun Ocean slab during the Early Paleozoic. Thus, the final closing time of the South Altun Ocean is between 413 and 428 Ma.

Late Paleoproterozoic collision-related granitic magmatism in the Cuoke Complex, SW China: New evidence for the early evolution of the Yangtze Block

The Paleoproterozoic tectonic evolution of the southwestern Yangtze Block has been ambiguous due to the scarce preservation of geological records, confusing the history of the entire Yangtze Block in the Nuna supercontinent. We here report an integrated study involving petrology, whole-rock geochemistry, zircon U-Pb geochronology and Hf-Nd isotopes of the recently identified late Paleoproterozoic granitoids from the Cuoke Complex in the southwestern Yangtze Block. LA-ICP-MS zircon U-Pb dating reveals three episodes of granitic magmatism at ca. 1.94 Ga, 1.89 Ga, and 1.85 Ga. Geochemically, the ca. 1.94 Ga albite granites (AGs) and ca. 1.89 Ga and 1.85 Ga monzogranites (MGs) exhibit features of I-type granite, while the ca. 1.85 Ga AGs display characteristics of A-type granite. The zircon εHf(t) values range from −13.0 to −8.1 for the 1.94–1.89 Ga granitoids and from −8.9 to −7.2 for the ca. 1.85 Ga granitoids, with two-stage model ages of 3.3–3.1 Ga and ca. 3.0 Ga, respectively, indicative of their derivation from remelting of Mesoarchean crustal materials. The relatively low heavy rare earth elements (HREEs) (e.g., Yb < 1.9 ppm) and Y (<18 ppm) contents, and moderately negative Eu anomalies of the ca. 1.94–1.89 Ga granitiods suggest they may have been produced in a late collisional or earliest post-collisional setting. The ca. 1.85 Ga AGs and MGs were probably formed in a post-collisional setting indicated by their high HREE (e.g., Yb > 1.9 ppm) and Y (>18 ppm) contents and strongly negative Eu anomalies. Combined with available data, we provisionally divided the tectonic evolution of the southwestern Yangtze Block into four stages: 1) ca. 2.01 Ga subduction, 2) ca. 1.97–1.95 Ga metamorphism associated with collision events, 3) ca. 1.94–1.89 Ga late collisional or earliest post-collisional stage, and 4) ca. 1.85 Ga post-collisional extensional stage. The subduction and collision of the southwestern Yangtze Block initiated slightly later than the northern part, but their near-synchronous tectonic process since ca. 1.97 Ga suggest they may have collaged together at that time. The ca. 1.94–1.89 Ga and ca. 1.85 Ga late collisional to post-collisional granitic magmatism likely recorded the convergence of discrete Archean rock provinces of the Yangtze Block during the Nuna supercontinent assembly.

Petrogenesis and geological implications of the qiyishan triassic granitoids in east Beishan orogen, inner Mongolia, NW China: evidence from geochronology, geochemistry and Nd-Hf isotopes

The Qiyishan deposit is a large-scale Rb polymetallic deposit in the Beishan orogen. However, there remain debates regarding its metallogenic age and tectonic setting. In addition, studies of Triassic tectono-magmatic events in the Beishan orogen are still insufficient, and conducting genesis studies on the Qiyishan Triassic granitoids will help to enhance the understanding of Triassic magmatism and tectonic evolution in the Beishan orogen. In this contribution, we report new data for the ore-forming granitoids of Qiyishan deposit, including zircon U-Pb ages, major and trace element concentrations and Nd-Hf isotope compositions to define the ages and genesis of the Qiyishan granitoids and discuss their origin and geodynamic implications. Zircon U-Pb dating of the Qiyishan ore-forming granitoids yielded three ages of 217.5 ± 1.3 Ma, 217.2 ±0.8 Ma, and 207.5 ± 2.0 Ma, respectively. The age of Rb mineralization can be constrained to 207.5± 2.0 Ma, while the age of W-Sn-Mo mineralization is considered to be slightly younger than approximately 217 Ma. The Characteristics of major and trace elements of the rock samples indicate that the Qiyishan granites can be classified to highly fractionated I-type granite, and characterised by a transition to A-type like granite to some extent. The granites were not only affected by fractional crystallisation, but also underwent magmatic-hydrothermal interaction. The zircon εHf(t) values of the Qiyishan granitoids ranged from 3.28 to 16.07 and the Hf model age (TDMc) ranged from 0.216 to 1.042 Ga, revealing that the Qiyishan granitoids originated from the partial melting of both mantle and crustal sources. εNd(t) values ranged from −0.52 to −0.25, with Nd model ages of 0.998 Ga to 1.007 Ga. These results indicate that the granitoids originated from the mantle-derived magmas intruding into the lower crust within an intracontinental extensional environment. Combining the previous studies of Triassic granites in the Beishan orogen and this work, the Triassic granites exhibit a transition from I-type to A-type along the northeast direction, indicating a decrease in the contribution of ancient crustal to the magma source. We propose that the Qiyishan granitoids formed in a transitional tectonic environment, signifying the shift from post-orogenic to intracontinental extensional settings in beishan orogen during late Triassic.

Middle Devonian Evandale porphyry Cu-Mo (Au) deposit, southwestern New Brunswick, Canada: Analysis of petrogenesis to potential as a source for distal intrusion-related epithermal gold mineralization

The 391.2 ± 3.2 Ma (U-Pb on zircon) Evandale Granodiorite of southwestern New Brunswick is quite a unique intrusive rock in the southern part of the northeastern Appalachians. This research examines the relationship between the porphyry Cu-Mo-(Au) and epithermal systems with Evandale Granodiorite and environs. This Middle Devonian multi-phase I-type granite intrudes along the northern boundary of the deformed Silurian sedimentary and mafic volcanic rocks of the Mascarene Basin. This granitoid is identified as an oxidized I-type system with adakitic geochemical signatures and associated porphyry Cu-Mo-(Au) mineralization, possibly linked to slab failure sourced from decompression melting of the lower crust caused by post-collisional uplift, similar to the Magaguadavic Granite to the southwest. The Evandale adakitic intrusion is divided into two phases that consist of (1) a calc-alkalic coarser phase ranging from medium- to coarse-grained, seriate to porphyritic granodiorite to monzogranite with metaluminous to peraluminous features, and (2) the later stage alkali-calcic fine-grained (to aplitic) locally porphyritic phase ranging from a monzogranite to syeno-granite with peraluminous characteristics. The primary mineralogy of the intrusive rocks consists of K-feldspar + albite + plagioclase + quartz + biotite + hornblende + apatite ± muscovite ± zircon, along with several alteration phases, such as biotite, chlorite, sericite, and calcite. Geochemical analyses (using INAA, ICP-MS, and XRF) indicate that both phases of the Evandale granodiorite show a high concentration of Cu (108 ppm) and Au (33 ppb) associated with the presence of pyrite, chalcopyrite, and arsenopyrite in the fine-grained dyke samples. Up to 6 ppm Mo was contained within the granitic phase, whereas lesser amounts of Mo were confined to the fine grained to aplite phases. Microprobe analyses of primary biotite as both phenocrysts and groundmass shows 0.55 avg. wt.% Cl and 0.21 avg. wt.% F, which are relatively concentrated compared to other high-grade porphyry deposits. Hydrothermally altered rocks, veins, and sulfides associated with the porphyritic suite result from buoyant magmatic-hydrothermal fluids from a deeper intrusion exsolving fluids (quenched porphyry related), depressurizing, and reacting with the host coarser grained granodiorite and even some of the dykes locally. Based on the geothermometry and geobarometry of amphibole (actinolite-magnesiohornblende), the crystallization temperature and pressure of the Evandale coarse-grained granite and aplite are 674–755 °C, 0.2–0.7 kbar (20–70 MPa) and 838 °C, 0.42–1.4 kbar (42–140 MPa), respectively. This is consistent with biotite formation at temperatures ranging from 670° to 760 °C, based on Ti-in-biotite thermometry. Also, zircon saturation temperatures of the earlier coarse-grained porphyritic granites and later fine-grained porphyry to aplitic dykes are 736 °C and 787 °C, respectively. Spatially and temporally associated gold deposits beside Evandale and within this region of southwestern New Brunswick suggests that these oxidized I-type intrusions are a potential source for distal, low sulfidation epithermal gold deposits in the region.

Mantle contributions to granitoids associated with Sn mineralization: Geochemical and isotopic evidence from the giant Dachang deposit, South China

Major Sn deposits are commonly linked to crust-derived and highly evolved granites, with magma generation aided by mantle heating. However, whether and how the mantle components contribute to Sn polymetallic mineralization remains unclear. In this study, in combination with a compilation of equivalent data in the region, we provide new constraints on this issue based on detailed investigations on the petrogenesis and metallogenic significance of granitoids including the causative batholith and later granodiorite porphyry dike in the giant Dachang Sn deposit from South China. The former has zircon U-Pb ages of 93–91 Ma and belongs to highly evolved S-type biotite granite, which experienced fractionation of massive feldspar. The latter shows zircon U-Pb ages of 90 Ma and displays I-type granite features. The batholith was mainly derived from the dehydration melting of biotite in the metasedimentary sources, as revealed by the relatively low whole-rock Pb contents (<30 ppm) and high Ba/Pb ratios (2.71–17.1) and initial T(ti-zr) of 790 ℃. Compared with the adjacent crust-derived S-type granites (−24.8 – −5.1) and I-type granites (−11.0 to −5.2), the Dachang S-type biotite granites present higher zircon εHf(t) values (−9.1 to −2.1). Furthermore, the low magmatic zircon δ18O values (6.2 ‰) and higher apatite LREE (3277–4114 ppm) and Sr (1137–1357 ppm) contents than of arc-type basic rocks were discerned. These characteristics jointly hint the contributions of mantle components. The higher initial T(ti-zr) (>850 °C), whole-rock Mg# (52 to 58), apatite εNd(t) (−9.2 to −6.5) and zircon εHf(t) (−7.6 to 2.5) values but lower zircon δ18O values (6.33 to 8.30 ‰) of the later granodiorite porphyry dike than those of the batholith also suggest that mantle material was involved in the generation of the dikes, which is evident by the variational features of zircon and apatite trace elements. In addition, at the zircon Hf <12000 ppm and Eu/Eu* > 0.05, the higher zircon ΔFMQ values (mostly from −1.8 to 2.0) and H2O contents (100–1100 ppm) of the Dachang granitoids than the pure crust-derived S-type granites (ΔFMQ = mostly from −3.7 to −1.5; H2O < 100 ppm) imply that mantle materials involved are relatively rich in water and oxidized. These suggest that the addition of mantle components is conducive to the extraction of Sn from metasedimentary sources, and moderately facilitates the increase of oxygen fugacity which still maintains the incompatibility of Sn in magmas with ΔFMQ < 2. Also, the involvement of mantle components upgrades the H2O contents in S-type magmas, favoring the migration of ore-forming elements from magmas to hydrothermal fluids. The sediment-derived causative granites displayed higher εHf(t) and εNd(t) values with greater Sn tonnages of their associated world-class Sn polymetallic deposits, supporting the opinion that the contributions of mantle components play an important role in the generation of giant Sn deposits.

Petrology, mineralogy, and geochemistry of the Carboniferous Katbasu Au-Cu deposit, western Tianshan, Northwest China: Implications for petrogenesis, ore genesis, and tectonic setting

The Katbasu Au-Cu deposit in the Chinese western Tianshan is hosted in the ca. 355 Ma granite intrusion. This paper reports whole-rock geochemical and zircon Hf-O isotopic data for the granites and the mafic enclaves as well as in situ S isotopic data for the sulfides from the Katbasu Au-Cu deposit. Our results provide constraints on the petrogenesis and ore genesis of the Katbasu Au-Cu deposit. Geochemical characteristics suggest that the Katbasu granites are metaluminous rocks, exhibiting mineral assemblages and geochemical characteristics of I-type granites. The granites have positive zircon εHf(t) values of 7.1–10.2 and zircon δ18O values of 6.2–7.2‰, suggesting a juvenile crustal origin. Mixing processes between felsic and mafic magmas were involved in their generation. The mafic enclaves are enriched in LILEs and depleted in HFSEs, and have zircon εHf(t) values of 7.5–15.8 and zircon δ18O values of 5.4–6.9‰, suggesting that they were derived from a subduction-modified mantle and underwent subsequent crustal contamination and/or magma mixing processes. In situ S isotopic analyses show that pyrite grains from the pre-ore stage and post-ore stage have positive δ34S values of 7.0–8.5‰ and 8.2–9.0‰, respectively. Pyrite and chalcopyrite grains from an early magmatic-hydrothermal Cu-Au mineralization stage show δ34S values of 8.8–11.1‰, and pyrite grains from the main orogenic Au mineralization stage have positive δ34S values of 5.9–8.4‰. The heavy S isotope characteristics of magmatic-hydrothermal Cu-Au mineralization indicate that the magma source might be metasomatized by subduction materials, whereas the heavy S isotope characteristics of the late orogenic Au mineralization suggest that the ore-forming materials mainly originated from the metamorphic devolatilization of the source rocks. The ca.352–349 Ma early magmatic-hydrothermal Cu-Au mineralization in the Katbasu deposit formed in a subduction tectonic setting, whereas the ca. 323–311 Ma late orogenic Au mineralization formed in an orogenic environment during the final stage of subduction.

Strongly Peraluminous Highly Fractionated I-Type Granite from Bangong–Nujiang Metallogenic Belt, Tibet: Implications for Continental Evolution and Evaluation of Economic Potentiality

The research on highly fractionated granite has significant implications for both the evolution and compositional maturation of the continental crust and metallogenic exploration. As a means of further understanding crustal evolution and promoting ore exploration in the Bangong–Nujiang metallogenic belt (BNMB), we present the petrography, zircon LA–ICP–MS U–Pb age, and Hf isotopic data, along with the whole-rock geochemical and Sr–Nd isotopic composition on Kese highly fractionated granite in the Baingoin area within the BNMB, central Tibet. The results show that Kese granite possesses a zircon U–Pb age of 127.8 ± 1.7 Ma and a relative enrichment in zircon Hf isotopic composition (−12.8~+0.3) with a two-stage Hf model age of 1.2~2.0 Ga. This granite belongs to the high-K calc-alkaline series, characterized by a strongly peraluminous feature, and is enriched in large-ion lithophile elements (LILEs) and Nd isotopes (−7.86~−7.74). The granite was likely to have been derived from the mixed melts derived from 40%~45% juvenile basaltic lower crust, 15%~20% ancient lower, and 40% middle–upper, following intense fractional crystallization processes involving amphibole, biotite, plagioclase, and some accessory minerals during the magma’s evolution. We infer that Kese highly fractionated granite can be formed from the continental collision of the Lhasa–Qiangtang terranes initiated before 128 Ma. The reworking of pre-existing juvenile and ancient crustal materials drove the composition of the northern Lhasa terrane to that of a mature continental crust. Moreover, the distinctive geochemical features have shown that the high degree of differentiation led to intense magmatic–hydrothermal interaction during the formation of Kese granite. A comparison of the geochemical characteristics of mineralized and barren granites suggests that the highly fractionated granites in Baingoin from the BNMB have a high economic potential and are suitable for preliminary exploration of Sn–W-(U) deposits.

Early to Middle Jurassic (ca. 182–164 Ma) fractionated granitoids in the Korean Peninsula: Implication for the tectonomagmatic history of East Asia

The Jurassic granitoids (200–164 Ma) are distributed in the Korean Peninsula due to the Paleo-Pacific plate subduction. Early Jurassic (200–182 Ma) granitoids are mainly distributed in the southern Korean Peninsula. By contrast, Early to Middle Jurassic (182–164 Ma) granitoids are distributed in the central Korean Peninsula. In this study, we report detailed petrology, zircon U–Pb ages, and whole-rock geochemistry from the Seoul–Uijeongbu and Pocheon–Gimhwa pluton units in the central Korean Peninsula. The Seoul–Uijeongbu unit is dominated by biotite granite, with minor porphyritic biotite and garnet-biotite granite while the Pocheon–Gimhwa unit consists of biotite granite and porphyritic biotite granite, garnet-biotite granite, and two-mica granite. Zircon U–Pb age from those granites gives 180–167 Ma. The granitoids in the Pocheon-Gimhwa unit formed through fractional crystallization from biotite granite and porphyritic biotite granite to garnet-biotite granite, and two-mica granite based on gradually decreasing their Nb/Ta, Zr/Hf, and Eu/Eu* ratios. The strongly fractionated granitoids are garnet-biotite granite and two-mica granite. The LILE enrichment, Ta–Nb, Sr–P, and Eu–Ti troughs, and Ba depletion in most granitoids are similar to those of granitoids due to the subduction in the arc environment. Thus, these Jurassic granitoids (180–167 Ma) are mainly peraluminous granites with moderate crystal fractionation corresponding to I-type granite. Alkali feldspar granite associated with ore mineralization occurs in the Gwanaksan pluton from the southwestern Seoul–Uijeongbu unit. The alkali feldspar granite displays distinct negative Eu anomaly with high contents of Rb, Hf, Cs, and Nb compared with other granites. These characteristics imply that alkali feldspar granite experienced strong hydrothermal activity leading to feldspar ore mineralization compared to the other granites. The formation of a wide range of moderately evolved peraluminous granitoids is presumed to be related to rapid flat-subduction during 182–164 Ma, and the mineralization-related alkali feldspar granite indicates the termination of Jurassic granitoid magmatism in the central Korean Peninsula.

Geochemical characteristics of arc fractionated I-type granitoids of eastern Tak Batholith, Thailand

Abstract The Tak Batholith is located in the western part of Thailand’s eastern granitoid belt. To better understand the geochemical characteristics of granitoid and identify their occurrence, rock samples collected from the eastern part of the Tak Batholith were used for petrographical, mineralogical, and geochemical analyses. According to field investigation and lithology, petrography classifies these granitic rocks as medium-grained granodiorite and granodioritic dike. The granodiorites are composed chiefly of plagioclase, orthoclase, quartz, hornblende, and biotite, with tiny amounts of zircon, apatite, and opaque minerals. Meanwhile, the granitic dike shows a highly porphyritic texture, presenting mostly plagioclase phenocrysts, with a small amount of orthoclase and unidentified mafic phenocrysts sitting in a fine-grained groundmass comprising K-feldspar and quartz with a small amount of plagioclase and present granophyric intergrowth. Geochemical data of the amphiboles classified them as Ferro-edenite symbolizing the I-type granite. Whole-rock geochemistry indicates that these rock suites are I-type metaluminous granodiorite, and diorite fractionated from the high K calc-alkaline magma melted from the mafic crust of arc magmatism agreeable with the enrichment of large ion lithophile elements and depletion of highfield-strength elements, and rare earth element patterns.

A newly defined latest Carboniferous-Permian ridge subduction in the southern Altaids: Insights from adakitic, S-type, and I-type granitoids in the northern East Junggar (NW China)

ABSTRACT Late Palaeozoic evolution of the Chinese Altai-East Junggar orogenic collage is vital for a better understanding of the accretionary evolution in the southern Altaids. This paper reports new geochronological, geochemical, and isotopic data for the magmatic rocks collected from the northern part of the Dulate arc. The ~304.6 Ma tonalite samples present typical adakitic features of high Sr (396–714 ppm), low Y (1.42–2.60 ppm), Yb (0.11–0.24 ppm), and high Sr/Y (177.25–440.23) ratios. Combining high Mg# (55.35–57.21) and depleted isotopic composition (εHf(t): +9.89 to +13.37 and εNd(t): +5.36 to +6.06), we suggest that they were derived from the partial melting of a subducted oceanic slab. The ~299.4 Ma monzogranite samples have high A/CNK values (1.08 to 1.25), CIPW normative corundum contents (1.28–3.25 wt.%), and positive εHf(t) (+5.14 to +8.63) and εNd(t) (+1.08) values, which are similar to S-type granite that may be generated by the melting of greywackes. The monzogranite (~286.9 Ma) and rhyolitic porphyry (~283.9 Ma) are high-K calc-alkaline and similar to the highly fractionated I-type granites with depleted isotopic features (εHf(t): +11.68 to +14.99 and +0.75 to +7.18, εNd(t): +5.91 and +6.18). The monzogranite and rhyolitic porphyry could have been derived from a depleted mantle source, but the rhyolitic porphyry probably suffered partial assimilation of the overlying crust materials. Combining regional rock associations of mafic-ultramafic complexes, adakitic rocks, high-Mg diorites, and A-type granites with close spatial-temporal relationship, we conclude that a mid-oceanic ridge of the Ob-Zaisan Ocean subducted southward beneath the Dulate arc during the latest Carboniferous to Permian. With the opening of the slab window, the upwelling asthenosphere provided high heat flux and triggered various magmatism in the upper plate. We propose that ridge subduction is one of the most effective mechanisms of continental growth in the southern Altaids.

U-Pb and Re-Os geochronology and geochemistry of the Ulgen hidden porphyry Mo deposit in the Derbugan metallogenic belt (NE China): Insights into petrogenesis and tectonic setting

The Ulgen porphyry Mo deposit, recently discovered in the northeastern segment of the Derbugan metallogenic belt, NE China, is a large and hidden ore deposit. Investigation of this deposit provides insights into the geodynamic background and metallogenic mechanism of Mesozoic porphyry Mo deposits that are exposed elsewhere in NE China. The host rocks consist of muscovite monzonitic granite (MMG) and biotite granitic porphyry (BGP), which are intruded into Lower and/or Middle Jurassic intermediate-felsic volcanic-sedimentary rocks and pre-ore monzogranitic porphyry (MP). Zircon laser ablation−inductively coupled plasma−mass spectrometric (LA-ICP-MS) U-Pb age dating indicates that the MMG and BGP were emplaced at 144.9 Ma and 144.7 Ma, ca. 14 m.y. younger than the intrusion age of MP (159.3 Ma). Molybdenite Re-Os isotopic dating indicates that Mo mineralization occurred at 144.9 Ma, almost simultaneously with the 145 Ma magmatic activity. Geochemically, all of the Ulgen granitoids are enriched in large ion lithophile elements (e.g., Rb, Th, U, and K) and light rare earth elements, and are depleted in high field strength elements (e.g., Nb, Ta, and Ti). The pre-ore MPs belong to I-type granites with moderately negative Eu anomalies (Eu/Eu* = 0.62−0.65), whereas the syn-ore MMGs exhibit S-type affinity with pronounced negative Eu anomalies (Eu/Eu* = 0.29−0.39). The ore-forming BGPs display adakite-like geochemical features in terms of high-Sr, low-Y, and low-Yb contents, and slightly negative Eu anomalies (Eu/Eu* = 0.72−0.74). All intrusive rocks have relatively low initial (87Sr/86Sr)i ratios (0.7044−0.7055) and positive εNd(t) values (+1.15 to +2.65), positive εHf(t) values (+4.0 to +9.4), young two-stage Nd and Hf model ages (tDM2(Nd) = 841−731 Ma, tDM2(Hf) = 943−604 Ma), and moderate (206Pb/204Pb)i (18.300−18.402), (207Pb/204Pb)i (15.557−15.564), and (208Pb/204Pb)i (38.180−38.307) ratios. Therefore, it is most likely that these intrusive rocks originated from a mixture of two sources of magma derived from the mantle and juvenile lower crust, in which there were variable degrees of the fractional crystallization of ilmenite, apatite, and plagioclase. Rather than the partial melting of oceanic slabs, the fractional crystallization of hornblende and accessory minerals (e.g., ilmenite and apatite) induces the adakitic geochemical signature of BGPs. Compared with the BGPs, the MPs had a relatively deeper magma source region, whereas the MMGs had a relatively shallower magma source region. The BGPs and the Mo-bearing fluids of the Ulgen deposit were most probably derived simultaneously from magma that was generated at an extensional setting following the closure of the Mongol-Okhotsk Ocean during the latest Jurassic. Enrichment of Mo by late-stage fractional crystallization most likely played an important role in concentrating Mo during the formation of the Ulgen hidden Mo deposit.

Multi-episodes of pre-Cenozoic bimodal magmatism in the Himalaya in response to arc-back-arc settings

The Himalayan orogen preserves multi-episodes of pre-Cenozoic magmatic history, but remains a subject of debate for their tectonic settings, limiting a better understanding of the Himalaya litho-tectonic structure. This study demonstrates the protolith nature of granitic gneisses and garnet amphibolites collected from three areas (Kangmar, Cona, and Arun Valley) in the east-central Himalaya. Then we investigated the bulk-rock major and trace elements, Sr-Nd isotopes, zircon U-Pb ages, and Hf isotopes. The garnet amphibolites are classified into sub-alkaline basalt and show tholeiite affinity. Garnet amphibolites from the Kangmar and Cona areas show Paleozoic (512–450 Ma) and Neoproterozoic (803 ± 8 Ma) protolith ages, respectively. Geochemically, they display similar MORB-like trace element features and enrich in large ion lithophile elements (LILEs: Rb, Th, U, Sr, Pb) and Ta, Ti, and mantle-like Sr-Nd isotopes with initial 87Sr/86Sr of 0.667787–0.705088 and εNd(t) of 2.9–5.0. The high Th/Yb and Ba/Th ratios and varied εHf(t) (−22.3–11.0) indicate subduction-related material contributions. The geochemical affinity to MORB and slab contributions is associated with a back-arc basin setting. Besides, garnet amphibolites from Arun Valley yield a protolith age of 1869 ± 10 Ma and are divided into two groups. Group I exhibits enriched LREE patterns [(La/Yb)N = 5.99–6.44] and shows wide εNd(t) of −1.3 to 7.1, variable Th/Ta and Nb/La, and high Zr/Y ratios. These features suggest the protolith of Group I might be continental flood basalts. In comparison, Group II exhibits MORB-like REE patterns, enrichments of LILEs, and depletions of high field strength elements (HFSEs) similar to island arc basalt. Thus, the geochemical affinity to MORB and arc-like features indicates they are metamorphosed from back-arc basalts. As for the granitic gneisses, the Kangmar and Cona samples give a Paleozoic age range of 552–438 Ma, due to a protracted (∼110 Myr) magmatism. The Kangmar granitic gneisses were metamorphosed from arc-related I-type granites, by contrast, the Cona granitic gneisses belong to A-type granites formed in a back-arc setting. These Paleozoic granitic gneisses show similar εHf(t) of −7.1–−2.5 and TDM2 of 1229–1923 Ma, indicating they were derived from partial melting of Meso- to Paleoproterozoic crust. Furthermore, the Arun Valley granitic gneisses give an 1819 ± 6 Ma protolith age and show arc features with enriched LILEs and depleted HFSEs. The wide εHf(t) of −5.3–13.2 indicates the varying degree of mantle contributions resulting from slab break-off or roll-back. Therefore, the Himalaya witnessed bimodal magmatism during Paleoproterozoic, Neoproterozoic, and Paleozoic related to Andean-type orogeny. The multi-episodes of Andean-type magmatism contribute to the formation of the Cenozoic Himalayan architecture.

Cretaceous magmatic migration and flare-up in Pamir–Karakoram

The Pamir–Karakoram terrain contains abundant Cretaceous granitoids, and minor coeval volcanic rocks and mafic intrusions, which represent a wide (ca. 400 km) continental arc developed during northward subduction of Neo-Tethys oceanic lithosphere. However, little is known of the tectonic controls on the magmatic flare-ups and their implications for crustal thickening. In this paper, we report new zircon UPb age and Hf isotope data for Cretaceous biotite granites, two-mica granites and mafic microgranular enclaves (MMEs) from the large-scale granitic batholiths in Pamir. These and previously published results show there were four episodes of Cretaceous magmatism (124–108, 107–103, 102–92, and 80–70 Ma). The Cretaceous arc migrated progressively landward from Karakoram to Central Pamir with a maximum arc–trench distance of ca. 400 km during the first magmatic episode (124–108 Ma). The igneous rocks are mainly S-type granites with enriched zircon Hf isotopic compositions (ɛHf(t) = −19.8 to −5.4), indicating derivation by partial melting of metasedimentary units. A magmatic flare-up at 105 ± 2 Ma generated voluminous I-type granites and minor mafic igneous rocks that cover ca. 30% of the study area. The I-type granites have higher zircon ɛHf(t) values (−19.0 to −2.0) as compared with those of the earlier S-type granites, which reflect the addition of mantle-derived materials (ca. 30%). The third episode of magmatism (102–92 Ma) generated mainly intermediate–silicic volcanic rocks, which are geochemically similar to I-type granites and have ɛHf(t) values of −15.0 to −1.5. The final episode of magmatism (80–70 Ma) was dominated by alkaline and mafic igneous rocks formed in a post-collisional setting, which have variable ɛHf(t) values of −6.6 to 10.5. Our study highlights that the Early Cretaceous magmatic flare-up in the Pamir–Karakoram terrain was related to foundering of the flat-slab of Neo-Tethys oceanic lithosphere that was previously subducted, which induced voluminous underplating of mantle-derived magma in the lower crust. This process had a key role in crustal thickening in the Pamir–Karakoram terrain prior to the Cenozoic India–Asia collision.

High Fractionated Granites of the Raumid Massif (S. Pamir): O-Isotope and Geochemical Study

The processes of crystallization differentiation, retrograde isotopic exchange, and autometamorphism are considered using the “natural laboratory” – Eocene granites of the Raumid massif, which has eight intrusion phases. The work is based on a comprehensive (oxygen isotope, petrographic, geochemical) study of representative samples of each of the intrusion phases of the massif. Isotopic and geochemical studies of rock-forming minerals (Qz, Pl, Kfs, Bt), as well as their altered varieties, have been carried out. The geochemical features of the Raumid’s granites are correspond to both A-type granites and highly fractionated I-type granites. We show that the rocks of the Raumid massif are not the geochemical analog of the Qiangtang Eocene granitoids of the Central Tibet and the Vanj complex, as previously assumed (Chapman et al., 2018). The differentiation conditions for acidic melts that formed the Raumid pluton (T = 750–800°C, P = 4.5–7.8 kbar with predominant Pl crystallization) were estimated. The intrusion of melts into the hypabyssal zone proceeded at least in two stages: early (γ1–γ3) and late (γ4–γ8), although it is possible that the rocks of the γ7 and γ8 phases belonged to a separate stage. The closing temperature of the oxygen isotopic system of quartz (Тq) varies from 420 to 610°C, which indicates a wide range of cooling rates for these rocks. The effect of the multiphase nature of melt intrusion on the Тq and apparent cooling rates is considered. The study of altered and unaltered minerals makes it possible to establish that autometamorphism partially overlapped with the retrograde oxygen isotope exchange in the cooling rock. The modelling of the δ18О values of feldspars during autometamorphism in a system closed with respect to fluid show that the Pl saussuritization and Kfs kaolinitization proceeded at a limited fluid/mineral ratio (W/M = 0.3–0.05), which could be provided by aqueous fluid separated during the Raumid pluton cooling.

Petrogenesis, tectonic setting and geodynamic implications of keziergayin granites in the kelan basin (Chinese Altai): constraints from geochemistry, zircon U-Pb geochronology and Nd‒Hf‒Pb‒O isotopes

The Chinese Altai is characterized by abundant granitoids, which not only are indicators of the interaction between crust and mantle but also provide critical constraints on the tectonic evolution of the orogen. This study presents zircon U‒Pb‒O isotopes, whole-rock major and trace element and Nd‒Hf‒Pb isotopes data for granite porphyries from the Keziergayin region in the Kelan Basin. The granite porphyries intrude in the Kangbutiebao Formation with zircon U‒Pb dating of 394 ± 3 Ma. They have the characteristics of subalkaline and metaluminous to weakly peraluminous and show geochemical affinity with I-type granite. The granite porphyry samples display negative εNd(t) (−1.9 to −1.4), positive εHf(t) (+4.3 to +11.4) values, with Nd–Hf decoupling; low Pb isotope compositions; δ18OV-SMOW (6.38‰–8.45‰) is less than 10‰, within the range of O isotopes of medium-basic igneous rocks. These geochemical signatures indicate that the granite porphyries originated from lower crust medium−basic igneous rocks extracted from the lithospheric mantle metasomatized by subducted melt. They are characterized by high SiO2 contents and Rb/Sr ratios; low CaO contents and K/Rb ratios, hinting that they were formed by highly evolved magmas, with fractionation crystallization of feldspar, apatite, garnet, allanite and/or monazite. The granite porphyries possess positive Rb, Th, U, Nd, Zr, Pb and light rare Earth elements (LREEs) anomalies with strong negative Ba, Nb, Ta, Sr, P, Ti and Eu anomalies, implying that their formation were related to an island arc. Combined with previous studies, it is suggested that the existence of the Early Devonian arc-basin system associated with subducting slab rollback in the Chinese Altai, which belongs to the Siberian active continental margin system.

Lithospheric dripping triggered by slab break-off: A possible mechanism for Late Carboniferous magmatism in the eastern Central Asian Orogenic Belt

In this paper, we present zircon UPb dating, elemental geochemistry, and Sr–Nd–Hf isotopic compositions for Late Carboniferous intrusive rocks in the northern Great Xing'an Range, northeast China. We decipher the mechanisms which triggered lithospheric thinning under microblock-microblock collision and provide a new perspective on the Late Paleozoic evolution of the eastern Central Asian Orogenic Belt. Zircon UPb dating indicates that Jifeng gabbroic diorites and Xinlin granites were formed during a short time interval at 322–321 Ma, whereas the Xinlin gabbros were crystallized at 300 ± 2 Ma. The Jifeng gabbroic diorites exhibit typical arc characteristics, depleted in HFSEs and enriched in Pb and have positive εNd(t) (+1.88 to +2.00) and εHf(t) (+6.6 to +10.7) values, suggesting they originated from the partial melting of depleted lithospheric mantle modified by slab fluids. The Xinlin gabbros belong to alkaline series and are characterized by the enrichment in HFSEs with positive Nb and Ta anomalies and depleted NdHf isotopic compositions (zircon εHf(t) = +12.5 to +18.9, whole rock εNd(t) = +8.0 to +8.1). High Nb concentrations and low La/Nb (0.81–0.83) and La/Ta (12.50–14.61) ratios of the Xinlin gabbros indicate an origin from a depleted asthenospheric mantle. The Xinlin granites have high-K calc-alkaline compositions, belonging to I-type granites. These granites have positive εHf(t) values (+0.2 to +15.1) and juvenile two-stage model ages (1314–506 Ma) with low Sr and high Yb contents, indicating they were formed by the partial melting of a juvenile lower crust under low-pressure conditions. These data, together with the temporal and spatial distribution and the geochemistry characteristics of the Carboniferous igneous rocks in the Great Xing'an Range, suggest that the amalgamation between the Erguna–Xing'an and Songnen blocks occurred before the Late Carboniferous. The occurrence of asthenospheric mantle-derived mafic rocks indicates localized thinning process of lithosphere. Late Carboniferous magmatism on the Erguna–Xing'an Block attributed to dripping or piece removal of the lithosphere due to asthenospheric fluctuation triggered by slab break-off.

Petrogenesis and tectonic implications of the early Paleozoic granites in the Lincang granitic batholith, southwestern China: Constraints from geochronology, geochemistry and Hf isotopes

This study presents the recently discovered Wulao Shan Ordovician granite within the Lincang granitic batholith, discusses its geochemical affinity, genesis, and tectonic significance, and interprets the proto-Tethys orogenic model in southwest Yunnan. LA-ICP-MS zircon U-Pb analyses indicate a crystalline age of 473.0 ± 2.9 Ma for the Wulaoshan gneissic granite. Geochemical analyses show that the Wulaoshan granite exhibits relatively high SiO2 concentrations (73.4–77.3 wt.%), strong peraluminous properties (ASI > 1.1), strongly Eu-negative anomalies, light and heavy rare earth fractionation, and relative Ba, Nb, Ta, Sr, P, and Ti depletion. SiO2 and P2O5 exhibit a strong negative correlation, whereas Rb and Y-Th with a positive correlation. The magmatic zircons have negative εHf(t) values of -5.47∼2.74. Petrographic observations and whole-rock geochemical and isotopic analyses imply no aluminum-rich minerals such as cordierite, indicating that the Wulaoshan granite is a highly fractionated, high-temperature I-type granite, which may have formed via partial melting of the magnesian-iron igneous crust. Additionally, K-feldspar, plagioclase, and biotite within the granite samples may have undergone intense fractional crystallization. The Wulao Shan gneissic granite is an arc granite associated with subduction, indicating that the Lincang Block underwent proto-Tethys subduction. This finding provides evidence for proto-Tethys subduction down to the Lincang-Simao block and further supports the bidirectional subduction model of the proto-Tethys.