Early Jurassic Granitoids Research Articles

Geochronology and Geochemical Characteristics of Granitoids in the Lesser Xing’an–Zhangguangcai Range: Petrogenesis and Implications for the Early Jurassic Tectonic Evolution of the Mudanjiang Ocean

This article focuses on zircon U-Pb isotope dating and a whole-rock elemental analysis of granodiorites, monzonitic granites, granodioritic porphyries, and alkali feldspar granites in the Yangmugang area of the Lesser Xing’an–Zhangguangcai Range. The zircon U-Pb isotope-dating results revealed that these granitic rocks formed during the late Early Jurassic period (182.9–177.2 Ma). Their geochemical characteristics and zircon saturation temperatures suggest that the granodiorites are moderately differentiated I-type granites and the monzonitic granite, granodioritic porphyries, and alkali feldspar granites are highly differentiated I-type granites. The degree of magma differentiation progressively increased from granodiorites to alkali feldspar granites. By combining the regional Nd and Hf isotope compositions, it was inferred that the magma source involved the melting of lower crustal material from the Mesoproterozoic to the Neoproterozoic eras. By integrating these findings with contemporaneous intrusive rock spatial variations, it was indicated that the late Early Jurassic granitoids in the Lesser Xing’an–Zhangguangcai Range formed within an extensional tectonic setting after the collision and closure of the Songnen–Zhangguangcai Range and Jiamusi blocks. Additionally, this study constrains the closure of the Mudanjiang Ocean to the late Early Jurassic period (177.2 Ma).

In situ geochemistry of apatite: Petrogenetic and tectonic interpretations of Jurassic felsic magmatism in the Yanbian area, NE China

Geochemical analyses of individual minerals provide more detailed insights into the petrogenesis of igneous rocks than whole-rock analyses. This study conducted in situ geochemical and Nd isotope analyses of apatites from 10 Jurassic granitic plutons in the Yanbian area, NE China, to establish the petrogenesis and regional tectonic evolution. The results indicate that the apatite geochemistry of Jurassic granitoids in the Yanbian area was controlled primarily by the composition of parental melt. Post-magmatic alteration may lead to geochemical decoupling between apatite and parental melt, while Nd isotopes exhibit some resilience to such alterations. Apatites from Early Jurassic granitoids display characteristics that are consistent with an I-type origin, whereas those from Middle and Late Jurassic granitoids exhibit an adakitic affinity. Variations in apatite compositions indicate the fractional crystallization of other rare earth element (REE)-bearing minerals during magma evolution. The early crystallization of plagioclase and allanite led to decreases in Sr and Th contents in apatite, respectively, resulting in a negative Eu anomaly and light REE depletion. The fractional crystallization of titanite and hornblende resulted in the depletion of middle REE in apatite. Hornblende is regarded as the main residual phase in the magma source of Middle and Late Jurassic adakitic granitoids in the Yanbian area. Apatite Nd isotopic compositions suggest that the Jurassic granitoids in the Yanbian area originated from two crustal sources: the Central Asian Orogenic Belt and the North China Craton. Additionally, increasing trends in apatite Sr/Y and (La/Yb)N ratios from the Early to Late Jurassic suggest a gradual thickening of the regional crust, which is likely driven by the continentward migration of the subduction zone associated with the Paleo-Pacific Plate.

Early Jurassic A-type granite and monzodiorite from the Baoji batholith: Implication for tectonic transition from post-collision to post-orogenic extension in the Qinling Orogenic Belt, China

Introduction: The early Jurassic granitoids in the Qinling Orogenic Belt (QOB) play a crucial role in understanding the tectonic implications for the geological evolution of China. To elucidate the early Jurassic tectonic setting of QOB, we performed a comprehensive analysis of zircon U-Pb ages, whole-rock geochemistry, and in situ zircon Lu-Hf isotopes from early Jurassic monzodiorite and Kfeldspar granite within the Baoji batholith in western QOB.Geochronology Method and Results: The intrusions yielded zircon U-Pb ages of 186 ± 2 Ma and 188 ± 2 Ma, respectively.Geochemistry Results: The monzodiorites are characterized by relatively high MgO, Rb, Th, U, and LREE contents, as well as low P, Ti, and HREE contents. They also exhibit high Nb/Ta ratios (20.6–23.4). The zircon εHf(t) values for the monzodiorite sample range from −4.36 to 6.47, indicating significant contributions from a fertile continental lithospheric mantle with the involvement of crustal components. The K-feldspar granites are enriched in K2O+ Na2O, Rb, Zr, Hf, and Nb, and lower Ba, Sr, Ti, and P. They exhibit high Nb/Ta and Ga/Al ratios but low Y/Nb and Yb/Ta ratios. Their geochemical characteristics reveal an A-type granite affinity with elevated zircon saturation temperatures (848°C–900 °C). Additionally, the K-feldspar granite exhibits REE and trace element patterns similar to those observed in the monzodiorite. However, a wide range of zircon εHf(t) values (−4.72 to 3.98), differing from those of the monzodiorite, indicate that the parental magma of the K-feldspar granite experienced magma mixing between a monzodioritic magma and a crustal-derived felsic magma.Discussion: These findings suggest that both A-type K-feldspar granite and monzodiorite likely formed during post-orogenic processes. Additionally, the QOB commenced its postorogenic evolution as an extensional tectonic environment during the early Jurassic period.

Petrogenesis of Jurassic granitic plutons in the Yanbian area, NE China: Implications for the subduction history of the Paleo-Pacific Plate

It is widely accepted that the subduction of the Paleo-Pacific Plate beneath the Eurasian continent began during the early Mesozoic; however, the details of the subduction process remain uncertain. This paper presents new zircon U–Pb–Hf and whole-rock geochemical data for Jurassic intrusive rocks from the Yanbian area of NE China to provide a better understanding of the subduction history of the Paleo-Pacific Plate. Zircon U–Pb dating results reveal that three stages of Jurassic magmatism are recorded in the Yanbian area, namely, Early Jurassic (188–179 Ma), Middle Jurassic (172–163 Ma), and Late Jurassic (158–156 Ma). Early Jurassic intrusive rocks from the Yanbian area are predominantly calc-alkaline gabbro, gabbro-diorite, quartz monzonite, granodiorite, and syenogranite. These geochemical features and rock associations are indicative of formation in an active continental margin setting related to the initial subduction of the Paleo-Pacific Plate beneath the Eurasian continent. The Early Jurassic granitoids were formed mainly by the partial melting of heterogeneous lower crust. The Middle Jurassic granitoids are geochemically similar to adakites and have εHf(t) values of + 2.0 to + 10.1. These rocks are inferred to have been derived from magmas generated by the partial melting of thickened juvenile lower-crustal material. Their formation was related to the subduction of the Paleo-Pacific Plate. Late Jurassic adakites in the Yanbian area formed in a compressional tectonic setting. Their negative εHf(t) values (−17.2 to − 8.6) and TDM2 ages (2025–1552 Ma) indicate that the primary magma was derived from the partial melting of ancient continental crust. Combining our data with the distribution of Late Jurassic igneous rocks in the NE Asian continental margin and the northward migration of Jurassic accretionary complexes along the margin, we conclude that the subduction of the Paleo-Pacific Plate beneath the Eurasian continent during the Late Jurassic–earliest Early Cretaceous had a low angle of obliquity.

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.

Petrogenesis and Tectonic Setting of the Early and Middle Jurassic Granitoids in the Chaihe Area, Central Great Xing’an Range, NE China

To ascertain the Early-to-Middle Jurassic tectonic setting in the central Great Xing’an Range, this study investigated the Early and Middle Jurassic granitoids exposed in the Chaihe area in the central Great Xing’an Range based on isotopic chronology and petrogeochemistry. The results of this study show that the Early and Middle Jurassic granitoids have emplacement ages of 179–172 Ma. Moreover, the Early and Middle Jurassic granitoids are high-K calc-alkaline unfractionated I-type granitoids and high-K calc-alkaline fractionated I-type granitoids, respectively. The magma sources of the Early and Middle Jurassic granitoids both originated from the partial melting of newly accreted lower crustal basaltic rocks. Meanwhile, the Middle Jurassic magma sources were mixed with mantle-derived materials or ocean-floor sediments formed by the dehydration and metasomatism of subducted slabs. The Early and Middle Jurassic granitoids in the study area were formed in the subduction environment of the oceanic crust, in which the Mongol-Okhotsk oceanic plate was subducted southward beneath the Eerguna and Xing’an blocks. Moreover, the Siberian plate began to collide and converge with northeast China during the Middle Jurassic.

Zircon U–Pb geochronology and Hf isotope geochemistry of magmatic and metamorphic rocks from the Hida Belt, southwest Japan

Zircon U–Pb and Hf isotope data integrated in this study for magmatic and metamorphic rocks from the Hida Belt, southwest Japan, lead to a new understanding of the evolution of the Cordilleran arc system along the ancestral margins of present-day Northeast Asia. Ion microprobe data for magmatic zircon domains from eight mafic to intermediate orthogneisses in the Tateyama and Tsunogawa areas yielded weighted mean 206Pb/238U ages spanning the entire Permian period (302–254 Ma). Under cathodoluminescence, primary magmatic growth zones in the zircon crystals were observed to be partially or completely replaced by inward-penetrating, irregularly curved featureless or weakly zoned secondary domains that mostly yielded U–Pb ages of 250–240 Ma and relatively high Th/U ratios (> 0.2). These secondary domains are considered to have been formed by solid-state recrystallization during thermal overprints associated with intrusions of Hida granitoids. Available whole-rock geochemical and Sr–Nd isotope data as well as zircon age spectra corroborate that the Hida Belt comprises the Paleozoic–Mesozoic Cordilleran arc system built upon the margin of the North China Craton, together with the Yeongnam Massif in southern Korea. The arc magmatism along this system was commenced in the Carboniferous and culminated in the Permian–Triassic transition period. Highly positive εHf(t) values (> +12) of late Carboniferous to early Permian detrital zircons in the Hida paragneisses indicate that there was significant input from the depleted asthenospheric mantle and/or its crustal derivatives in the early stage of arc magmatism. On the other hand, near-chondritic εHf(t) values (+5 to −2) of magmatic zircons from late Permian Hida orthogneisses suggest a lithospheric mantle origin. Hf isotopic differences between magmatic zircon cores and the secondary rims observed in some orthogneiss samples clearly indicate that the zircons were chemically open to fluids or melts during thermal overprints. Resumed highly positive zircon εHf(t) values (>+9) shared by Early Jurassic granitoids in the Hida Belt and Yeongnam Massif may reflect reworking of the Paleozoic arc crust.

Ages and geochemistry of Early Jurassic granitoids in the Lesser Xing’an–Zhangguangcai Ranges, NE China: Petrogenesis and tectonic implications

Abstract Early Jurassic granitoids are widespread in the Lesser Xing’an–Zhangguangcai Ranges, providing excellent targets to understand the late Paleozoic to early Mesozoic tectonic framework and evolution of Northeast China, especially the Jiamusi block and its related structural belts. In this paper, we present new geochronological, geochemical, and isotopic data from the granitoids in the Lesser Xing’an–Zhangguangcai Ranges to constrain the early Mesozoic tectonic evolution of the Mudanjiang Ocean between the Jiamusi and Songnen blocks. Our results show that the granitic intrusions in the Lesser Xing’an–Zhangguangcai Ranges are mainly composed of syenogranite, monzogranite, granodiorite, and tonalite, which have crystallization ages from 196 to 181 Ma. Their geochemical features indicate that these Jurassic intrusions are all high-K calc-alkaline I-type granites with metaluminous to weakly peraluminous compositions. These granitoids are characterized by enrichments in large ion lithophile elements (e.g., Ba, Th, U) and light rare earth elements and depletions in high field strength elements (e.g., Nb and Ta) and heavy rare earth elements, which are typical for continental arc–type granites. The sources of these granitoids were likely derived from juvenile Mesoproterozoic to Neoproterozoic crustal materials (e.g., metabasaltic rocks). Integrated with data from regional coeval magmatism, metamorphism, metallogeny, and structure, our new data suggest that the granitoids in the Lesser Xing’an–Zhangguangcai Ranges were probably formed in an active continental margin setting, which fits well in our previous model of Early Jurassic westward subduction of the Mudanjiang Ocean between the Jiamusi and Songnen blocks.

Early Jurassic and Late Cretaceous granites in the Tongka micro-block, Central Tibet: Implications for the evolution of the Bangong-Nujiang ocean

The Tongka micro-block, located in the eastern section of the Bangong-Nujiang suture, and characterized by Mesozoic granitoids and high grade metamorphic rocks, holds the key to the evolution of the Bangong-Nujiang ocean (BNO). Here we present a systematic petrologic, geochemical, zircon U-Pb-Hf, and whole rock Sr-Nd-Pb isotopic investigation on six new granitoids in Tongka. The results suggest these granitoids yielded two stages of crystallization (171–177 Ma and 74 Ma) and two stages of metamorphism (201–215 Ma and 170–175 Ma). Combined with the existing work within BNS, the magmatism along the BNS can be divided into five stages: stage 1 (240–250 Ma), stage 2 (200–230 Ma), stage 3 (150–190 Ma), stage 4 (100–135 Ma) and stage 5 (73–100 Ma). Both the Early Jurassic and Late Cretaceous Tongka granitoids in this study are high-K calc-alkaline series, with enrichments in large ion lithophile elements (e.g., Cs, Rb, and K) and depletions of large ion lithophile elements (e.g., Nb, Ta, and Ti). The variable εHf(t) values (−17.3 to −7.6), εNd(t) values (−12.08 to −11.15) and ancient TDM2 (1.48–2.00 Ga) for the Early Jurassic granitoids and weakly negative εHf(t) values (−6.3 to −1.5), εNd(t) values (−8.75 to −8.60) and old TDM2 ages (1.07–1.33 Ga) for the Late Cretaceous granitoids, suggest that they are both mainly derived from the melting of ancient crust with minor mantle material input. However, the formation of the Early Jurassic and Late Cretaceous granitoids in Tongka is related to different tectonic settings: roll back after the Tongka micro-block subducted beneath the southern Qiangtang subterrane and extension-collapse after the Tongka micro-block collided with the northern Lhasa subterrane. The initial subduction of the BNO may start from 190 Ma, and the collision between the Lhasa and Qiangtang terranes may continute to the latest Cretaceous (<74 Ma). Ophiolites north of Amdo, Baqing and Dengqen were possiable lithospheric remanants of the Longmu Tso-Shuanghu ocean (LSO) rather than the BNO.

Switch of geodynamic setting from the Paleo-Asian Ocean to the Mongol-Okhotsk Ocean: Evidence from granitoids in the Duobaoshan ore field, Heilongjiang Province, Northeast China

This paper presents new zircon U-Pb ages and whole-rock geochemical data for Triassic granitoids in the Duobaoshan ore field, in the eastern Central Asian Orogenic Belt (CAOB). Dating results reveal that the Triassic granitoids in the Duobaoshan ore field were emplaced ca. 244–223 Ma. These samples are typical subduction-related arc magmatic rocks that are enriched with large-ion lithophile elements (LILEs), depleted in high field strength elements (HFSEs), and have relatively high Sr (average 1036 ppm) and low Y (average 10 ppm) and Yb (average 1 ppm) contents that exhibit adakite-like geochemical properties. The samples feature a juvenile whole rock average initial 87Sr/86Sr ratio of 0.70394 and an average ɛNd(t), zircon ɛHf(t), and two-stage Hf model age of 4.62, 10.29, and 766 Ma respectively. These geochemical features reveal a thickened lower crust source. Comprehensive analyses of the early Paleozoic, Triassic, and early Jurassic granitoids in the Duobaoshan ore field indicate that the magmatism of these three stages was related to the melting of the juvenile lower continental crust materials. The early Paleozoic was the primary period of vertical crust growth, during which time the juvenile lower continental crust was formed. The Triassic granitoids derived from magma were generated by partial melting of the thickened juvenile lower crust and the Jurassic granitoids derived from the partial melting of the delaminated juvenile lower crust. Geological observation and tectonic setting analyses reveal that the Paleo-Asian Ocean tectonic regime in the Duobaoshan ore field switched to the Mongol-Okhotsk Ocean in the Mesozoic after its closure. The early Paleozoic granitoids were formed in a subduction setting related to the northwestward subducted Paleo-Asian Oceanic slab underlying the Erguna-Xing'an composite block. The Triassic granitoids were formed under a supra-subduction extensional regime related to the southward subduction of the Mongol-Okhotsk Ocean, and the Jurassic granitoids were generated under a slab rollback setting related to the late stage subduction of the Mongol-Okhotsk Ocean.

Geochronology and geochemistry of early Mesozoic magmatism in the northeastern North China Craton: Implications for tectonic evolution

This paper reports geochronological, geochemical, zircon U–Pb and Hf–O isotopic data of the Late Triassic and Early Jurassic intrusive rocks in the northeastern North China Craton (NCC), with the aim of reconstructing the tectonic evolution and constraining the spatial–temporal extent of multiple tectonic regimes during the early Mesozoic. Zircon U–Pb ages indicate that the early Mesozoic magmatism in the northeastern NCC can be subdivided into two stages: Late Triassic (221–219 Ma) and Early Jurassic (180–177 Ma). Late Triassic magmatism produced mainly granodiorite and monzogranite, which occur as a NE–SW-trending belt parallel to the Sulu–Jingji Belt. Geochemically, they are classified as high-K calc-alkaline and metaluminous to weakly peraluminous granitoids, and are enriched in large-ion lithophile elements (LILEs) and light rare earth elements (LREEs), and depleted in high-field-strength elements (HFSEs; e.g., Nb, Ta, Ti, and P) and heavy rare earth elements (HREEs), indicating an affinity to adakite. Combined with their εHf(t) values (−17.9 to −3.2) and two-stage model ages (2387–1459 Ma), we conclude that the Late Triassic granitoid magma in the northeastern NCC was derived from partial melting of the thickened lower crust of the NCC and was related to deep subduction and collision between the NCC and the Yangtze Craton (YC). The Early Jurassic magmatism is composed mainly of monzogranites, which are classified as metaluminous, high-K calc-alkaline, and I-type granite. Their εHf(t) values and two-stage model ages are −16.7 to −4.2 and 2282–1491 Ma, respectively. Compared with the Late Triassic granitoids, the Early Jurassic granitoids have relatively high HREE contents, similar to calc-alkaline igneous rocks in an active continental margin setting. These Early Jurassic granitoids, together with the coeval calc-alkaline volcanic rocks and gabbro–diorite–granodiorite association in the northeastern (NE) Asian continental margin, comprise a NNE–SSW-trending belt parallel to the NE Asian continental margin, indicative of the onset of Paleo-Pacific Plate subduction beneath Eurasia.

Petrophysical Characteristics of the Intrusive Complexes of Different Age of the Gamow Peninsula (Southwestern Primorye)

The petrophysical data on the granitoids of the Gamow Peninsula are presented and compared with those of the granitoid complexes distributed on the adjacent territory. The physical properties of the Late Permian and Early Jurassic granitoid complexes are considered. Granitoids of different age sharply differ in petrophysical properties. The Late Permian granitoids developed on the Gamow Peninsula have higher density and lower magnetic characteristics relative to the same rocks distributed on the adjacent continental territory. It is established that the petrophysical properties of the Early Jurassic granitoids are similar to those of one phase of the Late Permian granitoids. The simultaneous formation of these complexes is proposed.

Early Mesozoic magmatism and tectonic evolution of east-central Tibet

The Early Mesozoic granitoids in the east-central Tibet are the key to understand the tectonic evolution of the Tibetan Plateau. In this study, three stages of Early Mesozoic granitic magmatism were indicated by LA-ICP-MS zircon U–Pb dating on 14 samples. The Early Triassic (248–243 Ma) and the Late Triassic (213–208 Ma) were distributed in the North Qiangtang terrane, and the Early Jurassic (ca. 187 Ma) occurred in the Tongka and Jiayuqiao blocks. The Late Triassic and Early Jurassic granitoids show similar negative zircon eHf(t) values (− 5.5 to − 16.6) with TDM2 model ages of 1.60–2.28 Ga, suggesting a Paleoproterozoic crustal source, whereas the Early Triassic granitoids have zircon eHf(t) values from − 3.4 to + 5.3 with TDM2 model ages of 0.94–1.50 Ga, indicating a Mesoproterozoic crustal source. Based on the whole-rock geochemical data, we suggest that the Early Triassic rocks from the North Qiangtang terrane include I- and S-type granites and the Late Triassic rocks are S-type granites, which were related to the northward subduction of the Longmu Tso–Shuanghu–Dingqing Paleo-Tethys Ocean and subsequent collision between the North Qiangtang terrane and Tongka block, respectively. The Early Jurassic granitoids from the Tongka and Jiayuqiao blocks also included both I- and S-type granites and were probably generated in an arc-related setting during the northward subduction of the Bangong–Nujiang Tethys Ocean. Therefore, we suggest a collision–accretion model that attributes the Early Mesozoic tectonic-magmatic event to the sequential multistage subduction and collision in the east of central Tibet.

Geology, geochemistry, and geochronology of the Cuihongshan Fe‐polymetallic deposit, Heilongjiang Province, NE China

The Cuihongshan deposit is a giant Fe‐polymetallic skarn deposit located in the northern zone of the Lesser Xing'an–Zhangguangcai Range (LXZR), NE China. It is predominantly hosted in skarn contact zones between marble and alkali‐feldspar granites and monzogranites, with minor in fracture zones of granodiorites. Because of dense vegetation cover, complex intrusions, and contact relation between orebodies and rocks, the metallogenesis of the deposit is poorly understood. Here, we present detailed whole‐rock geochemistry, zircon U–Pb geochronology of granitoids, and molybdenite Re–Os isotopic dating data. All of the granitoids in the Cuihongshan deposit area are silica and potassium rich, highly fractionated, showing affinities to high‐fractionated I‐type granites. However, compared with the other granitoids, the Late Triassic alkali‐feldspar granites have higher differentiation index, stronger enrichment in F, W, Mo, Pb, Th, U, and volatiles with partial mineralization. The zircon U–Pb dating of the granodiorite, monzogranite, and alkali‐feldspar granite yielded weighted average ages of 493 ± 4, 194 ± 1, and 204 ± 1 Ma, respectively. The Re–Os dating of molybdenites from the Cuibei and Cuizhong ore sections yielded isochron ages of 205 ± 2 and 204 ± 4 Ma, respectively, which are consistent with the emplacement age of the alkali‐feldspar granite. Combined with the lines of evidence from the contact relationship between the orebodies and alkali‐feldspar granite, the disseminated mineralization and the enrichment in ore‐forming elements and volatiles in the alkali‐feldspar granite, these indicate that the Late Triassic alkali‐feldspar granite rather than the monzogranite as previously reported, has a close genetic relationship with the Cuihongshan deposit. In addition, the alkali‐feldspar granites occur as apophyses and dikes, but the Late Cambrian and Early Jurassic granitoids occur as batholiths. This indicates that, according to the theory that “small intrusions form large deposits”, a potential Late Triassic (~204 Ma) buried batholith might have provided abundant ore‐forming materials. However, the top parts of the Late Cambrian and Early Jurassic granitoids have been denudated, which is unfavourable for significant deposit preservation and mineralization related to the 2 stages of granitoids. This study gives a significant suggestion that exposed, and blind apophyses and dikes should be further considered in the exploration and study of metal deposits in NE China. Three phases of mineralization occurred in the LXZR in the Triassic–Jurassic, namely, porphyry–skarn Cu–Mo polymetallic mineralization (~250–240 Ma), skarn Fe–Pb–Zn polymetallic mineralization (~204–190 Ma), and porphyry Mo polymetallic mineralization (~180–160 Ma). On the basis of regional data, the LXZR experienced subduction and collisional settings during ~260–185 Ma and ~180–160 Ma, respectively. Hence, the Early Triassic (~250–240 Ma) and Late Triassic–Early Jurassic (~204–190 Ma) mineralizations represented by the Baoshan and Cuihongshan deposits, respectively, are related to the early and late subduction of the oceanic plate between the Songliao and Jiamusi massifs beneath the Songliao Massif, respectively. This also indicates a potential mineralization in the LXZR in the Middle Triassic. However, the genesis of the late large‐scale porphyry Mo polymetallic deposits (~185–160 Ma; e.g., Daheishan, Luming, Huojihe, Xinghualong, Xingshan, and Wulugetushan deposits) is constrained by the collision of the Songliao and Jiamusi massifs.

Juxtaposition of allochthonous terranes in the central Korean Peninsula: Evidence from zircon U-Pb ages and O-Hf isotopes in Jurassic granitoids

The eventual docking of an exotic continental mass over the course of a Wilson cycle is marked by intracontinental sites of prograde metamorphism, contractional deformation, and syn- or post-collisional magmatism. This study shows that inherited premagmatic zircon in subsequently emplaced granitoid rocks provides another line of evidence for the collisional orogeny. Following the continental collision between the North and South China Cratons, Jurassic granitoids intruded widely throughout the central Korean Peninsula in association with the subduction of the Paleo-Pacific plate. The latest Early to Middle Jurassic (177–167Ma) granitoids occur throughout the cratonic Gyeonggi Massif, whereas Early Jurassic (194–184Ma) granitoids occur locally along the Okcheon Metamorphic Belt to the southeast of the massif. These two spatiotemporal groups differ profoundly in their age patterns and O-Hf isotopic signatures of inherited zircon. The younger group yields a typically North China-like Archean-Paleoproterozoic (mostly 2.5–1.8Ga) zircon inheritance. In contrast, inherited zircons from the older group exhibit exclusively Neoproterozoic (ca. 0.9–0.7Ga) and Paleozoic (ca. 0.4Ga) cluster along with Archean-Paleoproterozoic populations. The exotic feature of the protolith of the older group is further indicated by significantly lower δ18O (−0.9 to +4.9‰) and positive εHf (+3 to +15) values of the Cryogenian zircon cores. The results of zircon analysis demonstrate that South and North China-like terranes were juxtaposed infracrustally along the southeastern margin of the Gyeonggi Massif during the pre-Jurassic collisional orogeny, and then selectively provided major source material to the older and younger Jurassic granitoids, respectively.

Early Jurassic granitoids from deep drill holes in the East China Sea Basin: implications for the initiation of Palaeo-Pacific tectono-magmatic cycle

ABSTRACTThe timing of the Palaeo-Pacific Plate (PPP) subduction in East Asia, following the amalgamation of the North and South China Blocks (NCB and SCB), remains equivocal despite several investigations on the widespread subduction-related Mesozoic magmatism in this region. Here we report newly discovered granodiorites in the East China Sea Basin (ECSB) from deep boreholes (2945–2983 m), which yield SHRIMP zircon U–Pb age of 174 ± 1.1 Ma. The rock shows relatively high Sr/Y and La/Yb ratios, low contents of Ni, Cr, and MgO, and markedly negative values of εHf(t) (21.0 to −27.0). These geochemical and isotopic features are similar to those of the tonalite-trondhjemite-granodiorite (TTG) suites produced by the partial melting of the thickened lower continental crust. Our data, together with the ca. 190–180 Ma I-type granites reported from the eastern Zhejiang–Fujian and Taiwan areas, lead us to conclude that the continental crust in the coastal areas of South China underwent some degree of thickening during the Early Jurassic. A comparison with the coeval magmatic rocks in South Korea and Japan suggests that a large NE-trending continental arc (ca. 190–170 Ma) might have been constructed along the eastern margin of Asia at this time. Our study provides insights into the initiation of the Palaeo-Pacific tectono-magmatic cycle immediately following the consolidation of the SCB and NCB.

Early Mesozoic ferroan (A-type) and magnesian granitoids in eastern South China: Tracing the influence of flat-slab subduction at the western Pacific margin

Zircon U–Pb ages, Hf isotopes and whole-rock geochemical data are used to constrain the petrogenesis of the Late Triassic–Early Jurassic granitoids in southeastern China and their tectonic settings. The 225Ma Qiuwang and 178Ma Xiepu granites at Ningbo, Zhejiang Province, have εHf(t) values of −15.7 to −9.9 and −17.6 to −13.4, respectively. They are both ilmenite-series granitoids derived from the Paleoproterozoic basement of the Cathaysia Block in South China. The Late Triassic Qiuwang granite is strongly peraluminous with high zircon saturation temperatures (850–900°C), and high Gd/Yb (2.7–4.8) and Ga/Al ratios (3.7–4.6×10−4). In contrast, the Early Jurassic Xiepu granite is weakly peraluminous with low zircon saturation temperatures (~670°C), low Gd/Yb (1.0–1.1) and high Ga/Al ratios (2.4–2.6×10−4). The Qiuwang granite records higher melting temperatures and pressures than the younger Xiepu granite, reflecting a change in the tectonic regime from collisional tectonics to orogenic collapse. A regional review indicates that Triassic flat-slab subduction along the western Pacific may have led to thickening of the continental crust and metasomatism-oxidation of the continental lithosphere in the regions relatively close to the trench, where Cordilleran-type magnesian granitoids were generated. However, contemporaneous magnesian granitoids were produced in the thickened crust away from the trench, where the source rocks have uniformly moderate oxygen fugacities and metasomatism-oxidation was insignificant. Such Early Mesozoic “A-type” granitoids in the coastal region of South China are related to water-deficient and reduced melting conditions rather than an anorogenic tectonic setting.

Timing and evolution of Jurassic–Cretaceous granitoid magmatisms in the Mongol–Okhotsk belt and adjacent areas, NE Asia: Implications for transition from contractional crustal thickening to extensional thinning and geodynamic settings

The Mongol–Okhotsk belt and adjacent areas are key areas to study the relationship between the Okhotsk and Paleo-Pacific tectonic regimes and their superposition on the older Paleo-Asian regimes during late Mesozoic times. This paper summarizes the spatial–temporal evolution of Late Mesozoic (Jurassic–Cretaceous) granitoids and related intrusions in these areas, and interprets the magmatic evolution in terms of a transition from contractional crustal thickening to extensional thinning. According to 407 published zircon ages, these granitoids were mainly emplaced during the intervals 200–180Ma, 180–165Ma, 165–145Ma, 145–135Ma and 135–100Ma. Jurassic granitoids (200–145Ma) predominately occur in the Baikal–NE Mongolia (BNEM) and Great Xing’an Range. Early Cretaceous (145–100Ma) granitoids are mainly occur in the Great Xing’an Range, and display a southward-younging migration. Significantly, Early Cretaceous granitoids also extend into the Trans-Baikal area across the Mongol–Okhotsk suture, far away from the Paleo-Pacific plate margin (in NE China); thus they were more plausibly related to post-orogenic collapse of the Mongol–Okhotsk orogen. From the Late Jurassic to Early Cretaceous, the granitoids evolved compositionally from calc-alkaline and high-K calc-alkaline, I-type, with some adakite-like features, to high-K calc-alkaline and shoshonitic, highly fractionated I-, transitional I-A or, A-type, characterized by a significant decrease in their Sr/Y ratios. This evolution coincided with a tectonic transition from contractional crustal thickening to extensional thinning. Combined with regional geology, we speculate that the Jurassic granitoids were likely derived from melting of the deep-seated, thickened lower continental crustal (LCC) sources, whereas the Cretaceous granitoids produced through crustal melting from an extensional thinning setting. Our results provide a case study demonstrating that the petrogenesis of granitic magmatism was closely associated with crustal tectonics. Early Jurassic granitoids along the Okhotsk belt formed in a subduction/collision setting related to closure of the Mongol–Okhotsk Ocean, whereas Late Jurassic granitoids in the Great Xing’an Range and in the northern North China Craton may have formed in a syn- or post-collisional setting superposed by far-field affects of subduction of the Paleo-Pacific plate. Early Cretaceous granitoids in these areas formed in response to post-orogenic extensional collapse of the Mongol–Okhotsk belt, coupled with back-arc extension related to Paleo-Pacific plate subduction.

Highly fractionated Late Triassic I-type granites and related molybdenum mineralization in the Qinling orogenic belt: Geochemical and U–Pb–Hf and Re–Os isotope constraints

We present new data on the highly fractionated Late Triassic I-type Liyuantang granite, which is located in the middle segment of the South Qinling Subzone of central China and is associated with molybdenum mineralization. Zircon U–Pb dating indicates that the granite was emplaced at 210.1±1.9Ma, with a single zircon containing an inherited core that yielded an age of 449.8±7.1Ma. Magmatic zircons from the granite have εHf(t) values of −4.0 to +1.5, whereas the inherited zircon core has a εHf(t) value of −5.3. Calculated Hf model ages of crust formation are indicative of substantial contributions from melting of Proterozoic crust that ranges in age from 1501 to 1155Ma. The granite contains high concentrations of Si, Al, Na, and K, is enriched in Rb, Th, and U, has elevated Rb/Sr and Ga/Al ratios, and is depleted in Ti, Fe, Mn, Mg, Ca, and P, with significantly negative Eu anomalies (δEu=0.33–0.50), similar to other highly fractionated I-type granites. These data indicate that the magmas that formed the Liyuantang pluton were produced during partial melting of Proterozoic garnet-absent quartz amphibolites. The magmas then fractionated apatite, feldspar, Ti-bearing phases, biotite, and hornblende prior to emplacement.Re–Os isotope analysis of molybdenite from the study area yields a mineralization age of 200.9±6.2Ma, suggesting that the Liyuantang molybdenum deposit formed during a previously unrecognized mineralization event. The present results, together with previous data, demonstrate that highly fractionated I-type granites associated with the second pulse of magmatism in the South Qinling subzone should be considered highly prospective for mineral exploration, focusing on Triassic–Early Jurassic granitoids.

Geochronology of Paleozoic terranes at the Pacific Ocean margin of Zealandia

Rb–Sr and U–Pb zircon ages are reported from basement rocks on Campbell Plateau. On Campbell Island, Rb–Sr ages of Complex Point schists are (1) at Complex Point, 462 ± 53 Ma similar to Western Province, early Paleozoic metasediments in New Zealand, and Antarctic correlatives and (2) at Garden Cove, 526 ± 18 Ma, (pre-Late Cambrian). Schist detrital zircons have a youngest age peak 524 ± 5 Ma, suggesting an Early or early Middle Cambrian stratigraphic age not seen in New Zealand and possibly correlative with Sledgers Group, North Victoria Land, Antarctica. On Bounty Island, granodiorites yield an Rb–Sr age, 183 ± 9 Ma, with correlates known only in eastern Marie Byrd Land, Antarctica. Metasediments at a seafloor locality on Bounty Platform, have a minimum U–Pb detrital zircon age, 482 ± 5 Ma, and an Rb–Sr metamorphic age 174 ± 32 Ma, correlative with Western Province metasediments in South Island. The age data suggest that Campbell Plateau is mostly underlain by Western Province, early Paleozoic metasediments, intruded by (1) early to mid-Cretaceous granitoids along the western margin, extending north to New Zealand and south to Antarctica, and (2) Early Jurassic granitoids on Bounty Platform extending to Marie Byrd Land.