Central Asian Orogenic Belt Research Articles

Estimated Age and Metamorphic Parameters of High-Pressure Blastolites in the Gonzhinskii Block, Argun Superterrane, Eastern Part of the Central Asian Orogenic Belt

Estimated Age and Metamorphic Parameters of High-Pressure Blastolites in the Gonzhinskii Block, Argun Superterrane, Eastern Part of the Central Asian Orogenic Belt

The Ordovician Arc–Basin System in the Northern Great Xing’an Range (Northeast China): Constraints from Provenance Analysis of the Luohe Formation

The Northeast China Block is a major component of the Central Asian Orogenic Belt, and its tectonic evolution has attracted much research attention. Ordovician strata are important in reconstructing the tectonic evolution of the Northeast China Block. This paper presents the results of sedimentological, zircon U–Pb, and geochemical analyses of sandstones of the Luohe Formation in the Wunuer area, Northern Great Xing’an Range, Northeast China. Lithological data, sedimentary structures, and grain-size analysis indicate that the Luohe Formation was deposited in a shallow marine environment. Detrital zircon U–Pb dating yields age peaks of 463, 504, 783, 826, 973, and 1882 Ma for sandstones from the Luohe Formation. The youngest zircon grain age of 451 ± 6 Ma represents the maximum depositional age of the Luohe Formation. The peak age at 463 Ma is consistent with the timing of post-collisional magmatism and the formation of the Duobaoshan island arc, while the peak at 504 Ma is consistent with the timing of magmatic activity related to the collision between the Erguna and Xing’an blocks. The peaks at 788, 826, 973, and 1882 Ma correspond to magmatism in the Erguna block, these ages indicate that the sandstones of the Luohe Formation were derived mainly from the Erguna block. Sandstone modal compositional analysis indicates that the provenance of the Luohe Formation was mainly a magmatic arc. The geochemical compositions of the sandstones suggest that the source rocks have continental island arc signatures. Based on the depositional age, sedimentary environment, provenance, and regional geology, it is concluded that the Luohe Formation was deposited in a back-arc basin setting during the formation of the Duobaoshan island arc–basin system in response to subduction of the Paleo-Asian oceanic plate.

A uniform basement: Implications for the tectonics of Beishan Orogenic Belt in the southern Central Asian Orogenic Belt

The orogen is a significant window for studying the history and architecture of Earth; its architecture involves many significant issues. Currently, research on the architecture of orogenic belts mainly focuses on the process of orogeny, and few studies focus on the tectonics before the orogeny, which somewhat constrains orogen evolution. The nature of the basement(s) of microcontinents in the Beishan Orogenic Belt (BOB) in the middle Central Asian Orogenic Belt (CAOB) has been debated for a long time, which causes confusion about the tectonics of the BOB. This study conducted field surveys, geochronology, geochemistry, and Hf isotope analysis on the major microcontinents of BOB. The age information of ca. 1.4 Ga and the Paleoproterozoic-Archean with small scale were found in the northern BOB. The northern BOB (NBOB) and southern BOB (SBOB) (separated by the Hongliuhe-Niujuanzi-Xichangjing ophiolitic mélange belt) have experienced similar magmatic thermal events at ca. 1.4 Ga and ca. 0.9 Ga, which are revealed by the analogical tectonic setting, formation ages, and Hf isotopic features. The Precambrian basements of the NBOB and SBOB are analogous in terms of rock assemblages, detrital zircon ages, magmatic rock ages, εHf(t) of Precambrian rocks, and Hf crustal model ages TDMC of Paleozoic igneous rocks, which imply that they shared similar history and provenance and might originate from a uniform basement. The basement has no close tectonic affinity to the adjacent cratons or blocks, except the Baltica Craton and Laurentia Craton. And it might have been involved in the amalgamation of the Columbia Supercontinent and be situated on the periphery of the Rodinia Supercontinent, and then fragmented when the Rodinia Supercontinent rifted apart.

Contrasting Cu mineralization styles across the Dananhu Arc, Eastern Tianshan: insights from the geochronology, geochemistry, and Sr–Nd–Hf isotopes of Carboniferous arc rocks

ABSTRACT 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.

Permian mafic-ultramafic magmatism and sulfide mineralization in the Central Asian Orogenic Belt: A review

World-class magmatic Ni-Cu-(PGE) deposits have been extensively studied and are thought to occur in extensional intraplate settings. Recent reports indicate significant magmatic sulfide mineralization within mafic–ultramafic intrusions in convergent margin setting, including the Central Asian Orogenic Belt, Kunlun Orogenic Belt, Appalachian Orogen, and Variscan Orogenic Belt, highlighting notable Ni-Cu resources. Understanding the petrogenesis and metallogeny of these sulfide-bearing intrusions is thus critical for comprehending the magmatic Ni-Cu-(PGE) sulfide mineralization of basaltic magmas. Preliminary studies suggest that magmatic sulfide deposits in convergent margin setting show characteristics distinct from those in intraplate settings. These deposits formed from siliceous high-magnesium basaltic (SHMB) magma, contrasting with high-magnesium basalt in intraplate settings. SHMB-like magmas result from hydrous melting of the metasomatized mantle sources at relatively lower temperature compared to those in intraplate settings. Intrusions in convergent margin settings generally arise from multiple magma injections of varying compositions, a feature of the unique magma emplacement process in compressional settings. SHMB-like magmas, rich in Cu and Ni, can achieve sulfide saturation through selective crustal contamination during emplacement. Comparing deposits in convergent margin and intraplate settings reveals that the difference of magmatic sulfide deposits stem from different mantle sources and evolution histories of magma conduit systems.

Petrogenesis of the early Permian A-type granites in eastern North Tianshan, Central Asian Orogenic Belt: Implications for the final geodynamic evolution of the Kalamaili suture zone

The understanding of the detailed geodynamic mechanism and crustal evolution of the tectonic transition along the Kalamaili suture zone from the late Carboniferous to early Permian remains limited. We conducted an integrated study of the petrology, geochronology, and geochemistry of the early Permian syenogranites (Yingzuishan and Shihuiyao syenogranites) in eastern North Tianshan, south of the Central Asian Orogenic Belt, aiming to elucidate the aforementioned tectonic transitional processes. The zircon U-Pb dating reveals that the studied syenogranites were intruded at ca. 280 Ma. These syenogranites exhibit medium to high SiO2 (67.5–78.8 wt%), high Na2O + K2O (8.1–10.6 wt%), and low CaO (0.27–1.39 wt%) concentrations. They are enriched in Rb, Th, and light rare earth elements, while depleted in Ba, Sr, and Ti. They display positive zircon εHf(t) values ranging from + 11.2 to + 15.6, initial 87Sr/86Sr ratios between 0.512371 and 0.512643, and εNd(t) values from + 1.8 to + 7.2. Integrating with regional geological data, we propose that the studied syenogranites are A2-type granites, primarily derived from the partial melting of juvenile felsic intrusive rocks under low-pressure conditions in the shallow crust. These syenogranites were formed within a post-collisional extensional setting triggered by the slab break-off of the Kalamaili oceanic plate. Throughout the tectonic transition induced by the slab break-off, there were episodic thickening and thinning of the crustal thickness along the Kalamaili suture zone, and the concurrent crustal evolution was predominantly marked by crustal reworking.

Transition from oceanic subduction to continental collision: Insights from volcanogenic-sedimentary rocks of the Tannuola terrane (northern Central Asian Orogenic Belt)

Magmatism associated with oceanic subduction plays a dominant role in crustal growth during the Earth’s evolution. The Tannuola terrane, situated in the northern Central Asian Orogenic Belt (CAOB), is a key area to understanding oceanic subduction and initial collision processes in the northern CAOB. In order to investigate the switch from subduction to collision settings, detailed field mapping, zircon SHRIMP U-Pb geochronological and whole-rock geochemical studies of volcanogenic-sedimentary rocks from the Tannuola terrane were carried out. Zircon U-Pb ages indicate multi-stage volcanism lasted at least 30 Ma from ∼540 to ∼510 Ma, that can be divided into three events: the late Ediacaran (before ∼540 Ma), the early Cambrian (∼520 Ma) and the middle Cambrian (∼510 Ma). These ages are interpreted to the initial, main and final stages of oceanic subduction during the late Proterozoic – early Paleozoic. During the late Ediacaran, tholeiitic basalts with high εNd(t) values (from +7.4 to +8.5) were emplaced. Likely forming by the 10 %–30 % partial melting of spinel – garnet mantle source during slab subduction. During the early Cambrian, transitional from tholeiitic to calc-alkaline basaltic rocks with εNd(t) value (+5.6) and coeval intermediate–felsic volcanic rocks with similar εNd(t) values (+5.9 and +6.5) formed. The early Cambrian basaltic rocks are interpreted to be derived by 10 %–30 % partial melting of a depleted mantle source metasomatized by slab-derived fluids released from the subducting oceanic slab. The middle Cambrian calc-alkaline basaltic rocks with εNd(t) value of +6.2 might be emplaced as a result of low (5 %–10 %) degree partial melting of a metasomatized mantle followed by fractional crystallization of clinopyroxene and plagioclase. Associated intermediate-felsic volcanic rocks with εNd(t) values from +6.0 to +6.8 were formed through fractionation of the juvenile Neoproterozoic sources. The middle Cambrian volcanism is interpreted to be triggered by the slab break-off during the transition to a collisional setting.

Petrogenesis and geodynamic implications of the Late Devonian dioritic and granitic intrusive rocks in the Dananhu Belt, Eastern Tianshan Orogenic Belt

The Late Devonian magmatism of the Dananhu arc belt in the Central Asian Orogenic Belt provides a critical geological record. This study provides new comprehensive geochronological, geochemical, and Sr–Nd isotopic data of granodioritic and dioritic intrusions in the Dananhu belt. These findings contribute to unraveling the regional tectonic history and constraining the geodynamic processes involved. Zircon U–Pb dating indicates that the granodiorites and diorites were formed at 382.7 ± 3.8Ma and 363.1 ± 4.3Ma, respectively. The granodiorites show characteristics similar to I-type granites with high SiO2, low MgO and Mg# and aluminium saturation index (<1.1), negligible Eu anomalies, low (K2O + Na2O)/CaO ratios and zircon saturation temperatures (average = 696 °C). Granodiorites also show depleted isotope signatures (εNd(t) = +5.85 to +6.27 and low (87Sr/86Sr)i = 0.704082–0.704583) and juvenile TDM ages (741–793Ma), indicating their origin from a juvenile crust. The diorites are characterized by enrichments in large ion lithophile elements, U and Pb, but depleted in Nb and Ta displaying typical geochemical features of a subduction-related origin, together with high εNd(t) (+6.10 to +6.84) and low initial Sr isotopes (0.703745–0.704601), suggesting that they originated from a subduction fluid modified depleted mantle. The petrogenesis of both granodiorites and diorites in the Dananhu arc provides evidence that they formed through magmatic processes in a subduction tectonic setting. Considering the adakites associated with slab melting from previous studies in the Dananhu arc, it is plausible that the north-dipping subduction of the North Tianshan oceanic lithosphere have contributed to the Dananhu arc magmatism during the Late Devonian.

Paleomagnetism of Phanerozoic Strata of the Central Part of the Central Asian Fold Belt

Paleomagnetism of Phanerozoic Strata of the Central Part of the Central Asian Fold Belt

Zircon U–Pb ages of the Paleozoic volcaniclastic strata in the Junggar Basin, NW China

Abstract A large set of Paleozoic volcaniclastic rocks is exposed in the northwestern margin of the Junggar Basin from the southern part of the Central Asian Orogenic Belt. The Carboniferous volcaniclastic strata in this area have been studied in depth, and an accurate chronostratigraphic framework of these strata has been established. However, there is a lack of sufficient geochronological data for the deposition times of the other Paleozoic volcaniclastic strata. In this study, zircon U–Pb dating of the Ordovician, Silurian, and Devonian volcaniclastic strata in the area reveals that the youngest age of the tuffite sample collected from the originally defined Ordovician strata is 398 ± 11 Ma, which represents the age of volcanic activity during the period of tuffite deposition. Based on this finding, the originally defined Ordovician strata are redefined as the Lower Devonian. The youngest ages of the silty tuff samples collected from the originally defined Silurian strata peak are 445–418 Ma, so its age is Upper Silurian. The youngest ages of the tuffaceous sandstone samples collected from the originally defined Devonian strata peak are 346–342 Ma, so these Devonian are redefined as the Early Carboniferous strata. Two Archean ages (2,501 ± 12 and 3,193 ± 8 Ma) were obtained in Silurian strata, thus confirming the existence of metamorphic rock basement in the provenance areas from which the sediments were derived.

Paleogeotectonic position of the Kyzyk Chadr porphyry copper ore field, Republic of Tyva

Regional-scale localization conditions of the Kyzyk-Chadr molybdenum-copper porphyry ore field in the southern folded frame of the Siberian Platform are considered. The porphyry mineralization of the field formed at the Salairian (Early Caledonian) phase of development of the Altai-Sayan segment of the&#x0D; Central Asian Orogenic Belt (CAOB), in connection with small intrusions of the gabbro-diorite-granodioritegranite Kyzykchadr Complex (Є2–3). The formation of the ore-bearing complex was associated with an accretionalcollisional magmatic belt superimposed on a Vendian–Early Cambrian volcanic-sedimentary island-arc substrate. The complex is only known within the local Ozhu uplifted block with a “batholitic” massif of the gabbrotonalite-plagiogranite Tannu-Ola Complex (Є2), but it is suggested that there could existed some analogous accretional-collisional Cambrian intrusions productive for Mo-Cu porphyry mineralization in some other areas, that were later overlapped by Ordovician–Silurian and Early Devonian volcanosedimentary deposits or broken by&#x0D; intrusive massifs of the Caledonian collisional volcano-plutonic belt. The rocks of the Salairian and Caledonian magmatic belts were deformed during subsequent geotectonic stages, primarily the Late Paleozoic collision, and overlain by younger sedimentary deposits. The position of economic-grade Mo and Mo-Cu porphyry deposits in the southern Altai-Sayan segment of the CAOB is assumed to be confined to areas of spatial superposition&#x0D; (overlapping) of magmatic belts of the three geotectonic stages: 1) island-arc volcanic belts (V–Є1), 2) “batholithic” intrusions and small intrusions of the magmatic belt of the accretional-collisional stage (Є2–3), 3) the collisional volcano-plutonic belt (O–D1).

Arc-arc amalgamation during accretionary orogenesis: Insights from mid-Paleozoic tectono-magmatic records in eastern Junggar, NW China

Abstract Arc-arc amalgamation occurs during the evolution of composite orogens at convergent plate margins and plays a critical role in controlling accretionary patterns and processes. The eastern Junggar terrane in the southern Central Asian Orogenic Belt underwent a long-lived subduction-accretion process in the Paleozoic, but whether and how the Yemaquan and Dananhu-Harlik arcs were amalgamated remain debatable. A systematic U-Pb–Hf-O isotopic study was conducted on zircons from Silurian granitic rocks in the Yemaquan arc. The U-Pb dating results suggest that these rocks were emplaced at 433–422 Ma and inherited abundant 536–435 Ma zircons representing a predominant magmatic episode in the Yemaquan arc. Their positive εHf(t) values and young Hf model ages indicate that the Yemaquan arc is dominated by juvenile basement with significant crustal growth during the Neoproterozoic to early Paleozoic. The variations in zircon Eu/Eu*, εHf(t), and δ18O values reveal that the Yemaquan arc experienced remarkable crustal thickening and remobilization at ca. 450 Ma, similar to the northern Dananhu-Harlik arc, and this was followed by extension that initiated at ca. 420 Ma. These features support the amalgamation of these two arcs occurring ca. 450–420 Ma. Integrated with regional data, we correlated this amalgamation event in the eastern Junggar terrane with the orogenic event in the Chinese Altai terrane, and we propose a middle Paleozoic tectonic evolution model in the eastern Junggar–Altai area from arc assembly to dispersal in association with a transition in accretionary mode. This scenario probably took place as a response to plate reorganization during the breakup of the northern margin of Gondwana.

Compositionally variable basement and tectonic affinity of the Bainaimiao arc belt: Implications for crustal growth of the Central Asian Orogenic Belt

As an important part of the southeastern boundary of the Central Asian Orogenic Belt (CAOB), the Bainaimiao arc belt, particularly its tectonic affinity and Precambrian basement composition, is an important element to provide new insights about the crustal growth of the CAOB. However, these remain poorly understood. This paper presents new geochronological, whole-rock geochemical and zircon Hf isotope data on early Paleozoic intrusive rocks from the Bainaimiao arc belt in the southeastern CAOB. The Ordovician gabbroic diorites in the Zhengxiangbaiqi area of the western Bainaimiao arc belt have low SiO2 contents (51.73–54.82 wt%), high TiO2 (0.99–1.07 wt%) and TFe2O3 contents (9.68–9.89 wt%), depletions in Nb, Ta and Ti, and positive εHf(t) values (6.8–11.3). These rocks generated from partial melting of a mantle wedge that has been metasomatized by subducted-derived fluids. The Silurian monzogranites in the Zhengxiangbaiqi area have high contents of SiO2 (72.61–75.12 wt%) and K2O (2.75–4.12 wt%), positive εHf(t) values (0.7–9.3) and abundant Precambrian inherited zircons. These monzogranites originated from partial melting of the thickened juvenile crustal components with significant ancient crustal contamination. The Silurian granites and granodiorites in the Faku area of the eastern Bainaimiao arc belt are characterized by high Na2O contents (4.00–4.52 wt%), high Sr/Y ratios, low MgO (1.15–1.74 wt%) and K2O contents (0.52–1.42 wt%), low K2O/Na2O ratios, and positive εHf(t) values ranging from 0.6 to 8.1. These rocks were derived from partial melting of a subducted slab interacted with mantle peridotite. New zircon U-Pb-Hf isotope data from these early Paleozoic intrusive rocks combined with previous results indicate that the Precambrian basement of the Bainaimiao arc belt is laterally heterogeneous, with Neoarchean-Paleoproterozoic basement beneath the western Bainaimiao arc belt and Paleo-Mesoproterozoic basement beneath the central Jilin area in the eastern Bainaimiao arc belt. The Bainaimiao arc belt has a tectonic affinity different from the North China Craton (NCC) and represents a composite arc system consisting of an ensialic island arc with a basement composition similar to that of the Precambrian microcontinents in the CAOB in the Bayan Obo-Damaoqi-Bainaimiao-Zhengxiangbaiqi and central Jilin areas and an oceanic island arc in the Ongniud-Faku and southern Jilin areas. The involvement of composite arc systems in the amalgamation of the accretionary orogenic belt could be an important mechanism for crustal growth in the CAOB.

From early Paleozoic subduction to end-Carboniferous post-orogenic collapse: New constraints on the tectonic evolution of the Central and South Tianshan (NW China)

Recognition of extensional events during orogenesis is critical for the reconstruction of geodynamic evolution of orogens, but is also a challenge due to multi-stage tectonic superimpositions. The South Tianshan is the southern margin of the Paleozoic Central Asian Orogenic Belt (CAOB) and a key for understanding the geodynamic evolution of the CAOB. Here we present new structural, geochronological and geochemical data for the Paleozoic sedimentary, igneous and metamorphic rocks in the Central and South Tianshan (NW China). Based on our new results and published data, we suggest that a neritic to terrestrial back-arc basin existed to the south of the Central Tianshan magmatic arc during the Early-Middle Devonian. We document a crustal anatectic event (∼304 Ma) associated with peraluminous granitic magmatism (∼305–295 Ma) in the South Tianshan. Multi-stage ductile deformation events witnessed the Paleozoic evolution from subduction-accretion to post-orogenic collapse of the Tianshan Orogen: (1) Late Devonian-Carboniferous regional top-to-the-north ductile shearing is related to the southward subduction of the South Tianshan back-arc basins; (2) late Carboniferous south-verging folds and brittle-ductile axial-plane cleavages correspond to back-thrusting resulted from the collision between Central Tianshan and Tarim; (3) latest Carboniferous ductile normal faults developed in migmatites define a dome-like structure linked with syn-anatectic exhumation of the middle crust during the post-collisional extension; and (4) regional dextral strike-slip faulting attributed to Permian lateral extrusion. Therein, two stages of crustal extension are key puzzle pieces to reconstruct the accretionary orogenic processes of the Paleozoic Tianshan.

Heavy mineral indicators of ridge subduction beneath the Bainaimiao arc in the southeastern Central Asian Orogenic Belt

As one of the major subduction-accretionary systems in the southeastern Central Asian Orogenic Belt, the Bainaimiao arc presents a valuable opportunity for investigating the subduction–accretion process of accretionary orogens. It is located adjacent to the northern margin of the North China Craton and developed arc-related deposits during the Silurian–Devonian period. In this paper, we employed heavy mineral geochemistry and U–Pb ages of zircon and rutile, to determine the provenance of the Silurian–Devonian deposits and reconstruct the paleogeography of the source area. The stratigraphic units involved include the Xuniwusu Formation of Early Silurian and the Xibiehe Formation of Early Devonian.Both the Xuniwusu and Xibiehe formations exhibit heavy mineral assemblages dominated by zircons and tourmalines. Nevertheless, the Xibiehe Formation contains Cr-spinels and garnets which are absent in the Xuniwusu Formation. Geochemical analyses of the detrital Cr-spinels exhibit characteristics of a supra-subduction zone ophiolite. The garnets originated from middle- to high-grade metamorphic rocks, as well as mafic and felsic rocks. The tourmalines in both formations primarily indicate a metasedimentary rock source, with a small percentage of Li-poor granitoid species in the Xuniwusu Formation. The U–Pb age spectra of both detrital zircon and rutile in the Xuniwusu Formation show multiple peaks. The age spectra consist of Precambrian ages, indicative of a recycled origin, as well as Paleozoic ages, suggesting a magmatic origin. In contrast, the U–Pb age spectra of zircon and rutile in the Xibiehe Formation display a unimodal age peak at ca. 455 and 490 Ma, respectively. These differences suggest a provenance shift from the Xuniwusu to Xibiehe formations. The Xuniwusu Formation was sourced from the Bainaimiao arc itself, whereas the Xibiehe Formation has a mixed origin of the Bainaimiao arc and Ondor Sum accretionary complex. The provenance change correlates with the unconformity between the two formations, suggesting a forearc uplift event. In combination with the previous research on the Tulinkai ophiolite, it can be inferred that the forearc uplift was triggered by ridge subduction of the Paleo-Asian Ocean plate at ca. 450–430 Ma. This research provided a new perspective on the ridge subduction of the oceanic slab in fossil orogens.

LA-ICP-MS zircon U–Pb ages, geochemistry, and genesis of Paleozoic granites from Biezhentao Mountain, Western Tianshan, Xinjiang

The geologic history of the Western Tianshan region is important for understanding the evolution of the Central Asian Orogenic Belt and accretionary orogenesis. Paleozoic and Mesozoic igneous rocks are present along the northern margin of the Yili Block; however, studies of Paleozoic subduction and collisional events have been relatively limited. Published geochronologies of Middle Devonian magmatic rocks in this region are also lacking. Therefore, this study analyzed the zircon U–Pb ages and major and trace elemental compositions of three granite types collected from Biezhentao Mountain (Wenquan County, Western Tianshan). The medium-grained diorite (384.1 ± 3.6 Ma) and diorite–porphyrite (382 ± 3.2 Ma) are silica-rich, weakly peraluminous, alkali-rich, enriched in large-ion lithophile elements, depleted in high field strength elements, and belong to the calc–alkaline series, with A-type granite characteristics. The monzogranite (423.3 ± 9.4 Ma) exhibits A-type granite characteristics and belongs to the peraluminous calc–alkaline series. The findings suggest that the granitoids recorded two stages of tectonomagmatism during the Middle Devonian–Late Silurian. The Middle Devonian medium-grained diorite and diorite–porphyrite formed in a back-arc extensional setting, whereas the Late Silurian monzogranite formed in an active continental margin setting during the subduction of the North Tianshan Ocean. These results provide insights into the tectonic and magmatic processes that occurred during the evolution of the Western Tianshan region and the formation and evolution of the Central Asian Orogenic Belt.

Geochronology, geochemistry, and geological significance of early Jurassic intrusive rocks in the Lesser Xing'an- Zhangguangcai Range, northeast China.

The Lesser Xing'an-Zhangguangcai Range of northeast China is located in the eastern segment of the Central Asian Orogenic Belt (CAOB), which records intense magmatism during the Mesozoic. The petrogenesis and geodynamic setting of the Early Jurassic intrusive rocks in this region are unclear. In this paper, we present new zircon U-Pb age and whole-rock geochemical data for these intrusive rocks to investigate their origins and tectonic setting. Zircon U-Pb dating suggests these intrusive rocks were emplaced during the Early Jurassic (197-187 Ma). The granites are enriched in silica and alkali, and depleted in MgO and CaO. They are metaluminous to weakly peraluminous, and have high A/CNK values and low zircon saturation temperatures (TZr ~ 779°C), suggesting they are highly fractionated I-type granites derived by partial melting of lower crustal materials. The granites exhibit negative Nb, Ta, P, Eu, and Ti anomalies due to fractional crystallization. The diorites and gabbros have low SiO2 contents and high Mg# values, and are enriched in light rare earth and large-ion lithophile (Ba, K, and Sr) elements, and depleted in heavy rare earth and high field strength (Nb, Ta, and Ti) elements. The geochemical characteristics show that the mafic magmas were derived by partial melting of mantle that had been metasomatized by subduction-related fluids. Based on the geochemical characteristics of coeval intrusive rocks and the regional geological setting, we suggest the Early Jurassic intrusive rocks in the Lesser Xing'an-Zhangguangcai Range were formed along an active continental margin, possibly as a result of bidirectional subduction of the Mudanjiang Oceanic plate between the Jiamusi and Songnen-Zhangguangcai Range massifs.

Fluid evolution and genesis of the Changchunling Pb–Zn deposit in the Southern Great Xing'an Range, Northeast China: Constraints from fluid inclusions and H–O–S–Pb isotopes

AbstractThe southern Great Xing'an Range (SGXR), an important polymetallic metallogenic province in the eastern Central Asian Orogenic Belt (CAOB) in Northeast China, containing numerous ore deposits of Cu, Fe, Pb, Zn, Au, and so forth. The Changchunling Pb–Zn deposit, located in the eastern segment of the SGXR, is primarily hosted by a Permian conglomerate and siltstone unit. The paragenetic sequence of the deposit can be divided into three stages involving arsenopyrite–quartz (stage I); pyrite–sphalerite–galena–quartz (stage II); and barren quartz–carbonate (stage III). Fluid inclusion (FIs) microthermometric studies revealed that only liquid‐rich aqueous inclusions (VL‐type FIs) are observed in the ore‐bearing quartz veins. The FIs of stages I, II, and III yield homogenization temperatures of 190–314, 170–268, and 140–195°C with salinities of 9.73–13.44, 7.86–10.74, and 4.94–5.99 wt% NaCl eqv., respectively. The ore‐forming fluids are characterized by low temperature and low salinity of the H2O–NaCl fluid system. The δ18OH2O and δD values range from −11.8‰ to 0‰ and −120.4‰ to −99.9‰, respectively, indicating that the source of the fluids was primarily derived from a mixed fluid of magmatic water and meteoric water. Fluid cooling, mixing and fluid‐rock reactions were the major ore precipitation mechanisms at Chanchunling. Sulfur‐lead isotopes of pyrite and sphalerite (δ34S = 2.3‰–3.7‰, 206Pb/204Pb = 18.259–18.285, 207Pb/204Pb = 15.544–15.57, and 208Pb/204Pb = 38.136–38.215) indicate that ore metals had a magmatic source. Integrating the available geological, mineralization, fluid inclusion, and H–O–S–Pb isotope evidence, we conclude that the Changchunling Pb–Zn deposit is an epithermal system, which shares many similar features with the regional Pb–Zn polymetallic deposit.

Geochronology and geochemistry of granitoids from northern Alxa, northwest China: Petrogenesis and tectonic implications

AbstractMultiple branch oceans existed in the Paleo‐Asian Ocean (PAO), but their closure times are in dispute and unclear, which constrains our understanding of the final closure time of the PAO and the tectonic evolution of the Central Asian Orogenic Belt (CAOB). This study focuses on the Permian plutons of the northern Alxa, which is located in the middle segment of the southern CAOB that recorded the final subduction history of the PAO. We performed the 1:50000 mapping, whole‐rock geochemistry, geochronology, and Sr‐Nd‐Hf isotopic analysis and compiled the Sr‐Nd‐Hf isotopic compositions and whole‐rock geochemical data of igneous rocks from the northern Alxa. LA‐ICP‐MS zircon U–Pb dating reveals the study plutons emplaced in the Early Permian (285–296 Ma). Whole‐rock geochemical data show the intrusion belongs to medium‐K calc‐alkaline peraluminous highly fractionated I‐type granite, enriched in Rb, K, Th, Pb, and depleted in Nb, Ta, Ti, Sr, and P elements, which suggest a subduction arc‐related setting and metaluminous to weak peraluminous parental magma. The weak negative εNd(t) (from −2.3 to −1.2), relatively high ISr (0.704772–0.708037) and depleted mantle model ages TDM (1.14–1.49 Ga), combining with weak negative to slightly positive εHf(t) (from −2.0 to +4.1) and crustal model ages TDMC (1.18–1.43 Ga), indicate that the parental magma might originate from remelting of the Mesoproterozoic lower crust and mixing with mantle‐derived materials. The field occurrence, deformation, and geochemical features, integrating with the compiled data and regional geology, show that the igneous rocks formed before or after the late Early Permian show different features in terms of deformation, zircon saturation temperatures, crustal thickness, potassium contents, and εHf(t) values. This might relate to the closure of the Yagan branch ocean of the PAO in northern Alxa.

The formation mechanism of the Xilekuduke porphyry Mo‐Cu deposit, NW China, revealed by the fluid inclusions and H‐O‐S isotopes

AbstractThe Xilekuduke porphyry Mo‐Cu deposit is located in the Altay‐East Junggar region of the Central Asian Orogenic Belt, northwest China. The orebodies occurring as vein type are host within the monzogranite and granite porphyry. Ore minerals include mainly molybdenite, pyrite, and chalcopyrite, whilst the major alteration include potassic, sericite, carbonate, and silicic. Mineralization can be divided into three stages: quartz‐K‐feldspar–polymetallic stage (Stage I), quartz‐polymetallic stage (Stage II), and quartz–calcite–pyrite (minor) stage (Stage III). Three types of fluid inclusion are present in the Mo‐Cu sulfide–calcite–quartz veins: CO2‐bearing (C‐type), aqueous (W‐type), and daughter mineral‐bearing (S‐type). Petrographic and microthermometric analyses of the fluid inclusions yielded homogenization temperatures for Stage I, II, and III to be 402–499°C, 214–391°C, and 136–254°C, respectively, with corresponding salinities of 39.2–59.6, 3.7–44.9 and 4.1–14.4 wt% NaCl equivalent. The δ18OH₂O and δD values of fluid inclusions in quartz are determined to be 5.3–6.0 ‰ and −76 to −60 ‰ (Stage I), 1.7–3.2 ‰ and −96 to −90 ‰ (Stage II), and −2.6 to −2.4 ‰ and −106 ‰ (Stage III), respectively. These results indicate that the primary ore‐forming fluids (stages I and II) were derived from granitic magma and were mixed with meteoric water in stage III. For the sulfide and sulfate (anhydrite), their δ34S values are of 0.4–5.8 ‰, 13.9–14.4 ‰, respectively, also that suggest a magmatic source. Fluid immiscibility, meteoric water interaction, and ore fluid‐wallrock interactions may have been critical for molybdenum precipitation.