This study focuses on the geochronology and elemental and Nd isotopic geochemistry of the Baogutu Cu deposit and the newly discovered Suyunhe W-Mo deposit in the southern West Junggar ore belt (Xinjiang, China), as well as the geology of the newly discovered Hongyuan Mo deposit in the southern West Junggar ore belt and the Kounrad, Borly, and Aktogai Cu deposits and the East Kounrad, Zhanet, and Akshatau W-Mo deposits in the North Balkhash ore belt (Kazakhstan). The aim is to compare their petrogenesis, tectonic setting, and mineralization and to determine the relationship between the southern West Junggar and North Balkhash ore belts. Based on our newly acquired results, we propose that the Kounrad, Borly, Aktogai, and Baogutu deposits are typical porphyry Cu deposits associated with calc-alkaline magmas and formed in a Carboniferous (327–312 Ma) subduction-related setting. In contrast, the East Kounrad, Zhanet, Akshatau, Suyunhe, and Hongyuan deposits are quartz-vein greisen or greisen W-Mo or Mo deposits associated with alkaline magmas and formed in an early Permian (289–306 Ma) collision-related setting. Therefore, two geodynamic–metallogenic events can be distinguished in the southern West Junggar and North Balkhash ore belts: (1) Carboniferous subduction-related calc-alkaline magma – a porphyry Cu metallogenic event – and (2) early Permian collision-related alkaline magma – a greisen W-Mo metallogenic event. The North Balkhash ore belt is part of the Kazakhstan metallogenic zone, which can be extended eastward to the southern West Junggar in China.
A dominantly NW-SE directed extensional tectonics in the Early Cretaceous significantly reworked the Late Permian-Triassic orogenic framework of the Dabie orogenic belt. The North Dabie complex (NDC) is the principal domain recording this tectonic event. However, the precise structure-kinematic architectures, particularly those observed in the ductile regime, along with the respective time scales for different extensional stages, have not been adequately established. This significantly impedes our comprehensive understanding of the extensional style and deformation history in the North Dabie complex. To better address these issues, we conducted a systematic structural study and LA-ICP-MS zircon U-Pb dating of the pre-, syn-, and post-kinematic intrusions and syn-kinematically metamorphosed high-grade gneisses/migmatites of the NDC. Our results demonstrate that the extensional deformation in the NDC may initiate at ca. 144 Ma, which is characterized by a pervasive NW-SE oriented coaxial plastic flow in the ductile regime of the middle-lower crust. A large-scale detachment processing zone subsequently started activating at ca. 140 Ma at the upper-middle level of the middle crust, and concentratedly accommodated the extensional strain by top-to-NW ductile shearing. Locally, there was uprising of sub-magmatic flow in the atatexite-diatexite from the deeper lower crust taking place in the manner of top-to-outward shearing as early as ca. 137 Ma. This composite process of extension manifests vertical strain partitioning across the ductile middle-lower crusts and progressive strain localization during the lithospheric thinning. The NW-SE orientation dominated extensional tectonics was strongly driven by the westward subduction of the Paleo-Pacific oceanic plate during the Late Mesozoic.
The uplift of the Tibet Plateau (TP) during the Miocene is crucial to understanding the evolution of Asian monsoon regimes and alpine biodiversity. However, the northern Tibet Plateau (NTP) remains poorly investigated. We use pollen records of montane conifers (Tsuga, Podocarpus, Abies, and Picea) as a new paleoaltimetry to construct two parallel midrange paleoelevation sequences in the NTP at 1332 ± 189 m and 433 ± 189 m, respectively, during the Middle Miocene [~15 million years ago (Ma)]. Both midranges increased rapidly to 3685 ± 87 m in the Late Miocene (~11 Ma) in the east, and to 3589 ± 62 m at ~7 Ma in the west. Our estimated rises in the east and west parts of the NTP during 15 to 7 Ma, together with data from other TP regions, indicate that during the Late Miocene the entire plateau may have reached a high elevation close to that of today, with consequent impacts on atmospheric precipitation and alpine biodiversity.
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.
Abstract The interactions between plate tectonic processes and ecosystems are well-documented, but the precise influence of tectonic evolution on ecosystems remains elusive. This study investigates Jurassic–Cretaceous Northeastern Asia, where the Yanliao and Jehol Biotas flourished amid a prominent tectonic transition from crustal shortening to extension. To explore the impact of these processes on the ecosystem, we use innovative whole-rock geochemical composition-elevation models, alongside a large dataset from Late Triassic–Early Cretaceous arc magmatic rocks, to estimate regional-scale variations in paleo-crustal thickness, paleo-elevation, and paleo-temperature. Our results suggest that during the Jurassic, Northeastern Asia experienced significant crustal thickening, elevation increasing, and inland-ward magmatism due to plate convergence. By the Early Cretaceous, magmatism migrated outboard, driven by Paleo-Pacific slab rollback, leading to differential crustal thickness and elevation across the region. We propose an orogenic plateau with elevations of 2.0–4.5 km and mean annual temperatures of -1.0–12.8°C, creating complex topography that impacted spatiotemporal evolution of regional ecosystems and explains the high-elevation and cold habitats of the Yanliao and Jehol Biotas.
EPMA data, monazite U-Pb data and P-T estimates using conventional geothermometers and geobarometers for felsic granulite, Chencai Complex, West Cathaysia terrane, South China
The Kumishi ophiolitic mélange contains well-preserved large-scale serpentinites and their accompanying granulites in the eastern South Tianshan Accretionary Complex (STAC), southwestern Altaids. Previous studies have mainly focused on the thermodynamic conditions and tectonic setting of granulites. However, the petrogenesis of the widespread serpentinites in the Kumishi ophiolitic mélange remains largely unexplored. In this paper, petrological, geochemical, and geochronological studies were carried out on the Kumishi serpentinites, as well as the host sediment and intermediate–felsic volcanic rocks. The serpentinites show variable LOI values of 8.3–16.5 wt% and relatively consistent SiO2/(sum oxides) ratios of 0.81, which demonstrate that the major elements of their protoliths have been preserved well during serpentinization. Multi-trace element and REE diagrams suggest that the protoliths of the Kumishi serpentinites have experienced varying degrees of refertilization, with distinct natures seen between the Yushugou, Tonghuashan, and Liuhuangshan serpentinites. Zircon U-Pb chronology of the Tonghuahsan serpentinites yields a mean age of 355.8 ± 7.3 Ma (MSWD = 1.0, N = 26). Detrital zircons from the host sediment record a maximum depositional age of 375 ± 10 Ma (MSWD = 0.4, N = 3), with a peak at ca.419 Ma. Subduction-related volcanic rocks yield ages of ca.437 Ma. Hence, clues are provided to the petrogenesis of the Kumishi serpentinites, with calls for future in-depth works from an isotopic perspective.
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