Acta Geologica Sinica ‐ English Edition最新文献

Large-scale Cenozoic alkali-rich magmatic rocks are exposed at the eastern margin of Tibet due to the interaction between the Indian and Eurasian plates. However, their petrogenesis and associated geodynamic processes remain poorly understood. We analyzed the Xifanping porphyries in the Sanjiang orogenic belt to provide new insights. Our study shows a successive assembly of porphyry intrusions during three magmatic episodes. The magnitude and duration of the magmatic activities diminished sequentially, and mineralization occurred during the intermediate phase. Geochemically, the Xifangping porphyries display an adakitic affinity. According to zircon Hf isotope data, we propose that these porphyries originated from the partial melting of the thickened mafic lower crust beneath the western Yangtze Craton in response to lithospheric extension and asthenospheric upwelling. Analogous to the coeval alkali-rich porphyries in western Yunnan, the petrogenetic model of the Xifanping porphyries indicates regional north–south and east–west fractures caused by the clockwise rotation of the continental lithosphere and the Jinshajiang–Red River strike-slip during the post-collision phase of the India–Eurasia collision. In this context, we argue that the collision in eastern Tibet may have extended eastward to southwestern Sichuan during the post-collision period, persisting until approximately 30 Ma.

The Qinling orogenic belt in central China underwent long-term tectonic evolution during an amalgamation between the North China and South China cratons. However, intense compressional deformation and uplift erosion resulted in the transformation and disappearance of much geological record from the Qinling orogenic belt, and the tectonic evolution of this belt remains poorly constrained during the Triassic. Located in the northernmost margin of the South China Craton, the Sichuan Basin preserves the complete Triassic sedimentary succession, and can provide significant information for understanding the Triassic tectonic evolution of the Qinling orogenic belt. We present detrital zircon U-Pb dating, trace element and in situ Lu-Hf isotope data for the Middle Triassic Leikoupo Formation and the Late Triassic Xujiahe Formation samples from the eastern Sichuan Basin, South China. The detrital zircon U-Pb ages of the Leikoupo Formation show seven age clusters of 280–242, 350–300, 500–400, 1000–800, 2000–1750, 2100–2000 and 2600–2400 Ma, while those of the Xujiahe Formation show five age clusters of 300–200, 500–350, 1050–950, 2000–1750 and 2600–2400 Ma. Combined with published paleocurrent and paleogeographic data, the sediments of the Leikoupo Formation are interpreted to be sourced from the North China Craton, Yangtze Craton and North Qinling orogenic belt, and the potential main source regions of the Xujiahe Formation included the South and North Qinling orogenic belts. Provenance analysis indicates that the North Qinling orogenic belt was in inherited uplift and coeval denudation in the Middle Triassic. The proportion of the detritus formed in the South Qinling orogenic belt increases gradually from the Leikoupo to Xujiahe formations. This significant provenance change indicates that rapid tectonic uplift and extensive denudation of the South Qinling orogenic belt occurred in the early Late Triassic, which is related to the collision between the North China and South China cratons during the Triassic.

Emerald mineralization from the Bahutiya and Gurabanda areas of Jharkhand in the eastern part of India is a recent discovery. In this deposit, emerald mineralization occurs along the contact zone between pegmatite and epidiorite-hornblende schist of the Dhanjori Group (2.1–2.9 Ga). Host rock petrographic characteristics, along with the spatial distribution of the emerald, suggest a metasomatic origin for the emerald mineralization in the study area. The well-developed emerald crystals are found along the S₂ schistosity plane, suggesting lithological and structural control on the mineralization. Electron microprobe data of the emerald indicates that the green hue is primarily due to the variable chromium content and Be could have been derived from the soda-granite of the Singhbhum Shear Zone. The average Cr₂O₃ and Cr concentration in the emerald is 0.038 wt% and 0.003 apfu, respectively. The ternary diagrams FeO–MgO–Cr₂O₃ and FeO–Cr₂O₃–V₂O₅ are plotted and superimposed on global emerald data, compiled from the literature, which shows the similarity of this deposit to other emerald deposits of the world. From the present study, it is inferred that the emerald deposits of Bahutiya and Gurabanda, Jharkhand, belong to the Type-IA category.

Apatite (U-Th)/He and fission track dating and tectono-thermal history modeling were used to reconstruct the Meso–Cenozoic tectonic evolution of the Huangling paleo-uplift in the Middle Yangtze Block, South China. The tectonothermal evolution showed different tectonic exhumation/subsidence processes in the tectonic evolution of the foreland basin. The apatite (U-Th)/He ages ranged from 31.3 to 77.8 Ma, recording the thermal events of the Cenozoic Himalayan movement and indicating progressive exhumation extending from the southeast to the northwest. The thermal information of the Mesozoic Yanshan movement period was recorded by the apatite fission track age with a pooled age of 93.8 to 147 Ma. The exhumation of the Huangling paleo-uplift began in the Late Jurassic. The tectono-thermal evolution was characterized by a rapid uplift during 140–115 Ma, subsidence during 115–60 Ma, a rapid uplift during 40–30 Ma, and a slow uplift from 30 Ma to the present. The western Hunan–Hubei Depression was exhumed in the Middle Jurassic, and the tectono-thermal evolution was characterized by a rapid uplift during 160–135 Ma, a slow uplift during 135–50 Ma, a rapid uplift during 50–25 Ma, and a slow uplift from 25 Ma to the present. This Cenozoic exhumation was a response to the far field effect of the eastward growth of the Tibetan Plateau. The Cretaceous basins exposed in the surrounding areas of the Huangling paleo-uplift (Zigui basin, Yichang slope, and Huaguoping synclinorium) are foreland basins formed by the bi-directional compression of the Qinling–Dabie orogenic belt and the Xuefengshan intracontinental deformation system.

Controversy is ongoing regarding the relationship between ore formation and the structural evolution of the Hadamengou gold deposit. To address this issue, we conducted a comprehensive investigation of mineralization-related structures, geochronology and Fe isotopes. From the perspective of spatial evolution, hydrothermal fluids originating from the Shadegai and Xishadegai plutons have extracted accumulated ore-forming elements from the Wulashan Group (Ar₂WL) and then evolved, initiating at Exploration Line 11 and migrating eastwards and westwards along the EW-trending thrust fault system to form orebodies. From the temporal evolution standpoint, the Wulashan Group (Ar₂WL) experienced diagenesis (2591.00 Ma to 2204.00 Ma) and metamorphism (2074.00 Ma to 1625.00 Ma) from late Neoarchean to early Paleoproterozoic, when ore-forming materials were initially accumulated; in the early Paleozoic (440.71 Ma to 425.00 Ma), the collision led to the formation of early-stage EW-trending imbricated thrust faults, which established a fundamental structural framework for the orefield and further accumulated ore-forming materials; from the late Paleozoic to the Mesozoic, multiple subsequent episodes of regional tectonic-magmatic-hydrothermal events have superimposed, modified and reactivated the thrust fault system. Notably, the Triassic period, particularly between 245.00 Ma and 217.90 Ma, is considered to be a primary ore-forming stage. In summary, the intricate relationship between ore-formation and structural evolution has been fundamentally elucidated.

The key factor that controls the genesis of porphyry Cu deposits (PCDs) in collisional orogens remains a debated topic. This study employs whole-rock La/Yb proxies to quantitatively constrain the spatial and temporal variations in crustal thickness of the South Armenian–Iranian magmatic belt (SAIMB) within the Zagros orogen (central Tethys region) since the Eocene. Our results show that rapid crustal thickening occurred first in the NW section of the SAIMB at ~35 Ma, then propagated southeastward into the central and SE sections at ~25 Ma and 20 Ma, respectively, indicating that the Arabia–Eurasia collision was diachronous. The formation of the large and giant collision-related PCDs in the SAIMB might have been controlled by the collision process because they developed first in the NW section of the SAIMB and subsequently propagated southeastward into the central and SE sections. More importantly, crustal thickness mapping shows that the PCDs are preferentially developed in the thickened crust areas (>50 km). Our findings propose that thickened crust is critical for the formation of the PCDs in collisional orogens by promoting Fe²⁺-rich minerals as a fractionating phase, driving magmatic auto-oxidation and releasing Cu into the magmas. The Cu is then partitioned into magmatic fluids, sustaining the porphyry systems. Furthermore, our research highlights that the thickened crust hosting PCDs was characterized by a previously thinner crust (<40 km), where magmas had low oxygen fugacity due to the absence of the auto-oxidation process. Consequently, chalcophile elements (e.g., Cu) efficiently separated from the melt through sulfide segregation, forming large Cu-bearing lower-crustal cumulates. These cumulates can be mobilized with an increase in oxygen fugacity, incorporating into subsequent porphyry mineralization. We thus propose that the crustal thickness evolution over time controls the formation of the PCDs in collisional orogens. There are two essential stages in the collision-related PCDs formation: the first is high-flux magmatism in the thin crustal setting (<40 km), leading to metal-fertilized lower crust through sulfide segregation, and the second is the intracrustal auto-oxidation during crustal thickening (>50 km) which facilitates pre-enriched sulfides in the lower crust to re-dissolve, releasing Cu into the magmas.

East Asian continental tectonics challenges the plate tectonics paradigm with its diffuse intraplate deformation, magmatism, and earthquakes. Despite extensive studies, fundamental questions persist. This review examines ten critical questions of East Asian tectonics, including the thickness of the continental lithosphere, the origin of the North–South Gravity Lineament, and the northern extent of the Indian plate beneath the Tibetan Plateau. Additional questions address the Tibetan Plateau's lateral growth, the Tianshan mountain building, the mantle flow in response to the Indo-Asian collision, and the formation of the Shanxi Rift. The review also explores the subduction along the eastern margins of the East Asian Continent and the origins of the Changbaishan volcanic field, the destruction of the North China Craton, and the development of the Mesozoic Large Granitic Province in South China. Originally presented at the DEEP2024 workshop to stimulate discussion of how SinoProbe-II research initiatives could advance our understanding of Asian tectonics, this review provides context for each question, summarizes current knowledge, and identifies promising research directions.

The approximately 3000 km long Tan–Lu fault zone (TLFZ) in East Asia is the longest continental strike-slip fault zone in the world and exemplifies how such a fault zone forms and propagates on a continental scale. Structural and geochronological data from the TLFZ and surrounding regions indicate that the fault zone originated as NE/SW-striking sinistral ductile shear zones along an oblique continental convergence margin during the Triassic indentation collision between the North China Craton and the Yangtze Block. The Triassic fault zone, with a total length of about 720 km between the Dabie and Sulu orogens, exhibited an apparent sinistral offset of approximately 300 km along the TLFZ. The second stage of sinistral movement occurred in the earliest Late Jurassic, reactivating the pre-existing southern segment and propagating northwards to the southern coastline of present-day Bohai Bay, as well as forming a significant portion of the Dunhua–Mishan fault zone. The third stage of sinistral movement, in the earliest Early Cretaceous, was the most intense strike-slip movement of the Mesozoic, leading to the complete linkage of the TLFZ. This stage included further northward propagation of the southern–middle segment, both southward and northward propagation of the Dunhua–Mishan fault zone, as well as the formation of the entire Yilan–Yitong fault zone. The fourth stage, in the earliest Late Cretaceous, involved the reactivation of the entire TLFZ. Following its Triassic origin due to the indentation collision, the subduction of the Paleo-Pacific Plate and the subduction and closure of the Mongol–Okhotsk Ocean were responsible for the multi-stage sinistral movements from the Late Jurassic to the Cretaceous. The evolution of the TLFZ demonstrates that a continental-scale strike-slip fault zone (>1000 km long) forms through multiple stages of propagation and linkage in dynamic settings of plate convergence.

Twelve new dinosaur teeth have recently been recovered from three localities in the Upper Cretaceous Nenjiang Formation of the Songliao Basin. Although fragmentary, the material offers enough evidence to identify the following taxa: tyrannosaurids, dromaeosaurines, velociraptorines, hadrosauroids, and titanosaurs. In addition to the previously known dinosaurs from the basin, several new ones have been identified, extending the paleogeographic range of related taxa. The discovery of these new fossil remains provides valuable insights into dinosaur diversity and sheds light on the terrestrial ecosystem during the Late Cretaceous in the Songliao Basin.