Acta Geologica Sinica ‐ English Edition最新文献

The Gejiu tin-copper-(tungsten) (Sn-Cu-(W)) polymetallic district is located in the southwest of the W-Sn metallogenic belt in the western Youjiang Basin, Yunnan, Southwest China. Abundant W minerals have been identified in the region via exploration. However, metallogenic sources and evolution of W remain unclear, and the existing metallogenic model has to be updated to guide further ore prospecting. Elemental and Sr-Nd isotopic data for scheelites assist in the determination of sources and evolution of the W-mineralizing fluids and metals in the district. Based on field geological survey, the scheelites in the Gejiu district can be categorized into three types: altered granite (Type I), quartz vein (Type II) from the Laochang deposit, and skarn (Type III) from the Kafang deposit. Types I and II scheelites have low molybdenum (Mo) and strontium (Sr) contents, and Type II scheelite has lower Sr contents than Type I as well as higher Mo and Sr contents than Type III scheelites. Varying Mo contents across the scheelite types suggests that the oxygen fugacity varied during ore accumulation. Type I and Type II scheelites exhibit similar rare earth elements (REE) patterns; Type III scheelite contains lower REE content, particularly HREE, compared with the other scheelites. All scheelites exhibit negative Eu anomalies in the chondrite-normalized REE patterns. As the W-mineralization and two-mica granite share close spatial and temporal relationships, the negative Eu anomalies were likely inherited from the two-mica granite. Type I and Type II scheelites display varied (⁸⁷Sr/⁸⁶Sr)_{82 Ma} (0.7090–0.7141) and ε_Nd(82 Ma) (from –9.9 to –5.4) values, similar to those of granite. However, Type III scheelite exhibits lower (⁸⁷Sr/⁸⁶Sr)_{82 Ma} (0.7083–0.7087) and lower ε_Nd(82 Ma) (from –10.5 to –6.9) values than the two-mica granite. This indicates that the two-mica granite alone did not provide the ore-forming fluids and metals and that the Type III scheelite ore-forming fluids likely involved external fluids that were probably derived from carbonate rocks. The implication is that highly differentiated two-mica granites were the source of primary W-bearing metals and fluids, which is consistent with earlier research on the origin of Sn ore-forming materials.

Metallogenic research on structural levels can reveal vertical patterns of mineralization and facilitate the deep exploration of economic minerals. However, research focusing on the correlation between structural levels and mineralization remains limited. In this study, we summarize the deformation patterns and associated mineral deposits observed at different crustal levels (i.e., surface, shallow, middle, and deep structural levels, corresponding to depths of <2, 2–8, 8–15, and >15 km, respectively). Furthermore, we examine the genetic association between structural levels and metallogenesis, demonstrating that distinct structural levels are linked to specific types of mineralization. Key factors that vary across crustal levels include temperature, pressure, and fluid circulation. Ore-forming processes involve interactions between structures and fluids under varying temperatures and pressures. Structural levels influence mineralization by controlling the temperatures, pressures, and deformation mechanisms that drive the activation, migration, and enrichment of ore-forming materials.

Pore structure directly affects the occurrence and migration of shale hydrocarbon, and the lack of research on the mechanism of the pore structure is an important reason for the hindrance of shale hydrocarbon exploration. By analysing the geochemistry and reservoir characteristics of Jurassic lacustrine shales in Sichuan Basin, this study recovers their paleoenvironments and further discusses paleoenvironmental constraints on pore structure. The results show that the Lower Jurassic lacustrine shales in the Sichuan Basin are in a warm and humid semi-anoxic to anoxic lake environment with high productivity, a strong stagnant environment, and a rapid sedimentation rate, with water depths ranging from about 11.54–55.22 m, and a mixture of type II/III kerogen is developed. In terms of reservoir characteristics, they are dominated by open-slit pores, and the pores are relatively complex. The percentage of mesopores is the highest, while the percentage of macropores is the lowest. Further analysis shows that paleoclimate controls the overall pore complexity and surface relaxation of shales by influencing the weathering rate of mother rocks. Paleoredox conditions control the proportion and complexity of shale pores by influencing TOC content. The research results will provide theoretical basis for improving the exploration efficiency of lacustrine shale resources and expanding exploration target areas.

We report a new eusauropod dinosaur, Huashanosaurus qini gen. et sp. nov., based on a partial skeleton recovered from a bed in the Lower to Middle Jurassic Wangmen Formation (Fm.) from Huqiu Quarry near Mingjiang River, Ningming County, Guangxi Zhuang Autonomous Region, southern China. The new taxon can be diagnosed by the following autapomorphies: posterior process of the ulna hook-shaped; the cross-section of the proximal part of the ulna crescent-shaped; groove structure present at the posterodistal surface of the fibula. Phylogenetic analysis reveals that H. qini is later-diverging than the Middle Jurassic Shunosaurus. Previous work showed that the Wangmen Fm. is early Early Jurassic in age whereas the new eusauropod discovery indicates that the Wangmen Fm. is probably somewhat younger Early–Middle Jurassic in age. The find increases the diversity of Jurassic eusauropods in China.

As a highly coupled aggregate of tectonism, magmatism, and metamorphism, a gneiss dome is usually taken as a vital window for understanding the crustal internal structure and the exchange of material and energy during orogenic exhumation. The Qinghe gneiss dome located in the eastern Chinese Altai orogen, lies in Qinghe County, Xinjiang, records important information of late accretionary orogeny associated with continental uplift and crustal growth. According to the field investigation, the dome shows core–mantle–margin domains, in which the core is composed of migmatized granite and gneiss, the mantle consists of banded gneiss, schist, and leptynite, and the margin has rock assemblages of phyllite, schist, and meta-sandstone. From the margin to the core, the dome can be divided into chlorite–sericite, andalusite–staurolite, sillimanite–biotite, and sillimanite–garnet metamorphic zones, recording progressive metamorphism. Detailed structural analyses in the Qinghe gneiss dome indicate progressive deformation from the margin to the core. Internal and external detachment faults are clarified, with the former characterized by inflow and outward migration of crustal material and the latter marked by brittle-ductile deformation with a lineation indicating lateral slip of the upper wall when the dome uplifted. Based on these faults, upper, middle, lower structural layers are observed from the outer to inner domains of the dome. Considering the general geological background and new data, the Qinghe gneiss dome probably predominantly underwent early ductile shear deformation and late heat-flow diapirism in the early Permian, closely related to upwelling of asthenosphere mantle that resulted from slab break-off in the extensional tectonic setting.

The tectonic setting of the Himalaya during the Early Paleozoic has been a subject of enduring debate within the scientific community. Newly discovered bimodal intrusive rocks from comprehensive field geological investigation in the central mountain range were subjected to petrology, zircon U-Pb geochronology, zircon Hf isotopes and whole-rock geochemistry analyses. The Palie bimodal intrusive rocks, comprising amphibolite and granitic gneiss, were formed at ∼489 Ma. The amphibolite exhibits geochemical characteristics consistent with N-MORB, while the granitic gneiss is classified as high potassium calc-alkaline peraluminous S-type granite. Both igneous rocks exhibit negative zircon ε_Hf(t) values and display ancient T_DM^C ages. In conjunction with regional geological survey findings, it can be inferred that the formation of the Palie bimodal intrusive rocks occurred within a post-collision extensional tectonic setting. The amphibolite genesis involved partial melting of an enriched lithospheric mantle with some crustal assimilation, whereas the origin of the granitic gneiss can be attributed to partial melting of pre-existing felsic crust. Our data indicate that during the Early Paleozoic, the Himalaya underwent a transition from a pan-African collisional setting to post-collisional extensional tectonics.

The Govanda Formation was deposited during the Miocene in the intermontane areas between the Zagros suture and imbricate zones. The Govanda Formation was studied in the Sherwan Mazin area within Mergasor district, Erbil Governorate to identify the lithostratigraphy and microfacies analysis in order to determine the depositional environment of the formation. The formation in the studied section is 116 m thick and mainly consists of reddish-brown, hard, thick-bedded, chert-bearing conglomerate, pinkish shale and yellowish-grey, thick-bedded, detrital, fossiliferous limestone. The formation is unconformably underlain by the Upper Cretaceous Tanjero Formation and conformably overlain by the Merga Red Beds series. Four different lithostratigraphic units were identified, based on field observation and petrographic analysis, including a basal conglomerate unit (A), a shale unit (B), a well-bedded limestone unit (C) and a thick and massively-bedded limestone unit (D). The presence of a thick conglomerate bed at the base of the formation indicates a large unconformity that lasted nearly 40 million years. Based on detailed microfacies analysis of carbonate rocks, five main microfacies and 15 submicrofacies are recognized. The main microfacies types include mudstone, wackestone, packstone, grainstone and boundstone microfacies. Based on the microfacies types the depositional environment are defined as open lagoon, reef, fore-reef and back-reef environments of normal to saline, nutrient rich water.

Silicalites are extensively developed in the Liujiang Formation (Fm.) of the Frasnian in the Dianqiangui Basin and are often associated with carbonaceous shales. This stratigraphic combination represents a special sequence stratigraphy formed in special deep-water environments, which not only gives the shales unusual spatio-temporal distribution features, but also induces the shales in the Liujiang Fm. to frequently be rich in organic matter (OM). This study summarises the special deep-water sedimentary succession of the Liujiang Fm., which is mainly distributed around synsedimentary faults, as well as establishing the sequence stratigraphic frameworks of the Liujiang Fm. in the west–east and southwest–northeast directions. Under the sequence stratigraphic frameworks, the spatio-temporal distribution features of the organic-rich shales of the Liujiang Fm. and the regional variations of the Liujiang Fm. were investigated. In addition, the rock components and OM occurrence states of the organic-rich shales were also observed and described in detail under the microscope. The results show that the organic-rich shales were formed temporally primarily during the third-order sea-level falling stage, developed spatially mainly on the east and west sides of the study area, as well as that the OM accumulation is closely related to tentaculitoids and seems to be influenced by a ‘biological pump’.

The phenomenon of ‘bamboo-like’ thin interlayers developed in rock salt is one of the most prominent features of Paleogene salt-bearing strata in eastern China, where centimeter-thick rock salts appear separately, forming rhythmic units. At present, detailed analyses of these rhythms of rock salt are still limited, which directly affects the achievement of comprehensive and in-depth understanding of the developmental laws pertaining to this kind of saline lake. Therefore, we selected the typical rhythmic ‘bamboo-like’ rock salts of the Shizhai Depression in Jiangsu Province as the research subject. Through careful observation of rock salts in hand samples and detailed petrographic and mineralogical analyses, we analyzed the hydrogen and oxygen isotopic compositions, homogenization temperatures and chemical compositions of individual fluid inclusions in halite crystals. Early-stage rhythmic deposition was a product of continental saline lake evolution in winter or spring, late-stage rhythmic deposition being the product of evolution in the summer. The seasonal evolution of the halite sequences was determined and two brine enrichment events were identified. In addition, the quiet saline lake environment with concentrated brine represented by rock salt was more likely to precipitate potassium. This study provides a new reference for the evolution of both Paleogene climate and saline lakes in eastern China.

Four Pb-Zn deposits, namely Bangpu (BP), Digei (DG), Nabuding (NB) and Cuoga (CG), are located within a 20 km distance of each other in the Gangdese porphyry copper belt (GPCB). The age and nature of the Pb-Zn mineralization, especially its relationship to magmatism, remain uncertain. In order to address this issue, mica from the four deposits was selected for in situ Rb-Sr dating, with sphalerite additionally being selected for in situ trace element analysis. Detailed geological research has revealed that the BP and NB deposits are primarily skarn-type Pb-Zn mineralization, while DG and CG are associated with magmatic hydrothermal breccia and are characterized by banded-type mineralization. The Rb-Sr isochron ages of syn-mineralization muscovite at the BP and CG deposits are 11 ± 6 Ma and 19.7 ± 0.7 Ma respectively. Fe, Cd, In, Mn and Sn occur as lattice substitutions in sphalerite from the four deposits. Cu exists as microinclusions in BP, but occurs isomorphically in the DG, NB and CG deposits. The formation temperatures of the four deposits, as calculated from sphalerite geothermometry, range from approximately 200°C to 300°C, indicating that they belong to medium temperature deposits. BP and NB are classified as skarn Pb-Zn deposits, while DG and CG are categorized as hydrothermal filled Pb-Zn deposits. These results suggest that, in addition to porphyry Cu mineralization, the GPCB also contains significant Miocene Pb-Zn mineralization.