Acta Geologica Sinica ‐ English Edition最新文献

Granite origin is crucial to understanding the evolution of continental crust, yet many concerns about granite genesis remain yielding ongoing debates. A new integrated study of petrology, geochronology, mineral chemistry and whole-rock geochemistry of the Dupangling granitic complex in South China, indicate that the granites in the western complex were emplaced during the Caledonian (418 Ma); they have SiO₂ contents of 68.1–70.4 wt%, and are calc-alkaline and strongly peraluminous with high maficity [(TFe₂O₃ + MgO) > 4.0 wt%] and exhibit ⁸⁷Sr/⁸⁶Sr(t) of 0.7234–0.7311 and ε_Nd(t) of –9.0 to –6.7. The granites in the eastern complex, emplaced during the Indosinian (212 Ma), have high SiO₂ contents (73.3–79.8 wt%) and exhibit affinities with A-type granites, such as enrichment in alkalis and rare earth elements (REEs), and depletion in Sr and Ba along with high TFeO/(TFeO + MgO), Ga/Al and Zr + Y + Ce + Nb; these granites exhibit ⁸⁷Sr/⁸⁶Sr(t) of 0.7221 and ε_Nd(t) of –9.2 to –7.5. Geochemical characteristics suggest that the older Caledonian granites were derived through dehydration melting of Paleoproterozoic metasedimentary rocks plus additional (∼20%–32%) input from mafic magma, whereas the Indosinian granites were generated through shallow dehydration melting of the Caledonian granitoids.

The Cretaceous andesites were discovered in the Biluocuo area, and provided key records to understand the late Mesozoic geodynamic evolution and crustal basement for the southern Qiangtang block in the central Tibet. In this study, we present a detailed study of zircon U-Pb dating, major and trace elemental composition, and Sr-Nd-Hf isotopes for the Biluocuo trachy-andesites. The trachy-andesites yielded zircon U-Pb ages at ca. 97 Ma, and exhibited SiO₂ contents ranging from 55.92 to 69.04 wt%, low TiO₂ contents (0.37 to 0.75 wt%) and low Mg^# values (18.6 to 53.7), suggesting that they belong to high-K calc-alkaline series. They showed adakitic signatures, such as high Sr/Y ratios (almost 24 to 55) and low Y (<20 ppm), implying they were generated at great depths (>15 kbar). The samples have initial Sr isotopic ratios of 0.70963 to 0.70964, ε_Nd(t) values of –4.7 to –4.6, and zircon ε_Hf(t) values of –1.2 to +1.3 with two-stage Hf model ages of 0.95 to 1.09 Ga. Elemental and Sr-Nd-Hf isotopic signatures suggest that the trachy-andesites were derived from the partial melting of the thickened lower crust with involvement of metasomatized mantle components. Combined with coeval high-Mg andesites, we proposed that underplating of mantle induced melting of the lower crust at ca. 97 Ma in the southern Qiangtang block, following by lithospheric delamination. Inherited/xenocrystic zircons from the trachy-andesites revealed magmatic activities at 2562 Ma, 1850–1804 Ma, 1768–1665 Ma, 1043–935 Ma, 851–736 Ma and 642–540 Ma. There is a Precambrian crustal basement in the southern Qiangtang block, which may have experienced the assembly and break-up of the Columbia, Rodinia, and Gondwana supercontinents.

Recent studies have highlighted the presence of lithium enrichment in coals within the Ordos Basin, which has garnered significant attention due to the potential economic value. However, most research has concentrated primarily on the coal seams of the Taiyuan and Shanxi formations, with limited reports on the Benxi Formation. To address this gap, our study focused on elucidating the geochemical characteristics and origins of the lithium enrichment in the No. 8 coal of the Benxi Formation through the use of optical microscopy and inductively coupled plasma mass spectrometry (ICP-MS). The results showed that the No. 8 coal was a bituminous coal, characterized by medium ash yield, low volatile matter, high total sulfur content and medium vitrinite proportion. The No. 8 coal was enriched in Li (average 91.7 ppm, CC = 6.55) and Zr (average 191 ppm, CC = 5.30), the unusual enrichment of Li being primarily located in the middle of the coal. The minerals in the coal were predominantly clay minerals, along with minor amounts of pyrite, quartz and calcite. The occurrence mode of Li in the No. 8 coal was associated with aluminosilicate minerals, presumably kaolinite. Based on geochemical characteristics, the sedimentary source of the No. 8 coal was intermediate-felsic volcanic rock from the Yinshan oldland. The enrichment of Li can be attributed to the supply of terrestrial debris from the Yinshan oldland and the depositional environment. Our analysis identifies three distinct stages of lithium enrichment, emphasizing the critical role played by the terrestrial debris, as well as the acidic to partially reducing conditions, in facilitating this process. In conclusion, our study sheds light on the mechanisms underlying lithium enrichment in the No. 8 coal of the Benxi Formation, highlighting the significance of geological factors in shaping the distribution and concentration of critical metals in coal.

This study presents whole-rock major, trace elements and Sr-Nd-Hf isotopic compositions, as well as zircon U-Pb geochronological data, for the peraluminous and aluminous granitoids in northern Guangdong Province, South China, in order to investigate their petrogenesis and tectonic implications. The Qingzhou granodiorites (458.5–455.4 Ma) are peraluminous (A/CNK = 1.05–1.96). They have relatively high initial ⁸⁷Sr/⁸⁶Sr ratios (I_Sr = 0.7087–0.7148), low ε_Nd(t) values (–11.2 to –10.1) and a variety of zircon ε_Hf(t) values in the range –13.4 to +4.81. By contrast, the Damaoshan granodiorites (458.1 Ma) are metaluminous (A/CNK = 0.79–0.94) in composition, with I_Sr values of 0.7083 to 0.7110, ε_Nd(t) values of –7.92 to –5.28 and zircon ε_Hf(t) values of –8.69 to –2.06. The Gaoshou quartz diorites (449 Ma) are metaluminous-peraluminous. Their I_Sr values vary from 0.7104 to 0.7111 with ε_Nd(t) values from –9.64 to –8.63. Geochemical data and Sr-Nd-Hf isotope compositions indicate that the Qingzhou, Damaoshan and Gaoshou intrusions are primarily derived from the partial melting of metagreywackes, tonalitic rocks and amphibolite, respectively. The crustal materials in northern Guangdong, from top to bottom, consist of Paleozoic sequences, metasediments with a V_p of < 6.0 km/s, metaigneous rocks with a V_p of 6.3–6.7 km/s and amphibolite with a V_p of ∼7.03 km/s.

We report new material of the zalambdalestid, Zhangolestes jilinensis, from the Quantou Formation (lower Upper Cretaceous, Cenomanian to Turonian), Gongzhuling City, Jilin Province, NE China. Using micro-CT-scan, the material is shown to include dentocranial and postcranial elements recovered from the same matrix block containing the holotype specimen. The CT-images also show the labial and internal structures of the holotype fragment of the lower jaw of Z. jilinensis. Based on the preservation, relative size, and tooth wear, the new material and the holotype lower jaw likely belong to the same individual animal, whereas the hypodigm mandibular fragment assigned to Z. jilinensis in the original study is thought now to belong to a different individual, potentially representing a different species, which, if true, would increase the eutherian diversity in the Late Cretaceous Changchunsaurus Fauna. Furthermore, the new CT-images show that the incisor morphology is diverse within zalambdalestids and probably evolved independently from the enlarged incisors in placental mammals, such as Glires.

Organic-rich mudstones and shales, which hold significant potential for shale oil resources, characterize the first member of the Upper Cretaceous Qingshankou Formation (K₂qn¹) in the Sanzhao sag of the Songliao Basin, NE China. Focusing on 30 core samples obtained from the first shale oil parameter well, named SYY3 in the study area, we systematically analyzed the composition and stratigraphic distribution of the K₂qn¹ heteroatomic compounds using electrospray ionization Fourier transform–ion cyclotron resonance mass spectrometry (ESI FT-ICR MS), to assess their geological relevance to shale oil. The findings indicate that in the negative ion mode, the heteroatomic compounds predominantly consist of N₁, N₁O₁–N₁O₈, O₁–O₈, O₁S₁–O₆S₁; contrastingly, in the positive ion mode, they are primarily composed of N₁–N₂, N₁O₁–N₁O₄, N₂O₁, O₁–O₄, O₁S₁–O₂S₁. Heteroatomic compound distributions vary significantly with depth in the negative ion mode, with minor variations in the positive ion mode. These distributions are categorized into three types based on the negative ion ratio ((N₁ + N₁O_x)/O_x): Type I (>1.5), Type II (0.8–1.5), and Type III (<0.8); types I and II generally exhibit a broader range of carbon numbers compared to Type III. The distribution of double bond equivalent (DBE) values across various sample types exhibits minimal variance, whereas that of carbon numbers shows substantial differences. Variations in heteroatomic compound compositions among the samples might have resulted from vertical sedimentary heterogeneity and differing biotic contributions. Type III samples show a decrease in total organic carbon (TOC) and free oil content (S₁) compared to types I and II, but an increased oil saturation index (OSI), indicating a lower content of free oil but a higher proportion of movable oil. The reduced content of N-containing compounds implies lower paleolake productivity during deposition, leading to a reduction in TOC and S₁. A lower TOC can enhance oil movability due to reduced oil adsorption, and the decreased presence of polar nitrogenous macromolecules with fewer high-C-number heteroatomic compounds further promote shale oil movability. Additionally, the negative ion ratios of N₁/N₁O₁ and O₂/O₁ exhibit positive and negative correlations with the values of TOC, S₁, and extractable organic matter (EOM), respectively, indicating that the salinity and redox conditions of the depositional water body are the primary controlling factors for both organic matter en

Both fractional crystallization and fluid-melt-crystal interaction are involved in the formation of highly fractionated granites. This paper assessed those two processes using geochemistry of muscovite and tourmaline and bulk-rock chemistry of multi-phase Wangxianling granitoids, South China. Compositional variations suggest the coarse-grained muscovite granite is produced from fractional crystallization of the two-mica granite whereas the fine-grained muscovite granite represents a distinct magma pulse. Progressive fractionation of quartz, feldspar and biotite leads to elevated boron and aluminum content in melt which promoted muscovite and tourmaline to crystallize, which promotes two-mica granite evolving towards tourmaline-bearing muscovite granite. Fluid-melt-crystal interaction occurred at the magmatic-hydrothermal transitional stage and resulted in the textural and chemical zonings of tourmaline and muscovite in finegrained muscovite granite. The rims of both tourmaline and muscovite are characterized by the enrichment of fluid mobile elements such as Li, Mn, Cs and Zn and heavier δ¹¹B values of the tourmaline rims (–15.0‰ to –13.6‰) compared to cores (–15.7‰ to –14.3‰). Meanwhile, significant M-type REE tetrad effects (TE_1,3 = 1.07–1.18) and low K/Rb ratios (48–52) also correspond to fluid-melt-crystal interaction. This study shows zoned muscovite and tourmaline can be excellent tracers of fractional crystallization and late-stage fluid-melt-crystal interaction in highly evolved magmatic systems.

A subducted continental slab is sometimes torn during collision, yet the exact impact of slab-tearing on the overlying lithosphere remains unclear. Here, we image the structure and architecture of the Asian lithosphere above the Indian slab in the eastern Tibetan Plateau using multiscale seismic tomography models and zircon Hf isotopic mapping, respectively. Our mantle V_p model shows that a large low-velocity anomaly extends laterally beneath the thinned Asian lithosphere above the tear zone roughly along the 26°N. The V_s images, magmatic records and Hf isotopic mapping indicate that this low-velocity anomaly recorded an asthenosphere flow eastward along the tear zone, which thermally eroded and refertilized the overlying Asian lithosphere, leading to the lithospheric melting, thinning and root delaminating. The vertical tear also generated a tectonic weak zone with associated Cenozoic potassic and carbonatitic magma suites. We argue that such a hot lithosphere discontinuity provided a reasonable mechanism for the abrupt change of crust thickness and the transformation of crust-mantle deformation from coupling to decoupling across the tear zone.

The marine-continental transitional shale of the Upper Permian Longtan Formation is widely distributed in Hunan and shows significant exploration potential. Frequent changes in lithofacies have however notably influenced the shale gas enrichment. The strata of the Longtan Formation in the Shaoyang Depression, central Hunan, were taken as the study object for this project. Three lithofacies assemblages were identified: shale interbedded with sandstone layer (SAL), sandstone interbedded with shale layer (ASL) and laminated shale layer (LSL). The SAL shale shows significant variability in hydrocarbon generation potential, which leads to shale gas characterized by ‘hydrocarbon generation in high total organic carbon (TOC) shale, retention in low TOC shale and accumulation in sandstone’. The ASL shale, influenced by the redox conditions of the depositional environment, shows a lower concentration of organic matter. This results in an enrichment model of ‘hydrocarbon generation and accumulation in shale, with sealing by sandstone’. The laminar structure of LSL shale causes both quartz and clay minerals to control the reservoir. Shale gas is characterized by ‘hydrocarbon generation in mud laminae, retention and accumulation in silty laminae, with multiple intra-source migration paths’. In the marine-continental transitional shale gas system, the enrichment intervals of different types of shale gas reservoirs exhibit significant variability.