Acta Geologica Sinica ‐ English Edition最新文献

In the Alpine Corsica (France), the Santa Lucia Nappe represents a peculiar unit preserving the unique relicts of Paleozoic lower to medium continental crust. It consists of composite basement affected by Permian granulite facies metamorphic conditions unconformably covered by a Late Cretaceous clastic sequence (Tomboni Conglomerate and Tralonca Flysch) affected by polyphase deformation and low-grade-metamorphism. In this work, we present a new reconstruction of the deformation events registered by the Tralonca Flysch during the Alpine orogeny. The D1 phase was testified by rare isoclinal folds. The D2 phase produced a continuous foliation and a map-scale sheath-fold with a top-to-W sense of shear. The D3 phase produced E-verging non-cylindrical folds and S3 crenulation cleavage that is not associated to metamorphic blastesis. We present the first temperature-pressure-deformation (P-T-d) path for the Tralonca Flysch, demonstrating that the Santa Lucia Nappe underwent accretion and then first stage exhumation in the Alpine wedge during the D1 phase with pressure and temperature peaks both occurred under blueschist metamorphic conditions. The D2 phase occurred at lower pressure-temperature conditions during a second stage exhumation. This pressure-temperature-deformation path is comparable with those of the Lower Units (i.e., the subducted continental units of Alpine Corsica) suggesting a common geodynamic history.

The continental Asia is mainly composed of three major tectonic regimes, the Tethys, Paleo Asian Ocean, and West Pacific. It underwent multi-stage plate convergences, ocean-continent transformations, and subductions, collisions and/or collages, and post collisional (orogenic) extensions in Phanerozoic. Tectonic evolution of the Asia brings up a unique fault system and tectonic geomorphological features in the mainland China. Also, it provides a geodynamic background for the formation and evolution of metallogeneses and mineral systems, resulting in nonuniform distribution of tectono-metallogenic systems and metallogenic belts. The spatiotemporal distribution of mineral deposits in China and adjacent areas exhibits periodic variation under controlling of the full life Wilson cycle and tectonic evolution, forming the plate convergence-related mineral system in East Asia. Porphyry Cu deposits are mainly related to compressional systems in Paleozoic and early Mesozoic, and more closely related to post-collision extensional settings in late Mesozoic and Cenozoic. Orogenic Au deposits mainly formed in post-orogeny extensional setting. Alkaline rock related rare earth element deposits formed mainly at margins of the North China and Yangtze cratons. Granite-pegmatite Li and other rare metal deposits formed mainly in early Mesozoic, related to Indosinian post-orogeny extension. Tectono-metallogenic systems provide important basis for the prospecting of mineral resources.

Mineralogical and geochemical studies have been undertaken on the Triassic to Lower Jurassic Adigrat Sandstone of the Blue Nile Basin of central Ethiopia to infer its source rock type, paleoweathering, and paleoclimatic history. The Adigrat Sandstone occurs at the basal section of the Mesozoic sedimentary formation and unconformably overlays the Neoproterozoic–Paleozoic crystalline rocks, or locally, the Karroo sediments in the northern Blue Nile Basin. A mineralogical study reveals that quartz (Q), feldspars (F), and lithic fragments (L) are the framework grains of the sandstone. On the QFL diagram, the plot of the modal composition of the sandstone mainly falls within the feldspathic arenite and quartzose arenite fields. The geochemical data of the lower section of the sandstone mainly falls within the arkose and subarkose fields, whereas the upper section data falls within the quartzose and sublithic arenite fields. Mineralogical and geochemical weathering indices indicate that the provenances of the Adigrat Sandstone were exposed to pronounced weathering intensity, where the lower part of the sandstone was controlled by arid to semi-arid conditions, whereas the upper section was linked to humid to semi-humid (tropical to subtropical) climatic conditions. Mineralogical and geochemical data also indicate that mafic to intermediate basement rocks were the primary source rocks of the sediment. Perhaps the sediment was assumed to have been reworked by multi-cyclic sedimentary processes. The discriminant function diagram, the REE pattern, La/Th vs. La/Yb, and the Th–Hf–Co plot are consistent. A comparison of provenance studies for the Adigrat Sandstone in the Blue Nile Basin and the Mekele outlier of northern Ethiopia indicates that the sediment of the former is highly sorted, experienced higher weathering intensity, and compositionally derived from mafic to intermediate crystalline rocks. On the other hand, the sediment of the latter is essentially a weathering product of felsic rocks.

Inertinite-rich coal is widely distributed in the Ordos Basin, represented by the No. 2 coal seam of the Middle Jurassic Yan'an Formation. This paper combined coal petrology and geochemistry to analyze the origin of inertinite, changes in the coal-forming environment and control characteristics of wildfire. Research has shown that there are two forms of inertinite sources in the study area. Alongside typical fusinization, wildfire events also play a substantial role in inertinite formation. There are significant fluctuations in the coal-forming environment of samples at different depths. Coal samples were formed in dry forest swamp with low water levels and strong oxidation, which have a high inertinite content, and the samples formed in wet forest swamp and limnic showed low inertinite content. Conversely, the inertinite content of different origins does not fully correspond to the depositional environment characterized by dryness and oxidation. Nonpyrogenic inertinites were significantly influenced by climatic conditions, while pyrofusinite was not entirely controlled by climatic conditions but rather directly impacted by wildfire events. The high oxygen level was the main factor causing widespread wildfire events. Overall, the combination of wildfire activity and oxidation generates a high content of inertinite in the Middle Jurassic coal of the Ordos Basin.

Field work focused on the Kuedinskie Kluchiki locality, Perm region, Urals, Russia, which contains a rich assemblage of diverse fossil organisms including higher plants (equisetophytes, pteridosperms, ginkgophytes, conifers, vojnovskyans) represented by stems, leaves and reproductive organs; invertebrates (mollusks, arthropods), and tetrapods (temnospondyl amphibians, seymouriamorphs, cotylosaurs, synapsids, diapsids), as well as bony fishes. General characteristics of the taxonomical composition of the Kuedinskie Kluchiki locality are given. A new peltaspermalean pteridosperm taxon, Compsopteris longipinnata sp. nov., and a voltzialean conifer Archaeovoltzia kuedensis sp. nov. are described. General considerations on the paleoecologic and paleogeographic conditions of the Kuedinskie Kluchiki locality origin are given.

Numerous new records of Ferganiella, Podozamites, and Schidolepium, including a new species, Ferganiella ivantsovii sp. nov., are described from the Early Jurassic (Toarcian) Middle Subformation of the Prisayan Formation from the Euro-Sinian paleofloristic region in the Irkutsk Basin, Eastern Siberia, Russia. An analysis of the paleogeographic distribution of Ferganiella and Podozamites shows that both genera were the most diverse and numerous in the East Asian province of the Euro-Sinian region and in the Northern Chinese province of the Siberian region during the Early and Middle Jurassic. These phytochoria were located in the subtropical and temperate subtropical climate zones, which allows us to consider Ferganiella and Podozamites as thermophilic plants, which are important indicators of the Early Toarcian climatic optimum. Their abundance in the Irkutsk Basin thus may indicate Early Toarcian warming; further abundant Schidolepium cones, which produced Araucariacites pollen, typical for Euro-Sinian flora complement the scenario. Thus, the new finds are the first macrofloristic indicators of the Toarcian climatic optimum in the Irkutsk Basin.

This study investigated the calcareous nannofossil assemblages in detail from the early Miocene aged Lice Formation outcropping in the Kahramanmaraş basin. The biostratigraphy of calcareous nannofossils was outlined and paleoenvironmental features determined. In 81 samples taken from three measured sections in the region, 17 calcareous nannofossil genus and 48 nannofossil species were identified. These calcareous nannofossil genus and species identified the Lice Formation as being in the CNM4 nannofossil biozone. The abundance and diversity of early Miocene calcareous nannofossil species varied in the measured sections, with the samples generally moderate-poor, apart from a few samples. The relative abundance of individuals of Cyclicargolithus floridanus, Coccolithus pelagicus, Reticulofenestra hagii and Sphenolithus moriformis species, with paleoecological importance identified in the study region, indicate that in early Miocene times, the basin in which the Lice Formation deposited was meso-eutrophic with excess nutrient input, temperate and generally stable shallow marine conditions.

The Guanpo pegmatite field in the North Qinling orogenic belt (NQB), China, hosts the most abundant LCT pegmatites. However, their emplacement conditions and structural control remain unexplored. In this contribution, we investigated it combining pegmatite orientation measurement with oxygen isotope geothermometry and fluid inclusion study. The orientations of type A1 pegmatites (P_f < σ₂) are predominantly influenced by P- and T-fractures due to simple shearing in Shiziping dextral thrust shear zone during D₂ deformation, whereas type A2 pegmatites (contemporaneous with D₄) are governed by hydraulic fractures aligned with S₀ and S₀₊1 stemming from fluid pressure (P_f <σ₂). Additionally, type B pegmatites (P_f ≤ σ₂) exhibit orientations shaped by en echelon extensional fractures in local ductile shear zones (contemporaneous with D₃). The albite-quartz oxygen isotope geothermometry and microthermometric analysis of fluid inclusions in elbaites from the latest pegmatites (including types B and A2) suggest that the crystallization P-T for late magmatic and hydrothermal stages are 527.5–559.2°C, 320°C, 3.1–3.6 kbar and 2.0 kbar, respectively. Our observations along with previous studies suggest that the genesis of the LCT pegmatites was a long-term, multi-stage event during early Paleozoic orogeny (including the collision stage) of the NQB, and was facilitated by various local fractures.