Petrogenesis of highly fractionated S-type granite in the Longling area, southwest China: Implications for tectonic settings and mineralization

Geology, geochemistry and tectonic settings of molybdenum deposits in Southwest China: A review

The Datang Formation black rock series deposited in an inter-platform basin are considered to be one of the main source rocks in Southwest China. However, their depositional conditions and organic matter enrichment in such a setting are not well understood. In this study, geochemical characteristics of total organic carbon (TOC), major, trace and rare earth elements (REEs) of thirty black rock series samples from a newly-cut roadside outcrop (Zhenning section) in Southern Guizhou, Southwest China are systematically investigated to examine provenance, paleoredox conditions, paleoclimate, paleoproductivity and sedimentary rate, and further to explore their influence on organic matter enrichment. Results show that TOC contents of the investigated samples range from 0.90% to 2.83%, with an average of 1.45%, with TOC variations being in accord with the stratigraphic cyclicity. These data also indicate that the target black rock series were deposited in a combination of continental island arc and active continental margin tectonic setting that exhibited moderate weathering, oxic/dysoxic oxygen levels, hot and arid to semiarid climate, and a higher sedimentary rate. Multiple paleoredox indicators (e.g., Ni/Co, V/Cr, U/Th and V/(V + Ni) ratios), together with slightly negative Ce anomalies and EFU-EFMo covariation, totally suggest an oxic/dysoxic water environment, which is usually considered unfavorable for organic matter preservation. Average (La/Yb)N ratios (1.41) reflect a higher sedimentary rate, resulting in shortening the exposure time of organic matter in the degradation region of aerobic bacteria under oxic/dysoxic conditions. Of the three factors that could affect organic matter enrichment, including paleoproductivity, paleoredox conditions and sedimentary rate, the relatively high paleoproductivity indicated by the relatively high TOC contents appears to be the dominant factor. In contrast, the other two factors, i.e., paleoredox conditions and the rate of sedimentation play relatively less significant roles. Based on these factors, an enrichment model of organic matter for the black rock series in Southern Guizhou Depression is established. These findings also contribute to constraining the sedimentary environment in such a setting and further deepen our understanding of the potential shale gas resources of the Southern Guizhou Province.

Climate and tectonic-driven deposition of sandwiched continental shale units: New insights from petrology, geochemistry, and integrated provenance analyses (the western Sichuan subsiding Basin, Southwest China)

The genetic relationship between the large Guanfang W deposit and granitic intrusions, in Yunnan Province, southwest China: Evidence from U[sbnd]Pb and Re[sbnd]Os geochronology and Pb and Sr isotopic characteristics

Understanding the tectonic evolution of the Yangtze Block during the late Mesoproterozoic and Neoproterozoic is crucial for gaining insights into the assembly and breakup of the Rodinia supercontinent. Here, we present an integrated geochronological, whole-rock geochemical, and Nd-Hf isotopic study of the late Mesoproterozoic Shuiqiaosi (ca. 1104−1045 Ma) and mid-Neoproterozoic Yaoxingcun (ca. 768 Ma) granites of the Xujie area, central Yunnan Province, China. Our investigations focus on their petrogenesis and tectonic setting, aiming to constrain the evolution of the supercontinent. The Shuiqiaosi granites are A2-type granites, with positive whole-rock εNd(t) (0.0−1.5) and zircon εHf(t) (3.9−17.5) values, indicating derivation from the partial melting of juvenile crustal rocks. In contrast, the Yaoxingcun granites exhibit an S-type affinity, with negative whole-rock εNd(t) (−5.8 to −4.6) and variable zircon εHf(t) (−3.0 to +8.7) values, suggesting origination from the partial melting of Al-rich, metasedimentary sources with some involvement of mantle materials. Combined with results from previous studies in the western Yangtze Block, we propose that the Shuiqiaosi A-type granites and Yaoxingcun S-type granites—both of which exhibit high-temperature features—are related to the assembly and breakup of the Rodinia supercontinent, respectively. Based on the ultramafic-mafic and felsic rocks examined in previous studies, we further suggest that the western margin of the Yangtze Block was situated in a subduction-related extensional setting during ca. 1.1−1.0 Ga, which marked the assembly of Rodinia. The breakup of Rodinia began at ca. 0.83 Ga, driven by a mantle plume, with specific regions, including the study area, experiencing slab tearing or breakoff in an oceanic subduction environment during ca. 0.80−0.75 Ga.

The Phan Si Pan zone in northwest Vietnam is an important tectonic unit for understanding the geological evolution of the southeast Asian Block. Numerous late Permian A‐type granites outcrop in this zone. In this study, new geochemical and geochronological data derived from the Muong Hum alkaline granitic pluton in the Phan Si Pan zone were investigated for its petrogenesis and tectonic setting. Zircon U–Pb analyses of three samples yielded 206Pb/238U ages of (251.1 ±3.5) Ma, (251.2 ±3.8) Ma, and (253.9 ±1.5) Ma, respectively, coinciding with the ages of the acid member of magma from Emeishan large igneous province, southwest China. The Muong Hum granite has 10 000 × Ga/Al and A/CNK values of 4.70–4.93 and 0.87–0.90, respectively, as well as negative Eu anomalies. It shows significant depletion of Ba, Sr, Ti, and P, similar to features of A‐type granite. Zircons have positive εHf(t) values (+1.9 to +8.6) and Hf model ages (TDM1) of 595–846 Ma, originating a mantle source. Compared with the Panzhihua A‐type granite of the southwest China domain and other A‐type plutons of the Phan Si Pan zone, including Ye Yen Sun, Phu Sa Phin, Nam Xe, Tam Duong Phan Si Pan, and Taihe, the geochemical characteristics and zircon Hf isotopic compositions of the Muong Hum granite demonstrate an affinity of mantle magma. It is believed that the Phan Si Pan zone is an important part of Emeishan large igneous province. It was reworked by the Cenozoic Aillaoshan‐Red River shear fault to its present location.

Fluid injection activities related to hydraulic fracturing (HF) and salt mining may induce moderate earthquakes. In the Changning area in southwest China, the Ms 6.0 earthquake on 17 June 2019 is the largest and the most damaging event ever recorded in this region. This earthquake occurred in the Changning anticline, which hosts multiple active faults and industrial production activities, raising an extensive controversy on the cause of the earthquake. Beyond seismogenic faults, a detailed 3D velocity structure of the source region is missing. Here, we applied an improved ambient noise tomography method to seismic data recorded by a portable dense seismic array to reveal the characteristic of 3D shear-wave velocity (VS) structure with high resolution in the Changning region. Our VS structure model provides some new observational evidence favoring that the Ms 6.0 Changning earthquake and the related seismicity in Shangluo shale gas field were, respectively, induced by fluid injection for salt mining and hydraulic fracturing. Moreover, it is suggested that the shallow segment of the pre-existing thrust faults were reactivated by fluid injection. This result provides some implications of VS structure of the induced-seismicity source region and warn us to pay more attention to the seismic risk assessment for such areas that have both similar industrial operation intensity and tectonic settings.

Characteristic granites of the East Tethyan Tectonic Domain (ETTD) are primarily exposed along the Himalayan orogenic belt and Gangdese batholith in the north, extend from western Yunnan in the centre, and through the Burma batholith to Peninsular Malaysia in the south. Western Yunnan is an important part of the ETTD magmatic arc, featuring characteristic granites that mainly developed between the Jurassic and Paleogene. Nonetheless, compared to other regions of the ETTD, Miocene magmatism has been poorly documented in western Yunnan. The Xiaomasa granite occurs in the Ximeng area of western Yunnan. In this study, we present U–Pb ages, and Hf–O isotope data for zircon crystals from the Xiaomasa granite pluton. Laser Ablation–Multicollector–Inductively Coupled Plasma–Mass Spectrometry (LA–MC–ICP–MS) zircon U–Pb dating yields precise emplacement ages of 15.8–16.1 Ma for the Xiaomasa granite, indicating that Miocene granitic magmatism occurred in western Yunnan. Zircons from the Xiaomasa granite have negative εHf(t) values ranging from −6.6 to −11.6, relatively high δ18O values (6.8%–10.2‰), and two‐stage Hf isotopic model ages (1.51–1.83 Ga). Zircon Hf–O isotopic characteristics indicate that the Xiaomasa granite was mainly derived from partial melting of ancient continental crust. The Ximeng Precambrian metamorphic basement is a probable material source for the granite. The Xiaomasa granite was probably produced by partial melting of the thickened Ximeng ancient metamorphic basement under a reduced pressure environment, reflecting a cumulative effect of the escape of Sundaland caused by the dynamics of the continuous India–Asia collision.

The Karakoram Highway links north Pakistan with southwest China. It passes through unique geomorphological, geological and tectonic setting. This study focused 200-km-long section of the highway starting from Besham until Chilas. Landslides are frequent and are mostly triggered by torrential rain during Monsoon and Westerlies, leading to highway blockade. Rockfall and debris flow are prime mode of slope failures. Regional to site-specific approach was implemented to assess risk associated with these two modes. Remote sensing-based techniques were used to identify potential hazardous sites, which were further investigated for risk assessment. Modified Pierson’s rockfall hazard rating system (RHRS) rated potential rockfalls, whereas semi-quantitative technique was employed to assess debris flows. Normalized scores of each site shaped the final map, further classified into four zones: very high, high, intermediate and low risk.

A synthesis of mineralization styles with an integrated genetic model of carbonatite-syenite-hosted REE deposits in the Cenozoic Mianning-Dechang REE metallogenic belt, the eastern Tibetan Plateau, southwestern China

Permian of West Yunnan, Southwest China: a biostratigraphic synthesis

<p>Early Mesozoic development of Southeast Asia involved oceanic subduction, closure, accretion and collision of discrete terranes rifted from Gondwana. South China, as an important continental terrane, is bound to the north by the Qinling-Dabie collisional orogenic belt, to the south by the Indochina Block, and to the east by the Pacific Plate. The role of continental collision and subduction during the Early Mesozoic development of South China has sparked the interest of geologists worldwide and stimulated considerable research. The Triassic tectonic history of the southwestern South China Block is marked by the Indosinian orogeny that records amalgamation of the Indochina and South China blocks during the late Permian to Triassic as a result of closure of the eastern branch of the Paleo-Tethys Ocean. In South China, there is widespread granitic magmatism, metamorphism and deformation. The closure of eastern Paleo-Tethys Ocean and subsequent collision between the South China block and Indochina Block has caused the collision zone metamorphism and formation of granites during the Permo-Triassic, with the Song Ma fault zone as the collision boundary. The Indosinian magmatism in the Pingxiang region was the magmatic products in this period. We report the new results of bulk-rock major and trace element, Nd, Hf isotopic compositions and zircon U–Pb dating of granites and rhyolites in the Pingxiang region in Guangxi Province, Southwest China, to decipher their petrogenesis and tectonic settings. The granites and rhyolitics in the Pingxiang area have low Mg<sup>#</sup> values (11.1–36.7), low Nb/Ta ratios (9.26–13.74) exhibiting a both affinity from S-type to I-type granaite. The isotopic features of these rocks show negative ε<sub>Hf</sub>(t) with the values ranging from -9.89 to -6.09, negative ε<sub>Nd</sub>(t) values ranging from -12.89 to -12.02 and T<sub>2DM</sub> values of 1.8–3.3 Ga, suggesting that the Pingxiang granites and rhyolites was derived from partial melting of paleoproterozoic crust rocks. The granites yielded <sup>206</sup>Pb/<sup>238</sup>U ages ranging from 243 to 241 Ma, and the rhyolites yielded <sup>206</sup>Pb/<sup>238</sup>U ages ranging from 247 to 245 Ma, which are both within the age range of the subduction to collision. Combine the regional geology, we suggest these granitoids and rhyolites were formed by the partial melting of crustal rocks during a transition from subduction to post-collisional environment with closure of Paleo-Tethys Ocean between the South China block and Indochina Block.</p><p>This study was financially supported by Guangxi Natural Science Foundation for Distinguished Young Scholars (2018GXNSFFA281009) and the Fifth Bagui Scholar Innovation Project of Guangxi Province (to XU Ji-feng).</p>

A tale of two vein types: Bed-parallel fibrous versus blocky filled fractures in organic-rich shales and their overpressured hydrocarbon fluids

Stratigraphy and depositional evolution of the terminal Ediacaran platform in the central to northern Sichuan Basin, Southwest China

Genesis of the Dachang Sn-polymetallic and Baoshan Cu ore deposits, and formation of a Cretaceous Sn-Cu ore belt from southwest China to western Myanmar