Solid Earth Sciences最新文献

The Wujiaping Sn deposit is located at the northern Dayishan ore field, South China, whose ore veins are mainly hosted in the Dayishan pluton. LA–ICP–MS zircon U–Pb dating for the medium-fine grained- and medium-coarse grained-biotite monzogranite of Dayishan pluton yields emplacement ages of 154.5 ± 1.6 Ma (MSWD = 2.0) and 155.5 ± 0.5 Ma (MSWD = 1.9), respectively, which are consistent with the muscovite ⁴⁰Ar-³⁹Ar plateau age of 150.4 ± 0.9 Ma for the quartz vein type ore veins. It is indicated that the Sn mineralization in the Wujiaping deposit is related to the Late Jurassic granitic magmatism. These granites show the geochemical features of highly fractionated S-type granite: 1) low Zr + Nb + Ce + Y contents (<209 ppm); 2) high A/CNK ratios (>1.1); 3) low crystallization temperature (mean = 688 °C); 4) high Rb/Sr ratios (mostly > 48); 5) high differentiation index (DI > 90); and 6) low CaO, P₂O₅, Sr, and Eu contents. Whole rocks isotopes show that these granites shows variable initial ⁸⁷Sr/⁸⁶Sr ratios (0.70251–0.71208), negative ε_Nd(t) values (−7.94–5.62) and old two stage Nd model ages of 1491–1563 Ma. LA–MC–ICP–MS zircon Lu–Hf isotopes show that the medium-fine-grained monzogranite have positive ε_Hf(t) values of 0.37–8.5 and two stage Hf model ages of 662–1180 Ma, whereas the medium-coarse grained-biotite monzogranite have negative ε_Hf(t) values of −6.42–3.55 and two stage Hf model ages of 1431–1599 Ma. It is proposed of that these granites are originated from melts mixed by crustal- and mantle-constituents and are formed in an extensional setting caused by the subduction of the Palaeo-pacific plate. The low LogfO₂ values calculated through zircons (−21.2–13.1) and high F contents (3630–5120 ppm) indicate the granites derived from reduced and F-rich melts. Therefore, the reduced melt is highly fractionated and enriched in Sn and F, resulting in the large scale Sn mineralization in the Dayishan ore field.

How the Dabie Orogenic Belt (DOB) and the Tan-Lu Fault Zone (TLFZ) transformed during the early Indosinian period is the key to reveal the convergence process between the North China Block (NCB) and the South China Block (SCB). Tongcheng area in the eastern margin of northern DOB is the tectonic node that connects the WNW-trending DOB and the NE-trending TLFZ. The typical ENE-NE-trending gneiss belts penetrably developed in Tongcheng area provide an ideal natural lab to decipher the transformation between the DOB and the TLFZ. Here we conduct an integrated structural and geochronological research on the ENE-NE-trending gneiss. Zircon U–Pb dating on the ENE-NE-trending gneiss yielded metamorphic ages ranging from 255 ± 9 Ma to 203 ± 10 Ma. The weakly deformed veins which intruded the surrounding gneiss yielded two groups of ages, 825 ± 29 Ma to 713 ± 7 Ma and 125 ± 2.6 Ma (weighted mean age), which indicate the protolith age of surrounding rocks and the intrusive timing of the vein, respectively. Integrated structural, microstructural and kinematic analysis indicate that no lateral structural superposed on the gneiss or veins. Therefore, it can be speculated that the deformation and metamorphism of the gneiss should simultaneously formed during the Early Triassic, as a result of continuous tearing from the DOB to the northeastern Sulu Orogenic Belt (SOB) during subduction of the Yangtze block beneath the NCB. Formation of the tearing belts, i.e., the ENE-NE-trending gneiss belts, accomplished the tectonic transformation between the DOB and the TLFZ. They could be regarded as an embryonic form of the TLFZ, which are also apparently different from the TLFZ by characteristics of non-strike slipping.

A suite of highly fractionated granites and associated pegmatite, were revealed through drill hole in the Anqing ore-cluster region in the Lower Yangtze River Belt (MLRB), Eastern China, for the first time. The pegmatite has abundant tourmaline. This discovery provides new clues for the prospection of boron and rare metals in this region.

The Yangzhuang iron deposit is a Kiruna-type iron oxide-apatite (IOA) deposit within the Ningwu mining district of the Middle and Lower Yangtze River Metallogenic Belt (MLYRMB), China. This study applies a numerical modeling approach to identify the key processes associated with the formation of the deposit that cannot be easily identified using traditional analytical approaches, including the duration of the mineralizing process and the genesis of iron orebodies within intrusions associated with the deposit. This approach highlights the practical value of numerical modeling in quantitatively analyzing mineralizing processes during the formation of mineral deposits and assesses how these methods can be used in future geological research. Our numerical model links heat transfer, pressure, fluid flow, chemical reactions, and the movement of ore-forming material. Results show that temperature anomaly and structure (occurrence of the contact of intrusion and the Triassic Xujiashan group) are two key factors controlling the formation of the Yangzhuang deposit. This modeling also indicates that the formation of the Yangzhuang deposit only took some 8000 years, a reaction that is likely to be controlled by temperature and diffusion rates within the system. The dynamic changes of temperature and the distribution of mineralization also indicate that the orebodies located inside the intrusions most likely formed after magma ascent rather than representing blocks of existing mineralization that descended into the magma as a result of stoping or other similar processes. All these data form the basis for future research into the forming processes of Kiruna-type IOA systems as well as magmatic–hydrothermal systems more broadly, including providing useful insights for future exploration for these systems. The simulation approach used in this study has several limitations, such as oversimplified chemical reactions, uncertainty of pre-metallogenic conditions and limitation of 2D model. Future development into both theories and methods will definitely improve the practical significance of numerical simulation of ore-forming processes and provide quantitative results for more geological issues.

Tuff of Middle Permian as a record of volcanic activity are widely distributed in the northern hemisphere, such as South China, but origin of the tuff bed remains unclear. Stratigraphy, geochronology, geochemistry, and zircon Hf isotopic composition of the tuff layers from Gufeng Formation in Chaohu region, South China, are systemically investigated to reveal the origin of the tuff. The stratigraphical investigation and geochronological dating reveal that zircon U–Pb age of 271.6 ± 3.1 Ma for lower tuff layer is identical to the formation age (272 Ma) of the bottom boundary in the Gufeng Formation, while the zircon U–Pb age of 263.6 ± 3.8 Ma for upper tuff layer represents the boundary age between the lower and upper Gufeng Formation. The tuff with a lot of clastic materials has high Th/Ce (0.18–0.84) and Th/La (0.29–1.23) ratios, enrichment in LREE, Th, U and Hf, and depletion in Ba, Nb and Sr, with obviously negative Eu anomalies (δEu = 0.41–0.58). Compared with the lower tuff layer, the upper tuff layer has higher zircon εHf (t) values (−5.65 to 10.2) and lg fO₂ values (−14.6 to −7.42). The distinctly chemical and isotopic results indicate that the intermediate-felsic tuff in the Chaohu region were originated from more crustal materials in early stage of the Gufeng Formation and increased juvenile crustal materials and higher oxygen fugacity in late stage of the Gufeng Formation.

Two newly discovered Mesozoic Group II kimberlites in the southeastern margin of North China Craton show extremely high ΣREE contents (ranging from 1046 to 1869 ppm), which also higher than the nearby Weishan carbonatite and other REE-bearing rocks in China. We proposed that the possible of a new type of REE-deposit, and there is a wide range of potential prospecting area of the REE deposit in the southeast margin of NCC.

The Shangjiazhuang Mo deposit is located in the east of Shandong Peninsula, which is tectonically the eastern extends of the Dabie-Sulu orogenic belt. The ore bodies occur in the Early Cretaceous Yashan porphyritic granodiorite, which are stratiform, vein-like and lentoid. The orebodies are controlled by the fractures with NW direction, and have similar orientations, with strike of 337°–344° and dips of 20°–26° to the northeast. The potassic alteration, biotitization, silicification, sericitization, chloritization, and carbonatization are developed in the country rock. According to the relationship of mineral symbiotic assemblage and the cutting relationship of the hydrothermal veins, the hydrothermal metallogenic period of Shangjiazhuang Mo deposit can be divided into three stages: quartz-molybdenite (early stage), quartz-chalcopyrite and molybdenite (middle stage) and quartz-pyrite (late stage). We studied S–H–O isotopes, fluid inclusions and mineralization age of the Shangjiazhuang Mo deposit, aiming to clarify the genesis mechanism for the Mo deposits in the eastern Jiaodong Peninsula. The δ³⁴S value of molybdenite and chalcopyrite in the main metallogenic stage range from 4.5‰ to 5.0‰, which is consistent with magmatic sulfur. The δ¹⁸O_H2O valve decrease gradually from the early metallogenic stage (4.5‰–5.0‰) to the late metallogenic stage (0.39‰–1.48‰), indicating that the ore-forming fluids were mainly magmatic water at the early stage and a mixture of meteoric and magmatic water at the late stage. The ore-forming fluids evolved from moderate temperature, CO₂-rich and high salinity at the early stage to low temperature, CO₂-poor with nearly constant salinity in the late stage. Different types of inclusions with similar temperature and different salinity coexist in the main metallogenic period, indicating that as temperature drops, fluids in the system were either immiscible or boiling, leading to CO₂ escape, and finally leads to the precipitation and enrichment of ore-forming elements.

We report systematical zircon U–Pb datings, Hf isotopic data, major and trace element date on the Zhangshiying (ZSY) and the Taishanmiao (TSM) two plutons at the southern margin of the North China Craton (NCC), in order to investigate their petrogenesis and geological evolution. LA-ICP-MS U–Pb zircon of the ZSY and TSM granites dating yield a weighted mean ²⁰⁶Pb/²³⁸U age of 122.8 ± 1.5 Ma and 112.1 ± 3.2 Ma. The ZSY quartz syenite enriched in SiO₂ (65.59–68.1 wt.%), Al₂O₃ (15.39–15.64 wt.%), high Sr (468–666 ppm), Sr/Y (35–45), (La/Yb)_N (20.1–22.1) ratios, low Y(13.1–16.6 ppm), Yb (1.46–1.77 ppm), depleted in Nb, Ta, P, Ti, Mg, Y and negligible Eu anomalies, which suggesting that the quartz syenite are similar to adakitic rocks. Zircons from this pluton give ε_Hf(t) values from −17.6 to −5.7 with an average of −15.2, and their T_DM2 ages (1.29–1.91 Ga) are much younger than the basement rocks of the south margin of the NCC, which indicate that the ZSY quartz syenite were generated by partial melting of thickened lower crust with minor involvement of mantle-derived materials. The TSM pluton has characteristic of A-type granite, such as, high SiO₂ (69.7–71.87 wt.%), total alkalis (Na₂O + K₂O = 8.5 to 9.41 wt.%), HFSE (Zr, Nb, Ga, Y), low CaO (0.27–1.25 wt.%), Ba, Sr and Eu. Their ε_Hf(T) values ranges from −12.4 to −1.6 with an average of −7.6 and T_DM2 ranges from 1.10 to 1.63 Ga with an average of 1.38 Ma. We propose that the TSM granites results from partial melting of tonalitic crustal sources with a plagioclase-rich residual at high temperatures and low pressure. Materials input from the mantle also is involved for the higher ε_Hf(t) values than tonalitic crustal at the southern margin of NCC and high temperatures. Our results suggested that the thickened LCC at the south margin of the NCC is still existence before the intrusive of the ZSY adakitic rocks (∼123 Ma). During the intrusive of the TSM granites (∼112 Ma) it turns to extensional environment. This extensional event reflects the background of lithospheric thinning and decratonization of NCC.