State Key Laboratory of Geological Processes and Mineral Resources

The East Kunlun Orogen, the northwestern part of the Central China Orogenic Belt, is a long-lived accretionary orogenic belt that records the evolution and eventual destruction of branches of the Tethys Ocean, from the Cambrian to the Triassic. Here we report an Early Paleozoic eclogite belt that extends for $500 km within the East Kunlun Orogen. This belt consists of eclogite blocks, metasedimentary rocks and minor serpentinite blocks, accompanied by ophiolites (530-460 Ma) and concurrent arc volcanic sequences and granitic plutons. Geochemical data show that the eclogites have normal mid-ocean ridge basalt-to ocean island basalt-like compositions. U-Pb dating of metamorphic zircons from eclogites and their surrounding rocks gave peak and retrograde metamorphic ages of 430-410 Ma. Coesite pseudomorphs in garnet, quartz exsolution rods in omphacite and P-T calculations suggest that some eclogites experienced ultrahigh-pressure (UHP) metamorphic conditions at 29-30 kbar and 610-675 C; these could represent oceanic crust subducted to and exhumed from coesite-forming depths (100-120 km). The UHP metamorphic eclogite belt in the East Kunlun Orogen may represent the final closure of the Proto-Tethys Ocean (opening at $580 Ma, subduction initiating at $520 Ma) at $430-410 Ma in the East Kunlun, with the formation of the Pan-North-China Continent in the Early Paleozoic and expansion of the Paleo-Tethys Ocean in the south.

Proper correction of mass-dependent and mass-independent isotopic fractionation is crucial to obtain accurate isotope amount ratios by multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS).

Combining high-efficiency cones with the addition of nitrogen in laser ablation MC-ICP-MS not only enhances the sensitivity and mass bias stability, but also suppresses the non-linear mass fractionation for Nd isotope analyses.

With a 5% NaCl rinse solution, the Li background can be effectively reduced by a factor of 15 to 70.

The Beiya skarn gold deposit is located in the eastern Tethyan orogenic belt in western Yunnan province, China. It is one of the largest gold deposits in China, with significant amounts of silver and base metals. To the end of 2014, the estimated resources are 125 million tonnes (Mt) of ore, grading 2.42 g/t Au, 0.48 wt % Cu, 25.5 wt % Fe, 38.85 g/t Ag, 1.24 wt % Pb, and 0.53 wt % Zn. Skarn alteration and mineralization are related to shoshonitic quartz monzonite porphyries that were emplaced in Triassic carbonates (Beiya Formation). Re-Os dating on molybdenite from a skarn orebody indicates an ore-forming age of 36.82 0.48 Ma, which is consistent with previous dating results of the quartz monzonite porphyries. At least two paragenetic stages of skarn minerals and associated sulfides were recognized, with the early stage typified by garnet pyroxene, magnetite, and calcite, and the late stage characterized by epidote, amphibole, chlorite, quartz, and calcite, containing up to 70% sulfides (pyrite, chalcopyrite, and minor pyrrhotite). The early skarn is dominated by anhydrous minerals, which were replaced by hydrous minerals formed during the late stage. The garnet in the Beiya deposit is andradite rich (Ad<sub>3697</sub>Gr<sub>361</sub>), and pyroxene is relatively diopside rich (Di<sub>891</sub>Hd<sub>789</sub>). This mineral assemblage indicates an oxidized skarn system, similar to other Au-Cu, Fe-bearing skarn deposits around the world. Fluid inclusions from pyroxene indicate precipitation from high-temperature and high- to moderate-salinity fluids (420530C, 11.143.3 wt % NaCl equiv), which probably results from boiling of a moderately saline magmatic fluid. Cooler (180365C) and moderate- to low-salinity fluids (1.616.5 wt % NaCl equiv) were trapped in garnet and quartz and are interpreted to be responsible for gold deposition. Chlorite chemistry indicates ore-forming temperatures between 300 and 340C, in agreement with fluid inclusion data. It appears that gold was transported as chloride complexes under oxidized conditions and was deposited at temperatures of about 300C, when transport of chloride complexes as gold carriers was less efficient.

Abstract Long‐period magnetotelluric (MT) data from project SINOPROBE were acquired and modeled, using three‐dimensional (3D) MT inversion, to study the electrical structure of Ordos Block, a component of the North China Craton. For the first time, a high‐resolution 3D resistivity model of the lithosphere is defined for the region. Contrary to what would be expected for a stable cratonic block, a prominent lithospheric conductive complex is revealed extending from the upper mantle to the mid‐to‐lower crust beneath the northern part of Ordos. Correlating well with results of seismic studies, the evidence from our independent magnetotelluric data supports regional modification of the lithosphere under the north Ordos and lithosphere thinning beneath Hetao Graben. The abnormally conductive structure may result from upwelling of mantle material in mid‐to‐late Mesozoic beneath the northern margin of the Ordos block.

The absolute determination of the Cu isotope ratio in NIST SRM 3114 based on a regression mass bias correction model is performed for the first time with NIST SRM 944 Ga as the calibrant.

The accuracy and precision of Cd isotope measurement at different injecting sample sizes.

A simple and rapid single-step Ca separation method implemented by using a combination of a DGA column and vacuum box.

An <italic>in situ</italic> Zr isotopic analytical method for zircons was developed using LA-MC-ICP-MS to reveal the Zr stable isotope variation in the complex mineral crystallization history.

International audience

High-precision Ca isotopic measurement using a MC-ICP-MS with a dummy bucket.

The current lithospheric root of the South China Block has been partly removed, yet what mechanisms modified the lithospheric structure remain highly controversial. Here we use a new joint seismic inversion algorithm to image tabular high-velocity anomalies at depths of ~90-150 km in the asthenosphere beneath the convergent belt between the Yangtze and Cathaysia blocks that remain weakly connected with the stable Yangtze lithosphere. Based on obtained seismic images and available geochemical data, we interpret these detached fast anomalies as partially destabilized lower lithosphere that initially delaminated at 180-170 Ma and has relaminated to their original position after warming up in the mantle by now. We conclude that delamination is the most plausible mechanism for the lithospheric modification and the formation of a Mesozoic Basin and Range-style magmatic province in South China by triggering adiabatic upwelling of the asthenosphere and consequent lithospheric extension and extensive melting of the overlying crust.

A flexible, easy and highly efficient Cr purification method was developed for high-precision measurement of Cr isotopes by double-spike MC-ICP-MS.

Abstract Gravity surveys in regional geophysical research can be used to estimate the depth of the sediment‐basement interface. In this study, we investigate a novel method using the convolutional neural network (CNN) for depth‐to‐basement inversion directly from gravity data. Based on the Random‐Midpoint‐Displacement method (RMD) and the features of the observed gravity data, we can generate a large set of realistic sediment‐basement interface models. This new method for model generation can significantly reduce the size of the training data sets which is usually considerably large to train a pervasive network. The application on synthetic models shows that the developed CNN inversion is able to capture the detailed features of the sediment‐basement interface for the complex geological model. However, so far, the training set obtained from the proposed method is still continuous and the CNN inversion still cannot effectively recover the models such as abrupt faults. We also successfully applied the developed method and workflow to a field study. The proposed approach opens a new window for estimating the physical contrast interfaces using potential field.

Similar signal intensities can be obtained using Ar instead of He as the carrier gas under high-velocity of the carrier gas on the ablation site or wet plasma conditions in 193 nm ArF excimer LA-ICP-MS analysis.

The Tancheng–Lujiang Fault Zone (TLFZ) can be subdivided into three segments that exhibit sharp contrasts in their deep structures. A deep seismic reflection profile (length ~ 600 km) across the north part of the TLFZ, which provides new constraints on the structural styles of the northern TLFZ, was recently completed by the Chinese Sinoprobe Project. Here, the TLFZ branches into the Yilan–Yitong Fault (YYF) to the west and the Dunhua–Mishan Fault (DMF) to the east. The YYF developed as an internal fault in the Songnen–Zhangguangcai massif, while the DMF serves as the tectonic boundary between the Nadanhada terrane and the Khanka massif. Both faults developed large-scale flower structures, with that of the YYF being negative and that of the DMF being positive with reverse faults. The Moho in the profile is at a depth of 25–39 km and is offset by the faults. The north part of the TLFZ extends into the upper mantle as thin shear zones with the reflectors truncated in the middle/lower crust. This feature differs from most crustal-scale strike-slip faults that distribute over a discrete shear zone in the lower crust, such as the San Andreas Fault.

Abstract The Hetian deposit, located south of the Tarim Basin in Xinjiang, China, is one of the world's largest dolomite‐related nephrite deposits. In the Alamas orebody of the deposit, nephrite occurs as veins or lenses along faults or fissures of the adjacent dolomitic marble. Chemical analyses using electronic microscope probe analysis and X‐ray fluorescence spectroscope were carried out on nephrite and dolomitic marble samples collected from a cross section in Alamas to investigate zonal structure of the orebody. The nephrite in Alamas is predominately composed of tremolite with minor calcite, titanite and phlogopite, and that dolomitic marble is relatively pure with a FeO content less than 0.20 wt. %. Contents of color‐inducing elements, such as Fe, Mn, and Cr, increase gradually as color changes from white through white‐green and then to green, resulting in the formation of color‐distinctive zones. Tremolite grain size increases as color changes from white through white‐green to green. The trend may be consistent with temperature changes from dolomitic marble to granodiorite, which, in turn, suggests that both change in color from white to green and variations of grain size with increasing temperature resulting in formation of the nephrite zonal structure. Both nephrite zonal structure and minor minerals, such as calcite, titanite and phlogopite found in the contact, indicate that this dolomite‐related nephrite orebody is of a metasomatic origin under assumed pressure of 100–200 MPa and temperature &lt;550°C.

Abstract The Tuwu porphyry Cu deposit is located in the northern segment of the Jueluotage metallogenic belt in Eastern Tianshan, on the southern margin of the Central Asian orogenic belt, Xinjiang, northwest China. Tuwu is hosted by diorite porphyry and tonalite porphyry intrusions, which intruded volcanic rocks of the Carboniferous Qi’eshan Group. Four stages (I-IV) of hydrothermal activity have been identified. Chalcopyrite is the dominant ore mineral and mainly occurs in vein stages II (quartz-chalcopyrite-pyrite ± sericite ± bornite ± enargite veins with phyllic halos) and III (quartz-molybdenite-chalcopyrite ± pyrite ± chlorite ± epidote veins). Re-Os dating of molybdenite samples yielded an isochron age of 335.6 ± 4.1 Ma (2σ, mean square of weighted deviates = 0.15, n = 8). Silicon, oxygen, and carbon stable isotope compositions of quartz and calcite provide evidence for predominantly magmatic contributions with a late meteoric water component at Tuwu. Chalcopyrite samples from stages I and III record a narrow range of bulk δ34S values between −3.9 and 0.4‰, whereas pyrite samples from stages I to IV show decreasing δ34S values from 1.7 to 0.2‰. Chalcopyrite has 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios similar to those of porphyry intrusions, and Pb isotope data from sulfide samples display a positive trend transecting the growth curves of crustal lead. The ore-forming components (metals and sulfur) were sourced from a mantle-derived magmatic reservoir with some upper crustal components in a subduction-related arc setting. Plagioclase compositions in the porphyry intrusions are consistent with magmatic H2O contents of ~7 wt %. Copper sulfides in the high-grade phyllic alteration zones at Tuwu are characterized by elevated δ65Cu values consistent with deposits from oxidized and hydrous magmatic-hydrothermal fluids, whereas lower δ65Cu values and low copper grades correspond to the potassic alteration zones. Recognition of copper isotope zonation patterns at Tuwu has potential applications in the exploration of porphyry Cu deposits.

A new method for stable zirconium isotope ratio measurements was achieved based on the combination of a single DGA resin column and the double-spike TIMS technique.