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Understanding the tectonic evolution of the Proto-Tethys Ocean is important for exploring the initial assembly of the Gondwana supercontinent. The closure of the Proto-Tethys Ocean represents the end of convergence along the northern edge of Eastern Gondwana. However, the timing and processes of the closing of the ocean have different interpretations. This work focuses on the Early Paleozoic granitic rocks in the Baoshan Block, SW China to constrain the tectonic evolution of the Proto-Tethys Ocean. Zircons from the Pinghe and Zhen'an granitic plutons yield concordant U–Pb ages from 489.8 to 467.7 Ma. The bulk-rock geochemical features suggest that these samples are high-K calc-alkaline, S-type granites enriched in light rare earth elements and depleted in heavy rare earth elements. With obvious negative Eu anomalies and high K2O/Na2O ratios (1.01–2.57), they are enriched in large ion lithophile elements and depleted in high field strength elements. These rocks were therefore derived from partial crustal melting associated with subduction of the converging plate. Previous studies on the Changning–Menglian suture zone have suggested that the Early Paleozoic magmatic activity in the Baoshan Block was related to the westward subduction of the Proto-Tethys Ocean. Combined with the Early Paleozoic subduction-related magmatic activity to the east, it is therefore suggested that the Changning–Menglian Ocean experienced bidirectional subduction. [ABSTRACT FROM AUTHOR]

Three parallel east–west-trending shear zones are components of the polyphase shear zones in the eastern Jiangnan belt. The meso- and microstructural characteristics and the estimates of deformation temperatures, vorticities and geochronology of these shear zones provide significant information regarding the tectonic evolution of the South China Block (SCB) during the early Paleozoic. Most shear sense indicators (e.g. asymmetric folds, S-C fabrics and rotating porphyroclasts) reveal that the kinematics were characterized by east–west dextral shear. Finite strain measurements indicate an oblate strain ellipsoid shape with S-type and SL-type tectonites. The rotated rigid porphyroclasts and Mohr circle methods yield vorticity (Wk) values of 0.58–0.80 and 0.66–0.89, respectively, indicating that the flow was generally shear-dominated with almost equal proportions of simple and pure shear. Both mineral deformation thermometers and quartz c-axis fabrics indicate that the deformation occurred at medium temperature conditions of 400–550°C. Combined with our new age and regional geological data, the east–west-trending shear zones might represent an increment of deformation during the last period of the early Paleozoic orogeny in the SCB. [ABSTRACT FROM AUTHOR]

Yanshanian granitoids (178–120 Ma, Jurassic to Cretaceous), which intruded into Precambrian crystalline base- ment and Paleozoic strata, are widely distributed at the junction of the Zhejiang, Jiangxi and Anhui provinces (the ZGW region) in southern China, along with coeval volcanic rocks. This paper summarizes zircon U–Pb age data, geochemi- cal characteristics and Sr-Nd isotopic characteristics of the Late Jurassic to Middle Cretaceous granitoids and volcanic rocks from the ZGW region. We demonstrate that members of the Shiling rhyolite formed during two different periods of magmatic activity at 154.7 ± 2.5 Ma and 139–134 Ma and that igneous rocks from the different periods have distinct geochemical characteristics. Jurassic igneous rocks of the ZGW region have relatively low SiO2and high Al2O3contents, and show enrichment of large ion lithophile elements (LILEs) and depletion of high field strength elements (HFSEs). They are strongly enriched in LREE and depleted in HREEs with weakly negative Eu anomalies and strongly negative Nb, Ta anomalies. Rb and Y concentrations follow the trends of I-type and S-type granites. By contrast, Cretaceous igneous rocks of this region are characterized by high SiO2and low Al2O3contents with negative Eu anomalies. They have typical wing- shaped rare earth element (REE) distribution patterns and show enrichment of Rb, Th, U, Nb, Ta and depletion of Ba, Sr, P and Ti. They have affinity to A-type peraluminous granites or highly-fractionated felsic rocks. Overall, the igneous rocks evolved from high-Sr low-Yb to low-Sr high-Yb, which might reflect the evolution of the tectonic setting from subduction to lithospheric extension/thinning, i. e., a transition from a continental margin subduction setting during the Late Jurassic to a within-plate extensional setting during the Early Cretaceous, at c. 142 ± 3 Ma. The repeated alternation between lava extrusion and extension and extensional fault kinematics in the late Mesozoic is related to the changes of direction and rate of plate movement of the Izanagi and Pacific plates.

Abstract: The dating of the uplift onset of the Huangshan pluton in the southern part of Anhui Province associated with the collision between paleo-Pacific Block and the Eurasian Block is a fundamental issue to better understand the uplift mechanisms and the regional tectonic evolution. χ 2 values of seven zircon fission track (ZFT) samples collected from the south part of the Huangshan pluton were all <5%. Based on the grain ages of four typical ZFT samples, three thermal overprints ranging in 113–123, 72–95 and 49–66 Ma were distinguished respectively using the binomial peak-fitting method in accordance with the tectonic thermal events after south China shifted into circum-Pacific tectonic region. Apatite fission track (AFT) study of the Huangshan pluton shows ages lie between 15±3 and 56±6 Ma with all χ 2 values >5%, and all are significantly younger than their host rock formation ages, indicating that the samples have experienced post-formation thermal history. Based on the AFT results and topography characteristics in the Huangshan pluton, three zones with different denudation intensities caused by the differential uplift of the fault blocks were recognized in this paper, indicating that denudation was driven by the increase in elevation significantly. Modeling of the AFT data shows that the earlier cooling phase took place in the early Cenozoic and involved 3.3, 3.8 and 6.0°C/Ma of cooling rates equivalent to the exhumation rates of 90, 104 and 167 m/Ma in different fault blocks. The last phase of cooling took place from ∼10 Ma with average cooling rate of ∼5.6°C/Ma, equivalent to average denudation rates of ∼156 m/Ma. The fission track results imply that the regional compression field plays an important role for the differential exhumation between individual fault blocks of the Huangshan pluton.

In order to get rid of health hazard of asbestos fiber, a new kind of non-asbestos fiber reinforce composite by beater-addition process, which is used for sealing and gasket, has been developed to replace traditional asbestos gasket materials. The mechanical properties of the new composite were tested, and the performance between it and asbestos sheet paper were contrasted. Results show that the density, cross direction tensile strength, machine direction tensile strength and ignition loss at temperature of 300°C of the new composite are 1.19g/cm3, 2.62MPa, 3.15MPa and 15.61% respectively, while the performances of asbestos paper produced under the same condition are 1.26g/cm3, 2.87MPa, 3.24MPa and 12.03% respectively. Excellent performance, low cost and simple manufacture process of the new composite make it is possible to substitute traditional asbestos paper and apply widely.