Crustal deformation occurred widely in the Yanshan tectonic belt, north of the North China Craton, and its time and mechanism remain as open problems. On the basis of new structural data and 40Ar-39Ar dating on hornblende and biotite from the rocks in the belt, a dynamic link between the deformation and plate interaction is established. Abundant structures in the Fengning-Longhua fault zone indicate that it is a transpressional fault zone including both strike-slip (dextral) and compressional (south-directed) components and is kinematically conformable to the Huade-Chifeng fault zone in the Neimeng Uplift and to the Pingquan-Gubeikou and Miyun-Xifengkou-Jinxi transpressional fault zones in the Yanshan fold and thrust belt, suggesting coupled deformation in the overall Yanshan tectonic belt during the Late Permian–Early Triassic. This phase of deformation coincides well in age and in kinematics with the Late Permian collision between the North China Block and Mongolia arc terranes, implying that the most intense Late Permian–Early Triassic transpressional deformation in the Yanshan belt was developed as a result of the convergence of the Central Asian Orogenic Belt.
The Qingtonggou deposit is the largest Hg-Sb deposit in the Qinling orogenic belt, but the deposit genesis remains unclear. Fluid inclusion study indicates that the homogenization temperature range from 139.9 °C to 217 °C and the salinities vary from 0.7 to 2.1 wt% (NaCleq). The δ13C value in ore-stage calcite is from-7.6 ‰ to −7.1 ‰, and the δ18OSMOW value is between 13.6 ‰ and 15.3 ‰. The δ18OV-SMOW value in hydrothermal quartz is from 21.5 ‰ to 24.8 ‰, and the δD value is between −138 ‰ to −99 ‰. The δ34SV-CDT value range from 4 ‰ to 11.6 ‰, the 206Pb/204Pb values range from 18.0351 to 18.5080, the 207Pb/204Pb values range from 15.6390 to 15.6672, and the 208Pb/204Pb values range from 38.1586 to 38.4128. The hydrothermal calcite Sm-Nd isochron age for ore-stage calcite is 98.02 ± 0.42 Ma. The Hg-Sb mineralization is controlled by tectonic space formed by the left strike-slip fault, the ore-forming fluid has the characteristics of medium–low temperature, low density, and supergene mineralization, the ore-forming fluid comes from meteoric water and formation water, the ore-forming material comes from the stratum and basement of Yaolinghe group and Lower Cambrian, the Hg-Sb mineralization occurred at early Late Cretaceous. The complete metallogenic process is that the Yaolinghe Group and Lower Cambrian in this area are the source areas for Hg-Sb mineralization, the subsequent high background values Hg and Sb strata which received the denudation deposit of the source bed all contributed ore-forming materials, with the Qinling collision orogeny and extrusion in the Indosinian period and the continuous contraction of the Paleozoic basin, porous meteoric water and formation water extracted the ore-forming materials in source bed, formed ore-forming fluids, during the strike-slip process in intracontinental environment, deep and large faults provide a channel for the upward discharge of ore-forming fluids, with the decrease of fluid temperature, sulfide precipitation occurs in secondary fracture.
ABSTRACT Yunfuconcha bimenta, a new genus and species of bivalve from the Ordovician of western Guangdong, China, is described. Its unusual hinge consists of a palaeotaxodont-like dentition anteriorly and a heteroconch-like dentition posteriorly. The posterior hinge area exhibits a remarkable, broad, deeply inset, concave ligament area, which is reminiscent of the ventrally expanded ligament of some Recent and fossil lucinoids and the triangular resilifer in late Palaeozoic crassatellid heteroconchs. Lamellar posterior teeth and sockets complete the posterior dentition. The unusual combination of features, normally associated with either the Order Cardiolariatida (used here in place of Order ‘Afghanodesmatida’—the type genus Afghanodesma, is known only from wax impressions rendering it and its nominal higher taxa invalid) or various crassatelloids and lucinoids, make systematic placement of Yunfuconcha n. gen. uncertain below subclass rank. In view of presumed derived heteroconch-like characters of the posterior hinge, we place Yunfuconcha n. gen. in the Subclass Autobranchia, possibly as a stem archiheterodont or a stem heteroconch.
As a necessary micronutrient for algal growth, iron (Fe) has importanteffects on the physiological metabolism and enzymatic reactions of algae. There arevarious forms of iron in nature, and soluble iron exists mainly in two forms: Fe2+ andFe3+. In this study, a series of experiments were designed to compare the effects ofFe2+ and Fe3+ on the growth of natural mixed algal colonies and single-species coloniesof Scenedesmus quadricauda. The results show that Fe2+ and Fe3+ have different effectson the reproductive processes of these two algal populations. The optimal growthconcentration of both Fe2+ and Fe3+ for natural mixed algae is 0.3 mg/L; at that concentration,algal biomass reaches its peak, with values of 1.74 × 106 cells/L and 6.82× 105 cells/L for the two iron forms, respectively. At the same time, the average growthrates of these algae also reach their maximum, which are 0.3620 d–1 and 0.3398 d–1,respectively. The optimal growth concentrations of Fe2+ and Fe3+ for S. quadricaudaare about 0.4 mg/L. We propose that Fe2+ exhibits higher biological time-effectivenessthan Fe3+ for algal reproduction, and while Fe2+ and Fe3+ exhibit similar facilitation in thegrowth of both natural mixed algae and S. quadricauda, differences exist between theirfacilitation effects. The results of the study further suggest that problems involving ironuptake priority and inter-specific competition could arise during the reproductive processin mixed algal colonies.
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