Zircon U-Pb SHRIMP ages of high-pressure granulite in Yushugou ophiolitic terrane in southern Tianshan and their tectonic implications

Zircons from two high-pressure granulite samples from the Yushugou ophiolitic terrane, southern Tian shan have been investigated by cathodoluminescence, LA ICPMS and ion microprobe (SHRIMP) for their internal textures, trace elemental compositions and in situ dating. The weighted mean ages of these two samples are 392±7 and 390±11 Ma, respectively, representing the granulite-facies meta morphic age of the ophiolitic terrane, and indicating that the southern Tianshan ocean initiated its northward subduction since the early Devonian.     

Multi-stage evolution of gneiss from North Dabie： evidence from zircon U-Pb chronology

TTG gneiss is a common rock to outcrop in the northern part of the Dabie orogen, a few of which are closely associated with eclogites that experienced the Triassic ultrahigh pressure metamorphism. Although they were thermally metamorphosed by a large-scale magma activity in this region at the Early Cretaceous, it is unclear whether or not they are also affected by the Triassic metamorphism during continental subduction and exhumation. In order to resolve this issue, SHRIMP zircon U-Pb dating was carried out for the host gneiss of eclogites in North Dabie. The results show that cores from the gneiss have an age of 746~.31 Ma, consistent with the protolith ages of granitic gneisses in the Dabie orogen. Zircon overgrowing with different U and Th concentrations give concordant ages of 212~21 and 120~11 Ma, respectively. Th/U ratios of overgrown zircons are both lower than 0.1, suggesting a metamorphic genesis. The present resuits suggest that the gneiss in North Dabie has the similar protolith ages of Neoproterozoic to those granitic gneisses elsewhere in the Dabie orogen, and experienced not only the Triassic metamorphism but also the thermal metamorphism due to the Early Cretaceous magmatism. This provides an important insight into the geodynamic evolution of gneissic rocks in the Dabie orogen.     

苏北超高压变质带榴辉岩型金红石矿床及其成因

在苏鲁超高压变质带南部数千个榴辉岩体中，已发现了40个含金红石榴辉岩体，金红石储量达数百万吨。在综述、分析该带榴耀岩的空间分布、岩石矿物学、含矿性等特性的基础上，确定了块状榴辉型和片麻状榴辉岩型两种主要矿石类型。金红石在矿石中主要呈包裹体、粒间充填、蚀变残余和热液充填四种赋存形式，分别代表了四个不同的形成阶段。电子探针分析显示，在高压、超高压变质作用期间，富含Na的深部流体对金红石的成矿可能起了重要的作用。该矿床属典型的榴耀岩型金红石矿床，在成因上与超高压变质作用有关，类似于挪威的Engebφfjellet、俄罗斯的Shubino村和意大利的Pian Paludo矿床，而不同于我国已知的主要金红石矿床。     

秦岭杂岩残存高压不纯大理岩的确定及其意义

陕西商南试马寨秦岭杂岩中不纯大理岩的岩相学和矿物化学研究表明,该岩石的变质矿物组合可明显分为两期Ⅰ.方解石+白云石+多硅白云母+石英+镁电气石+金红石+金云母;Ⅱ.方解石+低铁白云石+多硅白云母+石英+高岭石,另有少量斜长石.通过特征矿物组合和矿物成分对比,并利用方解石-白云石地质温压计及多硅白云母压力计,获得该岩石早期变质温压条件为700℃±和》1.0GPa,属高压变质岩石.它的确定,为进一步阐明秦岭造山带核部新元古代高压变质岩带的存在及其演化提供了新的资料.     

桐柏围山城地区变质岩形成的温压条件

文章基于变质岩中的矿物共生组合和前进变质作用中的特征矿物,论述了桐柏围山城变质地体中发育的铁铝榴石+黑云母、蓝晶石+十字石和矽线石变质带与绿帘石角闪岩相及角闪岩相变质作用,并据矿物地质温压计和氧同位素地质温度计,估算了其形成时温压条件是500—650℃,500—700MPa。     

贵州峨嵋山玄武岩的显微斑状结构及其意义

本文从岩石结构的角度,研究了贵州西部峨嵋山玄武岩。以镜下依据为基础,结合岩石化学特征和其他地质事实,认为贵州西部峨嵋山玄武岩曾经历了埋藏变质作用的改造。本区玄武岩Na_2O偏高,MgO偏低,并非岩石原有特征。这一认识,对今后进一步研究本区玄武岩及其有关矿产,是值得重视的。     

铸造铝合金ZAlSi7MgA处理工艺的优化设计

分析了合金成分对ZAlSi7MgA合金性能的影响，进行合理的成分设计，采用Sb、Te复合变质处理提高合金性能，并对该合金的热处理工艺进行对比性试验和正交分析，获得最佳热处理工艺方案，通过对ZAlSi7MgA合金进行变质处理和热处理等处理工艺的优化设计，提高了该合金的综合机构性能并使其具有良好的长效变质性能。     

Confirmation of ultrahigh-temperature metapelitic granulite in the Altay orogen and its geological significance

Through petrography, mineral compositions and P-T estimate results, an ultrahigh-temperature(UHT) metapelitic granulite has recently been identified from near Kalasu in the east of Altay city, with an assemblage gt-opx-silcd-sp-bt-pl-qtz. The orthopyroxene has a high-Al feature, and its Al2O3 content is as high as 8.7 wt%, indicating a UHT metamorphic condition. Its peak metamorphic condition is estimated as: P = *0.80 GPa, T = *960 °C. Metamorphic textural relations and P-T estimate results show a post-peak near-isobaric cooling anticlockwise P-T path. Zircon U-Pb age results(271 ± 5 Ma) support that the UHT metamorphic event in the region occurred in the Permian. The identification of the UHT metapelitic granulite from near Kalasu confirms the existence of the Permian UHT metamorphism in the Altay orogen, implying that the Permian extensional tectonic setting of a high-heat flow in the southern part of the Altay orogen may be closely associated with the Permian Tarim mantle plume activity.     

Impact-derived features of the Xiuyan meteorite crater

Up to now, 176 meteorite impact craters have been found on the Earth. Among these craters, none of them lies in China. The Xiuyan crater is located in the Liaodong Peninsula of China. This bowl-shaped crater has a diameter of 1.8 km and depth of about 150 m. The impact-derived features include planar deformation features （PDFs） in quartz, shatter cones, impact breccia, and radial valleys on the wall of rim. It is the first confirmed meteorite impact crater in China.     

Continental subduction channel processes: Plate interface interaction during continental collision

The study of subduction-zone processes is a key to development of the plate tectonic theory. Plate interface interaction is a basic mechanism for the mass and energy exchange between Earth＇s surface and interior. By developing the subduction channel model into continental collision orogens, insights are provided into tectonic processes during continental subduction and its products. The continental crust, composed of felsic to mafic rocks, is detached at different depths from subducting continental lithosphere and then migrates into continental subduction channel. Part of the subcontinental lithospheric mantle wedge, composed of perido- tile, is offscrapped from its bottom. The crustal and mantle fragments of different sizes are transported downwards and upwards inside subduction channels by the corner flow, resulting in varying extents of metamorphism, with heterogeneous deformation and local anatexis. All these metamorphic rocks can be viewed as tectonic melanges due to mechanical mixing of crust- and man- lie-derived rocks in the subduction channels, resulting in different types of metamorphic rocks now exposed in the same orogens. The crust-mantle interaction in the continental subduction channel is realized by reaction of the overlying ancient subcontinental lithospheric mantle wedge peridotite with aqueous fluid and hydrous melt derived from partial melting of subducted continental basement granite and cover sediment. The nature of premetamorphic protoliths dictates the type of collisional orogens, the size of ultrahigh-pressure metamorphic terranes and the duration of ultrahigh-pressure metamorphism.