扬子陆块西缘安益南华纪火山岩的厘定及其地质意义     

刘兵  李静  邓仁宏  熊波  关奇  李小军  刘军平  陈光艳  胡绍斌  张虎  李维科  曾文涛 《地质通报》2018,37(11):1980-1990

扬子陆块西缘安益大湾山地区出露一套由变质玄武岩等组成的变质基性火山岩,前人将其归为中元古界,并作为寻找磁铁矿的主要对象。调查发现,安益大湾山变质基性火山岩与下伏浅变质岩系间发育一套稳定沉积的砾岩。应用LA-ICP-MS技术对其底砾岩之上最底部的变质玄武岩进行了锆石U-Pb年龄测定,获得了781.3±1.9Ma的岩浆锆石~(206)Pb/~(238)U年龄加权平均值和1008±14Ma、1142±15Ma、2714±10Ma的继承性岩浆锆石~(207)Pb/~(206)Pb年龄,指示该套变质基性火山岩形成于南华纪,并将其从浅变质岩系中解离出来,对比为澄江组。继承性锆石年龄数据指示,扬子地块西缘安益地区存在新太古界和中元古界物质记录。结合前人研究成果和近来获得的年龄数据,将滇中澄江组的时代界定于820～740Ma,并将南华系的底界界定于820Ma。大湾山中-大型磁铁矿产于扬子地块西缘澄江组的变质基性火山岩中,其主成矿期为南华纪,可能属于热液氧化物-铜-金矿床。  相似文献   

顾及多因子影响的中国区域T_m模型精化研究     

李浩杰  刘立龙  黄良珂  莫智翔  蔡猛 《大地测量与地球动力学》2022,42(4):393-397

利用中国区域2015~2017年探空数据,建立一种顾及地表温度、地表水汽压、高程和纬度的中国区域大气加权平均温度T_m模型（BET模型）。以2018年探空站T_m数据为参考值,分析BET模型精度,并与Bevis模型和GPT3模型进行对比。结果表明,BET模型年均RMSE与bias分别为3.15 K和0.04 K,相比于Bevis模型、1°×1°分辨率的GPT3模型和5°×5°分辨率的GPT3模型,年均RMSE分别降低29.2%、32.8%和39.1%,年均bias分别降低96.4%、96.7%和97.4%,且该模型在中国区域不同高程和纬度上的精度与稳定性优于Bevis模型和GPT3模型。  相似文献   

基于GRACE-FO的微波与激光星间测距数据的重力场模型对比分析     

朱紫彤  闫易浩  梁磊  穆庆禄  王长青  冯伟  钟敏 《大地测量与地球动力学》2022,42(12):1262-1268

为分析GRACE-FO微波测距系统KBR及激光干涉测距系统LRI对时变重力场结果的影响,以动力学方法为基础,分别采用KBR数据和LRI数据反演2019-01~2021-08的90阶无约束时变重力场模型APM_KBR和APM_LRI,并进行对比分析。 从重力场模型阶方差和等效水柱高的空间分布来看,在两类测距数据完整且质量较好的前提下,两者精度处于同一水平,而当发生较多月卫星机动或其他卫星事件时会使LRI数据缺失,从而导致APM_LRI模型在该月得到的等效水柱高时间序列信噪比略低。由后验残差结果可知,APM_LRI后验残差RMS比APM_KBR减少约50%,且在高频处(大于等于60 CPR)LRI的后验残差显著低于KBR。总体来说,在现有条件下,由于背景场模型等其他因素影响,两类测距数据反演重力场的阶方差和等效水柱高结果基本一致,但后验残差上LRI测距具有更低的噪声。因此,未来可直接使用LRI测距数据探测、分析较弱的地球物理信号。  相似文献   

激光跟踪仪测量精度的评定   总被引：4，自引：0，他引：4  

于成浩  柯明  赵振堂 《测绘工程》2006,15(6):39-42

介绍了影响激光跟踪仪测量精度的各种因素及对其测量精度进行评定的意义、指标及方法,阐述了比较法在仪器现场检查和校准中的应用,并以100MeV直线加速器的测量控制网为例,说明统计分析法在验后精度评定中应用。  相似文献   

基于激光跟踪仪的三维控制网测量精度分析   总被引：5，自引：3，他引：2  

于成浩  柯明 《测绘科学》2006,31(3):25-27

介绍三维控制网的优点及激光跟踪仪测量系统的特点,讨论了光束法平差原理及不同观测值的权比问题,并以100MeV电子直线加速器安装测量控制网的模拟计算和实测结果,论证了利用激光跟踪仪进行三维控制网的精度。  相似文献   

RIEGL LMS-Q140i-80激光扫描仪精度评定   总被引：1，自引：0，他引：1  

王冬  卢秀山  张占杰 《测绘科学》2006,31(5):115-116

RIEGL LMS-Q140i-80激光扫描仪是863课题“近景目标三维测量技术”中关键传感器之一,其精度直接影响课题所能达到的精度指标。为衡量扫描仪实际精度与其标称精度的一致性,设计扫描仪在静止情况下进行扫描实验。实验结果表明:扫描仪的实际精度与其标称精度相一致,满足课题对传感器的精度要求。  相似文献   

Testing a new combined (U,Th)–He and U/Th dating approach on Plio-Pleistocene calcite speleothems     

《Quaternary Geochronology》2022

The geochronology of cave deposits in the Cradle of Humankind UNESCO World Heritage Site in South Africa provides a timeframe essential for the interpretation of its fossils. The uranium-lead (U–Pb) and uranium-thorium disequilibrium (U/Th) dating of speleothems, mostly flowstones that underlie and blanket the fossil-bearing sediments, have been effective in this sense, but U–Pb is limited by the requirement of ∼1 ppm U concentrations and low common Pb contents, and U/Th has a c. 500 ka limit of applicability. Here we report age results for calcite-aragonite speleothems obtained using a new combined uranium-thorium-helium ((U,Th)–He) and U/Th dating routine. We reproduced within analytical uncertainty, the published U–Pb or U/Th ages for (a) flowstone in three drill core samples in the range 2000–3000 ka, (b) a flowstone hand sample taken at surface with an age of 1800 ka, and (c) five underground flowstone samples in the range 100–800 ka. Calcite retentivity for He under cave conditions is thus demonstrated. In the few cases where helium loss was observed in speleothems, only some of the subsamples were affected, and to varying degrees, suggesting loss by lattice damage not related to diagenetic processes, rather than volume diffusion. In the 100 to 800 ka range, the combined U/Th disequilibrium and (U,Th)–He method also yielded reliable values for initial (²³⁰Th/²³⁸U) and (²³⁴U/²³⁸U) activity ratios. Importantly, most subsamples had high initial (²³⁰Th/²³⁸U) values, ranging from 1.0 to 19.7, although having low Th/U ratios. This is probably due to incorporation of Fe–Mn oxides-hydroxides dust, on which ²³⁰Th was previously adsorbed. Such samples are mostly not dateable by U/Th without the additional input from the He analysis. If not detected and corrected for, such high initial (²³⁰Th/²³⁸U) values can lead to inaccurate U/Th and U–Pb ages. Our study shows that the incorporation of He analysis in U/Th dating has broad potential application, with four methods for calculating the ages, in carbonates from different environments where U-Pb or U/Th dating would not work.  相似文献   

Maximized erosion at the last glacial maximum revealed by thermoluminescence thermochronometry     

《Quaternary Geochronology》2022

Increased erosion rates during the last 2 Myr of Earth history are commonly associated with widespread glaciation and global cooling. However, whether erosion rates actually increased during that period of time remains debated. This is in part because the respective role of fluvial and glacial erosion is difficult to assess, and because many existing techniques used to estimate erosion rates may be affected by averaging biases that may produce increased erosion rates towards the present. Here, we apply thermoluminescence thermochronometry to granitic bedrock samples of the southern-central Chilean Andes, a region which experienced a full transition from glacial-humid to fluvial-dry conditions during the Quaternary. Inverse modelling of the thermochronological data enables us to extract unbiased time series of erosion rates during the last ∼100 kyr. We find that erosion rates were systematically higher during around the last glacial maximum than at present, with differences exceeding an order of magnitude. Our findings indicate that glacial erosion is probably more efficient than fluvial erosion and imply that erosion has remained transient during the Quaternary.  相似文献   

Tracing exhumation record in high-pressure micaschists: A new tectonometamorphic model of the evolution of the eastern part of the Fore Sudetic Block,Kamieniec Metamorphic Belt,NE Bohemian Massif,SW Poland     

Jacek Szczepański  Marcin Goleń 《Chemie der Erde / Geochemistry》2022,82(1):125859

The Kamieniec Metamorphic Belt comprises a volcano-sedimentary succession exposed within a collision zone between the Saxothuringian and Brunovistulian crustal domains of the European Variscides. The studied rocks recorded two metamorphic episodes. The first episode, M₁, occurred at conditions of c. 485 ± 25 °C and 18 ± 1.8 kbar related to burial within a subduction zone. The subsequent episode, M₂, was linked to the final phases of exhumation to mid-crustal level, associated with pressure and temperature (P–T) conditions ranging from c. 520 ± 26 °C and 6 ± 0.6 kbar through 555 ± 28 °C and 7 kbar ± 0.7 to ~590 ± 30 °C and 3–4 ± 0.4 kbar. The documented deformation record is ascribed to three events, D₁ to D₃, interpreted as related to the burial and subsequent exhumation of the Kamieniec Metamorphic Belt. The D₁ event must have witnessed the subduction of the Kamieniec Metamorphic Belt rock succession whereas the D₂ event was associated with the exhumation and folding of the Kamieniec Metamorphic Belt in an E-W-directed shortening regime. A subsequent folding related to the D₂ event was initiated at HP conditions, however, the planar fabric produced during a late stage of the D₂ event, defined by a low-pressure mineral assemblage M₂, indicates that the D₂ final stage was synchronous with the onset of the M₂ episode. Consequently, the entire D₂ event seems to have been associated with the exhumation of the Kamieniec Metamorphic Belt to mid crustal level. The third deformation event D₃, synchronous with the M₂ episode, marked the last stage of the exhumation, and was linked to emplacement of granitoid veins and lenses. The latter resulted in heating and rheological weakening of the entire rock succession and in the formation of non-coaxial shear zones.  相似文献   

Seismic performance of two-story subway station structures with different isolating systems     

《地震研究进展（英文）》2022,2(4):100155

When the sliding bearing is fixed only at the top of the middle column of the underground structure, the cracks at the side end of the middle plate should be aggravated while the seismic damage of the mid-column should be alleviated. To enhance the seismic performance of the mid-plate, a new isolation design method has been mentioned while the elastic sliding bearings are set at the top of the mid-columns and between the side end of the mid-plate and the side wall at the same time. By establishing a nonlinear finite element analysis model for the static-dynamic coupling interaction system, the seismic response characteristics of the cast-in-place station structure without a sliding bearing have been analyzed and compared with those of the station structure with the sliding bearing fixed only at the top of the middle columns, and those of the station structure with sliding bearing be fixed between the mid-plate and the sidewall at the same time. The results show that the new isolation station structures suffer fewer earthquake damages at the mid-plate and mid-columns at the same time, which can improve the overall seismic performance of the subway station structure.  相似文献