内蒙古沙巴尔吐地区中二叠世蛇绿构造混杂岩及同期花岗质杂岩的发现及地质意义

中亚造山带东段内蒙古兴安盟扎赉特旗地区作为二连-贺根山断裂的东延部分,蕴含了古亚洲洋俯冲消亡过程及洋-陆转换的关键信息,然而对于该区蛇绿构造混杂岩的研究相对薄弱,成为制约古亚洲洋构造演化研究的瓶颈.本文在扎赉特旗沙巴尔吐地区发现了蛇绿构造混杂岩、与岛弧环境相关的英云闪长岩-奥长花岗岩和碱长花岗岩组合.对蛇绿构造混杂岩中...     

A new understanding of Demala Group complex in Chayu Area,southeastern Qinghai-Tibet Plateau: Evidence from zircon U-Pb and mica 40Ar/39Ar dating

The Chayu area is located at the southeastern margin of the Qinghai-Tibet Plateau. This region was considered to be in the southeastward extension of the Lhasa Block, bounded by Nujiang suture zone in the north and Yarlung Zangbo suture zone in the south. The Demala Group complex, a set of high-grade metamorphic gneisses widely distributed in the Chayu area, is known as the Precambrian metamorphic basement of the Lhasa Block in the area. According to field-based investigations and microstructure analysis, the Demala Group complex is considered to mainly consist of banded biotite plagiogneisses, biotite quartzofeldspathic gneiss, granitic gneiss, amphibolite, mica schist, and quartz schist, with many leucogranite veins. The zircon U-Pb ages of two granitic gneiss samples are 205 ± 1 Ma and 218 ± 1 Ma, respectively, representing the ages of their protoliths. The zircons from two biotite plagiogneisses samples show core-rim structures. The U-Pb ages of the cores are mainly 644 –446 Ma, 1213 –865 Ma, and 1780 –1400 Ma, reflecting the age characteristics of clastic zircons during sedimentation of the original rocks. The U-Pb ages of the rims are from 203 ± 2 Ma to 190 ± 1 Ma, which represent the age of metamorphism. The zircon U-Pb ages of one sample taken from the leucogranite veins that cut through granitic gneiss foliation range from 24 Ma to 22 Ma, interpreted as the age of the anatexis in the Demala Group complex. Biotite and muscovite separates were selected from the granitic gneiss, banded gneiss, and leucogranite veins for ⁴⁰Ar/³⁹Ar dating. The plateau ages of three muscovite samples are 16.56 ± 0.21 Ma, 16.90 ± 0.21 Ma, and 23.40 ± 0.31 Ma, and the plateau ages of four biotite samples are 16.70 ± 0.24 Ma, 16.14 ± 0.19 Ma, 15.88 ± 0.20 Ma, and 14.39 ± 0.20 Ma. The mica Ar-Ar ages can reveal the exhumation and cooling history of the Demala Group complex. Combined with the previous research results of the Demala Group complex, the authors refer that the Demala Group complex should be a set of metamorphic complex. The complex includes not only Precambrian basement metamorphic rock series, but also Paleozoic sedimentary rock and Mesozoic granitic rock. Based on the deformation characteristics, the authors concluded that two stages of the metamorphism and deformation can be revealed in the Demala Group complex since the Mesozoic, namely Late Triassic-Early Jurassic (203 –190 Ma) and Oligocene –Miocene (24 –14 Ma). The early stage of metamorphism (ranging from 203 –190 Ma) was related to the Late Triassic tectono-magmatism in the area. The anatexis and uplifting-exhumation of the later stage (24 –14 Ma) were related to the shearing of the Jiali strike-slip fault zone. The Miocene structures are response to the large-scale southeastward escape of crustal materials and block rotation in Southeast Tibet after India-Eurasia collision.©2021 China Geology Editorial Office.     

泥质砂岩复电阻率的频散特性实验

不同孔隙流体特性的岩石复电阻率频散实验,是复电阻率测井资料评价水淹层和低阻油层的岩石物理基础。通过水驱水、水驱油、油驱水的岩石复电阻率频散特性的实验研究,发现泥质砂岩的复电阻率频散特性受含油饱和度的影响较大,受地层水矿化度的影响较小,尤其是异相电阻率,受地层水矿化度的影响更小;与含水泥质砂岩相比,含油泥质砂岩的相角相对较大,且随着含油饱和度的增加而增大;含水岩石和含油岩行在频散特性上存在着较大差异。实验研究结果表明,利用基于岩石频散特性发展起来的复电阻率测井技术,可以有效地识别油水层。     

青藏高原东缘构造演化的SHRIMP锆石U-Pb年代学框架

青藏高原东缘一直被普遍认为是一个吸收印度—欧亚大陆碰撞变形的调节带。本文所获得的最新SHRIMP锆石U-Pb测年结果显示:青藏高原东缘具有更加复杂的地质历史。测年结果表明,高原东缘最古老的前寒武纪结晶基底形成于古元古代(2401~1912Ma)。这一古老基底首先受到中元古代构造热事件(1361~1040Ma)的影响,随后受到新元古代与弧岩浆活动有关构造热事件(791~817Ma)的强烈改造。松潘—甘孜复理石杂岩的基底是亲洋壳型的,形成于晚新元古代的大陆裂解作用(681~655Ma)。高原东缘的前寒武纪微地块可能是由这次裂解作用从扬子或青藏地块拉裂出去形成的。这些微陆块先增生拼贴于东冈瓦纳大陆、然后又从中裂离,并最终卷入高原东缘的特提斯构造演化过程中。伴随东冈瓦纳大陆裂解,高原东缘古特提斯洋于石炭纪至二叠纪早期拉开(328~292Ma),经早中生代弧-陆碰撞作用闭合(224~213Ma)。中侏罗世这一地区发育显著的构造岩浆活动(175Ma),但其动力学背景仍不十分清楚。晚白垩世岩浆活动(97Ma)可能是印度板块初始俯冲阶段的产物。新生代岩浆作用(18Ma)与陆-陆碰导致的大规模走滑断层作用所引起的同熔作用有关。     

风水复合侵蚀研究述评

风水复合侵蚀或风水交互作用是干旱、半干旱地区常见的侵蚀过程。这种风力与流水对同一侵蚀对象 (区域) 的共同作用或交替作用塑造了风蚀水蚀交错区特有的侵蚀地貌景观。作为一个相互联系、影响的复杂系统,风水复合侵蚀具有明显的时空分布特征,其侵蚀过程可以划分为古代过程与现代过程。由于以往的风蚀和水蚀研究相互独立,风水复合侵蚀的研究起步较晚。在研究中存在着尺度转化与研究方法不成熟等问题。对风水复合侵蚀的机理与防治以及土壤复合可蚀性的研究都将成为今后研究中的重点与难点。     

面向问题的空间应用表达与实现

讨论空间应用的一种面向问题的表达方法与实现机制。为解决空间应用的描述问题,在建立时空一体化空间数据模型基础上,定义了对SQL进行扩展的时空复合查询语言,实现了对空间应用问题的非过程化描述;研究复杂空间应用的表达问题,讨论时空复合查询语言的限制,并在语言中引入流机制,通过空间应用问题的组合实现更为复杂的空间应用,并支持空间数据分布式计算;最后给出若干空间应用实例及其面向问题的表达。     

在SeisDps实时系统中用零点、极点计算ML的过程

在SeisDps地震处理软件的实时系统中,不是用系统的幅频特性计算震级ML,而是利用台站的零点、极点和增益,将记录的数字地震波形仿真成伍德-安德森地震仪记录的波形,计算具有3 大优点的ML震级,本文主要介绍用零点、极点和增益计算ML的过程。     

SH波入射时多个半圆形沉积谷地附近浅埋圆形孔洞的动力分析

本文采用辅助函数的思想,利用复变函数和多级坐标的方法给出了SH波入射条件下多个半圆形沉积谷地附近浅埋圆形孔洞动力分析问题的解答。将整个求解区域分割成两部分来处理,区域I为多个半圆形沉积谷地,区域II为浅埋圆形孔洞附近带半圆形凹陷的半无限弹性空间。在区域I和II中分别构造位移解,并在二个区域的“公共边界”上实施位移应力的连续条件,建立求解该问题的无穷代数方程组。最后,本文给出了算例和数值结果,并对其进行了讨论。     

基于随机振动理论确定桥梁地震碰撞的临界间隙

确定梁桥邻跨间避免地震碰撞的最小间隙,对于梁桥地震碰撞危险性预测及防地震碰撞措施的设计有着显著意义。本文基于随机振动理论建立梁桥地震碰撞邻跨临界间隙的计算方法,分析模型采用跨径不等的两跨简支梁桥,且考虑隔震支座非线性恢复力的影响。文中首先建立了系统的非线性运动方程;随后运用随机等效线性化理论将其线性化;最后在复模态空间推导了临界碰撞间隙的均值与方差的计算方法。人工地震动的非线性时程分析结果验证了本文算法的正确性。参数分析表明,临界间隙随邻跨长度比增大而增大,随支座屈服力与上部结构重量比值减小而增大,随隔震支座屈服位移增大而增大,随桥墩振动周期增大而增大。隔震支座屈服前后刚度比值对临界间隙大小影响很小。     

基于线框模型的复杂断层三维建模方法

建立了包含复杂断层面地质体的三维数学模型.为准确表达复杂地质体各要素的空间几何形态及其相互之间的关联关系,设计了线框单元体模型,并提出了整体描述断层面的技术思路,解决了地层交错情况下断层面和地层面的模拟难题;在上述基础上,结合平面地质图数据,实现了复杂地质条件下三维地质体模型的构建.