Early Ordovician strongly peraluminous granite in the middle section of the Yarlung Zangbo junction zone and its geological significance

LA-ICP-MS zircon U-Pb isotopic dating and rock geochemical analysis were done of the Xarru granite in the middle section of the Yarlung Zangbo junction zone.Zircon 206Pb/238U weighted mean ages of 474.9±2.3 and 478.3±1.7 Ma have been obtained for two gneiss granite samples respectively,which represent the formation age of the granite.This is the first discovery of the Early Ordovician magmatism in the Yarlung Zangbo junction zone.The rocks are high-K calcic-alkalic granite,contain tourmaline but not hornblende,with aluminum saturation index(ASI) of A/CNK1.1(1.10–1.20),and are enriched in Rb,Th and U and relatively depleted in Ba,Nb,Sr,Zr,Ti and Eu.They are strongly peraluminous S-type granite,resulting from partial melting of argillaceous components in the crust in a syn-collisional setting.According to previous studies as well as the analysis in this paper,the formation of the Xarru granite is probably related to the Andean-type orogeny in the process of subduction of the Proto-Tethys Ocean towards the Gondwanaland,and it is a product of partial melting of the thickened upper crust as a result of collision between blocks or micro-blocks in the northern margin of the Gondwana supercontinent in the process of oceanic subduction.The Xarru granite is identified as the Early Ordovician granite,indicating that the wall rocks had probably formed in the Cambrian or Precambrian.A crustal basement may exist in the Xarru region.     

马尔洋地区康西瓦结合带地质特征

康西瓦断裂位于新疆西昆仑地区,为青藏高原西北缘重要断裂构造,构成了西昆仑板块和喀喇昆仑板块边界,前人已在该带发现有麻粒岩.近年来,在康西瓦结合带西段马尔洋地区开展1∶5万区域地质调查,发现了超高压变质硬玉岩,证实其为一板块俯冲带,应为中央复合造山带西延部分.     

班公湖-怒江结合带西段侏罗纪木嘎岗日群的重新厘定及意义

沿班公湖—怒江结合带西段出露的侏罗纪木嘎岗日群是一套复理石碎屑沉积组合,代表了班公湖—怒江中特提斯洋盆早—中侏罗世深海—半深海沉积。本文通过详细的地层剖面研究,依据沉积建造、岩性组合及古地理、古生物面貌特征,将原木嘎岗日群进行了重新划分。重新厘定的木嘎岗日群可划分为一、二两个组。在1∶〖KG-*2〗25万区调成果的基础上,分析了重新厘定的木嘎岗日群的沉积层序、沉积构造环境及地质意义。     

雅浦-马里亚纳海沟连接区深层流季节内变异的特征和机制

雅浦-马里亚纳海沟连接区东深水通道是太平洋深层经向翻转环流携带南极绕极水进入西太平洋的首要入口。基于高分辨率的再分析数值模型结果,研究发现该通道深层流速和温度具有显著的40～90d周期的季节内变异,且季节内变异强度随深度的增加而增加,进一步研究揭示地形罗斯贝波(topographicRossbywaves,TRW)是引起上述季节内变异的主要原因,TRW波解可以解释深层流和温度季节内振幅的垂向变化。通过建立全水体的动力关联研究发现TRW在不同时刻具有不同的能量来源,首先次表层强涡旋经过时可以通过位涡守恒激发深层的TRW;第二,大洋中层存在的强涡旋也可激发深层的TRW;第三,深层平均流可以主要通过正压不稳定过程向季节内TRW提供能量。     

Computation of Design Load and Motion for Floating Structures Navigating in Waves

—Analytical and numerical investigation is made of the source potential for floating structurewith forward speed in waves.A particular form is selected for numerical applications,where the double in-tegral of the Green function is transformed into the single one and the oscillation characteristics forintegrands in the specific computation domain are treated numerically.A comparison of calculated exam-p1es with published data is given and it shows that the numerical simulation is satisfactory and the accura-cy is adequate to engineering application.     

陕西勉略蛇绿构造混杂结合带组成及演化

勉略蛇绿构造混杂结合带是晚古生代以来裂解扩张、在裂谷基础上发育的有限洋盆，属古特提斯海域北部陆缘分支，于早中生代俯冲消亡，印支期碰撞拼合遗留的缝合带。其兼收南北陆缘不同时期的变形基质及古特提斯洋演化过程不同构造坏境增生拼贴构造残块，与基底变质岩块混染间列，经早期剥离—滑脱、主期剪切—逆冲、晚期隆升走滑，组成强带、弱域间互网结状蛇绿构造混杂结合带。     

考虑桩土效应的天津站交通枢纽地震反应分析

为弄清楚带有地下室大型复杂结构的抗震性能,本文针对天津站交通枢纽工程,分别取结构典型的横向及纵向剖面,应用大型通用有限元分析软件ANSYS,建立了结构-桩-土体系相互作用的有限元模型,采用动力时程分析方法,研究体系在水平地震作用下的弹塑性动力反应规律,分析结构在地震动作用下的位移和内力的分布;并与假定刚性基础周边土简化为弹簧的结构模型的计算结果进行比较,通过两种模型的地震反应的对比分析,得到了一些有益的结论。     

Crustal seismic velocity structure near Faial and Pico Islands (AZORES), from local earthquake tomography

The Azores archipelago (Portugal) is located on an oceanic plateau, in a geodynamic environment prone to intense seismic and volcanic activity. In order to investigate the crustal structure in this region, we have conducted a local earthquake tomography study in the area of the islands of Faial, Pico and S. Jorge using data recorded in July 1998. The July 9th 1998 earthquake, near Faial Island, triggered an aftershock sequence of thousands of events that lasted for several months and were recorded by a total of 14 stations located on the three islands surrounding the epicentral area. In the upper crustal layers, consistency is seen between the tomographic results and the islands' surface volcanic units. Beneath the Faial central volcano a low Vp (< 6.0 km/s) anomaly roughly located at 3–7 km depth, suggests a connection to the plumbing system, possibly the presence of a magma chamber. In NE Faial, a high Vp (> 6.3 km/s) body was found located at mid-lower crust, most likely an intrusion of gabbroic composition, that is bordered by the registered seismic activity; its shape suggesting a tectonic controlled mechanism. The relocated hypocenters, together with the overall analysis of the Tomographic model, suggest a tectonic segmentation of Faial Island. The crustal thickness under the islands volcanic buildings of the Faial–Pico area was estimated at around 14 km.