怀安蔓菁沟早前寒武纪高压麻粒岩混杂岩带地质特征、岩石学和同位素年代学

华北克拉通北缘中段怀安蔓菁沟高压麻粒岩混杂岩带产在太古宙怀安杂岩南缘与花岗岩带交界处,由高压基性麻粒岩、辉长质麻粒岩、英云闪长质麻粒岩和少量夕线石榴片麻岩相间排列的席状岩层构成,岩层间被高应变带或剪切带分隔。高压基性麻粒岩是石榴辉石麻粒岩。据石榴石斑晶内包裹的早期矿物(Cpx+Q)估算的早期高压变质作用条件:T=800℃,P>1.4GPa。环绕斑晶的后成合晶反应边矿物组合(P1+Opx+Hb+Cpx)的变质条件为:T=820℃,P为0.7～0.9GPa。全岩Sm-Nd等时线年龄2.65Ga,矿物Sm-Nd等时线年龄1.82Ga,锆石U-Pb一致线年龄1.83Ga。高压基性麻粒岩的原岩代表晚太古代陆壳的最下部,大约在2.7Ga从上地幔分异出来,可能经壳下垫托作用加在早期陆壳底部,随后经历高压变质作用。早元古代晚期,由于地壳规模的大型逆冲作用,使其上升,并经受褶皱形变、剪切推覆和退变质等作用的改造,形成高压麻粒岩混杂岩带。     

大别造山带钾氩年龄的解释—差异上升的地块

根据冷却年龄理论和大别造山带变质岩K-Ar表面年龄的平面分布,指出这些年龄既不代表岩石形成事件,也不简单地反映后期热事件,而代表岩石经剥蚀隆起温度下降到该矿物封度温度以来的时间,即反映地区的构造隆起历史。现有资料说明大别造山带整体在印支期开始隆起,但中部罗田—英山一带则隆起较快或地热增温率高,因而表现出年轻(燕山期)的表面年龄。     

Calculated and observed seismic behaviour of exposed upper mantle

In order to determine the seismic properties of rocks representing the continental crust/upper mantle transition, a structural and petrographical study of peridotites of the Ivrea-Verbano zone (N. Italy) has been undertaken. The seismic behaviour (Vp, Vs, birefringence, orientation of the fast shear-wave polarisation plane) has been calculated from the modal composition of rock samples, together with the crystallographic preferred orientation and the single crystal elastic constants, using the methods of Mainprice (1990). It is shown that the intrinsic anisotropy of peridotites is mainly due to the lattice preferred orientation (LPO) of olivine and to the competing effects due to the LPO of orthopyroxene. If present, well-oriented hydrous phases such as phlogopite, leads to both P- and S-waves velocities becoming drastically reduced, but the anisotropy and the S-wave splitting (mainly on the foliation plane) is increased. An attempt has been made to apply this petrologic and microstructural approach to understand the seismic properties of ultramafic rocks with the aid of a mobile seismic network set up in the Ivrea-Verbano zone. Five recording units with 3-component geophones were installed on the most representative lithologies of the Ivrea-Verbano zone: kinzigites, gabbros, stronalites, and on metapelites of the adjacent outcrop of the Serie dei Laghi. During five months the seismic network recorded 49 events that were mainly regional earthquakes. The preliminary analysis of the first arrival revealed a high-velocity anomaly near the Finero ultramafic massif. Rough calculations indicated that this anomaly could be due to a shallow-depth, peridotitic body about six kilometres thick. S-wave polarisation analysis was carried out on the horizontal components of the seismograms of four regional earthquakes that showed a first arrival propagating almost vertically at the recording sites. Four earthquakes were chosen in order to reconstruct the orientation of the polarisation plane of the shear phases. The preliminary results of this analysis have shown a qualitatively good agreement between the orientation of the polarisation plane of the fast shear-wave and the strike of the foliation at the station near Finero, located on kinzigites of the Ivrea-Verbano zone, although the relationships between the local structural setting and the polarisation orientations at the other recording sites is not yet so clear.     

关于青藏高原地壳的隆升与增厚

本文扼要地评述了国内外地质学家、地球物理学家关于青藏高原地壳隆升与增厚机制的研究成果,并对大地测量学者深入该项研究提出了几点意见。     

水系分维的构造含义

本文运用分数维几何学,研究了河流水系分维与地壳里向运动、活动断裂格局及运动学特征的关联性。结果表明:1)地壳垂向运动控制大型河流主干的总体形态;2)活动断裂格局复杂、水平运动强烈的地区,水系分维值高;3)走滑断裂较斜滑断裂对水系发育的控制强烈,而后者主要起到对水系的分区作用。     

地台活化与层控铅锌矿床

本文主要介绍大多数层控铅锌矿床是产在半封闭沉积盆地碳酸盐岩中,属同生沉积成因。在地台活化时期,由于扬子地台西南缘从稳定地块转向活化。在构造-岩浆作用时期,火山喷气导致了金属聚积。因此,所有的矿床均表现出受超壳大断裂控制,这些矿床可认为是同生沉积-火山喷气成因。