Trace-element mobilization during Ca-metasomatism along a major fluid conduit: Eclogitization of blueschist as a consequence of fluid-rock interaction

In the subduction complex of the Tianshan mountains, western China, massive blueschist is cross-cut by an eclogite-facies major fluid conduit surrounded by a reaction zone which is mainly composed of omphacite and garnet. Petrological as well as geochemical evidence suggest that formation of the vein and the eclogitic selvage around the vein was caused by fluid infiltration under peak metamorphic conditions of 21 ± 1.5 kbar and 510 ± 30 °C. The combination of whole-rock with mineral trace-element data as well as mass-balance calculations indicate that substantial differences exist between the unaltered host rock and the part of the system which was altered by fluid-rock interaction. These differences include: (1) depletion of mainly large-ion lithophile elements (LILE) and Li of up to 60% relative to their concentrations in the unaltered host rock; (2) an extreme enrichment of CaO (∼115%), Sr and Pb (>300%) in the altered parts of the vein-wall-rock system; (3) redistribution of heavy rare earth elements (HREE) from partly replaced rutile and recrystallized titanite in the blueschist-eclogite transition zone into newly grown garnet rims in the eclogitic selvage around the vein; (4) transformation of high Nb/Ta rutile into low Nb/Ta titanite which is associated with preferred mobilization of Nb over Ta; and (5) decoupling of Zr and Hf from Nb and Ta; the latter are depleted by ∼30% relative to the unaltered blueschist host rock whereas the former are depleted by only ∼10%. The prerequisite for the transformation of Ca-poor blueschist (6-7 wt.% CaO) into Ca-rich eclogite (up to 13 wt.% CaO) was the infiltration of a Ca-rich fluid. The release of trace elements can be attributed to partitioning of these elements into the passing fluid phase during dissolution-reprecipitation processes in the course of eclogitization. The reactivity of the precursor mineral assemblage and the chemical gradients between the reacting and passing fluid of the conduit are mainly responsible for trace-element mobilization in the studied samples. The suite of trace elements released upon fluid-induced eclogitization of the reactive wall-rock resembles that in island arc magmas showing strong enrichment of LIL elements, strong depletions in HFS elements and intermediate concentrations of REE.     

LITHOPROBE——加拿大地球探测计划

LITHOPROBE是加拿大的国家级地球科学研究计划。选择10个典型剖面,每个都不同程度地代表了加拿大典型的地质特征或具全球意义的重要构造过程。时间上其地质演化跨越了40多亿年漫长的地质年代。通过地震深反射技术为先锋的以及多种不同学科的综合研究,取得一系列成果,如证实3.0Ga前即发生与板块构造有关的作用,对古老岩石圈板块碰撞和新地壳形成过程进行了重大修正,揭示了若干大型矿集区的深部控矿构造的反射影像,使加拿大的地球科学研究走到世界的前列,本文拟通过较系统介绍LITHOPROBE,为我国深部探测技术与实验研究提供参考。     

芳烃化合物组成及其在油气地球化学中的应用

芳烃化合物是烃源岩和原油中非常重要的有机族组分,与饱和烃一样含有丰富的地球化学信息。应用GC-MS能检测到的芳烃化合物可分为常规多环芳烃、含NSO杂环芳烃、芳香甾萜烷及脱羟基维生素E。它们的一些参数可作为母质来源、热成熟度、沉积环境和油气运移判识的有效指标,是饱和烃地球化学研究的重要补充和佐证,对油气勘探与开发有重要的实际意义,但生物降解、混源油等因素会影响这些参数的正确性。应用全二维气相色谱-飞行时间质谱仪(GC×GC-TOF)对生物降解油芳烃中的鼓包化合物UCM(unresolve dcomple xmixtures)进行探索性研究取得了一定的效果,这也将是今后芳烃研究的重要方向。     

我国西南地区斑岩矿床区域成矿环境

本文对我国西南地区斑岩Cu(-Mo-Au)矿床形成的区域成矿环境进行了总结研究。我国西南地区斑岩矿床,构造上位于全球特提斯斑岩成矿带东段,与青藏高原演化密切相关,形成于青藏高原演化不同阶段。我国西南地区斑岩矿床形成时代为晚三叠世、早白垩世、古近纪和中新世等4个时期。斑岩矿床形成的区域成矿环境具有多样性,包括俯冲造山岛弧、同碰撞、后碰撞和大陆转换板块边界等四类构造环境。根据斑岩矿床成岩成矿时代和成矿环境,我国西南地区斑岩矿床可划分为义敦-中甸印支期斑岩成矿带、玉龙-马拉松多古近纪斑岩成矿带、丽江-金平古近纪斑岩成矿带、冈底斯古近纪-新近纪斑岩成矿带和班公湖-怒江燕山期斑岩成矿带等五个成矿带。与世界上多数斑岩矿床一样,我国西南地区斑岩矿床与区域深大走滑断裂存在着明显的空间分布关系。     

各向异性介质多波速度分析方法及软件实现

速度分析是多波资料处理的核心问题之一,在高精度地震勘探的今天,建立在各向同性假设条件下的速度分析已经不能满足高精度勘探要求。这里以自然界广泛存在的具有垂直对称轴的横向各向同性（VTI）介质为基础,研究各向异性条件下P波和P～SV转换波旅行时公式,并进一步研究了P波和P～SV转换波速度分析的方法步骤,在此基础上用QT开发出一套各向异性介质多波速度分析的交互处理软件。用该方法及软件对理论资料和实际资料进行处理,取得了较好的处理效果,验证了该方法及软件的正确性。     

2010年度地理学基金项目评审与成果分析

着重分析了2010年度面上项目、青年基金项目及地区基金项目的申请情况,在研项目的进展情况,以及2009年底结题项目完成情况,同时介绍了2009年度主要学科方向取得的研究进展。     

REE and Sr-Nd Isotope Geochemistry for Yixian Fluorite Deposit,Western Liaoning Province,China,and Its Geological Implications

Up to now,there were no systematic studies of geochemistry and isotopic age for the Yixian(义县) fluorite deposit,western Liaoning(辽宁) Province,China.Based on the analysis of metallogenic geological setting,we studied the REE,Rb-Sr and Sm-Nd isotopes.The chondrite-normalized REE patterns of fluorite are characterized by moderate LREE depletion(LREE/HREE=0.95-3.57,(La/Yb)N=0.08-2.84) and enrichment of Sr(146×10-6-596×10-6) and moderately positive Eu anomalies(δEu=1.10-1.34),which are similar to those of the ho...     

西昌市地质灾害发育分布规律及防灾建议

西昌市地处川西的安宁河流域,区内地质条环境件复杂,生态环境脆弱,泥石流、滑坡等地质灾害发育,给当地居民生命财产安全及经济发展带来了较大影响。本文通过对西昌市目前发育的153处不同类型的地质灾害进行统计,总结了地质灾害在流域、高程、时段等方面的分布规律;对影响或控制西昌市地质灾害发育的地形地貌、构造、岩土体结构、地震、降雨及人类工程活动等因素进行了分析、总结;并针对西昌市的地质灾害类型及发育分布特征提出了适用于该地区的科学、合理的地质灾害防灾建议。     

变渗透系数软土一维非线性固结沉降数值模拟

固结沉降计算是工程建筑中的重要内容之一。传统的固结沉降计算多是基于渗透数为常数的Terzaghi模型,这与实际的固结过程有较大的差别。采用Carman—Koze模型与一维非线性固结沉降模型进行耦合来模拟固结沉降过程。结果表明,固结导致的渗透系数的变化对固结有较大的影响,特别是在后期这种影响会越来越大。