Rare-earth elements as source indicators of Pan-African granites from Obudu Plateau,Southeastern Nigeria   总被引：1，自引：1，他引：0  

V. U. Ukaegbu  F. T. Beka 《中国地球化学学报》2008,27(2):130-134

The rare-earth element （REE） concentrations of representative granite samples from the southeast of the Obudu Plateau, Nigeria, were analyzed with an attempt to determine the signatures of their source, evolutionary history and tectonic setting. Results indicated that the granites have high absolute REE concentrations （190×10^-6-1191×10^-6; av.=549×10^-6） with the chondrite-normalized REE patterns characterized by steep negative slopes and prominent to slight or no negative Eu anomalies. All the samples are also characterized by high and variable concentrations of the LREE （151×10^-6-1169×10^-6; av.= 466×10^-6）, while the HREE show low abundance （4×10^-6-107×10^-6; av.=28×10^-6）. These are consistent with the variable levels of REE fractionation, and differentiation of the granites. This is further supported by the range of REE contents, the chondrite-normalized patterns and the ratios of LaN/YbN （2.30-343.37）, CeN/YbN （5.94-716.87）, LaN/SmN （3.14-11.68） and TbN/YbN （0.58-1.65）. The general parallelism of the REE patterns, suggest that all the granites were comagmatic in origin, while the high Eu/Eu＊ ratios （0.085-2.807; av.=0.9398） indicate high fo2 at the source. Similarly, irregular variations in LaN/YbN, CeN/YbN and Eu/Eu＊ ratios and REE abundances among the samples suggest behaviors that are related to mantle and crustal sources.  相似文献   

Mesoproterozoic Continental Arc Type Granite in the Central Tianshan Mountains: Zircon SHRIMP U-Pb Dating and Geochemical Analyses     

YANG Tiannan  LI Jinyi  SUN Guihu  WANG Yanbin 《《地质学报》英文版》2008,82(1):117-125

The Central Tianshan belt in northwestern China is a small Precambrian block located in the southern part of the Central Asia Orogenic Belt （CAOB）, which is considered as ＂the most voluminous block of young continental crust in the world＂ that comprises numerous small continental blocks separated by Paleozoic magmatic arcs. The Precambrian basement of the central Tianshan Mountains is composed of volcanic rocks and associated volcano-sedimentary rocks that were intruded by granitic plutons. Geochemical analyses demonstrate that the granitic plutons and volcanic rocks were generated in the Andean-type active continental arc environment like today＇s Chile, and the zircon U-Pb SHRIMP dating indicates that they were developed at about 956 Ma, possibly corresponding to the subduction of the inferred Mozambique Ocean under the Baltic-African super-continent.  相似文献   

再论南岭侏罗纪“铝质”A型花岗岩的成因及其对古地温线的制约   总被引：5，自引：1，他引：4  

汪洋 《大地构造与成矿学》2008,32(3)

对南岭地区侏罗纪4个典型"铝质"A型花岗岩岩基——柯树北、寨背、西山和南昆山的成因分析表明:柯树北、寨背岩基中的低分异花岗岩SiO2≈70%,A/CNK<1.1,CaO≥1%,高Zr、Ba含量,是下地壳部分熔融产物;而SiO2含量较高者由低分异花岗岩岩浆通过分离结晶演化而来。西山花岗质火山-侵入杂岩也是下地壳部分熔融产物。南昆山花岗岩为高硅花岗岩,贫Zr、低Ba、Sr和Eu/Eu*值,但具有高的Nb、Ga、REE含量和Ga/Al比值,在Whalen等(1987)图解中地球化学参数落在A型花岗岩区域内。碱性玄武岩浆分离结晶的成岩模式无法解释南昆山岩基较大的体积、均一的成分和低的Nb/Ta比值。详细的成岩分析表明,南昆山花岗岩可能是先期侵入的(幔源)碱性正长岩在富水和相对低温低压条件下发生部分熔融的产物。由这些"铝质"A型花岗岩的熔融温压条件估算得出热流值达到80~95mWm-2的南岭地区侏罗纪古地温线。由古地温线推算出的岩石圈厚度45~75km。南岭侏罗纪高热流背景及其对应的花岗质岩浆活动可能与后碰撞造山阶段岩石圈地幔拆沉或被"热侵蚀"有关,但并不一定意味着岩石圈伸展的大地构造环境。  相似文献   

胶东地区晚中生代岩浆活动及对大地构造的制约   总被引：16，自引：1，他引：15  

邱连贵  任凤楼  曹忠祥  张岳桥 《大地构造与成矿学》2008,32(1):117-123

应用近十几年来胶东地区及其周边岩浆岩体的同位素测年资料,结合几个岩体的新的SHRIMP测年数据(牙山岩体117.7Ma,院格庄岩体113.4Ma,正长斑岩脉115.7Ma),系统研究了该区晚中生代以来的岩浆活动规律,结果表明,该区可分为4个岩浆活动期;(1)晚侏罗世构造-岩浆热事件(150~160Ma),以玲珑-滦家河型岩体为代表,是在区域挤压构造应力作用下侵入的,属同构造或同造山时期的岩浆作用。(2)早白垩世早期构造-岩浆热事件(135~125Ma),以郭家岭岩体为典型,该时期的岩浆活动均具有双峰式岩浆作用特征,反映了伸展动力学背景。(3)早白垩世中晚期构造-岩浆热事件(125~105Ma),以崂山花岗岩为特征,该阶段对应于中国东部岩石圈大规模的减薄时期,是大陆裂谷作用的高峰期。(4)晚白垩世-古新世基性-超基性火山作用。本文还探讨了岩浆活动的地球动力学因素及其对大地构造的制约。  相似文献   

造山带异源浆混花岗岩理论与方法研究   总被引：2，自引：0，他引：2  

窦全成  董琳  曹德云  刘永成  任鹏奎 《矿产与地质》2008,22(3):189-195

1：5万花岗岩填图方法在区调工作中推广以来,在造山带花岗岩调查实践中,由于造山作用及过程的复杂性,花岗岩浆的多源及多样性,使同源岩浆演化理论及方法遇到了难题。文章在新一轮1：25万造山带试点图幅,在对同源岩浆演化理论及方法的适用性进行探索的同时,提出了异源浆混理论指导造山带内部浆混花岗岩（H型花岗岩）的填图方法。并就异源浆混花岗岩鉴别标志等作了系统总结,提出了浆混组合、浆混单元、浆混体,填图的理论方法体系;给予了浆混花岗岩明确的定义。  相似文献   

甘肃北山印支燕山期花岗岩成矿作用与找矿工作再研究   总被引：2，自引：0，他引：2       下载免费PDF全文

殷先明 《甘肃地质》2008,(3):1-5,35

本文讨论了甘肃北山地区印支燕山期花岗岩的空间分布与构造,矿化集中区的耦合关系;与印支燕山期花岗岩活动有成因关系的几个典型矿床;印支燕山期作用强度、构造环境、矿源层和矿化集中区。  相似文献   

华南重要金属矿床的成矿规律——时代爆发性、空间分带性、基底继承性和热隆起成矿   总被引：5，自引：1，他引：4  

马东升 《矿物岩石地球化学通报》2008,27(3)

华南热液矿床形成的时代爆发性、空间分带性及其成矿元素对前寒武纪基底的继承性表明,构成华南基底和含矿建造的前寒武纪地层（主要为元古界）是华南陆内热液成矿作用的主要成矿物质来源,燕山期花岗岩类是热液成矿作用的主要成矿能量来源;华南热液成矿的区域分布趋势、矿床形成过程和成矿岩体演化等,均表现出与构造热隆起动态有关的成矿特征。多期花岗岩类侵入和迅速块断隆升造成地温梯度增高,基底含矿建造提供成矿物质,以及有利的热液通道和扩容空间是造成构造隆起带或盆地“凹中隆”成矿的重要条件。燕山期花岗岩成岩成矿与大陆地壳的多旋回熔融或再循环有密切的成因关系;地震层析图像资料显示,华南中生代软流圈上涌是造成华南陆壳热隆起的动力学因素。但其成因不同于地幔柱机制,具有被动上涌特征,可能与太平洋板块俯冲形成的大型冷幔柱下沉和地幔过渡带崩溃有关。  相似文献   

湖南香花岭花岗岩岩石化学特征及其构造环境   总被引：3，自引：0，他引：3  

赵龙辉  邹宾微  柏道远 《华南地质与矿产》2008,(1):1-6

湖南南部燕山早期香花岭岩体主要由铁锂云母二长花岗岩组成。岩石SiO：和K2O平均含量分别为73．72％和4．78％,Na2O＋KO平均8．47％,K2O／Na2O比值平均为1．40,A1：03平均为13．81％。总体属强过饱和铝质钙碱性一碱性花岗岩类。氧化物构造环境判别图解及区域构造演化背景反映香花岭岩体形成于后造山构造环境。  相似文献   

The Meso-Cenozoic thermo-tectonic evolution of the Eastern Pyrenees: an <Superscript>40</Superscript>Ar/<Superscript>39</Superscript>Ar fission track and (U–Th)/He thermochronological study of the Canigou and Mont-Louis massifs     

O. Maurel  P. Moniè  R. Pik  N. Arnaud  M. Brunel  M. Jolivet 《International Journal of Earth Sciences》2008,97(3):565-584

Vertical displacements on the SW–NE Têt fault (Eastern Pyrenees Axial Zone, France), which separates the Variscan Canigou-Carança and Mont-Louis massifs, were constrained using a thermochronologic multi-method approach. ⁴⁰Ar/³⁹Ar data from the granitic Mont-Louis massif record its Variscan cooling history and reveal no ages younger than Early Cretaceous, while the Canigou-Carança gneiss massif records systematically younger ⁴⁰Ar/³⁹Ar ages. These younger ⁴⁰Ar/³⁹Ar ages in the Canigou-Carança gneiss massif are the result of partial to total rejuvenation of argon isotopic systems related to a thermal flow coeval with the Cretaceous HT-BP metamorphism in the North Pyrenean Zone. Only the deepest rocks from the Canigou-Carança suffered this extensive Mid-Cretaceous thermal overprint probably due to differential burial around 4 km at that time. The post Mid-Cretaceous vertical displacements along the Têt fault are recorded by “low” temperature thermochronology using K-feldspar ⁴⁰Ar/³⁹Ar, zircon and apatite fission track and (U–Th)/He datings. The Mont-Louis granite samples experienced a long period of protracted cooling reflecting a lack of thermo-tectonic activity in this area from Late Palaeozoic to Early Cenozoic, followed by cooling from 55–60 Ma to Late Eocene at a mean rate of 15–20°C/Ma in the final stage. This cooling stage corresponds to Têt fault reactivation with a reversed component, promoting exhumation of the Mont-Louis roof zone contemporaneously with the south-vergent Pyrenean thrusting. In the Canigou-Carança massif, the main cooling event occurred from 32 to 18 Ma at a maximum rate of 30°C/Ma during Early Oligocene followed by a more moderate rate of 3°C/Ma from Late Oligocene to Early Burdigalian, coeval with the normal reactivation of the Têt fault in brittle conditions that accommodated the final exhumation of the massif during the opening of the Gulf of Lion.  相似文献   

藏东八宿地区泛非期花岗岩锆石SHRIMP U-Pb定年   总被引：9，自引：1，他引：8  

李才  谢尧武  沙绍礼  董永胜 《地质通报》2008,27(1):64-68

卡穷细粒黑云母碱长花岗岩出露于藏东八宿县同卡地区,是藏东地区首次发现的泛非期花岗岩.卡穷微陆块呈岩片状夹持于班公湖-怒江缝合带内,卡穷岩群构成卡穷微陆块的主体,卡穷岩群是由花岗岩、花岗片麻岩、黑云斜长片麻岩、大理岩、黑云斜长变粒岩、退变榴辉岩等组成的构造地质体.卡穷细粒黑云母碱长花岗岩获得的锆石SHRIMPU-Pb年龄为507Ma±10Ma,为泛非事件的岩浆活动记录,进一步证实班公湖-怒江板块缝合带以南是泛非期基底,为解决青藏高原南部的构造演化问题提供了新资料.  相似文献