康滇地轴花岗岩类铀钍丰度特征及找铀前景初析

本文应用γ能谱资料，系统阐述了康滇地轴花岗岩类的铀钍丰度特征，总结了康滇地轴现有花岗岩型铀矿化的基本特点。在与华南产铀花岗岩类特征对比的基础上，对康滇地轴花岗岩类的找铀前景作了初步的分析探讨。     

西藏冈底斯带门巴地区印支期花岗岩地球化学特征及其构造意义

门巴地区晚三叠世花岗岩主要出露在西藏冈底斯构造带的弧背断隆上,主要岩石类型为黑云角闪花岗闪长岩和黑云二长花岗岩。岩石为钙碱性,具有富SiO2、K2O的特点。K2O/Na2O平均为1.13,相对富钾。Al2O3变化于13.27%～15.53%之间,A/CNK平均为1.0,为准铝质岩石。花岗岩体稀土元素总量∑REE变化于99.5×10-6～294.72×10-6之间,轻稀土元素富集,重稀土元素亏损,具弱至中等的负Eu异常。微量元素以富K、Rb、Ba、Th等大离子亲石元素和亏损Nb、Ta、Y、Yb等高场强元素为特征。岩石学和岩石地球化学研究表明,该时代的花岗岩具I型花岗岩的特点,形成于岛弧环境,是新特提斯洋早期俯冲作用的产物。同时它也暗示着冈底斯岩浆弧带在晚三叠世就已成雏形。     

华北地台和秦岭—大别—苏鲁造山带的中生代花岗岩与深部地球动力学过程

近年来的研究证实 ,华北地台和大别—苏鲁造山带的中生代花岗岩与同时代的镁铁质超镁铁质岩有类似的Sr、Nd同位素特点 ,许多花岗岩和火山岩还具有类似埃达克岩的地球化学性质。在此基础上 ,根据现已积累的大量Sr、Nd同位素资料 ,从整个华北地台岩石圈的角度论证了中生代岩石圈地幔富集的性质、富集地幔发生的时代及其形成机制 ,进而探讨了岩浆活动的动力学机制 ,指出本区岩石圈富集地幔的形成是在Pangea超大陆裂解时岩石圈大规模拆沉减薄 ,被拆沉的太古宙古老地壳重循环进入地幔改变了地幔成分所致 ,说明超大陆裂解、岩石圈大规模拆沉减薄和富集地幔形成之间有密切的成因联系 ,超大陆裂解伴随着大陆地壳生长和消亡 (重循环 )的大体平衡。结合全球地震层析资料 ,进一步探讨了由俯冲大洋残片转化的下地壳同古老克拉通地壳物质在花岗岩源区中的重要意义。     

新疆阿拉套山花岗岩类的岩石化学

新疆阿拉套山南坡东西向展布的花岗岩石的岩石化学研究表明，本区同时存在Ｉ型和Ｓ型两种类型的花岗岩，其分布受构造环境控制，靠近古板块缝合线为Ｉ型花岗岩分布区、远离古板块缝合线为Ｓ型花岗岩分布区。源岩性质和作用强弱等因素可能是造成岩石化学成分差异的原因。     

Mantle‐derived and crustal melts dichotomy in northern Greece: spatiotemporal and geodynamic implications

Two distinct groups of subduction‐related (orogenic) granitoid rocks, one Jurassic and the other Tertiary, occur in the area between the Vardar (Axios) Zone and the Rhodope Massif in northern Greece. The two groups of granitoids differ in many respects. The first group shows evolved geochemical characters, it is not associated with mafic facies, and evidence of magmatic interaction between mantle‐ and crustal‐derived melts is lacking. The second group has less evolved geochemical characters, it is associated with larger amount of mafic facies, and magmatic interaction processes between mantle‐derived and crustal melts are ubiquitous as evidenced by mafic microgranular enclaves and synplutonic dykes showing different enrichment in K₂O, Ti, and incompatible elements. This kind of magmatism can be attributed to the complex geodynamic evolution of the area. In particular, we suggest that two successive subduction events related to the closure of the Vardar and the Pindos oceans, respectively, occurred in the investigated area from Late Jurassic to Tertiary. We relate the genesis of Jurassic granitoids to the first subduction event, whereas Tertiary granitoids are associated with the second subduction. Fluids released by the two subducted slabs induced metasomatic processes generating a ‘leopard skin’ mantle wedge able to produce mafic melts ranging from typical calc‐alkaline to ultra‐potassic. Such melts interacted in various amounts with crustal calc‐alkaline anatectic melts to generate the wide spectrum of Tertiary granitoids occurring in the study area. Copyright © 2004 John Wiley & Sons, Ltd.     

Mesozoic Granitoid Types and Metallogeny of the East China Circum-Pacific Continental Margin

Abstract: This paper synthesizes the geotectonic background, genetic types and metallogenetic relations of the Mesozoic granitoids in the East China continental margin. By the Mesozoic, the Siberia Plate, North China Plate and South China Plate amalgamated together, resulting in formation of a unified Eurasia super–continent. Since the late Triassic to early Jurassic period, the territory of East China gradually became a Cordilleran style active continental margin. During the Jurassic to early Cretaceous (early to middle episodes of Yanshanian orogeny), the Paleo-Pacific plate strongly collided with and subducted under the Eurasia continent, reactivated the consolidated East China continental margin. The granitoids of both transformation series and syntexis series were generated. Many granitoid-related large and giant metal deposits were formed. Furthermore, the W, Sn, Be, Nb, Ta and U mineralizations are mostly associated with the transformation series; while the Fe, Cu, Mo and Au mineralizations are mostly associated with the syntexis series. The late Yanshanian orogeny (late Cretaceous) began a transition to the western Pacific style continental margin. A tensional environment resulted in development of alkaline granitoids and formation of continental red basins. The Cenozoic orogeny was characterized by a backarc spreading and rifting regime in this region.     

Silicate melt inclusions in the Qiushuwan granitoids,northern Qinling belt,China: Implications for the formation of a porphyry Cu–Mo deposit as a reduced magmatic system

Melt inclusions (MIs) in quartz from granitoids in the northern Qinling belt were studied using microthermometry and laser Raman spectroscopy. The total homogenization of melt inclusions occurs in a mean range between 1050 and 1100 °C. Laser Raman experiments reveal H₂O, C₂H₆, C₄H₆ and CH₄ as the dominant volatile compounds. Our results provide insights into the temperatures of magma crystallization and the dominantly reducing environment during the early magmatic stage. Based on ore mineralogy, and on the volatile species content in the MIs, we evidence firstly that the Qiushuwan porphyry Cu–Mo deposit in the Qinling–Dabie–Sulu orogenic belt was derived from a reduced magmatic system, emplaced at relatively deep domains more than 10 km deep, and secondly, that the magmas that are responsible for the generation of Qiushuwan were either derived from an inherently reduced source, or reduced during ascent and emplacement. The mechanism might have involved the assimilation of sedimentary material with minimal crustal interaction. The parental magmas likely underwent reduction essentially by loss of all of their SO₂ by degassing, as evidenced by the low S content in melt inclusions. These reduced materials provided adequate sulfur source for the formation of the porphyry Cu–Mo deposits with obvious zonation, which plays a key role in the mineralization; finally, we conclude that the reduced environment and the relatively deep domain of magma emplacement probably limited the extent of mineralization, generating only a relatively small Cu–Mo deposit in Qiushuwan, located within the northern Qinling accretionary belt.     

西天山特克斯达坂一带晚古生代花岗岩类的地球化学特征及其构造意义

依据地质学、岩石学和年代学特征,西天山特克斯达坂一带花岗岩类被解体为早石炭世库勒萨依序列和早二叠世其那尔萨依序列,其同位素年龄分别为347Ma、291～292Ma。通过对该花岗岩类地球化学特征的研究得出,库勒萨依序列A/CNK平均值为1,K2O/Na2O平均值为0.96,（Na2O+K2O）/Al2O3平均值为0.66,里特曼指数δ平均值为3.2,为准铝质钙碱性花岗岩;其那尔萨依序列A/CNK平均值为1.05,K2O/Na2O平均值为1.17,富钾,为过铝质碱性花岗岩。库勒萨依序列为形成于岛弧环境的钙碱性花岗岩,是古亚洲洋向北俯冲的产物;其那尔萨依序列为形成于后造山期松弛阶段的碱性花岗岩。     

川西雀儿山花岗岩的地球化学和岩石成因

位于川西义敦岛弧北端的雀儿山花岗岩体主要由岩体边部或者作为包体的花岗闪长岩、主体似斑状花岗岩和较晚的呈条带状或者脉状伟晶质、细晶质花岗岩组成。这些花岗质岩石表现了较宽的常量元素变化范围,属于高钾钙碱性到shoshonite亚铝到过铝质岩石系列,表现了较平坦式具有负Eu异常的稀土配分模式。在原始地幔标准化的多元素图解上所有这些岩石表现Rb、Th和K等大离子亲石元素强烈富集,Nb、Sr、P和Ti等元素明显亏损。Sm-Nd同位素分析结果表明似斑状花岗岩亏损地幔模式年龄tDM=1.23~1.61Ga,εNd(t)=-5.3~-6.3,细晶花岗岩脉tDM=2.30Ga,εNd(t)=-6.9。这些岩石的εNd(t)分布在康定杂岩的Nd同位素演化范围内和上部。岩石地球化学和Nd同位素特征研究揭示其花岗岩岩浆起源于上部地壳杂砂岩、砂页岩和泥质岩石的部分熔融,经历了早期阶段的铁镁质矿物和副矿物的分离结晶,晚期钾长石等卷入了分离结晶。雀儿山花岗质岩浆活动发生于同碰撞到碰撞后隆升构造背景。     

华北花岗岩类的大地构造岩石化学特征

华北花岗岩类为酸性深成岩.以正长花岗岩和二长花岗岩为主,按照地洼学说的大地构造分类,它们分属于地槽、地台和地洼三个演化阶段,其岩石化学各具特征. 从地槽、地台至地洼阶段,华北花岗岩类具有明显的化学演化规律.例如,在化学成分方面表现为K_2O含量递增,而MgO和CaO含量递减;在岩石化学指数方面.表现为里特曼碱性指数、长英指数、钾质指数和碱度递增.而铝质指数,镁质指数和钠质指数则递减等等.