京西房山岩体南侧青白口系下马岭组构造片岩中红柱石的变形特征及其地质意义

在房山岩体南侧下马岭组构造片岩中发现红柱石横截面上发育一组共扼裂隙和“环带状”构造,环带形状与红柱石变斑晶横截面的形状相似,均压扁为长方形,红柱石的变形是同构造递进变形的结果。裂隙及环带均被流体包裹体所充填,流体包裹体的热爆温度为604～685℃,利用黑云母-石榴子石温度计得出变质温度为592℃。计算出变质发生深度为2.69～3.11km。     

西藏羌塘地块西北部银利沟早白垩世钾玄质侵入岩的发现——来自地球化学和锆石U—Pb年龄的证据

银利沟二长岩分布于西藏羌塘西北部,岩石具有高碱、低Ti的特征,在SiO2-K2O图解中位于钾玄岩区。二长岩的锆石U-Pb同位素年龄为121.3Ma±0.6Ma,具有富集LIL、LIEE及显著的Ta-Nb-Ti负异常的地球化学特征,表现出与俯冲有关的钾玄岩的地球化学特征,形成于晚造山—后造山构造背景。这种背景很可能与冈底斯和羌塘地块在晚侏罗世—早白垩世发生的碰撞作用有关。     

新疆东昆仑阿牙克岩体地球化学与^40Ar／^39Ar年代学研究及其大地构造意义

阿牙克岩体出露在新疆东昆仑阿牙克库木湖北侧的祁漫塔格山西段,侵入在早古生代低绿片岩相蛇绿混杂岩即“祁漫塔格群”之中。岩体地球化学特征显示其可能形成在伸展构造环境,角闪石的~(40)Ar/~(39)Ar坪年龄为420±4Ma;等时年龄为416±21Ma,证实早古生代末期东昆仑地区已从挤压构造体制转化为伸展构造体制,表明昆仑山具有多期造山作用叠合的大地构造特征。     

广西大厂地区黑云母花岗岩中电气石的化学组成及其对岩浆热液演化的指示

广西大厂地区笼箱盖黑云母花岗岩与区内晚白垩世锡多金属成矿作用在时空上密切相关。岩相学特征表明,笼箱盖黑云母花岗岩中的电气石可以分为三类:1)浸染状电气石; 2)石英-电气石囊; 3)电气石-石英脉。本文利用电子探针和激光剥蚀等离子体质谱系统测定三种不同产状电气石的化学组成。分析结果显示,三种产状的电气石均具有高的Fe/(Fe+Mg)和Na/(Na+Ca)比值,主体属于碱基亚类铁电气石。浸染状电气石为岩浆晚期结晶,其Fe/(Fe+Mg)比值变化于0. 85～0. 94,随着岩浆分异,电气石逐渐富集Li、F、Fe和Sn等元素。与浸染状电气石相比,石英-电气石囊中早阶段电气石具有低的Fe/(Fe+Mg)比值,高的V、Co和Sr含量,可能反映了岩浆演化晚期出现的不混溶富硼熔/流体对早期黑云母和长石的交代作用,从而使囊中早阶段电气石继承部分被交代矿物的化学组成特征;石英-电气石囊中晚阶段电气石的化学组成变化较大(如Li、F、Mg、Al、V、Fe和Zn),与热液成因电气石的推论一致。与浸染状和囊状电气石相比,石英脉中的电气石具有高的Fe/(Fe+Mg)和Na/(Na+Ca)比值;微量元素组成与囊状电气石相似。就成矿元素锡而言,三种产状的电气石均具有相对高的锡含量,与其他地区锡成矿花岗岩中电气石的成分特征相似。但是,从岩浆晚期到热液阶段,大厂地区电气石的锡含量并没有显著升高,可能反映了早期岩浆热液流体对熔体锡有限的萃取作用。     

北秦岭灰池子复式岩体的地质特征及其成因

灰池子复式岩体是北秦岭加里东造山带规模最大的花岗岩体，其成因争论较大。本文在１：５万区调工作的基础上，通过岩石学、岩石化学和同位素等方面的讨论，认为该岩体属于岩浆成因，其源岩与秦岭群无关，而是来自于地壳中的幔壳混合物，属于Ｈ型花岗岩。     

福建龙岭岩体同位素年龄及其地质意义

本文采用Rb-Sr,K-Ar法测年手段,对龙岭岩体及该岩体中的包体、岩体周围的富闪深成岩体等进行了同位素年龄测定,讨论了它们之间的成岩时间及热事件干扰。认为浅色包体351Ma代表了龙岭岩体原始岩浆上侵发生的时间,主岩340Ma则为该岩体的定位,冷凝结晶时间。富闪深成岩的角闪石K-Ar年龄345Ma,说明这些岩石与龙岭岩体在成岩时间上十分接近。对暗色包体的测定结果,指出了在解释一些年龄数据时必须填重。     

大兴安岭北段巴升河岩体锆石U-Pb年代学及其地质意义

大兴安岭北段扎兰屯地区巴升河岩体由碱长花岗岩组成.采用LA-ICP-MS方法对碱长花岗岩开展锆石U-Pb测年，结果为297.8±3.6 Ma，岩体形成于早二叠世.该岩体4个样品的全岩地球化学等特征显示：巴升河岩体中碱长花岗岩具有富Si、高K、富碱的特征，属于弱过铝质钾玄岩系列，同时，样品∑REE偏高，Eu负异常明显，富集大离子亲石元素，具有A型花岗岩特征，综合前人研究成果及同位素年代学特征，认为兴安地块与松嫩地块拼合的时间早于298 Ma.     

Characteristic Features and U—Pb Isotopic Ages of Zircons in a Middle Proterozoic Granite Pluton from Baohan Area,Hainan Province,China

The crystal form,chemical composition and U-Pb isotopic composition of various zircon fractions is a Middle Proterozoic granite pluton from the Baoban area suggest that the zircons are typically magmatogenic in nature,and different from those of sedimentary and epigenetic orgins.The various zircon fractions yielded and age of about 1440.87Ma,which may represent the ge of zircon crystallization.The so-called aoban-group migmatite is,as a matter of fact,a Middle Proterozoic granite pluton.     

Metamorphism and tectonic evolution of the Lancang paired metamorphic belts, south-western China

Abstract The Lancang metamorphic terrane consists of an eastern low- P/T belt and a western high- P/T belt divided by a N–S-trending fault. Protoliths of both units are mid–late Proterozoic basement and its cover. The low- P/T belt includes the Permian Lincang batholith, related amphibolite facies rocks of the Damenglong and Chongshan groups, and Permo-Triassic volcanic and volcaniclastic rocks. Most whole-rock Rb–Sr isochron and U–Pb zircon ages of the Lincang batholith are in the range 290–279 and 254–212 Ma, respectively. Metamorphism of the low- P/T belt reaches upper amphibolite with local granulite facies (735°C at 5 kbar), subsequently retrogressed at 450–500°C during post-Triassic time. The high- P/T rocks grade from west to east from blueschist through transitional blueschist/greenschist to epidote amphibolite facies. Estimated P–T conditions follow the high- P intermediate facies series up to about 550–600°C, at which oligoclase is stable. The ⁴⁰Ar/³⁹Ar plateau age of sodic amphibole in blueschist is 279 Ma.
The paired metamorphic belts combined with the spatial and temporal distribution of other blueschist belts lead us to propose a tentative tectonic history of south-east Asia since the latest Precambrian. Tectonic juxtaposition of paired belts with contrasting P–T conditions, perhaps during collision of the Baoshan block with south-east Asia, suggests that an intervening oceanic zone existed that has been removed. The Baoshan block is a microcontinent rifted from the northern periphery of Gondwana. Successive collision and amalgamation of microcontinents from either Gondwana or the Panthalassan ocean resulted in rapid southward continental growth of c. 500 km during the last 200 Ma. Hence, the Lancang region in south-east Asia represents a suture zone between two contrasting microcontinents.     

Synmetamorphic veining: origin of andalusite-bearing veins in the Vedrette di Ries contact aureole, Eastern Alps, Italy

Discordant andalusite-biotite-quartz-bearing veins occur in the contact aureole of the Vedrette di Ries pluton (Italian Eastern Alps), never outside the area of contact metamorphic andalusite development. Andalusite veins are found only within andalusite-bearing hornfelses, and vein biotite occurs wherever host-rock garnet is partially replaced by biotite. Veins formed during contact metamorphism, synchronously with the crystallization of andalusite and biotite within host rocks. Their pegmatitic structure and their orientation suggest that vein parageneses crystallized within fluid-filled cavities that opened by hydraulic fracturing. A mechanism of synmetamorphic veining is proposed to explain rock failure and subsequent mineral deposition within veins. During hydrofracturing induced by dehydration reactions in response to heating in the aureole, fissures were immediately filled with locally derived fluids. The lack of large-scale flux, together with high fluid pressures required by hydrofracturing, suggest fluid in the cavities was a virtually stagnant, passive medium, and that mass-transport toward fractures was driven by intergranular diffusion. Because temperature and P_f values within veins are similar to those in the host rock, vein assemblages are interpreted as the stable, high-T side of reactions taking place within pelitic schists, at the time when fractures opened. Once nucleation of product phases occurred, chemical components released by dissolution of reactant minerals were driven to precipitation sites by chemical potential gradients. Since nucleation was favoured at the strained grains of vein walls, andalusite and biotite simultaneously grew in vein and host rock. The proposed genetic model contrasts with generally adopted metasomatic mechanisms for the genesis of Al₂SiO₅-bearing veins, in not requiring large fluid/rock ratios or a highly ‘aggressive’ fluid composition. The mechanism of synmetamorphic veining may be particularly useful in the interpretation of vein occurrences in medium- and deep-crustal rocks which have undergone extensive devolatilization.