爆破角砾岩型金矿床的成因及其定位机制：——以河南祁雨沟金矿为例

本文系统地研究了祁雨沟爆破角砾岩型金矿床的地质特征、流体包裹体和硫、铅、氢、氧及碳同位素特征,认为成矿流体和成矿元素主要来自晚期的岩浆熔体,只在成矿晚期有少量大气降水的加入,应属典型的岩浆热液型金矿床。而矿床的形成和定位则是岩浆结晶分异作用的后期,岩浆熔体因水过饱和而发生“二次沸滕”,产生高压流体,从而在地表浅部发生隐爆作用,造成岩体坍塌,含金流体胶结而成含金角砾岩体。岩浆熔体脉动式的“二次沸滕”     

Kinematic significance of mingling-rolling structures in lava flows: a case study from Porri Volcano (Salina, Southern Tyrrhenian Sea)

 A basaltic andesite lava flow from Porri Volcano (Salina, Southern Tyrrhenian Sea) is composed of two different magmas. Magma A (51 vol.% of crystals) has a dacitic glass composition, and magma B (18 vol.% of crystals), a basaltic glass composition. Magma B is hosted in A and consists of sub-spherical enclaves and boudin-like, banding and rolling structures (RS). Four types of RS have been recognized: σ–type;δ–type; complex σ-δ–types and transitional structures between sub-spherical enclaves and rolling structures. An analysis of the RS has been performed in order to reconstruct the flow kinematics and the mechanism of flow emplacement. Rolling structures have been selected in three sites located at different distances from the vent. In all sites most RS show the same sense of shear. Kinematic analysis of RS allows the degree of flow non-coaxiality to be determined. The non-coaxiality is expressed by the kinematic vorticity number Wk, a measure of the ratio Sr between pure shear strain rate and simple shear strain rate. The values of Wk calculated from the measured shapes of microscopic RS increase with increasing distance from the vent, from approximately 0.5 to 0.9. Results of the structural analysis reveal that the RS formed during the early–intermediate stage of flow emplacement. They represent originally sub-spherical enclaves deformed at low shear strain. At higher strain, RS deformed to give boudin-like and stretched banding structures. Results of the kinematic analysis suggest that high viscosity lava flows are heterogeneous non-ideal shear flows in which the degree of non-coaxiality increases with the distance from the vent. In the vent area, deformation is intermediate between simple shear and pure shear. Farther from the vent, deformation approaches ideal simple shear. Lateral extension processes occur only in the near-vent zone, where they develop in response to the lateral push of magma extruded from the vent. Lateral shortening processes develop in the distal zone and record the gravity-driven movement of the lava. The lava flow advanced by two main mechanisms, lateral translation and rolling motion. Lateral translation equals rolling near the vent, while rolling motion prevailed in the distal zones. Received: 6 November 1997 / Accepted: 29 November 1997     

花岗岩类分类与定位机制研究动向和进展

近年来国内外花岗岩类研究工作已取得了新的进展。本文综合性地评述了花岗岩类主要岩石成因分类、构造环境分类与对比特点;着重叙述了花岗岩体定位机制研究方法及研究实例;对深化我国特别是华南花岗岩类岩石成因—构造分类及定位机制的研究提出了具体建议。     

Eclogitic metapelites in the western segment of the north Qaidam Mountains: Evidence on “in situ” relationship between eclogite and its country rock

In Yuka-Luofengpo area of the north Qaidam Mountains, eclogitic metapelites are recognized. The metapelites enclosed lenses of eclogites, and locally intercalated with eclogites. Their typical mineral assemblages are garnet+kyanite+chloritoid+phengite+quartz+rutile. Strong growth zoning is preserved in garnets of metapelites, and phengite contains up to 3.4 Si per formula units. The petrographic observations and textural relations testify to the following sequence of mineral assemblages connected to three metamorphic stage: (1) Grt+ChlI+CldI +PheI ± StI+Qtz; (2) Grt+Ky+PheII±CldII+Qtz; and (3) Grt+CldIII+ChlII+PheIII+StII ± ky+ Qtz. Applying THERMOCALC Program, Grt-Phe thermometer and Grt-Ky-Phe-Qtz barometry, P-T conditions for three metamorphic stages were obtained: P=1.07±0.31GPa, T=564±22? (prograde stage); P=2.3–3.1GPa, T=615–700°C-(peak stage); and P =1.22 ± 0.26GPa, T=581±20°C (retrograde stage). A hairpin shape P-T path similar to that of adjacent eclogite is inferred. In combination with eclogitic mineral relics in marbles and orthogneisses enclosing eclogites, we thought that the relationship between eclogites and country rocks is “in situ” rather than “tectonic emplacement”.     

新疆温泉地区晚石炭世古老地壳重熔: 花岗斑岩脉侵位年龄及其Sr、Nd同位素证据

新疆阿拉套山南缘分布有由众多岩性复杂的脉岩所组成的岩墙群,部分岩墙与成矿作用密切相关,是了解该地区地壳生长过程的重要窗口。其西段出露大量中酸性脉岩,脉岩侵入到上泥盆统托斯库尔他乌组地层,以闪长岩脉为主,含少量花岗斑岩脉和霏细岩脉。为了探讨花岗斑岩的形成时代、岩浆源区和构造背景,对其进行了锆石U-Pb年龄测定和Sr、Nd同位素研究。分析结果显示,花岗斑岩锆石U-Pb(加权平均)年龄为310 Ma,说明花岗斑岩脉形成于晚石炭世早期,该年龄与北天山沙湾流纹岩(形成于陆板内拉张环境)的喷发时代(310 Ma)以及区内察哈乌苏岩基的形成时代(313 Ma)十分接近,是阿拉套山西段最晚一期岩浆活动的产物。Sr、Nd同位素分析结果表明,该岩脉具有中等I_Sr值(0.709 328~0.710 018)、负的ε_Nd(t)值(-3.92~-2.33)和较大的Nd同位素模式年龄(1 294~1 502 Ma)特征,明显不同于同时期西天山乃至新疆北部众多的花岗岩类,后者普遍拥有低I_Sr值、正的高ε_Nd(t)值和较年轻的Nd同位素模式年龄,是幔源玄武质岩浆底侵、发生岩浆的同化分离结晶作用或岩浆混合作用的结果,说明该花岗斑岩脉不太可能是幔源岩浆底侵演化的产物,其岩浆源区可能来自成熟度比较高的前寒武纪基底岩石。310 Ma以后,阿拉套山地区逐渐进入后碰撞伸展阶段,处于陆壳垂向生长、区域构造应力场显示拉张的构造环境,花岗斑岩脉可能形成于同碰撞挤压向后碰撞伸展背景转换的过渡阶段。     

辽宁兴城新立屯地区岩浆杂岩岩石学特征、侵位顺序及地质意义

辽宁兴城新立屯地区岩浆杂岩主要由4种不同的岩石单元组成,分别为似斑状黑云母二长花岗岩,中细粒石英闪长岩,花岗细晶岩和花岗伟晶岩,前两者分布广泛且为研究区的主要岩石单元,后两者则呈脉状侵入到前两者中。应用LA-ICP-MS锆石U-Pb定年方法,测得似斑状黑云母二长花岗岩,中细粒石英闪长岩及花岗细晶岩的年龄分别为2 496±18 Ma,2 490±19 Ma,2 479±29 Ma,形成于古元古代早期。结合野外地质特征,侵位顺序由早到晚依次为:似斑状黑云母二长花岗岩,中细粒石英闪长岩,花岗细晶岩,花岗伟晶岩。岩石地球化学特征显示,新立屯地区岩浆杂岩主量元素方面具高硅(SiO2=61.38%~74.99%),富碱(Na2O+K2O=6.86%~9.41%),富Mg#(56~70)特征;A/CNK=0.91~1.18,属准铝质-过铝质岩石;微量元素方面,相对富集轻稀土元素,亏损重稀土元素,具有Eu异常(δEu=0.50~0.96);富集大离子亲石元素,亏损高场强元素;锆石Lu-Hf同位素特征εHf(t)值为-1.12~+6.13;TDM2(Hf)介于2 594~2 937 Ma,显示该套岩浆杂岩可能为地幔物质加入新生地壳再造的产物。     

粤北石人嶂莲花山隐伏花岗岩侵入体岩浆动力学特征分析

基于矿床地质特征的研究,以构造地质学、流体力学等为主要研究手段,对粤北石人嶂矿区含钨矿花岗岩侵入体进行分析。通过对岩体形成时的温压条件、岩浆密度、岩浆粘度、岩浆冷凝速度等岩浆动力学参数进行计算,并分析岩浆动力学特征,发现了密度值随温度的变化规律,对于侵位过程中的能量聚集有利,冷却速度缓慢,因而有足够的时间满足任何晶体生长。通过花岗岩体侵位机制的深入探讨,查明了岩体侵位与钨矿化的关系,为总结矿床的成因提供了流体动力学依据,为矿床成因探讨和矿山可持续开发利用提供了科学依据。     

小秦岭加里东期侵入岩地质特征及侵位机制

小秦岭加里东期侵入岩的全岩Rb－Sr等时线年龄值为503Ma。岩石类型为（变）辉名正长岩,依据岩石结构特征划分为两个单元,归并为东吉口超单元。其岩浆源于上地慢部分港融岩浆分异的产物,属同造山期侵入岩。依据岩体构造分析,确定为强力（主动）侵位机制。     

Magnetic Fabric of Cuizhao Pluton and Its Emplacement Significance

1NTRODUCTlONAcloseassociationbetweenthemagneticfabricsofrocksamplesandfieldmicro-structurehasbeenknownbyGraham(l954)andthemagneticsusceptibi1itymethodforstructuralstudieshasbeenusedcommonly(TikoffandTeyssier,l9941Rochetteetal.,1992jYuandZheng,l992;Hrouda,l982).Themagneticfabricsandcomparativepetrofabricstudiesofmanyrockshavebeenexaminedundergoing.Furthermore,thefieldandexperimentsstudiesshowedthat,undercertainconditions,themagneticsusceptibilityanisotropyandfinitestrainarecorrelated,soth…     

Lava flow internal structure found from AMS and textural data: An example in methodology from the Chaîne des Puys,France

Anisotropy of magnetic susceptibility (AMS) data analysis is a convenient method used to investigate strain and flow during lava flow emplacement. In order to make a sound interpretation, the origin of the AMS signal must be verified. Two questions must be answered: 1) what phase, or phases carry the AMS signal and 2) when was the AMS fabric acquired? The verification steps themselves can provide extra data for interpreting lava flow conditions. Here, we present a methodology to answer the two questions in a 6 km-long Chaîne des Puys trachybasaltic lava flow that descended into the future site of Clermont Ferrand (France) 45,000 years ago. Knowledge of lava flow emplacement will be useful specifically to this site, if a reactivation of the volcanic chain occurs. The results are also of more general interest to understand lava flow emplacement dynamics.