河北峪耳崖金矿区花岗岩体的岩石学特征

研究了峪耳崖岩体、葫芦峪岩体、三道湾岩体的岩石学、矿物学、岩石化学、地球化学特征，它们在板块内Ａ型俯冲过程中，由老基底太古代迁西群的变质中基性火山沉积岩系（属下地壳）重熔形成，为下地壳重熔型花岗岩．这种成因的花岗岩在华北板块存在普遍性，主要表现出Ⅰ型岩石的特征，但随重熔形成的岩浆中变质沉积岩组分的增多，亦有一些Ｓ型岩石的特征出现．     

麻棚岩体特征及其与金矿成因关系研究

麻棚岩体出露于土岭－石湖金矿田西北部，与围岩阜平群的变质岩成侵入接触关系。岩体内岩相分带清楚，矿物组成相对较简单，岩石化学特征反映其为铝、碱过饱和的角闪石黑云母花岗岩，岩石地球化学特征表现出金含量高，浓集系数达１２．２，稀土元素特征表明岩体不同相带为同源分异产物。与岩体有成因联系的石英闪长玢岩及花岗闪长斑岩空间上与金矿脉密切共生，或其本身就是含金脉岩，说明麻棚岩体为岩浆成因——相当于Ⅰ型花岗岩，其成岩物质来自上地幔或下地壳，它不但为矿田内金矿的形成提供热源，在某种程度上可谓成矿母岩。     

东准噶尔西部花岗岩带的岩石成因探讨

根据新疆东准噶尔西部花岗岩带各岩体在地质学、岩石学、岩石化学和稀土元素及同位素组成等方面的特征,探讨了它的成因和演化。结果表明,该区花岗岩,尤其是含锡花岗岩成岩方式为岩浆分异交代,物质来源主要为地幔与地壳的复合作用形成,属I型→同熔型→A型→改造型的过渡类型花岗岩,其中锡的来源主要与岩石演化的途径和方式有关。     

太行山南段符山岩体的成因:岩石学和地球化学证据

太行山南段符山岩体是一套辉长岩-闪长岩-二长岩杂岩体,这一套岩石具有相似的地球化学特点:轻稀土强烈富集而重稀土亏损,并具有Eu正异常;富集大离子亲石元素特别是Sr-Ba;Nd-Sr同位素成分相对均一,并具强烈富集的特征(I Sr 为0.706～0.7065,ε Nd (T)为-13.7～-16.8).岩石学和地球化学证据都表明,这是一套同源岩浆演化系列,共同起源于富集的岩石圈地幔的部分熔融,但幔源基性岩浆侵位到下地壳位置时被下地壳物质混染形成混浆,混浆又发生以铁镁矿物为主的分离结晶作用,形成符山岩体的一系列岩石类型.华北中生代岩浆作用主要来自富集的岩石圈地幔,这可能是导致中生代以来华北岩石圈地幔减薄的机制之一.     

北山中部地区闪长岩-花岗岩类成因及构造背景

北山中部地区中酸性侵入岩以海西中晚期为主，加里东晚期次之。岩石类型有辉长岩、闪长岩、花岗闪长岩、斜长花岗岩和花岗岩类。岩浆活动分为3个旋回6期，其中海西中期第2，3期和海西晚期岩浆活动员为强烈。研究区岩体多呈岩株、岩枝和岩基产出，围岩普遍发育混合岩化和同化混染，岩石具花岗结构，块状-(巨)斑状构造。岩石化学成分为钙碱性系列，闪长岩分异程度低，斜长花岗岩和花岗闪长岩分异程度中等，花岗岩类相对较高。加里东晚期和海西晚期花岗岩类属S(海西)型花岗岩类，海西中期闪长岩、花岗闪长岩和斜长花岗岩类则属I型(科迪勒拉)，闪长岩属交代(花岗岩化)成因，花岗闪长岩-花岗岩类属岩浆成因。加里东晚期花岗岩是中-晚志留世北山地区哈萨克斯坦板块向南俯冲使上地壳局部熔融的结果；海西中期闪长岩是混合岩化(花岗岩化)的产物；花岗闪长岩和斜长花岗岩是裂谷扩张阶段上地慢部分熔融的结果；而海西晚期花岗岩是裂谷萎缩和闭合阶段地壳局部熔融的结果。     

西秦岭美武花岗岩地球化学特征

美武花岗岩在揭示西秦岭地区中生界构造演化方面具有特殊的作用。本文通过岩石化学和微量元素地球化学特征研究,对美武花岗岩岩体演化过程中的地球化学特征变化、岩体戍因及其形成的构造演化背景进行了探讨。结果表明,该岩体随着侵入期次由早向晚演化,岩石化学和地球化学特征具有明显的变化规律,反映出美武复式岩体各单元为同源岩浆系列结晶而成。它们之间既有差异性,又具有继承性。美武花岗岩形成于地壳的部分熔融,其岩浆源岩主要为高钾角闪质类岩石。而岩浆混合作用也造成沉积性质物源的加入,同时造成不同侵入单元体之间地球化学性状差别。     

折多山花岗岩的成因及构造环境

每一地质环境都具有特定的岩浆－构造系列，对于花岗岩的类型与构造环境的关系一直是人们研究的热点之一。该文在综合同位素（Ｒｂ－Ｓｒ和Ｕ－Ｐｂ）和地球化学数据基础上，结合微观构造研究方法对康定西部沿鲜水河大型韧性平移剪切带分布的大型折多山花岗岩体的花岗岩类型及其相关的构造环境进行了细致的研究，并讨论了该岩体的侵位机制。研究表明，折多山花岗岩属地壳局部熔融产物，为Ｓ型花岗岩，它的侵位时间距今１２．８±１．４Ｍａ，是鲜水河大型韧性左行平移的同构造产物，并以不连续的方式侵位，南部岩体侵位最早     

粤北贵东岩体内基性岩脉的成因研究

对贵东花岗岩体内的基性岩脉研究结果表明,岩脉的锶、氧、硫同位素组成均一致显示幔源衍生物特征;岩脉常量元素、微量元素以及稀土元素分析表明、岩脉经历了较完全的结晶分异作用,并遭受到一定程度的陆壳混染作用。由此得出结论,认为形成岩脉的岩浆来自起源于地幔深处并侵位于地壳浅部(<15Km)的二次岩浆房,岩浆在这里发生结晶分异作用,在其随后的上升侵位过程中经受了陆壳的混染作用。     

滇西新生代赋矿斑岩及花岗岩包体的锆石年代和稀土特征的地质意义

滇西地区沿金沙江—哀牢山断裂带广泛发育新生代富碱斑岩及相关多金属矿床.以六合正长斑岩中与暗色深源包体共存花岗岩包体和马厂箐赋矿斑状花岗岩为研究对象,开展岩相学和LA-ICP-MS锆石U-Pb年代学研究及锆石稀土元素分析.研究表明,六合花岗岩浆活动起始时间约为(42.8士1.6)Ma B.P.,包体结晶成岩时间与主岩(正长斑岩)年龄一致(38.63 Ma B.P.±0.52 MaB.P.);马厂箐含矿富碱岩浆起始活动时间约为(38.51士0.52)MaB.P.,结晶成岩时间为(35.80士0.20)Ma B.P..结合花岗岩包体的液态不混溶现象和锆石稀土元素特征分析,初步揭示研究区富碱岩浆起源、演化及成岩成矿作用过程为:来自交代富集地幔源区的硅不饱和富碱岩浆伴随互不混溶含矿地幔流体同步上升运移;该富碱岩浆以其底劈作用和地幔流体交代作用引发地壳深熔形成长英质岩浆.此后的2类岩浆过程分为2部分:一是富碱岩浆直接捕获少量长英质岩浆以不混溶方式继续同步运移至地壳结晶成岩,形成含花岗岩包体的硅不饱和富碱斑岩;二是富碱岩浆与长英质岩浆发生同化混染形成混合岩浆运移至地壳,其中所含不混溶含矿地幔流体伴随其结晶成岩进行自交代蚀变,形成硅过饱和的赋矿斑状花岗岩.     

秦岭造山带佛坪地区花岗岩类的特征及其意义

通过岩石学和地球化学研究，认为佛坪地区花岗岩类可分为两种不同的成因类型：深熔混合岩化型和陆壳重熔型。它们具有截然不同的野外地质特征和稀土元素地球化学特征，反映造山带不同演化阶段的构造热事件。深熔混合岩化小岩体与晋宁期南秦岭强烈变质变形密切相关；大面积出露的陆壳重熔型岩体则是主造山期地慢上涌引起的垂向加积构造演化的物质反映，对佛坪穹窿的形成和穹窿中心基底结晶杂岩的抬升剥露有重要意义．     

打古寨——罗布里两种类型花岗岩的同位素地质研究

本文研究的打古寨和罗布里岩体是桃山复式花岗岩体内部两种不同成因类型的岩体,成岩时代均为燕山早期。根据Sr,Pb,O和S同位素资料,结合地质特征,笔者认为打古寨岩体是由上部地壳重熔改造形成,属陆壳改造型花岗岩;罗布里岩体是由壳幔混合岩浆形成,属同熔型花岗岩。     

Indosinian isotope ages of plutons and deposits in southwestern Miaoershan-Yuechengling,northeastern Guangxi and implications on Indosinian mineralization in South China

The Miaoershan-Yuechengling complex pluton is the largest granitoid complex in the western Nanling metallogenic belt with a surface exposure of >3000 km2.The complex pluton is composed of an early stage granitoid batholith and late stage small intrusions.The early stage batholith contains mainly medium-grained porphyritic mica granite and porphyritic monzonite granite,whereas the late stage intrusions are composed of muscovite granite porphyry and muscovite monzonitic granite.There are many W-Sn-Mo-Pb-Zn-Cu ores in the contact zone between the batholith and strata,forming an ore-rich belt around the batholith.Based on zircon LA-ICP-MS U-Pb ages,the southwestern part of the early stage batholith formed at 228.7 ± 4.1 Ma(MSWD = 2.49),with slightly earlier magmatic activity at 243.0 ± 5.8 Ma(MSWD = 2.62).The Yuntoujie muscovite granite was associated with W-Mo mineralization and has a zircon LA-ICP-MS U-Pb age of 216.8 ± 4.9 Ma(MSWD = 1.44).The Re-Os isochron age of molybdenite from the Yuntoujie W-Mo ore was 216.8 ± 7.5 Ma(MSWD = 11.3).Our new isotope data suggest that the late stage intrusive stocks from the southwestern Miaoershan-Yuechengling batholith were closely associated with W-Mo mineralization from the Indosinian period.These new results together with previous isotope data,suggest that South China underwent not only the well-known Yanshanian mineralization event,but also a widespread Indosinian metallogenic event during the Mesozoic period.Therefore,South China has a greater potential for Indosinian mineralization than previously thought such that more attention should be given to the Indosinian ore prospecting in South China.     

Hf isotope composition of zircons and implication for the petrogenesis of Yajiangqiao granite,Hunan Province,China

In the peralumineous granite of Yajiangqiao zircon population can be divided into two groups (i.e. Zircon Ⅰ and Zircon Ⅱ), which were formed in magmatic chamber and in emplacement place, respectively. The Hf isotope compositions of two stages of zircon show that the host magma was essentially derived from crustal material by melting. However, some higher 176Hf/177Hf ratios indicate that the granitic zircons should contain fine crystal of zircon formed in mantle-derived magma. In fact, the backscattered electron imaging and the electron microprobe analysis reveal that there is another type of zircon included within Zircon Ⅰ, which is quite different from Zircon Ⅰ and Zircon Ⅱ in morphology and chemistry. They are considered to be the product of the mantle-derived magma intruded into the granitic magma chamber at the beginning of anatexis. Thus,it is suggested that the formation of Yajiangqiao granite is related to the underplating of mantle magma.     

Hf isotopic composition of zircons from the Huashan-Guposhan intrusive complex and their mafic enclaves in northeastern Guangxi: Implication for petrogenesis

High precision zircon U-Pb dating indicates that main intrusive bodies (Tong'an,Niumiao,Huashan,Lisong),and a mafic microgranular enclave in the Huashan-Guposhan complex were formed at 160-163 Ma.The εHf(t) values of zircons from the Huashan granite vary from -2.8 to +0.3 and those from the Lisong granite vary from -2.3 to +0.3,which are obviously different with those values (+2.6 to +7.4) of the mafic enclaves from the Lisong granite.These Hf isotopic data indicate that the mafic enclaves and host granites...     

黑龙江鹿鸣钼矿床成矿岩体岩石地球化学特征

鹿鸣钼矿床产于燕山早期二长花岗岩-花岗斑岩岩体中,对其岩石学和地球化学特征进行分析.结果表明:SiO2质量分数在6384%~7132%之间,全碱质量分数为69%~84%,w(K2O)/w(Na2O)平均为137.岩体大部分属于偏铝-过铝质高钾钙碱性花岗岩.稀土元素总量值高,轻稀土富集,稀土分配模式为右倾曲线,同时Eu出现弱到中等程度的亏损.研究认为与成矿有关的二长花岗岩-花岗斑岩的岩浆属壳源岩浆演化形成的A2型花岗岩岩石组合,其形成背景应属于陆-陆碰撞之后的伸展体系.     

Discovery of a magma chamber and faults beneath a Mid-Atlantic Ridge hydrothermal field

Crust at slow-spreading ridges is formed by a combination of magmatic and tectonic processes, with magmatic accretion possibly involving short-lived crustal magma chambers. The reflections of seismic waves from crustal magma chambers have been observed beneath intermediate and fast-spreading centres, but it has been difficult to image such magma chambers beneath slow-spreading centres, owing to rough seafloor topography and associated seafloor scattering. In the absence of any images of magma chambers or of subsurface near-axis faults, it has been difficult to characterize the interplay of magmatic and tectonic processes in crustal accretion and hydrothermal circulation at slow-spreading ridges. Here we report the presence of a crustal magma chamber beneath the slow-spreading Lucky Strike segment of the Mid-Atlantic Ridge. The reflection from the top of the magma chamber, centred beneath the Lucky Strike volcano and hydrothermal field, is approximately 3 km beneath the sea floor, 3-4 km wide and extends up to 7 km along-axis. We suggest that this magma chamber provides the heat for the active hydrothermal vent field above it. We also observe axial valley bounding faults that seem to penetrate down to the magma chamber depth as well as a set of inward-dipping faults cutting through the volcanic edifice, suggesting continuous interactions between tectonic and magmatic processes.     

Zircon chronology and REE geochemistry of granulite xenolith at Hannuoba

The lower crustal xenolith of mafic two-pyroxene granulite (the majority) and hypersthene granulite in the Cenozoic basalt at Hannuoba have the characteristics of igneous blastic structure and granulite facies metamorphic recrystallization. Study on the zircon chronology and REE geochemistry of granulite xenolith shows that the underplating of basic magma into the lower crust during late Mesozoic led to the formation of mafic accumulate, which further through metamorphism of granulite facies formed the high-density and high-velocity crustal bottom layer at the lower crust. This suggests that the underplating of mantle magma is the important way for the vertical overgrowth of continental crust since the Phanerozoic and provides new evidence for crust-mantle interaction.     

Frozen magma lenses below the oceanic crust

The Earth's oceanic crust crystallizes from magmatic systems generated at mid-ocean ridges. Whereas a single magma body residing within the mid-crust is thought to be responsible for the generation of the upper oceanic crust, it remains unclear if the lower crust is formed from the same magma body, or if it mainly crystallizes from magma lenses located at the base of the crust. Thermal modelling, tomography, compliance and wide-angle seismic studies, supported by geological evidence, suggest the presence of gabbroic-melt accumulations within the Moho transition zone in the vicinity of fast- to intermediate-spreading centres. Until now, however, no reflection images have been obtained of such a structure within the Moho transition zone. Here we show images of groups of Moho transition zone reflection events that resulted from the analysis of approximately 1,500 km of multichannel seismic data collected across the intermediate-spreading-rate Juan de Fuca ridge. From our observations we suggest that gabbro lenses and melt accumulations embedded within dunite or residual mantle peridotite are the most probable cause for the observed reflectivity, thus providing support for the hypothesis that the crust is generated from multiple magma bodies.     

Ore-forming event and geodynamic setting of molybdenum deposit at Wenquan in Gansu Province, Western Qinling

The Wenquan molybdenum deposit is associated with a Triassic granite in this area. The Wenquan granite is enriched in LILE and LREE, poor in HFSE, and has significantly higher contents of alkali （K2O＋Na2O） and Sr, Ba than those of the island arc volcanic rocks. These geochemical characteristics are similar to post-collisional granites in high K calc-alkaline series. Studies of major elements, trace elements, REEs and chronology of the Wenquan pluton show that, in the geodynamic transition stage of continent-continent convergence to extension, the partial melting of the enriched lithospheric mantle generated the basaltic magma and triggered the partial melting of the thickened lower crust which produceded the acidic magma, and the Wenquan pluton was formed by mixing of the two magmas. Molybdenite Re-Os isotopic dating gave Os model ages of 212.7±2.6 Ma to 215.1±2.6 Ma with a weighted mean of 214.1±1.1 Ma, and an Re-Os isochron age of 214.4±7.1 Ma. These ages are close to K-Ar ages （223 to 226 Ma） and a SHRIMP zircon U-Pb age （223±7 Ma） for the Wenquan granite within the error range, but relatively younger. This implies that the Mo mineralization occurred in a late stage of the magmatic intrusion, and the metallogenesis took place in the transition stage from syn-collision to post-collision in the tectonic setting of the Qinling Orogenic Belt （QOB） after continental collision between the North China Block （NCB） and the South China Block （SCB）. This process is also corresponding to the geological events of metamorphism and deformation in South Qinling, closure of the Mian-Lue oceanic basin, and exhumation of the Dabie-Sulu ultrahigh-pressure metamorphic rocks. The large-scale continent-continent collision between NCB and SCB in the middle Triassic triggered significant crustal thickening and exhumation of subducted slab. In the late Triassic, the tectonic setting was transformed to the transition stage from collision to extension. Materials from the asthenospheric mantle would ascend into the root of the lower crust, which could induce partial melting of the lower crust and generate Mo-enriched granitic magma. The ore-forming elements enriched in the fluid derived from the condensation and fraction of the magma resulted in the Mo mineralization. The Mo deposits in the QOB are mainly formed in two episodes, namely 220± Ma and 140± Ma. The two episodes of metallogenesis were developed in the tectonic transition settings from compression to extension, but they were in the different stages of the tectonic evolution. The occurrence of the Wenquan Mo-bearing pluton indicates that the Triassic tectonic-magmatic belt of Western Qinling is another favorable region for Mo mineralization in the QOB. Therefore, it is significant to pay more attention to evaluation of the ore-forming potentiality in the Triassic granites in Western Qinling.     

相山高分异A型花岗岩的识别及地质意义

传统地球化学判别图解能够较好地区分I-S-M-A花岗岩岩石成因类型,但对于高分异花岗岩的判别并不可靠.相山火山侵入杂岩岩石成因一直存在S型和A型的争议,高度分离结晶作用可能是导致这一争议的原因所在.系统收集了相山火山侵入杂岩相关地球化学数据,进行了高分异花岗岩的地球化学判别及岩石成因类型的判别.结果表明,相山火山侵入杂...