秦岭岩群中两类斜长角闪岩的性质和时代及其地质意义

在北秦岭造山带核部秦岭岩群内发育两类不同产状的斜长角闪岩.一类与秦岭岩群中的大理岩紧密共生,呈规模较大的似层状或较小块体产于大理岩内,另一类则呈密集岩墙群型式侵入于秦岭岩群南段二云母石英片岩中.不同的产出状态表明两类斜长角闪岩的成因和时代存在显著差异,也具有不同的地质构造意义.地球化学上,两类不同产状的斜长角闪岩的原岩皆为玄武岩质的.侵入秦岭岩群二云母石英片岩中的斜长角闪岩墙群形成于板内拉张环境,SHRIMP锆石U-Pb测年揭示该类斜长角闪岩形成于晚奥陶世(449±11Ma),Sr-Nd同位素特征显示其岩浆源区为亏损地幔源区,40Ar/39Ar热年代学研究显示该类斜长角闪岩的角闪岩相变质作用发生于石炭纪末期(301.3±6.4Ma).地球化学和Sr-Nd同位素特征显示与秦岭岩群大理岩共生的似层状或块状斜长角闪岩的形成环境与侵入云母石英片岩中的斜长角闪岩墙群的存在显著差异,其形成于洋岛(OIB)或海山环境.40Ar/39Ar热年代学研究显示该类斜长角闪岩于晚二叠世(258.1±5.7Ma)发生了角闪岩相变质作用.不同性质、形成和变质时代、相似的变质作用等特点表明,秦岭岩群中的两类角闪岩分属不同性质的构造块体,秦岭岩群高级变地质地体可能是一个构造拼合地体.斜长角闪岩岩墙为晚奥陶世(449±11Ma)侵入秦岭岩群云英片岩中的基性岩墙群,是北秦岭晚加里东期后造山期热收缩而致的地壳伸展或岩圈拆离减薄的产物.与秦岭岩群大理岩共生的斜长角闪岩则可能是洋隆体的基性喷出岩+碳酸盐岩帽组合,是中二叠世(312～260Ma)期间构造移置而来的外来块体.     

东帕米尔变质核杂岩构造的厘定

卡拉库鲁木变质核杂岩是慕土塔格岩体的南缘部分，由长城系片麻岩以及燕山期花岗岩组成，其中长城系片麻岩为一套低角闪岩相的变质侵入岩，主要岩性为（石榴石）黑云二长片麻岩、（石榴石）黑云斜长片麻岩；根据变形程度，将其划分为内带、中带及外带，其中在内带见有燕山期花岗岩。剥离断层沿变质核杂岩边缘呈向南凸出的弧形展布。剥离断层上盘滑脱体由长城系赛图拉岩群高绿片岩－低角闪岩相的变质岩系构成。变质核杂岩构造的形成时代为早－中侏罗世。     

某地花岗伟晶岩脉和石英碳酸盐脉中褐帘石、独居石形成条件的讨论

脉岩分布在某地槽区一背斜构造轴部的太古代变质岩和燕山期花岗岩、花岗斑岩中。该区脉岩有中-基性脉岩(闪长岩、黑云母角闪岩、煌斑岩),酸性脉岩(花岗斑岩、花岗伟晶岩、霓石正长岩、石英斑岩)和石英碳酸盐脉,构成了一个脉岩群。 太古代变质岩系。下部出露在背斜构造的轴部,为黑云外长片麻岩、混合岩化黑云斜长片麻岩、角闪黑云斜长片麻岩,有时彼此互层出现,某些地段见大理岩夹层;上部分布在背斜构造的两翼,为黑云斜长片麻岩、角闪斜长片麻岩、花岗质混合片麻岩,局部夹大理岩     

内蒙古固阳县乌拉山(岩)群混合岩作用的机制及演化

内蒙古固阳一带广泛出露了一套太古宙乌拉山 (岩 )群的高角闪岩相—麻粒岩相的岩石。通过区域地质调查及重点地段的研究 ,确定其在区域变质作用中总体处于高角闪岩相 ,但也存在局部高温高压 (麻粒岩相 )的地段。根据脉体特征及相互关系 ,划分出第一期以富钠 (脉体为英云闪长岩、奥长花岗岩 )为特征和第二期以富钾 (脉体为钾长花岗岩 )为主的两期混合岩化作用。确定第一期为前构造期的混合岩化作用 ,是区域变质作用的延续与发展 ;第二期为同构造期的混合岩化作用 ,随着乌拉山旋回构造运动的加强而加强、构造运动的结束而结束     

东升庙地区基性岩系变质作用过程

狼山地区位于华北克拉通北缘内蒙古狼山西段,该区构造演化变形强烈,根据基性变质岩系的产出地层时代、产状以及它们与不同期次的变质、变形乃至混合岩化作用的关系,将基性岩系地体按形成时序划分出4个期次。不同产状及期次划分的基性系列变质岩为恢复区域地质演化史提供了重要信息。笔者通过岩相学观察、化学全分析和电子探针等手段对不同期次变质岩的岩石学和矿物学特征进行研究,探讨其温压条件和构造背景。岩石学特征表明,狼山基性变质岩除绿片岩外,原岩都为基性火山岩。第一期斜长角闪岩富集Pb、K、Nb、Ta,存在明显亏损,Hf、Zr、Ti弱亏损,轻重稀土分异较明显,属于岛弧玄武岩;第二、三期斜长角闪岩具有板内和岛弧过渡的特点;第四期脉状斜长角闪岩轻稀土相对较低,表现为产生在板内张裂环境侵位环境。绿片岩Sr、K、Rb、Ba亏损而Th的明显富集具有岛弧或弧后盆地玄武岩的特征。选用斜长石、角闪石共生矿物计算各期斜长角闪岩所经历过变质作用的温度和压力。第一期斜长角闪岩计算得出其属于早期高角闪岩相-麻粒岩相;第二期玄武岩计算得出其代表了早期为角闪岩相晚期向低角闪岩相退变的变质过程;第三期斜长角闪岩计算得出其属于低角闪岩相;第四期斜长角闪岩属于接触变质的绿帘角闪角岩相。     

新疆若羌县黑山梁地区北山岩群地质特征及构造环境

北山岩群是一套经角闪岩相主期变质作用和绿帘角闪岩相退变质作用的强变质变形地体.据岩石组合特征可划分为4个岩组:第一岩组为斜长角闪片岩夹黑云斜长片麻岩和变粒岩;第二岩组为片麻岩夹斜长角闪片岩、石英片岩、变粒岩;第三岩组为石英片岩夹大理岩、石英岩;第四岩组为石英岩夹石英片岩.经原岩恢复,第一岩组原岩主要为板内拉斑玄武岩,具向岛弧玄武岩过渡趋势;第二岩组原岩为快速沉积的碎屑岩和酸性火山岩;第三岩组原岩为碎屑岩夹碳酸盐岩;第四岩组原岩为成熟度较高的碎屑岩.据火山岩组合、碎屑组合岩特征及地球化学特征,判断其形成年代为早元古代,构造环境为早期裂谷发育速度较快,火山活动强烈,沉积物为快速沉积的碎屑岩;后期构造趋于平缓,碎屑岩成熟度升高,并夹有厚层碳酸盐岩.     

华北克拉通东北部新太古代晚期地壳生长:来自板石沟表壳岩年代学和Hf同位素的证据

对板石沟表壳岩中的斜长角闪岩和角闪片岩进行了锆石U-Pb年代学、地球化学以及Hf同位素分析,以探讨华北克拉通东北部新太古代晚期的构造环境和地壳演化。板石沟表壳岩主要岩石类型包括斜长角闪岩、斜长片麻岩、角闪片岩和磁铁石英岩,LA-ICP-MS锆石U-Pb测年显示斜长角闪岩(BA-1)岩浆锆石形成于2548±11Ma,绿帘角闪片岩(BA-6)岩浆锆石形成于2548±23Ma,代表了表壳岩的形成时代,在绿帘角闪片岩中识别出3颗年龄为2754±80Ma~2710±92Ma的捕获锆石,表明板石沟地区可能存在新太古代早期岩浆事件。斜长角闪岩和角闪片岩的原岩为玄武质火山岩,微量元素特征指示其形成于岛弧环境。Hf同位素分析结果显示斜长角闪岩εHf(t)为正值(0.29~8.89),单阶段模式年龄(tDM1)分布在2877~2469Ma之间,绿帘角闪片岩多具正的εHf(t)值(-0.78~8.03),tDM1介于2871~2544Ma,表明岩浆主要来源于亏损地幔,伴随少量古老地壳物质的再造,部分tDM1与207Pb/206Pb年龄相近,并同时具有高εHf(t)值的锆石反映板石沟地区新太古代晚期(2550Ma)发生过地壳增生事件。结合其他地区表壳岩研究成果,认为华北克拉通可能存在新太古代吉-辽-冀弧陆碰撞造山带,板石沟地区属于该造山带的一部分。     

河北承德庞家沟银多金属矿构造岩相学地层格架特征

<正>采用构造-岩相学方法(方维萱,2011,2012),将庞家沟银多金属矿构造-岩相学结构划分为四个层次,分述如下:(1)太古界单塔子群(下基底构造层)。发育角闪岩相、绿片岩相、混合岩化相的区域变质岩,且糜棱岩化相发育。(1)角闪岩相:由黑云母斜长片麻岩、角闪斜长片麻岩及石榴角闪斜长片麻岩、角闪岩等组成。(2)绿片岩相:由绿泥石片岩、绿泥石绢云母片岩组成。见于太古界凤凰咀组顶部。(3)混合岩化相:为     

潼关小秦岭金矿自然金标型特征及其意义

潼关小秦岭金矿田为我国金矿主要产地之一。矿区位于秦岭纬向构造带北缘太古界隆起。含金石英脉体产于太古界、太华群深变质岩系中,变质岩系主要由斜长角闪岩、黑云母或角闪斜长片麻岩夹薄层大理岩组成。含金矿物有硫化物类、氧化物类、碳酸盐类矿物。此外构造片岩、蚀变岩中也含少量金。各类矿物中Au、Ag的平均含量见表1。由表1可见,Au主要赋存于黄铁矿,其次是方铅矿,但因后者数量少,分布有限,因而无论在石英脉里,还是在构造片岩或蚀变岩中黄铁矿部都是主要载金矿物。     

吉林省珲春杨金沟白钨矿区地质特征及找矿方向

杨金沟矿区白钨矿体产于下古生界五道沟群地层与印支期二长花岗岩内外接触带中。矿化类型为花岗岩中的白钨矿—石英脉和斜长角闪片岩、云母石英片岩、红柱石片岩中的白钨矿—石英脉。矿体受南北向、北西向断裂及裂隙构造控制,矿床成因为岩浆热液—层控与岩浆热液复合型。     

江绍断裂两侧早元古代变质基底特征及形成的构造环境

江绍断裂东侧出露的早元古代变质基底以一套遭受中压型角闪岩相区域热流变质作用改造的黑云斜长变粒岩、云母石英片岩为主，夹少量斜长角闪岩和大理岩，已遭受４期构造变形作用改造，从原岩建造和主要岩类地球化学特点推测它可能形成于大陆或大陆边缘类似于内硅铝盆地环境。江绍断裂西侧早元古代变质基底则以星子杂岩为代表，由变粒岩、浅粒岩、（十字一石榴）云母片岩和少量斜长角闪岩组成，已遭受中压型高绿片岩相一低角闪岩相区域热流变质作用改造，推测其形成于活动性较强大陆一大陆边缘环境。江绍断裂两侧早元古代变质基底在原岩建造、变质一变形作用等特征上存在明显差异，因此华夏地块和扬子地块在早元古代可能是两个地块。     

冀东金厂峪金矿区钠长岩脉及青山口花岗岩体SHRIMP锆石U-Pb定年及其意义

金厂峪金矿床是冀东最大的金矿床 ,具有早期复脉型和晚期石英大脉型两种矿石类型。矿区产有多期钠长岩脉 ,且与含金矿脉有密切的时间和空间关系。青山口花岗岩体位于矿区西约 2～ 3km,有研究者认为金矿床成因上与花岗岩体有关。应用先进的 SHRIMP测年技术 ,测得肉红色钠长岩脉的锆石 w (2 0 7Pb) / w (2 0 6Pb)年龄为 (185 8± 8) Ma,青山口花岗岩体锆石 w(2 0 6Pb) / w(2 3 8U )年龄为 (199± 2 ) Ma。金厂峪金矿床的的复脉型矿化早于肉红色钠长岩脉 ,故其矿化的时代应在晚元古代。青山口岩体的年龄和区域上与辉钼矿化有关的花岗岩年龄一致 ,均为燕山早期。推测金厂峪金矿床晚期石英大脉型矿化中的辉钼矿化可能与青山口花岗岩体有关 ,石英大脉型金矿化时代为中生代燕山期     

京北琉璃庙地区变质杂岩变质变形特征

琉璃庙地区变质杂岩主要由变质上壳岩、变质深成侵入杂岩及其脉岩群组成.它们多数经韧性变形改造形成各种类型糜棱岩和构造片岩.研究表明,变质上壳岩原岩主要以钙碱性火山(熔)岩为主.本区变质杂岩经历了三期变质变形作用,即高角闪岩相区域变质作用形成大型复式同斜紧闭褶皱;绿帘角闪岩相动力变质作用及强烈的韧性变形,形成了以蓝闪石为特征的不同强度的糜棱岩带;绿片岩相动力变质作用和韧脆性变形作用.     

Genesis of the Shear Zone-related Gold Vein Mineralization of the Lega Dembi Gold Deposit, Adola Gold Field, Southern Ethiopia

The Lega Dembi Primary Gold Deposit in southern Ethiopia is related to the shear zone-hosted vein in the Neoproterozoic metamorphosed volcano-sedimentary succession of greenschist- to amphibolite-facies metamorphism. The rocks consists of a sequence of biotite-feldspar-quartz schists, carbonaceous mica-schists, amphibolites and basic to ultrabasic rocks. This unit is separated from a foot wall biotite gneiss by a major shear zone. The ore bodies are hosted in the volcano-sedimentary sequence and consist of swarms of quartz veins, lenses, and stockworks that propagated along mesoscale ductile to brittle-ductile shear zones.The mineralization is defined by a complex paragenesis of gold in association with Cu-Pb-Zn-Fe sulphides, tellurides and sulphosalts. The presence of Ni-bearing minerals in amphibolites of the host sequence, together with the ore mineral association, suggests an origin related to mafic volcanism.     

Shear-zone hosted copper mineralisation of the Omitiomire deposit — Structural controls of fluid flow and mineralisation during subduction accretion in the Pan-African Damara Belt of Namibia

The Omitiomire copper deposit is a relatively recent discovery in the Pan-African Damara Belt of central Namibia. The deposit is situated in Mesoproterozoic gneisses and amphibolites of the Ekuja Dome overlain by amphibolite-grade metaturbidites of the Southern Zone accretionary prism that formed during northward subduction of the Kalahari Craton below the Congo Craton between ca. 580–520 Ma. Copper mineralisation is confined to an anastomosing system of shallowly-dipping, retrograde mylonitic shear zones within the Ekuja Dome. The shear zones are centred around a lithologically heterogeneous amphibolite-gneiss sequence. Mylonitisation and copper mineralisation are closely associated with the retrogression of particularly amphibolites and the partial or complete replacement of amphibolites by biotite–epidote and biotite–chlorite–epidote schists that host the chalcocite-dominated mineralisation.Deformation and mineralisation in the heterogeneous shear-zone system can be shown to describe a progression. Initial strain localization is confined to lithological (amphibolite-gneiss) contacts and associated quartz veining and fluid flow are preferentially developed around the margins of competent amphibolite units. Fluid infiltration and the retrogression of amphibolites to biotite–epidote schists leads to strain localization into the marginal schists that envelop amphibolites. Further veining and fluid flow are localised into the central parts of amphibolite units leading to the pervasive retrogression to biotite–epidote schists that dominate the central parts of the shear-zone system. Earlier quartz-vein generations appear as isoclinally folded and dismembered ribbons or boudins in mineralised schists. The clearly syntectonic introduction of the copper mineralisation is underlined by the intergrowth of chalcocite with the retrograde assemblages and chalcocite forming part of the mylonitic shear-zone fabric.3D modelling of drillhole data combined with limited surface exposure delineates a shallow east dipping, gently undulating ore body parallel to the regional gneissosity of the Ekuja Dome. The ore body comprises several mineralised lenses varying in thickness from 10 m to > 100 m. Prominent ore shoots are gently doubly plunging to the N and S and parallel to the regionally developed L > S fabric in the gneisses. Kinematic indicators in the mineralised shear zone system point to a top-to-the S sense of shear, parallel to the regional L fabric and parallel to the southverging transport recorded in the structurally overlying prism metasediments.The regional setting of the Omitiomire deposit, kinematics, and retrograde, but high-temperature overprint of original mineral assemblages in the mineralised shear zones indicate deformation and fluid flow during the expulsion of the basement gneisses during N-ward direction subduction of the Kalahari Craton below the Congo Craton. Lithological, geochronological, structural and P–T data suggest numerous similarities and, indeed, correlations between the Omitiomire-style copper mineralisation of the Damara Belt with the large copper deposits hosted by basement gneisses in the Domes Region of the Lufilian Arc in Zambia.     

Proterozoic metavolcanics from western Sierras Pampeanas terrane, Argentina

A series of medium grade metamorphic rocks of the western sector of the Sierras Pampeanas Terrane in central western Argentina are represented by amphibolites, gneisses and schists derived from sedimentary as well as from igneous rocks. The metavolcanics consist of amphibolites, quartz-K-feldspar-muscovite schists, and hornblende-biotite and biotite-epidote-plagioclase schists. Based on petrographic and geochemical data they are interpreted as originating as basaltic tholeiites, rhyolites and mesosilicic volcanics. The distribution and geochemical behavior are similar to present day western Pacific lavas, mainly those developed on island arcs or heavily attenuated continental crust. Based on these characteristics, an accretionary tectonic model involving a series of island-arc collisions is proposed for the Proterozoic. The complex Proterozoic tectonic history of the western Sierras Pampeanas has been partially obliterated by the emplacement of the Early Paleozoic magmatic arc rocks.     

Oceanic and riftogenic metavolcanic associations of greenstone belts in the northwestern part of the Sharyzhalgai Uplift, Baikal region

The Onot and Bulun terranes are confined to the Sharyzhalgai Uplift in the southwestern margin of the Siberian craton. They consist of alternating blocks and nappes of Paleoarchean tonalite-trondhjemite-granodiorite complex and supracrustal metasedimentary-volcanogenic rocks of greenstone belts (GSB). The lower part of the Onot GSB is made up of a bimodal association of aporhyolite microgneisses with subordinate amphibolites, while the upper part consists of amphibolites associated with banded iron formation, metapelites, dolomitic marbles, and magnesites. The Urik GSB in the Bulun block comprises three rock associations: (1) garnet amphibolites and amphibolites alternating with kyanite-bearing mica schists and quartzite schists; (2) garnet-bearing biotite and amphibole crystalline schists with tectonic lenses of garnet amphibolites; (3) biotite and amphibole-biotite orthogneisses and biotite plagiogneisses. The microgneisses (metarhyolitoids) of the Onot belt are correlated with within-plate volcanic rocks and A-type granites. The composition of the amphibolites corresponds to high-Mg low-Ti tholeiitic basalts. The formation of metavolcanic rocks of the Onot GSB was related to the rifting of the Paleoarchean continental crust, which is supported by the formation of felsic metavolcanic rocks from an ancient tonalite source and by the geochemical signatures of crustal contamination of metabasalts. The amphibolites of the Urik GSB are subdivided into three petrogeochemical types. The first and second types correspond to high-and low-Mg tholeiitic basalts and have practically flat multielement patterns. The amphibolites of the third type correspond to subalkaline leucobasalts. Two types of orthogneisses are comparable with intermediate-acid volcanic rocks of the andesite-dacite and adakite series. In terms of geochemistry, the metamafic volcanic rocks of the Urik GSB represent the rocks of the oceanic crust. Oceanic settings of their formation are confirmed by an association of metavolcanic rocks with abyssal distal siliceous-argillaceous deposits. The formation of two types of intermediate-acid metavolcanic rocks of andesite-dacite and adakite associations, as well as garnet-bearing paraschists, was presumably related to subduction settings.     

内蒙中部岩金矿类型及找矿方向

内蒙中部地区金的成矿类型有含金石英脉型、含金蚀变岩型、含金钾长花岗岩脉型、含金石英钾长石脉型及不整合面金矿型.迄今已探明赛乌素、十八顷壕、后石花、酒馆、柏树沟、大桦背和白乃庙等金矿.进而提出蚀变岩型、石英脉型及钾长石化地区的金矿找矿方向.     

Reworking of intra-oceanic rocks in a deep sea basin: example from the Bou-Maiza complex (Edough massif,eastern Algeria)

Metagabbros and amphibolites exposed in the Bou-Maïza area of the Edough massif (northeast Algeria) are described in detail. Field and petro-structural observations point to the syn-sedimentary emplacement of gabbros as clasts, blocks and lenses of polymictic gabbroic breccias. Associated amphibolites display fine-scale parallel sedimentary bedding and represent mafic epiclastites, litharenites and mafic greywackes. The mafic beds and lenses are intercalated with aluminous pelitic schists of continental origin, quartzite and marble. It is concluded that all mafic rocks from this locality derive from the erosion of an oceanic plutono-volcanic complex of MORB affinity that was reworked in a block matrix mélange and emplaced as turbidites and debris flows during the Mesozoic. We propose a convergent plate margin setting for these formations connected with the subducted Calabrian branch of the Tethyan slab.     

GEOLOGY OF THE TAPLEJUNG WINDOW AND FRONTAL BELT, FAR EASTERN NEPAL HIMALAYA

GEOLOGY OF THE TAPLEJUNG WINDOW AND FRONTAL BELT, FAR EASTERN NEPAL HIMALAYA1　PecherA .Deformationandmetamorphismeassociesaunezonedecisaillement :Exampledugrandchevauchementcen tralHimalayan (MCT) [M ].Thesed’Etat,UnivGrenoble ,France ,1978.35 4. 2　RaiSM .LesnappesdeKathmandudtduGosainkund ,HimalayaduNepalcentral[M ].Thesededoctoral,Univ .Grenoble ,France ,1998.2 44 . 3　SchellingD ,AritaK .Thrusttectonics ,crustalshortening ,andthestructureofthe…