大别地块东南缘逆冲滑脱构造体系及其对金矿的控制作用

大别地块自晚元古代以来主要经受了自北而南的推挤,并且发生了两次较强烈的南移运动,造成了地块前线逆冲滑脱构造体系。特别是中生代的推挤和滑移,不仅构造变形强烈,而且还伴有热事件,大别地块东南缘郯－庐断裂南延部分和广济－宿松平移－推覆型韧性剪切带均是＂热线构造＂,它们提供了深层次岩浆活动的通道。本区岩石以绿片岩－角闪岩相变质岩为主,含金背景值高,逆冲滑脱构造和韧性剪切带的活动与金元素的活化、迁移和富集创造了良好的条件。     

扬子地块西南缘大面积低温成矿时代

中国西南地区(川、滇、黔、桂、湘)发育有世界上很典型的低温成矿域,其面积之大(约90万km2)、包含的矿种之多(Au、Hg、Sb、As、P、Pb-Zn、U、Ni-Mo-PGE、重晶石、冰州石和分散元素等)、矿床组成和组合之复杂,在全球十分鲜见。扬子地块西南缘是中国西南大面积低温成矿域的重要组成部分。近年来,作者采用Rb-Sr、Sm-Nd、Ar-Ar等多种同位素定年方法,对扬子地块西南缘产出的磷矿、金矿、锑矿等低温矿床的成矿时代进行了较系统的研究。文章总结了这些研究成果,并结合前人的资料,初步拟定出该区存在三期大规模低温成矿作用,它们分别相当于晚元古代—早古生代(晚震旦世—早寒武世)、晚加里东期(晚志留世—早泥盆地)和燕山期(晚侏罗世—中白垩世)。该区的磷矿、重晶石矿和黑色页岩中的镍钼铂矿主要形成于晚元古代—早古生代,同位素年龄主要为585～540Ma;赋存于前寒武纪浅变质碎屑岩中的金-锑-钨矿床主要形成于晚加里东期,同位素年龄主要为435～380Ma;产于寒武系以后地层中的锑矿床主要是在中燕山期成矿,同位素年龄主要为160～140Ma;而该区的卡林型金矿和汞矿主要在燕山中晚期大规模成矿,同位素年龄主要为170～80Ma。     

从黄铁矿特征论380地区金鸡岭岩体外带铀矿床成矿机理

本文以铀矿区广泛发育的黄铁矿为研究对象，通过成因矿物学方法探讨金鸡岭岩体外带铀矿床的成矿机理；论证了矿质来源于岩体的围岩，与花岗岩关系不密切；岩体侵位所引起的围岩热变质作用，以及由此而产生的变质热液，是导致成矿物质重新活化、迁移和富集成矿的根本原因。     

两广交界地区壶垌片麻状复式岩体的年代学和地球化学：对云开地块北缘早古生代构造-岩浆作用的启示

本文对两广交界地区发育的壶垌片麻状复式岩体进行了LA-ICP-MS锆石U-Pb定年和岩石学、地球化学、Sr-Nd-Pb同位素的分析研究。该复式岩体主要由片麻状英云闪长岩、片麻状花岗闪长岩和片麻状二长花岗岩组成,获得片麻状花岗闪长岩LA-ICP-MS锆石U-Pb谐和年龄为443.1±2.0Ma。其中片麻状英云闪长岩和片麻状花岗闪长岩总体具有较低硅(SiO2=62.92%~67.54%)、较低碱(K2O+Na2O=3.98%~5.17%)、准铝质(A/CNK=0.83~0.93)的化学组成特征,属于中钾含角闪石钙碱性花岗岩类(ACG);而片麻状二长花岗岩具有高硅(SiO2=71.55%~72.78%)、高碱(K2O+Na2O=6.65%~7.57%)、准铝-弱过铝质(A/CNK=0.92~1.05)的化学组成特征,属于高钾钙碱性花岗岩类(KCG)。岩石表现出富集大离子亲石元素(如U、Ba、Rb和Th)和轻稀土元素,而Nb、Ta和Ti等高场强元素和重稀土元素明显亏损,并具有较高的锶同位素初始比值((87Sr/86Sr)i=0.71268~0.71482)和较低的εNd(t)值(-9.4~-2.6),反映其具有俯冲消减作用形成的岛弧岩浆岩地球化学特征。结合区域地质特征分析认为,壶垌片麻状复式岩体很可能是在扬子板块和华夏板块之间的洋壳岩石圈向南俯冲的地球动力学背景下,引发软流圈地幔上涌,其所带来的热能诱发了岩石圈地幔和上覆云开地块的古老地壳物质重熔,形成以壳源为主的壳幔混源母岩浆,再经历不同程度分离结晶作用,从而形成了本区大陆边缘弧型岩浆岩。因此,壶垌片麻状复式岩体是云开地块北缘早古生代洋陆俯冲-碰撞的地质记录。     

Deep-seated structure and gold content of Russia and China contiguous territories

On the contiguous territories of southeastern Russia and northeastern China, many gold-bearing areas are conjugate in space with the gradient zones of the gravity field. Large gold-ore districts, defining in many respects the metallogenic signature of the region, are located on the joints of differently oriented gradient zones. In the best-studied districts, the Precambrian protrusions, staged distribution of magmatic chambers ( by vertical) above the Mohorovicic discontinuity and restriction to the peripheral parts of intrusive massifs have been recognized. Different-type gold deposits in the studied ore-placer districts and nodes are often located on the areas of joint of the granitoid massifs and subvolcanic bodieswith depressions. Availability of areals of metasomatic alterations of rocks, placers, and ore occurrences of precious metals on such but poorly studied areas can serve as the basis for the revision and detailed forecasting-prospecting works to develop the mineral-raw material base of the region for precious metals.     

班公湖-怒江带、羌塘地块特提斯演化与成矿地质背景

早古生代—泥盆纪,研究区沉积环境以陆棚碎屑岩相和碳酸盐台地相为主,代表冈瓦纳大陆北缘和特提斯南侧的被动大陆边缘。石炭纪—二叠纪,本区进入特提斯南、北缘弧盆系统演化阶段,龙木错-双湖带北部、金沙江带南部和冈底斯带分别在石炭纪、二叠纪形成岩浆弧。中生代是特提斯南缘弧盆演化阶段,SSZ型蛇绿岩形成岩浆熔离型铬、镍、铂族金属矿床和热液型金矿。班公湖-怒江带特提斯在中侏罗世至早白垩世向南、北两侧俯冲并形成岩浆弧,该岩浆弧是重要的成矿带,形成斑岩铜矿、矽卡岩型磁铁矿和热液型多金属矿床。北羌塘东段侏罗纪弧后前陆盆地有利于形成沉积型、沉积-热液改造型和热液型铁、铜、锑、金矿床。晚白垩世碰撞作用主要与热液型矿床有关,分布范围较大,也可能存在晚白垩世至新生代碰撞阶段的斑岩铜矿。     

~(40)Ar/~(39)Ar dating of shear deformation of the Xianshuihe fault zone in west Sichuan and its tectonic significance

TheNW-SEstrikingXianshuihefaultzoneslicesthesoutheasternTibetanPlateauandconnectssoutheastwardwiththeAnninghe-Zemuhe-Xiaojiangfaultzone,whichformahuge,activesinistralstrike-slipfaultzone(fig.1).ThisfaultzoneisanimportantseismicfaultineastTibet[1-5].EarthquakegeologystudiesandoffsetpatternsofyounggeologicalfeatureshaveshownthatlateQuaternarysinistralsliprateoftheXianshuihefaultzonereaches13mm/a[1,2].TheXianshuhefaultzoneconsistsoftwomainbranches,theDaofufaultbranchinthewestandtheXianshuih…     

全吉地块金泉山—化石沟一带古生代 花岗质岩体地球化学及其构造意义

柴达木盆地北缘之全吉地块花岗质岩体大量发育,具多期次多阶段特征。通过对全吉地块金泉山—化石沟一带古生代花岗质岩体岩石学、岩石化学特征及单颗粒锆石U-Pb同位素定年,发现该区花岗岩有4次侵入,侵入时代分别为早奥陶世(471~476Ma)、中奥陶世(459±5Ma)、早志留世(423±4Ma)和中泥盆世(366±2Ma)。岩石地球化学研究显示,该4期花岗岩均具典型的钙碱性特征,轻稀土富集、重稀土轻度亏损、Eu轻微负异常—正异常,大离子亲石元素K2O、Rb、Ba、Th等相对强烈富集,高场强元素Nb、Ta、Hf、Zr及Yb明显亏损,除第4期岩体即具I型,又具S花岗岩特征外,其它各期次均属I型花岗岩,总体显示岩体具壳源特征,为板块碰撞前消减地区花岗岩,研究推测,金泉山—化石沟一带古生代花岗质岩体第1、2组年龄为全吉地块与柴达木陆块碰撞的时代,第3组年龄反映了深俯冲地下的板块由于拆沉而折返的时代,第4组年龄为碰撞隆起后造山带伸展、滑塌的时代。     

Location of Triassic Tectonic Suture Between Collided Sino-Korean and Yangtze Cratons in Dabie-Sulu Region, China

INTRODUCTIONTheageofultrahigh-pressuremetamorphism(UHPM)andhigh-pressuremetamorphism(HPM)hasbeendeterminedat24OMato2loMabyseveralchronologicalmethods(Lietal.,1998;Maruyamaetal.,l998iAmesetal.,l9961Hack-erandWang,l995;Johnetal,,1994).Theseagedatare-f1ecttheTriassicobliquecollisionbetweentheSino-KoreanandYangtzecratons.ThermobarometricestimatesoftheUH-PMandHPMintheDabie-SuluregionshowthatthecoldcontinentalcrustmaterialoftheYangtzecratonwasunder-thrust,alongthesuture,northwardtoma…     

The Koshrabad granite massif in Uzbekistan: petrogenesis, metallogeny, and geodynamic setting

The Koshrabad massif, referred to as the Hercynian postcollisional intrusions of the Tien Shan, is composed of two rock series: (1) mafic and quartz monzonites and (2) granites of the main phase. Porphyritic granitoids of the main phase contain ovoids of alkali feldspar, often rimmed with plagioclase. Mafic rocks developed locally in the massif core resulted from the injections of mafic magma into the still unconsolidated rocks of the main phase, which produced hybrid rocks and various dike series. All rocks of the massif are characterized by high f (Fe/(Fe + Mg)) values and contain fayalite, which points to the reducing conditions of their formation. Mafic rocks are the product of fractional crystallization of alkali-basaltic mantle melt, and granitoids of the main phase show signs of crustal-substance contamination. In high f values and HFSE contents the massif rocks are similar to A-type granites. Data on the geochemical evolution of the massif rocks confirm the genetic relationship of the massif gold deposits with magmatic processes and suggest the accumulation of gold in residual acid melts and the rapid formation of ore quartz veins in the same structures that controlled the intrusion of late dikes. The simultaneous intrusion of compositionally different postcollisional granitoids of the North Nuratau Ridge, including the Koshrabad granitoids, is due to the synchronous melting of different crustal protoliths in the zone of transcrustal shear, which was caused by the ascent of the hot asthenospheric matter in the dilatation setting. The resulting circulation of fluids led to the mobilization of ore elements from the crustal rocks and their accumulation in commercial concentrations.