Discovery of A-type Granite Zone and Its Geodynamic Significance in the Western Kunlun Mts., China

l. IntroductionGranite distributes widely in western KunlunMts. Many researches have been conducted byscientists (Wang Yuzhen et.al., l987; Zhang Yuquanet.al., l989, Fang Xilian et.al., I990, Jiang Chunfaet.al., 1992; Pan Yusheng, l992, Xu Ronghua et.al.,l 994; Jing Daogui et.al., l996, Zhang Yuquan et.al.,l998). But all of the researches have been donealong Sino-Pakistan road and Xinjiang-Tibet roadt"ith fOcus on isotopic dating of the intrusion andconducted a few on origin and tect…     

Sr isotope evolution during chemical weathering of granites -- impact of relative weathering rates of minerals

The Sr isotopic systematics in the weathering profiles of biotite granite and granite porphyry in southern Jiangxi Province were investigated. The results showed that during the chemical weathering of granites, remarked fractionation occurred between Rb and Sr. During the early stages of chemical weathering of granites, the released Sr/Si and Sr/Ca ratios are larger than those of the parent rocks, and the leaching rate of Sr is higher than those of Si, Ca, K, Rb, etc. Dynamic variations in relative weathering rates of the main Sr-contributing minerals led to fluctuation with time in 87Sr/86Sr ratios of inherent and released Sr in the weathering crust of granite. Successive weathering of biotite, plagioclase and K-feldspar made 87Sr/86Sr ratios in the weathering residues show such a fluctuation trend as to decrease first, increase, and then decrease again till they maintain stable. This work further indicates that when Sr isotopes are used to trace biogeochemical processes on both the catchment and global scales, one must seriously take account of the prefer-ential release of Sr from dissolving solid phase and the fluctuation of 87Sr/86Sr ratios caused by the variations of relative weathering rates of Sr-contributing minerals.     

内蒙古西乌旗沙尔哈达晚侏罗世A型花岗岩：地球化学特征、岩石成因与动力学背景

内蒙古西乌旗沙尔哈达花岗岩侵入于贺根山缝合带蛇绿岩中。LA-ICP-MS锆石测年指示,沙尔哈达花岗岩岩株于晚侏罗世(154.6±1.2 Ma)侵位,矿物组合以石英、碱性长石和斜长石为主,富SiO2(74.86%~75.97%)、K2O(4.4%~4.95%),贫MgO(0.044%~0.22%)、CaO(0.38%~0.77%)、TiO2(0.046%~0.18%)和P2O5(0.007%~0.042%),A/CNK=1.03~1.09, 小于1.1,强烈亏损Ba、Sr、Eu、P、Ti,具有典型的右倾“海鸥型”稀土元素分配模式,表现出典型的铝质A型花岗岩的矿物组合及地球化学特征。沙尔哈达A型花岗岩具有低的(87Sr/86Sr)i值(0.7014~0.70374)、低正εNd(t)值(+3.96~+4.31)、高的εHf(t)值(+10.54~+14.72)。同位素地球化学特征指示,沙尔哈达花岗岩可能源于新生的中基性地壳物质部分熔融及其后的结晶分异作用。沙尔哈达A型花岗岩为晚侏罗世蒙古-鄂霍茨克洋闭合后造山伸展作用的产物,和蒙古-华北北部地块散布的其他A型花岗岩共同指示中晚侏罗世广泛的中下地壳伸展。     

Zircon U-Pb ages and geochemistry of the monzonitic granite in Rongguo area in Middle Gangdise Belt

In order to determine the geochronology, petrogenesis and tectonic background of the monzonitic granite in Rongguo area, the authors conducted the research on petrology, LA-ICP-MS zircon U-Pb geochronology and geochemistry. The results show that the zircons from the monzonitic granite are of magmatic genesis, and the zircon ²⁰⁶Pb/²³⁸U dating is (69±1) Ma, belonging to the Late Cretaceous. Al₂O₃, Na₂O, K₂O contents and K₂O/Na₂O ratio are 13.83%~14.41%, 3.68%~3.94%, 4.28%~4.35% and 1.08~1.18 respectively. The average aluminum saturation index (A/CNK) is 1.02, belonging to the weak peraluminous series. The rocks are enriched in LILE (Rb,U,K), strongly depleted in HFSE (Nb, Ta, Ti, etc.). Combined with the study of regional tectonics, the authors insisted that magma activity had not stopped from 80 to 69 Ma. The rock mass is the magmatic product of the subduction of the Neo-Tethys Ocean, forming in the orogenic environment during the whole orogenic movement period.     

新元古代地幔柱事件在Rodinia超大陆西缘的响应:来自马达加斯加的初步证据

对于Rodinia超大陆西缘在裂解过程中是否发育巨长安第斯型陆弧存在较大争议.马达加斯加即位于古地理再造Rodinia的西缘位置,其太古宙结晶基底中出露有大量新元古代侵入体,是澄清这一争议的理想研究区.由于基性岩浆岩组分识别不足等原因,前人曾认为这些侵入岩形成于俯冲带陆弧环境.但笔者在中北部Alaotra湖地区野外考察期间发现了大量辉长质岩石,对其中典型岩体的LA-ICP-MS锆石U-Pb测年表明其结晶于798~778Ma之间(最大误差估计).因此,这些辉长岩体事实上与岛内其他新元古代侵入体构成了双峰式侵入岩套,暗示了可能的陆内伸展环境.在此基础上,笔者重新审视了前人已发表的地球化学数据,发现该双峰式侵入岩套的基性组分显示富钾特征和拉斑演化趋势,局部甚至发育了强烈地钒钛磁铁矿化;酸性组分则显示富铁、偏铝-过铝质和碱钙-钙碱性特征,并具有相对较高的K₂O/Na₂O和Ga/Al比值以及高场强元素含量,属于A型花岗岩(铁质花岗岩).这些特征进一步表明该双峰式侵入岩套形成于陆内伸展环境而非陆弧环境.结合本文的初步研究结果和区域地质演化历史,笔者认为马达加斯加这一双峰式侵入岩套很可能是新元古代地幔柱事件在Rodinia超大陆西缘的响应.     

高放废物地质处置北山预选区旧井和新场花岗岩填隙方解石同位素地球化学

为了探讨高放废物地质处置甘肃北山预选区旧井和新场预选地段的古地下流体来源、成因、化学演化历史以及水-岩相互作用,文章系统研究了该地段花岗岩填隙方解石的产出特征及其碳、氧、锶同位素的组成特征。测试结果表明,旧井和新场方解石的δ13 C组成均较稳定且为负值(分别为-11.6‰~-5.7‰和-9.9‰~-5.1‰);δ18 O分别为-0.7‰~19.7‰和10.9‰~21.9‰,旧井方解石具有更宽的δ18 O取值范围。87 Sr/86 Sr也略有差异,旧井为0.708584~0.718749,新场为0.708838~0.732967,二者随深度增加而呈明显的降低趋势。研究表明,北山预选区地下流体来源及成因较复杂,浅部地下水受大气降水的影响较大,深部流体则主要源于地下咸水,为低温流体蚀变成因。花岗岩裂隙中的水-岩反应强度总体较弱,地下水环境相对稳定。相比较而言,新场岩体深部的地球化学环境更稳定,更有利于高放废物的长期处置。     

EXPLORATION ENGINEERING

正20141864 Deng Mengchun(Institute of Exploration Technology,CAGS,Chengdu 611734,China);Huang Shenghui Rock Sample Collection and Division Technologies for Air Reverse Circulation Sampling Drilling(Exploration Engineering,ISSN1672-7428,CN11-5063/TD,40(7),2013,p.73-76,80,16 illus.,5 refs.)     

个旧老卡岩体凹陷带岩矿特征与成矿机理分析

对云南个旧矿田的典型控矿地带——老卡岩体凹陷带内的矿化特征、岩相学及矿相学特征和流体包裹体进行分析,进一步研究花岗岩凹陷带的成矿机理。研究认为变玄武岩中普遍发育的金云母化是导致变玄武岩型矿床中锡矿化与金属硫化物伴生的原因之一,凹陷带内带所见的金云母化和绢云母化都与成矿有着密切的关系。花岗岩凹陷带的成矿作用经历了花岗岩侵位、花岗岩叠加改造玄武岩内的"矿胚"、花岗岩蚀变、矿化沉淀这四个过程。     

南非主要金矿集区研究现状及存在问题

南非是世界上金矿石资源量最为丰富的国家,其金矿床主要产于东北部地区,主要有三种类型:1赋存于兰德盆地砾岩型建造中的"兰德"砾岩型金矿床,2产在绿岩带中的绿岩带型金矿床,和3主要与白云岩有关的白云岩型金矿床,以前两种类型为主。"兰德"砾岩型金矿床通常品位高,开采规模最大,目前采矿的深度最大,是南非最重要的矿床类型,其矿床成因长期以来存有争议,主要有两种观点,分别是砂矿模式和热液模式,就目前资料来看笔者等认为其代表了两个不同的矿化阶段;绿岩带型金矿床则以巴伯顿地区为代表,矿床具有规模大、易开采等特征,因此在南非金矿床开采中占有重要位置,其矿床主要赋存于石英脉或剪切带中,矿床成因主要有三种,分别是火山成矿模式、转换滑脱构造模式和构造交叉模式。     

青海刚察大寺地区花岗岩类LA-ICP-MS锆石U-Pb年龄及其地质意义

应用LA-ICP-MS分析了青海刚察大寺地区花岗闪长岩和花岗岩锆石U-Pb同位素年龄,获得了花岗闪长岩的2期侵入年龄,花岗闪长岩10CL008样品谐和曲线年龄为254.8Ma±2.0Ma(N=13,MSWD=0.87),属于二叠纪;花岗岩10CL003样品谐和曲线年龄为236.3Ma±2.4Ma(N=13,MSWD=0.48),属于三叠纪。地球化学特征表明,花岗闪长岩和花岗岩分别属于钙碱性和高钾钙碱性过铝质岩,原始岩浆结晶分异作用由弱到强;稀土元素方面,二者的(La/Yb)N值分别为2.23~10.38和4.52~14.98,分馏程度由弱到强;具有Nb、P、Ti负异常和Ba正异常,显示出岛弧岩浆或活动大陆边缘岩浆的特征。综合研究表明,刚察大寺古生代花岗岩具有岛弧或活动大陆边缘花岗岩的属性,与板块的俯冲作用有关;中生代花岗岩继承了古生代花岗闪长岩的地球化学特征,岩浆物质成分以中上地壳为主,形成于早期深部幔源物质,与能量向上侵入下地壳过程中的重熔作用密切相关。