青藏及邻区新生代火山活动及构造演化

青藏高原是现今地球动力学和地质演化研究的一个热点。该区火山活动受中 -新生代以来高原深部地球物理 -化学反应的控制 ,是多种因素相互作用所表现的形式和结果。本区既有富钾质的 (主导 ) ,也有富钠质的火山岩 (次要 ) ;既有喷发熔岩流 (主导 ) ,也有一些浅源上侵的次火山岩体 ;火山活动发育在古近纪、新近纪与第四纪 ,而最强烈的发生在中新世期间。本区钠质和钾质两类火山岩在形成环境和时代上有很大的差异 :前者一般发育在古新世—始新世 (6 0～ 4 0MaBP) ,而后者主要形成在渐新世—中新世 (30～ 10MaBP) ;存在着钠质—钾质—酸性次火山岩的演化过程 ;大体上可划分为西羌塘、北羌塘、可可西里、中昆仑、西昆仑等 5个火山岩省。本文对比了青藏高原及邻区甘肃礼县和云南三岩区 (金沙江北段、腾冲和滇东南地区 )新生代火山岩的岩石组合、同位素年代学以及地球化学特征 ,大量的证据表明 ,这些火山岩形成在原始地幔、或“壳 -幔过渡带”或陆壳基底等源区。在实际考察和综合研究的基础上 ,探讨了岩石圈的区域构造特征及其与高原隆升的关系等     

长江中下游庐枞火山岩盆地南侧钾质侵入岩带的成因

庐枞火山岩盆地南侧的钾质侵入岩带由正长岩-石英正长岩-正长花岗岩组成,以石英正长岩为主。它们的形成时间介于123"130 Ma之间,峰值约为126 Ma,其中正长岩和石英正长岩的形成时间稍早,而正长花岗岩的形成时间略晚。整个钾质侵入岩带的侵位时间晚于庐枞盆地内的橄榄玄粗质火山作用约4"7 Ma,也是长江中下游地区除最东段的宁镇地区外中生代最晚的岩浆活动产物之一。地球化学上,该钾质侵入岩带以高钾、富碱、富集Rb、Th、U、K等强不相容元素和轻稀土元素、亏损高场强元素Nb、Ta和Ti为特征。它们的母岩浆主要是由富集型上地幔部分熔融形成的,从正长岩经石英正长岩到正长花岗岩的演化主要受矿物的分离结晶作用控制,地壳物质同化所起的影响不大。但与同样来自富集型上地幔部分熔融的庐枞盆地内火山杂岩的母岩浆相比,前者的母岩浆来源深度可能更大些或其中包含了更多来自软流圈地幔的组分。两者的演化路径也完全不同,钾质侵入岩带的母岩浆除经历过高压下的分离结晶作用外,晚期在低压下还经历过长石为主,可能还有黑云母的分离结晶,甚至上地壳物质一定程度的混染作用;而盆地内火山杂岩的母岩浆低压下矿物的分离结晶作用及上地壳物质的混染都不明显。庐枞盆地南缘的富钾侵入岩与盆地内的火山杂岩一样,地球化学上都具有明显的大陆弧的特征,暗示它们的岩浆源区可能形成于俯冲带环境,意味着扬子地块北缘先前(推测为古元古代晚期)曾发生过俯冲作用,上地幔的交代富集可能就与这次的俯冲作用有关。     

湘东北临湘地区钾质煌斑岩~(40)Ar-~(39)Ar定年及其地球化学特征

对出露于湘东北临湘地区的煌斑岩脉群进行了同位素年龄测定及岩石地球化学分析。研究表明,煌斑岩的全岩40Ar-39Ar年龄为(119.5±2.2)Ma,形成于早白垩世。岩石地球化学方面,岩石属碱性系列、钾质—超钾质煌斑岩;富集大离子亲石元素(LILE)和高场强元素(HFSE);稀土元素分配模式为相似的右倾轻稀土富集型;具有较小的TDMⅡ值(1.5Ga)和较低的εNd(t)(-7.3)。上述特征暗示煌斑岩物质来源于异常(交代富集)地幔,形成于后造山陆内拉张减薄的构造环境。     

Cenozoic high-K alkaline magmatism and associated Cu–Mo–Au mineralization in the Jinping–Fan Si Pan region,southeastern Ailao Shan–Red River shear zone,southwestern China–northwestern Vietnam

The Jinping–Fan Si Pan (JFP) Cenozoic magmatic and Cu–Mo–Au metallogenic belt in the southeastern part of the Ailao Shan shear zone host the Tongchang, Chang′an, Habo, and Chinh Sang Cu–Mo–Au deposits. These deposits form an integrated epithermal-porphyry regional mineralization system associated with 40–32 Ma high-K alkaline magmatism. The magmatic rocks in the belt have relatively low TiO₂ (<0.73 wt%), P₂O₅ (<0.29 wt%), and FeO^* (<4.99 wt%), and high Na₂O (2.86–4.75 wt%) and K₂O (4.01–7.98 wt%). They also have high contents of incompatible trace elements, and are enriched in LILE (Rb, Ba, K, Sr) and LREE. They have marked Nb, Ta, Ti and P depletion in primitive mantle-normalized spidergrams, and plot close to the EMII mantle field in the Sr–Nd isotopic diagram. These characteristics are similar to those of the Eocene high-K alkaline rocks along the northern Ailao Shan belt, eastern Tibet plateau. The sulfur and lead isotope analyses of sulfide minerals from both the ores and related magmatic rocks confirm the involvement of a magmatic ore fluid. The Cenozoic alkaline intrusions and Cu–Mo–Au mineralization in the JFP were formed prior to the initiation of left-lateral shearing along the Ailao Shan shear zone. The magmas appear to have been derived from enriched mantle, possibly with mixing of materials from the buried Tethyan oceanic lithosphere, and/or crust.     

Discovery of double-peaking potassic volcanic rocks in Langshan Group of the Tanyaokou hydrothermal-sedimentary deposit,Inner Mongolia,and its indicating significance

Since the mid-1980s,Tanyaokou large Zn-Cu-Fe sulfides deposit,located at the southwest end of Langshan-Zhaertaishan-Bayan Obo Mesoproterozoic metallogenic belt in the west section of the northern margin of the North China Platform[1?9](Fig.1),has been confirmed to be submarine volcanic exhalative-sedimentary metamorphosed deposit hosted in the miogeosynclinal mud-carbonaceous formation of the Langshan Group(LG)[1],or submarine volcanic exha-lative-deposition-altered deposit[2]or stratabo…     

内蒙古中部苏尼特左旗地区阿巴嘎组火山岩地球化学特征及成因

内蒙古中部苏尼特左旗地区阿巴嘎组火山岩主要由安山岩组成。岩石富碱、高钾和铝、低镁。富集大离子亲石元素(LILEs)Rb、Ba、U、K和轻稀土元素(LREE),相对亏损高场强元素(HFSEs),具明显的Nb、Ta和Ti负异常和Pb正异常。稀土元素总量较高,轻、重稀土元素分馏强烈且属轻稀土元素富集型,具弱负Eu异常。主量、微量元素地球化学特征表明,阿巴嘎组安山岩为钾质火山岩,岩浆上升演化过程中经历了斜长石和铁镁矿物的分离结晶作用,无地壳物质的混染。阿巴嘎组钾质火山岩的形成与新生代太平洋板片俯冲密切相关,其岩浆来源于滞留的俯冲太平洋板片释放流体交代的富集陆下岩石圈地幔,是在板内伸展体制下含金云母石榴子石二辉橄榄岩低程度部分熔融的产物。这种板内伸展体制可能是新生代滞留于地幔过渡带中的太平洋板片俯冲后撤引起的。     

Mineralization,geochronology, and Pb isotope studies of the shoshonitic lava-hosted Nariniya Pb deposit,central Tibet: linking ore formation to post-collisional potassic magmatism

Abstract

A newly discovered, shoshonitic lava-hosted Pb deposit at Nariniya in central Tibet provides an excellent example to help improve our understanding of the linkage between post-collisional potassic magmatism and ore formation in Tibet. The Pb ores exist as veins or veinlets in NWW-striking fracture zones within the potassic lava (trachyte). The veins contain quartz, galena, pyrite, and sericite (muscovite) as well as minor chalcopyrite, sphalerite, calcite, and dolomite with sericitization, pyritization, and minor silicification. The ⁴⁰Ar–³⁹Ar plateau age of the hydrothermal muscovite is 37.95 ± 0.30 Ma, which represents the Pb mineralization age. This obtained age is indistinguishable, within analytical error, from the zircon U–Pb age of 37.88 ± 0.22 Ma for potassic lava. Therefore, the ore formation can be genetically linked to potassic magmatism. Galena has similar Pb isotopic composition to magmatic feldspar from the host lava, suggesting the derivation of Pb from the magmatic system. Previous studies have suggested that S- and ore-forming fluids are of magmatic origin. Published data show that the Nariniya volcanic rocks are acidic, shoshonitic, akakitic, peraluminous, and enriched in Sr–Nd–Pb isotopes. Thus, they are geochemically different from other potassic volcanic rocks (no adakitic affinity) in the North Qiangtang terrane, but similar to the 46–38 Ma high-K calc-alkaline peraluminous adakitic rocks in this terrane and the late Eocene Cu-generating potassic porphyries from the Sanjiang region of eastern Tibet. As such, the Nariniya potassic magma likely originated from melting of subducted continental crust, with or without interaction with the overlying enriched mantle. Such post-collisional potassic rocks in Tibet are thought to be potential targets for prospecting of both Pb–Zn and porphyry Cu ores. Note that other ore styles (in addition to the Nariniya ore style) may exist in the potassic volcanic districts of Tibet.     

玉龙斑岩铜矿带莽总含矿斑岩体岩石学特征及锆石U-Pb年龄研究

莽总斑岩铜钼矿床位于玉龙斑岩铜矿带中部,含矿岩体侵入下二叠统和上三叠统火山岩和硅质沉积岩中.含矿岩体出露面积约0.27km2,普遍发生蚀变,可分为早晚两个阶段.本文分析了含矿岩体化学组成及用锆石LA-ICP-MS U-Pb 年龄分析斑岩体形成时代.早阶段岩体主要为花岗闪长斑岩,晚阶段岩体为石英二长斑岩及碱长花岗斑岩,晚...     

青海西部祁漫塔格地区主要矽卡岩铁多金属矿床成矿地质背景和矿化蚀变特征

青海西部祁漫塔格地区矽卡岩铁多金属矿床分布广泛,目前已成为中国西部最重要和最有找矿潜力的矽卡岩铁多金属成矿带.在大地构造上,该地区属东昆仑造山带;成矿主要与印支期(204～237Ma)闪长岩、花岗闪长岩和二长花岗岩有关;控矿地层包括蓟县系狼牙山组大理岩、硅质岩,奥陶系-志留系滩间山群大理岩、碎屑岩、硅质岩、中-基性火山岩和石炭系结晶灰岩、碎屑岩等.区内发育3类矽卡岩,即钙矽卡岩、镁矽卡岩和锰质矽卡岩,以前者为主.钙矽卡岩常伴生Fe、Cu、Mo(Pb,Zn)矿化,镁矽卡岩主要伴生Fe矿化,锰质矽卡岩则伴生Pb、Zn(Ag)矿化;矿石矿物组合多种多样,矿化具有一定的分带性.内接触带侵入岩广泛发育钾长石化,与矽卡岩类型一起构成该类矿床的重要找矿标志之一.     

长白山火山的历史与演化

长白山火山跨越中朝两国,在我国境内包括天池火山、望天鹅火山、图们江火山和龙岗火山,火山活动从上新世持续到近代,是我国最大的第四纪火山分布区。长白山火山的母岩浆是钾质粗面玄武岩,将长白山火山岩区称钾质粗面玄武岩省,岩浆结晶分异作用和混合作用主导了岩浆演化过程。天池火山之下地壳岩浆房和地幔岩浆房具双动式喷发特点,一方面来自地幔的钾质粗厨玄武岩浆直接喷出地表;另一方面钾质粗面玄武岩浆持续补给地壳岩浆房,发生岩浆分离结晶作用和混合作用,导致双峰式火山岩分布特征和触发千年大喷发。西太平洋板块俯冲-东北亚大陆弧后引张是长白山火山活动的动力学机制。