藏北羌塘中部果干加年山石炭纪蛇绿岩地球化学特征及LA-ICP-MS锆石U-Pb年龄     

吴彦旺  李才  徐梦婧  解超明  王明  熊盛青  范正国 《地质通报》2014,33(11):1682-1689

在羌塘地区开展1∶5万戈木日区域地质调查的过程中,为研究龙木错—双湖板块缝合带的演化历史,探讨青藏高原羌塘中部地区的构造演化,对果干加年山地区的蛇绿岩进行了详细研究。石炭纪蛇绿岩变质堆晶辉长岩是填图过程中的新发现。全岩地球化学研究结果显示,岩石ΣREE较低,LREE弱富集,轻、重稀土元素分异程度不高;富集Rb、Bb等大离子亲石元素,明显亏损Nb、Ta、Ti等元素,具有典型的SSZ型蛇绿岩特征,表明其形成于俯冲带之上。蛇绿岩中变质堆晶辉长岩的LAICP-MS锆石U-Pb年龄为354.8Ma±2.4Ma,属于早石炭世。最终研究表明,龙木错—双湖板块缝合带所代表的古大洋至少在早石炭世就已经存在俯冲。石炭纪变质堆晶辉长岩的发现对研究缝合带构造演化历史具有非常重要的意义,也为探讨羌塘地区的大地构造演化提供了基础资料。  相似文献   

New recognition of Gaxue Formation and Zedang Formation in Yalu Tsangpo Suture Zone     

ZHANG Xinquan  WANG Jingui  ZHANG Zhenli  ZHUAN Shaopeng  ZHANG Liguo  CHENG Zhou  DENG Ke  HE Jiaoyue 《中国地质调查》2014,7(2):72-80

On the basis of the 1:50 000 regional geological survey, the authors comprehensively studied Gaxue Formation and Zedang Formation in North Yalu Tsangpo Suture Zone, and compared their petrogeochemical parameters and tectonic environment with ophiolite. Combined with paleontological and high-precision isotope dating analysis, it is preliminarily considered that Gaxue Formation, Zedang Formation and ophiolite are products of different genetic types. Gaxue Formation and Zedang Formation were formed in the intra-oceanic arc tectonic environment from late Jurassic to early Cretaceous, and belonged to the front arc basalt (FAB type) which was the standard oceanic plate stratigraphic sequence. In the late subduction and collision process, the main body of Gaxue Formation and Zedang Formation was transformed into melange or existed in the melange belt in the form of a broken clip (block), mainly as the structure styles in subduction and accretionary complex zones. This understanding is of great geological tectonic significance for the rational restoration and establishment of the northern belt oceanic plate stratigraphic sequence of Yalu Tsangpo Suture Zone.  相似文献   

Hydro-climatic Characteristics of Yarlung Zangbo River Basin since the Last Glacial Maximum     

Shuang LIU  Kaiheng HU  Weiming LIU  Paul A.CARLING 《大气科学进展》2022,39(3):415-426

Global climate changes significantly impact the water condition of big rivers in glacierized high mountains. However,there is a lack of studies on hydrological changes within river basins caused by climate changes over a geological timescale due to the impossibility of direct observations. In this study, we examine the hydro-climatic variation of the Yarlung Zangbo River Basin in the Tibet Plateau since the Last Glacial Maximum(LGM) by combining δ18 O proxy records in Indian and Omani caves with the simulated Indian summer monsoon, surface temperature, precipitation, evapotranspiration and runoff via the Community Climate System Model and the reconstructed glacier coverage via the Parallel Ice Sheet Model. The mean river runoff was kept at a low level of 145 billion cubic meters per year until an abrupt increase at a rate of 8.7 million cubic meters per year in the B?lling-Aller?d interval(BA). The annual runoff reached a maximum of 250 billion cubic meters in the early Holocene and then reduced to the current value of 180 billion cubic meters at a rate of 6.4 million cubic meters per year. The low runoff in the LGM and Heinrich Stadial 1(HS1) is likely attributed to such a small contribution of precipitation to runoff and the large glacier cover. The percentage of precipitation to runoff was only 20%during the LGM and HS1. Comparison of glacier area among different periods indicates that the fastest deglaciation occurred during the late HS1, when nearly 60% of glacier area disappeared in the middle reach, 50% in the upper reach,and 30% in the lower reach. The rapid deglaciation and increasing runoff between the late HS1 and BA may have accelerated widespread ice-dam breaches and led to extreme outburst flood events. Combining local geological proxy records and regional simulations could be a useful approach for the study of paleo-hydrologic variations in big river basins.  相似文献   

北山蛇绿岩特征及构造属性   总被引：20，自引：0，他引：20  

杨合群  李英  赵国斌  李文渊  王小红  姜寒冰  谭文娟  孙南一 《西北地质》2010,43(1):26-36

概述了北山地区4条蛇绿岩带的岩石类型组合及岩石地球化学特征,并结合区域地质情况分析认为:红柳河-牛圈子-洗肠井蛇绿岩带形成于早古生代洋盆环境,特征最接近现代洋壳蛇绿岩,在该带北侧保存有标志活动陆缘的公婆泉-东七一山岛弧火山岩带,南侧保存有标志南北两个板块开裂前伸展拉张的浅海—次深海形成的寒武纪含磷钒铀锰沉积岩系地层,说明该蛇绿岩带指示南北两个板块间裂解与聚合的位置。芨芨台子-小黄山蛇绿岩带分布于公婆泉-东七一山岛弧与星星峡-旱山地块之间,形成于早古生代弧后盆地环境。红石山-百合山-蓬勃山蛇绿岩带和辉铜山-帐房山蛇绿岩带形成于晚古生代裂谷拉张最大化至初始小洋盆出现的阶段,即类似于"红海型"海槽的环境。  相似文献   

Alteration of Platinum-Group and Base-Metal Mineral Assemblages in Ophiolite Chromitites from the Dobromirtsi Massif,Rhodope Mountains (Bulgaria)     

José María González-Jiménez  Fernando Gervilla  Thomas Kerestedjian  Joaquín Antonio Proenza 《Resource Geology》2010,60(4):315-334

The Dobromirtsi Ultramafic Massif, located in the Rhodope Mountains (SE Bulgaria), is a portion of a Paleozoic sub-oceanic mantle affected by polyphase regional metamorphism. This massif contains several small, podiform chromitite bodies which underwent the same metamorphic evolution as their host peridotites. Like other ophiolite chromitites, those found in Dobromirtsi carry abundant platinum-group minerals (PGM) and base-metal minerals (BMM). The PGM consist mainly of Ru-, Os-, and Ir-based PGM (laurite RuS₂-erlichmanite OsS₂, Os-Ru-Ir alloys, irarsite [IrAsS], Ru-rich pentlandite, and an unknown Ir-sulfide) but minor Rh- and Pd-based PGM (hollingworthite [RhAsS] and a series of unidentified stannides and sulfantimonides) are also present. In contrast, the BMM are dominated by pentlandite (Ni,Fe)₉S₈, followed by heazlewoodite (Ni₃S₂), breithauptite (NiSb), maucherite (Ni₁₁As₈), godlevskite (Ni₇S₆), gersdorffite (NiAsS), millerite (NiS), undetermined minerals containing Ni, As and Sb, orcelite (Ni_5-XAs₂), awaruite (Ni₃Fe) and chalcopyrite (CuFeS₂). The detailed study of the textural relationships, morphology and composition of the PGM and BMM inclusions indicate the existence of two different PGM-BMM assemblages: (i) a primary or magmatic; and (ii) a secondary related with postmagmatic alteration. The PGM and BMM inclusions in unaltered zones of chromite crystals (mainly laurite-erlichmanite and pentlandite) are considered to be primary magmatic minerals formed under variable temperature (1200–1100°C) and sulfur fugacity (between −2 and −0.5 log fS₂). In contrast, PGM and BMM located along altered edges of chromite and serpentinised silicate matrix are considered to be secondary, formed from or re-equilibrated with altering fluids. Secondary PGM and BMM assemblages are considered as result of the combination of reducing and oxidising events related with regional metamorphism. Under low fO₂ states, fS₂ also drops giving place to the formation of S-poor Ni-rich sulfides and secondary Ru-alloys by desulfurisation of primary S-containing minerals. In contrast, predominance of platinum-group elements and/or base-metal arsenides and sulfarsenides associated with the altered edges of chromite (chromite strongly enriched in Fe₂O₃) is related with the fixing of remobilised PGE (mainly Ir, Rh and Pd) and base-metals (mainly Ni and Fe) when late oxidising fluids supplied As as well as Sb and Sn.  相似文献   

Geology of the southern Zambales Ophiolite Complex, Luzon, Philippines     

Graciano P. Yumul JR    Carla B. Dimalanta and  Ferdinand T. Jumawan 《Island Arc》2000,9(4):542-555

Abstract Field, geochemical and geophysical evidence show that the southern Zambales Ophiolite Complex attained its present-day configuration through the juxtapositioning of an arc terrane (San Antonio massif) to a back-arc crust (Cabangan massif). The San Antonio massif manifests island arc-related characteristics (i.e. spinel XCr [Cr/(Cr + Al)] >0.60; mostly plagioclase An92–95; pyroxene crystallizing ahead of plagioclase; orthopyroxene as an early, major crystallizing phase) which cannot be directly parental to the Cabangan massif transitional mid-ocean ridge basalt to island arc tholeiitic volcanic carapace. The two massifs are believed to be separated by a left-lateral strike–slip fault, the Subic Bay Fault Zone. Apart from the presence of highly sheared, allochthonous outcrops, the Subic Bay Fault Zone is generally defined by northwest–southeast trending magnetic and bouguer anomalies. The San Antonio massif was translated southward from the northern part of the Zambales Ophiolite Complex through the Subic Bay Fault Zone. This resulted into its suturing with the Cabangan massif and could have led to the formation of the present-day Subic Bay.  相似文献   

Evolution of the Pan-African Wadi Haimur metamorphic sole, Eastern Desert, Egypt   总被引：2，自引：0，他引：2  

H. Abd El-Naby  W. Frisch  & E. Hegner 《Journal of Metamorphic Geology》2000,18(6):639-651

By comparison with the general features of metamorphic soles (e.g. vertical and lateral extension, metamorphic grade and diagnostic mineral parageneses, deformation and dominant rock types), it is inferred that the amphibolites, metagabbros and hornblendites of the Wadi Um Ghalaga–Wadi Haimur area in the southern part of the Eastern Desert of Egypt represent the metamorphic sole of the Wadi Haimur ophiolite belt. The overlying ultramafic rocks represent overthrusted mantle peridotite. Mineral compositions and thermobarometric studies indicate that the rocks of the metamorphic sole record metamorphic conditions typical of such an environment. The highest P – T conditions ( c . 700 °C and 6.5–8.5 kbar) are preserved in clinopyroxene amphibolites and garnet amphibolites from the top of the metamorphic sole, which is exposed in the southern part of the study area. The massive amphibolites and metagabbros further north (Wadi Haimur) represent the basal parts of the sole and show the lowest P – T  conditions (450–620 °C and 4.7–7.8 kbar). The sole is the product of dynamothermal metamorphism associated with the tectonic displacement of ultramafic rocks. Heat was derived mainly from the hot overlying mantle peridotites, and an inverted P – T  gradient was caused by dynamic shearing during ophiolite emplacement. Sm/Nd dating of whole-rock–metamorphic mineral pairs yields similar ages of c . 630 Ma for clinopyroxene and hornblende, which is interpreted as a lower age limit for ophiolite formation and an upper age limit for metamorphism. A younger Sm/Nd age for a garnet-bearing rock ( c . 590 Ma) is interpreted as reflecting a meaningful cooling age close to the metamorphic peak. Hornblende K/Ar ages in the range 570–550 Ma may reflect thermal events during late orogenic granite magmatism.  相似文献   

西藏罗布莎豆荚状铬铁矿中发现超高压矿物柯石英   总被引：18，自引：0，他引：18  

杨经绥  白文吉  方青松  颜秉刚  戎合  陈松永 《地球科学》2004,29(6):651-660

在西藏雅鲁藏布江蛇绿岩带东段的罗布莎豆荚状铬铁矿床中发现典型的超高压矿物柯石英和蓝晶石, 二者呈针柱状交生, 产在一个以TiFe合金成分为主的颗粒(0.7mm× 0.5mm大小) 的最外部.该颗粒从内到外由4层矿物组成, 分别为TiFe合金主体、2 0~ 70 μm宽的自然钛、约10 μm宽的TiSi合金及30~ 5 0 μm宽的柯石英和蓝晶石为主的硅酸岩和氧化物层.主体矿物为高Ti低Fe的TiFe合金, 内部出现由细粒状低Ti高Fe的TiFe合金和自然钛组成的蠕英结构.最外层由柯石英和蓝晶石组成的格架中分布细粒的Si金红石和Ti-Mg -K -Na -Ca氧化物.初步认为TiFe合金从深部高温高压环境往浅部上升过程中, 内部发生局部熔融, 分解出自然Ti, 并在其边部与其他硅酸岩矿物或熔体发生反应, 形成柯石英和蓝晶石.这一过程可能发生在洋脊拉张环境, 由于地幔柱的上涌, 将深部的豆荚状铬铁矿带到浅部, 使得其中包裹的一些高温高压环境下稳定的矿物变得不稳定, 发生熔融和交代反应, 形成新的不平衡的矿物组合.罗布莎柯石英的这种不寻常产出特征说明是在减压过程中形成, 不同于造山带中常见的由板块俯冲增压过程中形成的柯石英   相似文献   

西藏东巧蛇绿岩的地球化学特征及其形成的构造环境   总被引：7，自引：3，他引：4  

叶培盛  吴珍汉  胡道功  江万  刘琦胜  杨欣德 《现代地质》2004,18(3):309-315

西藏东巧蛇绿岩主要由变质橄榄岩、辉长岩及玄武岩等组成。变质橄榄岩以富Mg、Fe、Cr,贫Ti、ΣREE为特征。辉长岩和玄武岩的主量元素、微量元素特征显示其具有扩张洋脊拉斑玄武岩的地球化学特征,其中高场强元素Nb、Ta、zr、Hf等亏损,大离子亲石元素Rb、sr、Ba等相对富集;在球粒陨石标准化稀土元素配分模式图上为LREE亏损的平坦型,无负Eu异常,与洋中脊玄武岩的特征类似。根据其地球化学属性,推测该区蛇绿岩形成于大洋盆地扩张的构造环境。  相似文献   

西藏"一江两河"中部流域地区土地沙漠化变化的驱动因素分析   总被引：21，自引：11，他引：10  

刘毅华  董玉祥 《中国沙漠》2003,23(4):355-360

土地利用/覆盖变化及其驱动力是当前研究的热点问题,现代土地沙漠化变化的机制及其驱动因素的研究更倍受关注。选择西藏"一江两河"中部流域地区为研究区域,依据该区1991年与1997年的两期土地沙漠化类型与面积数据,利用定量方法分析了同期土地沙漠化的发展变化与区内各种自然与人文因子间的数量关系,以定量辩识其变化的驱动因素。分析结果表明,该区近期土地沙漠化的变化是在多种气候因子、社会因子与经济因子共同驱动下自然变化过程与人为变化过程相互影响的结果,其中,自然驱动因素主要是风力与干旱程度,人为驱动因素主要是农作物播种面积与牲畜(超载)数量,但比较之下自然驱动因素的作用相对稍重,具有相对主导性。  相似文献