Ultramafic Blocks in Sumdo Region, Lhasa Block, Eastern Tibet Plateau: An Ophiolite Unit     

Chen Songyong  Yang Jingsui  Li Yuan  Xu Xiangzhen 《中国地质大学学报(英文版)》2009,20(2)

Recently, an over 100 kin long MORB-type eclogite belt of Permian was discovered in the Sumdo (松多) region of the Lhasa block, Tibet. A critical question thus is: what is the tectonic setting of the eclogite belt and is it related to an unrecognized suture in the region? Further investigations show that there are some mafic and ultramafic rocks spatially associated with the eclogite belt in the region. Three ultramafic massifs were recognized in the Sumdo region, and called the Luomaling (罗马岭),Gongbupala (贡布爬拉) and Qiazhasumdo (卡扎松多) massifs. All the massifs are fault-contacted with greenschist (Chasagang (岔萨岗) Formation) or muscovite-quartz schist (Mabuku (马布库) Formation), and individuals are about 100 m×50 m in size extending in EW as the regional structure. All the ultramafic rocks have been entirely serpentinized, and the Gongbupala massif has been selected for study in geochemistry. Eleven chemical analyses of the rocks from the Gongbupala massif show a narrow range in contents: SiO2(35.97-40.63) wt.%, MgO (37.02-38.60) wt.%, TiO2(0.01-0.08) wt.%, Al2O3 (0.80-1.64) wt.%, (Na2O+K2O) less than 0.1 wt.%, with high volatile contents (H2O+CO2) (11.24-14.91) wt.%. After recalculation without H2O+CO2, the mean values are SiO2 45.24 wt.%, MgO 43.54 wt.%, FeOT(7.45-9.97) wt.% (8.55 wt.% in average), (MgO+FeOT) 52.09 wt.%, Mg# (100×Mg/(Mg+Fe*), where Fe* represents total Fe)=89.42-90.08, (m+f)/Si ((atomicity Mg+atomicity Fe) /atomicity Si)=1.53-1.75 (1.59 in average), respectively. The mean M/F (atomicity Mg/atomicity Fe) ratio of the rocks is 9.05, which is classified as magnesium enriched-type of ultramafic rocks. The compositional features, depleted in K, Na, Ca, Al and Ti and enriched in Mg#, indicate the characteristics of peridotite originated from a depleted mantle. The rocks have low ∑ REE with (1.60-2.68)×10-6 similar to those of the primitive mantle. The chondrite-normalized REE patterns of all samples show slightly enrichment in LREE, with (Ce/Yb)N 1.03-2.46, but a little depleted in HREE. Most samples show a slight negative anomaly in Eu, a feature In REE from a relic mantle and common features In highly serpentinized ultramafic rocks in the Yarlung-Zangbo (雅鲁藏布) ophiolite and the Bangong (班公)-Nnjiang (怒江)ophiolite in Tibet. The primitive mantle-normalized spiderdiagram of trace elements for Gongbupala ultramafic rocks yields uniform distributed pattern. They are relatively enriched in Rb, Ba, La, P element (LHSE) and depleted in Sin, Ti, Y, Yb element (HFSE), a feature of metasomatic mantle peridotite. The geochemical features of the rocks suggest that the protofith of Gongbupala serpentinite in Sumdo region is harzburgite, a typical depleted mantle rock, and may represent a dismembered ophiolite unit in the region.  相似文献   

扎河坝蛇绿混杂岩内富铌玄武(安山)岩的地球化学特征及其地质意义   总被引：3，自引：2，他引：1  

牛贺才  单强  于学元  张兵  罗勇  杨武斌 《岩石学报》2009,25(4):916-924

在新疆北部东准噶尔的扎河坝蛇绿混杂岩中发现的富铌玄武（安山）岩,其SiO₂含量介于46.71%~57.65%,TiO₂含量为1.00%~1.76%,与太古代绿岩带内富铌玄武（安山）岩相似,Na₂O含量为3.86%~6.64%,P₂O₅为0.34%~0.82%,明显高于太古代绿岩带富铌玄武（安山）岩。扎河坝富铌玄武岩铌含量介于7.22×10^-6~21.91×10^-6之间,大于7×10^-6,与典型的富铌玄武岩相同。该岩石轻重稀土元素分馏较明显,其分布模式为无明显铕至弱负铕异常的右倾曲线。尽管铌的绝对含量较高,但由于钍和轻稀土元素更加富集,在微量元素蛛网图中扎河坝富铌玄武（安山）岩仍表现为铌的明显亏损,同时高场强元素Zr、Hf及Ti也表现出一定程度的亏损。微量元素地球化学特征显示,扎河坝蛇绿混杂岩内富铌玄武（安山）岩形成于古亚洲洋的洋内弧,它是被埃达克质岩浆交代的地幔楔橄榄岩部分熔融的产物,同时大洋沉积物及俯冲板块释放的流体对成岩作用也有一定的贡献。富铌玄武（安山）岩作为弧前增生楔定位在扎河坝蛇绿混杂岩体内,与早前报道的超高压变质岩共存表明,该蛇绿混杂岩体至少记录了两次性质不同的古亚洲洋洋壳俯冲,这更进一步证实新疆北部晚古生代新增陆壳是古亚洲洋多次俯冲作用的产物。  相似文献   

西藏东巧蛇绿岩中玄武质岩石成因和构造背景探讨   总被引：1，自引：0，他引：1  

陈晓坚  杨经绥  董玉飞  熊发挥  卢雨潇  李观龙  薄容众 《地质学报》2019,93(10):2509-2530

蛇绿岩记录了大洋裂解、俯冲消减和大陆增生的一系列过程,西藏北部班公湖-怒江缝合带中的蛇绿岩记录了青藏高原的地体拼合和隆升历史。班公湖-怒江缝合带中段的东巧蛇绿岩十分发育,地表出露较好,主要由地幔橄榄岩、堆晶杂岩、辉长辉绿岩和玄武岩组成。玄武岩呈多个露头产出,每个露头从十几平方米至数十平方米不等,辉绿岩呈脉状(或岩墙)产在玄武岩中。本文对东巧西出露的玄武岩和辉绿岩开展了详细的野外地质考察和室内岩相学、年代学和地球化学研究分析,探讨了该蛇绿岩的成因以及形成背景。研究表明,辉绿岩和玄武岩属低钾拉斑系列和钙碱性系列。辉绿岩轻稀土含量略高于N-MORB,兼具IAT和N-MORB的特征;玄武岩轻稀土相比重稀土稍富集,具有E-MORB的特征。样品的Nb/U值(30～48)均大于地壳平均值(10)以及(Th/Nb)N值(0.58～0.86)均小于1,表明岩石未遭受地壳混染。辉绿岩和玄武岩3个样品的锆石U-Pb年龄值均显示较大的变化区间,结合前人班怒带蛇绿岩年代学的研究成果,将其分为三组,第一组(156～239Ma)代表蛇绿岩自身的年龄,第二组(37～141Ma)为晚于蛇绿岩形成的年龄段,推测其为后期的岩浆事件成因,第三组(277～2454Ma)为早于蛇绿岩形成的年龄,推测其成因为原始地幔中残留的早期俯冲板片所携带的地壳中的锆石。通过岩石地球化学成分对比研究,认为辉绿岩和玄武岩为弧后盆地玄武岩(BABB)。结合前人地幔橄榄岩的研究,本文认为东巧玄武质岩石形成于俯冲带(SSZ)的弧后盆地扩张时期,并受到俯冲带流体不同程度的影响。  相似文献   

中国蛇绿岩与造山带大地构造研究:前言     

翟庆国  高俊  宋述光 《岩石学报》2019,35(10):2943-2947

<正>肖序常院士是我国著名的构造地质学家,他一生致力于蛇绿岩与中国大地构造的研究工作,为中国西部青藏高原、中亚造山带等地区的区域构造与大地构造,以及有关能源、矿产勘查等的研究做出了重要贡献。在肖先生90华诞暨从事地质事业70年之际,我们出版本专辑,向先生致敬!以此  相似文献   

洞错混杂带内部结构及构造岩片组合特征     

王长海  刘登忠  刘金龙  黄慧 《国土资源遥感》2012,(2):75-78

为了对洞错混杂带进行深入研究,通过遥感图像解译将其分为玄武岩岩片带、蛇绿混杂岩带和蛇绿岩带3个次级构造带,这3个次级构造带在平面上近平行延伸,向东、西方向收敛,在剖面上呈叠瓦式向南逆冲.实地检查证明,遥感解译结果符合实际情况,各带内岩块的物质组成、几何结构大不相同,中部的蛇绿混杂岩带是洞错混杂带的主带.  相似文献   

Seismic wave velocity and anisotropy of serpentinized peridotite in the Oman ophiolite     

Benoît Dewandel  Franoise Boudier  Hartmut Kern  Waris Warsi  David Mainprice 《Tectonophysics》2003,370(1-4):77-94

Shallow seismic measurements in harzburgite from the Oman ophiolite performed in a zone where the maximum horizontal anisotropy is expected (vertical foliation and horizontal lineation) point to a dominant dependence of seismic properties on fracturing.

Optical microscopy studies show that microcracks are guided by the serpentine (lizardite) penetrative network oriented subparallel to the harzburgite foliation and subperpendicular to the mineral lineation, and that serpentine (lizardite) vein filling has a maximum concentration of (001) planes parallel to the veins walls. The calculated elastic properties of the oriented alteration veins filled with serpentine in an anisotropic matrix formed by oriented crystals of olivine and orthopyroxene are compared with seismic velocities measured on hand specimens.

Laboratory ultrasonic data indicate that open microcracks are closed at 100 MPa pressure, e.g. (J. Geophys. Res. 65, (1960) 1083) and (Proc. ODP Sci. Results Leg 118, (1990) 227). Above this pressure, laboratory measurements and modeling show that P-compressional and S-shear wave velocities are mainly controlled by the mineral preferred orientation. Veins sealed with serpentine are effective in slightly lowering P and S velocities and increasing anisotropy. The penetrative lizardite network does not affect directly the geometry of seismic anisotropy, but contributes indirectly in the fact that this network controls the microcrack orientations.

Comparison between seismic measurements of peridotite and gabbro in the same conditions suggest that P- and S-waves anisotropies are a possible discriminating factor between the two lithologies in the suboceanic lithosphere.  相似文献   

An X-Ray Diffraction Study of an Inclusion in Diamond from the Luobusha Chromite Deposit in Tibet, China     

SHI Nicheng  BAI Wenji  MA Zhesheng  FANG Qingsong  XIONG Ming  YAN Binggang  DAI Mingquan  YANG JingsuiChina University of Geosciences  Beijing  E-mail: shinicheng@a-l.net.cn Institute of Geology  Chinese Academy of Geological Sciences  Beijing Liu Shuchun  Zhu Xiling 《《地质学报》英文版》2003,77(3):326-331

Diamond was found in podiform chromitites of ophiolite and harzburgite from Luobusha, Tibet. There are silicate inclusions in some diamond grains from this area. In the present work, the CCD (charge coupled detector) technology of X-ray powder diffraction was applied to the study of the inclusion in diamond from the ophiolite of Tibet. Diffraction patterns are obtained even though the inclusion is only 20 μm in crystal size. The results show that the inclusion in diamond consists of talc and clinochrysotile. Therefore, it is clear that the diamond from the ophiolite of Luobusha, Tibet, is natural diamond rather than a synthetic one.  相似文献   

西藏得几蛇绿岩体中玻安岩的地球化学特征及其地质意义   总被引：15，自引：0，他引：15  

陈根文  夏斌  钟志洪  王国强  王核  赵太平  汪劲草  张莉  漆亮  李荪蓉 《矿物学报》2003,23(1):91-96

西藏日喀则蛇绿岩是我国发育最好的蛇绿岩之一，目前有关日喀则蛇绿岩形成的构造背景存在多种不同的认识。作者在研究得几蛇绿岩剖面时发现存在玻安岩，从而为日喀则蛇绿岩具有弧前背景提供了直接证据。得几蛇绿岩中玻安岩类样品具有高硅、高镁、低铁的特征，岩石中Zr、Yb和Y的含量也较低，具有明显的玻安岩特征。根据这些岩石的地球化学性质，认为岩石是由早期经历过较高程度的部分熔融的残余在含水条件下再发生部分熔融形成的。得几蛇绿杂岩体部分形成于弧前环境。  相似文献   

北秦岭—北祁连(天水—宝鸡)间早生古代火山岩系及其构造连接关系的研究     

宋志高  贾群子  张治洮  张 《西北地质科学》1991,(4)

依据新发现的生物化石和同位素数据,将分布在陕、甘边界一带的原“牛头河群”哑岩系分解为元古代陇山群、秦岭群和早古生代葫芦河群与丹凤群(西延部分)。葫芦河群为北祁连加里东褶皱带的东廷部分,除局部为晚期宝鸡花岗岩侵位间隔外,基本上可与北秦岭地区的古生代斜峪关群相连接,在研究区内与北秦岭地区的奥陶纪草滩沟群,呈以寒武系为核心、两翼为奥陶系火山岩的复式背斜构造。解体后秦岭群呈断续相连的古老岩块,向西可与祁连中间隆起相衔接,丹风群向西延展可伸入祁连造山带的陇西一带,初步认为陇山群与走廊过渡带内的古老隆起相当。据早古生代葫芦河群及其火山岩系的研究,笔者发现从秦安至宝鸡,有近100km的基性枕状熔岩带,并依其相伴产出的超镁铁质-镁铁质(似)堆晶岩、辉绿岩墙及硅质岩等岩石组合单元,认为属与北祁连和北秦岭北带相当的蛇绿岩带。西延的丹凤群亦主要为火山岩(包括枕状熔岩)与超镁铁岩等岩石单元组成的蛇绿岩带。据此提出,北秦岭与北祁连不但是相互连接的,而且具有中间为古老隆起(秦岭群)岩块、两侧为早古生代火山岩(蛇绿岩)带的相同构造格架组合型式,同为我国华北与扬子板块间的碰撞拼合带产物。早古生代火山岩岩石学研究表明,各岩群皆以拉斑质(TH)+钙碱质(CA)岩石系列组合为主,部分岩群的钙碱系列呈双峰岩套特征,显示为岛弧或岛弧初期与裂谷末期阶段活动构造背景。依区内已知超镁铁岩体多呈断裂构造及其旁支系统产生情况,提出为岛弧根部或上地幔物质,受南、北板块碰撞挤压,沿断裂上升就位机制所形成。此外,对区内已知与火山岩有关的块状硫化物型矿床的矿床类型、特征和成矿规律等进行了研讨,提出它们的岩控和时控特征和一些发现新矿床可能性的远景地段。  相似文献   

流体在岩浆型铬铁矿和铂族元素成矿过程中的作用及意义     

苏本勋  刘霞  袁庆晗  罗扬  潘旗旗  白洋  崔梦萌  肖燕  唐冬梅 《地质学报》2022,96(12):4091-4100

镁铁- 超镁铁岩是揭示地幔物质组成和壳幔相互作用的重要窗口，也是Ni- Cu- PGE- Cr等金属矿产资源的重要载体。不同的镁铁- 超镁铁岩体赋矿特征明显不同：蛇绿岩以产出铬铁矿床为特征，阿拉斯加型岩体主要赋含铂族元素(PGE)矿床，大型层状岩体则可同时产出铬铁矿床、PGE矿床和Cu- Ni硫化物矿床。这种成矿差异显然与赋矿岩体形成的构造背景、母岩浆经历的岩浆演化过程有关，但缺少关键控制因素的研究。前人对上述不同种类矿床的研究工作主要集中于地幔源区的部分熔融、上升过程中或岩浆房内的围岩混染和结晶分异等岩浆过程，而极少关注流体作用。近年来，实验岩石学和岩石地球化学的研究均表明幔源岩浆演化过程中的流体活动可能对成矿元素的富集迁移起到至关重要的作用，同时这些成矿元素的赋存状态和分配系数也在不断更新。厘清Cr和PGE在熔体演化——尤其是流体出溶过程中的地球化学行为，刻画并揭示其迁移富集、分离和再富集的成矿过程及控制因素，已成为当前岩浆矿床研究的热点。本文围绕富水流体与铬铁矿和PGE成矿关系的科学问题，总结了不同镁铁- 超镁铁岩体的成矿差异以及铬铁矿和PGE矿床成矿过程中的流体活动记录，提出流体性质和组分对铬铁矿和PGE迁移富集的控制作用，强调有必要开展蛇绿岩、大型层状镁铁- 超镁铁岩体和阿拉斯加型岩体的对比研究。  相似文献