Zircon U-Pb SHRIMP ages of high-pressure granulite in Yushugou ophiolitic terrane in southern Tianshan and their tectonic implications

Zircons from two high-pressure granulite samples from the Yushugou ophiolitic terrane, southern Tian shan have been investigated by cathodoluminescence, LA ICPMS and ion microprobe (SHRIMP) for their internal textures, trace elemental compositions and in situ dating. The weighted mean ages of these two samples are 392±7 and 390±11 Ma, respectively, representing the granulite-facies meta morphic age of the ophiolitic terrane, and indicating that the southern Tianshan ocean initiated its northward subduction since the early Devonian.     

蛇绿岩研究新进展及其定义和分类的再讨论

蛇绿岩保存于大陆造山带中,在地质历史上产于洋--陆过渡区多种构造背景(活动大陆边缘、被动大陆边缘、弧前、弧后、弧内、弧问、板块三联点、转换断层、大陆裂谷或它们的复合背景等)的洋盆扩张脊.蛇绿岩以超镁铁质岩、镁铁质岩为主,是一套彼此具有成因演化亲缘关系的、古洋壳 大洋地幔岩石的有机组合.我们把蛇绿岩概括为产于洋盆扩张脊的洋壳 大洋地幔岩石组合.蛇绿岩按构造背景有红海萌芽型洋壳和大洋中脊型洋壳两个端元,可三分为近陆的活动大陆边缘型--科迪勒拉型、东地中海型(新特提型)过渡型、西地中海型--大洋中脊古特提斯型.科迪勒拉型和东地中海型均属俯冲带(SSZ)上叠型,更近陆靠俯冲带;环太平洋型和被动大陆边缘型属特提斯型.     

The Dongcaohe ophiolite from the North Qilian Mountains： A fossil oceanic crust of the Paleo-Qilian ocean

The Dongcaohe ophiolite, located at the south of the North Qilian subduction complexes, is a tectonic block with an exposed area of about 3 km×6 km. It consists of an intrusive section overlain by an ex- trusive section. The lower part of the intrusive section consists of cyclic layers of cumulate dunites, troctolites, anorthosites, anorthositic gabbros, and gabbros with small discordant dunite and troctolite bodies. This layered sequence grades upward to isotropic gabbros and gabbronorites, which are overlain by the extrusive sequence of diabasic sheeted dikes and basaltic lavas. The overall mineral crystallization sequence was olivine±Cr-spinel, plagioclase, clinopyroxene, orthopyroxene, and Fe-Ti oxides. The Cr-spinel (Mg#: 42-66, Cr#: 41-57) in these layered cumulates and present-day abyssal peridotites have similar compositions. Also, the compositional variations of the plagioclase and cli- nopyroxene in the intrusive section reflect crystallization from melts compositionally similar to the present-day ocean basalts. Moreover, the rare earth element (REE) and multi-element distribution pat- terns of the intrusive and extrusive lithologies in the Dongcaohe ophiolite are consistent with crystal- lization of mid-ocean ridge basalts. The zircon grains separated from the gabbronorite have an SHRIMP average 206Pb/238U weighted age of 497 ± 7 Ma, which is considered as the tectonic emplacement age of the Dongcaohe ophiolite. The field occurrence, mineral and whole-rock compositions indicate that the Dongcaohe ophiolite represents a well-persevered oceanic crustal fragment composed of a complete oceanic crustal section of layered cumulates at bottom upgrading through isotropic cumulates to sheeted dikes and lava flows.     

东秦岭松树沟蛇绿橄榄岩结构构造及其组构特征

东秦岭松树沟蛇绿岩的橄榄岩结构构造及组构研究表明，该蛇绿橄榄岩主要经历了３期塑性变形的叠加改造，分别为洋盆扩张阶段以动态重结晶作用为主要特征的塑性变形、蛇绿橄榄岩块底辟侵位于上覆玄武岩过程中的高温塑性变形和蛇绿岩构造侵位过程中的低温塑性变形，反映了其特征的构造演化过程。     

狮泉河—古昌—永珠蛇绿岩带特征及其地质意义

狮泉河、古昌、永珠等地区出露的超镁铁岩具有各种典型的蛇绿岩套特征,它们构成一个完整的带,中间的不连续地区为白呈系所覆盖。该蛇绿岩带是班公-怒江蛇绿岩带的李生分支,是西藏板块内部在中生代中期张开又封闭的残留构造。     

蛇绿岩型铬铁矿成因分类初探

本文讨论了上地幔部分熔融的岩石序列、蛇绿岩的两种成因机制、铬铁矿的向下沉陷作用、铬铁矿的富铝或富铬以及铬铁矿的特定赋存部位等问题。并在此基础上提出了关于蛇绿岩型铬铁岩的一个新的成因分类方案:a.上地幔部分熔融铬铁矿床;b.岩浆房结晶分异铬铁矿床;c.沉陷铬铁矿床。     

新疆西准噶尔萨尔托海地区英安岩锆石U-Pb年龄及其对达拉布特蛇绿岩侵位时限的约束

新疆西准噶尔达拉布特蛇绿岩在其北东段萨尔托海地区被下石炭统火山岩-沉积岩不整合覆盖。对这套沉积-火山岩系中的英安岩进行 LA-ICP-MS 锆石 U-Pb 定年, 获得 ²⁰⁶Pb/²³⁸U 加权平均年龄为 349±2 Ma(早石炭世杜内期)。英安岩REE 分配型式具有轻稀土富集、重稀土相对平坦、Eu 负异常明显的特点。微量元素原始地幔标准化图解中, 所有样品的标准化丰度都随着元素不相容性的增加而增大。与经典的弧英安岩以及埃达克火山岩相比, 太勒古拉组英安岩 Sr 含量平均值为 195 μg/g, Sr/Y 平均值为 5.2, La/Yb 平均值为4.6, 远小于经典的弧英安岩和埃达克岩。结合太勒古拉组变形、变质微弱的特点, 认为早石炭世英安岩形成于板内裂谷环境, 且在早石炭世之前达拉布特蛇绿岩已经就位。     

Silurian to Devonian foreland basin in the south edge of Tarim Basin

Based on the theory of plate tectonics, combin-ing with the isotopic dating of ophiolite, igneous and volcan-ics, geochemical test, rare earth element analyze and seismicinterpretation, this paper studies the pre-Carboniferous tec-tonics and sedimentary formation of the south edge of theTarim Basin and proves that there exists the Kunlun Oceanunder tensional tectonics during the Sinian and Cambrian inthe south edge of the Tarim Plate. After that, due to the colli-sion orogenesis, there formed the peripheral foreland basinin the south edge of Tarim. The Upper Silurian and Devo-nian molasses sedimentary system superposed on the Sinianand Middle Silurian passive margin flysch sedimentary sys-tem and formed the bivariate structure of the foreland basin.And at the same time, based on the field geology and seismicinterpretation, we have identified that the formation of theSilurian and Devonian have the character of half depositwhich shows thick in the south area and thin in the north,and the pre-Carboniferous thrust compression tectonics re-mained in the foreland thrust belt, which further demon-strates that there existed the Silurian and Devonian periph-eral foreland basin on the south edge of the Tarim Basin.     

Discovery of the boninite series volcanic rocks in the Bangong Lake ophiolite mélange, western Tibet, and its tectonic implications

The Bangong Lake ophiolite section, the western-most part of the Bangong Lake-Nujiang River ophiolitezone, is located to the south of the Bangong Lake andabout 10 km north of Rutog Town (Fig. 1). Being over2000 km long in Tibet, it extends westward to Kashmirand southeastward beyond Tibet along the Nujiang River.Although the section of the ophiolite is well exposed, nodetailed research work has yet been done. This ophiolitezone, which is one of the ophiolite zones in Tibet, servesas the…     

川西元古代蛇绿岩与扬子板块西缘元古代造山带

川西盐边、石棉两地的基性超基性杂岩和火山岩系为世界上少见的元古代高钛到蛇绿岩,这意味着该区曾经历过海洋化过程和板块运动。故康定至攀枝花一线的“康滇地轴”应为原始扬子板块西缘的元古代造山带。文章评述了该区蛇绿岩及有关基性超基性杂岩的研究现状,提出重建该造山带地质历史的思路和线索。