Estimating original thickness and extent of the Semail Ophiolite in the eastern Oman Mountains by paleothermal indicators     

《Marine and Petroleum Geology》2017

The Oman Mountains preserve Permo-Mesozoic sedimentary rocks of the Arabian passive margin that were overridden during Late Cretaceous time by deep-water sediments of the Hawasina units and by the Semail Ophiolite, a portion of the Neo-Tethyan oceanic crust and upper mantle. Passive margin sequences are exposed in the Jabal Akhdar Culmination (JAC) and in the Jabal Salakh Range at the Oman Mountains thrust front. Samples of these sequences were investigated by X-ray diffraction of the clay size fraction to evaluate the thermal evolution of the subophiolite rocks and estimate the thickness and extent of the obducted ophiolites.The sedimentary succession from the northern flank of the JAC shows a clay mineral assemblage characterized by long-range ordered mixed layer I-S with an illite content between 85% and 92% and the occurrence of pyrophyllite and/or paragonite, suggesting maximum paleotemperatures between 150° and 200 °C in deep diagenetic conditions. On the southern flank of the JAC, temperature dependent clay minerals indicate maximum paleotemperatures, ranging between 120° and 150 °C, indicating a reduced ophiolite thickness towards the south. Ooid strain analyses of the subophiolite rocks from the northern flank of JAC show a component of flattening and stretching in the z-x plane as a result of plastic deformation and pressure solution. On the southern flank, such ductile deformation is absent, suggesting a brittle rheology for the subophiolite carbonates and a reduced overburden. 1D thermal modeling reveals that the sub-ophiolite units of the JAC were overthrust by 4.5 km-thick Semail Ophiolite and Hawasina units during the Coniacian, and exhumed since the Campanian. The subophiolite rocks of the Jabal Salakh Range were buried under 1.35 km of synobduction clastics and overthrust by 2 km-thick Hawasina units, suggesting a decrease of the thickness of allochthonous units from NE to SW, consistent with strain analysis and their direction of emplacement.  相似文献   

基于ASTER的雅鲁藏布江缝合带泽当-罗布莎蛇绿岩套分析和组分识别   总被引：2，自引：0，他引：2  

黄照强  张显峰 《岩石学报》2010,26(12):3589-3596

本文通过对西藏雅鲁藏布江缝合带泽当-罗布莎地区蛇绿岩套的主要岩石组成和蚀变矿物的标准波谱吸收特征分析,比较了标准光谱库的相应岩性光谱吸收特征和ASTER数据波段特征之间的关系,采用连续统去除、比值法和光谱角制图法对ASTER影像数据进行处理及相关岩性和矿物提取。结果表明,蛇绿岩组分岩性中亚铁离子和Fe-OH,Mg-OH的可见-短波红外吸收特征显著,而且有一个宽波长范围的Si-O热红外光谱特征,基于这些光谱特征采用ASTER数据和比值法与光谱角制图法可有效地识别蛇绿岩的主要岩性和相关矿物成分及其空间分布,结果与地质资料基本吻合。  相似文献   

锆石SHRIMP测年对狮泉河蛇绿岩形成和俯冲的时间约束   总被引：7，自引：6，他引：7  

郑有业  许荣科  马国桃  高顺宝  张刚阳  马新民  茨邛 《岩石学报》2006,22(4):895-904

用锆石SHRIMP方法测定了狮泉河蛇绿混杂岩带中蛇绿岩的堆晶橄榄辉石岩、闪长岩墙和辉长闪长岩墙的U-Pb年龄,提供了狮泉河蛇绿岩形成和俯冲的时间约束。堆晶橄榄辉石岩的等时线年龄为193．1±3．2Ma,指示狮泉河带始于早侏罗世拉开形成洋壳;闪长岩墙的等时线年龄为165．8±1．7Ma、辉长闪长岩墙的等时线年龄为163．35±0．75Ma,可能代表了狮泉河带开始由扩张转化为俯冲消减的时间。  相似文献   

对“也谈铙钹寨超镁铁岩体的成因和构造类型的归属问题”一文评论的答疑     

王希斌 《岩石学报》2006,22(12):3084-3089

张旗先生的《评论》和他之前的工作没有提供饶钹寨岩体的“地幔交代作用”的证据；地幔交代作用不能作为判别地幔岩为大陆地幔和大洋地幔属性的标志，因为两者均可能发生地幔交代作用。根据铙钹寨岩体原岩为强烈亏损的方辉橄榄岩（和二辉橄榄岩）；伴有豆荚状铬铁矿及瘤状矿石和铬尖晶石成分具有蛇绿岩地幔岩属性（双峰分布）而非大陆地幔橄榄岩特征，认为该岩体带有蛇绿岩成员的某些特征，并认为该岩体经历了角闪岩相-麻粒岩相的变质作用。我们对《评论》中列举的所谓大陆地幔橄榄岩中也产有豆荚状铬铁矿的诸多例子给予了剖析，指出《评论》犯有基本概念的错误。  相似文献   

Petrological and source region characteristics of ophiolitic hornblende gabbros from the Aksaray and Kayseri regions, central Anatolian crystalline complex, Turkey   总被引：1，自引：0，他引：1  

K. Kocak  F. Is&#x;k  M. Arslan  V. Zedef 《Journal of Asian Earth Sciences》2005,25(6):883-891

Many Neo-Tethyan ophiolitic bodies are well exposed as thrust-slices in Central Anatolia and are predominantly represented by massive hornblende gabbros, most of which are cut by Supra Subduction Zone (SSZ) plagiogranites. The allochthonous gabbros are distinct from their autochthonous counterparts, with their mineralogy including both igneous hornblende, relict diopside rimmed by replacement hornblende and their chemical composition corresponding mostly to gabbro rather than diorite.The results of major and trace element analyses of forty-two samples, and REE analyses of nine samples, indicate that the hornblende gabbros are SSZ-type and formed from a wet magma by high-degree partial melting of peridotite possibly coupled with contamination by predominantly neighbouring-slab derived fluids within an intra-oceanic back-arc basin. The mafic magmas then underwent high-level fractional crystallization involving titaniferous magnetite, diopside, tschermakite and possibly olivine. Emplacement was followed by extensive ocean–floor metamorphism, which has induced crystallization (or recrystallization) of chlorite, biotite, amphiboles and mobilisation of most of the major elements such as alkali and alkali earth elements, and some LREE.  相似文献   

Chromium and nickel distribution in soils, active river, overbank sediments and dust around the Burrel chromium smelter (Albania)   总被引：2，自引：0，他引：2  

A. Shtiza  R. Swennen  A. Tashko 《Journal of Geochemical Exploration》2005,87(3):92-108

Chromium ore was treated to produce ferrochromium from 1979 until 2000 in a smelter in Burrel, 35 km NE of Tirana (Albania). As a consequence, large amounts of solid waste, i.e. slags (about 9.10⁶ m³) have been disposed next to the smelter, disfiguring the landscape. In an attempt to define contaminated sites, heavy metal content of the different sampling media have been compared with respective background samples.In the study area, the determination of background values in soil samples is complicated due to the different geological substrates. Cr and Ni background concentrations in serpentinite-derived soils, west of the smelting plant, are markedly higher than in the Pliocene gravel/sandy soils, where the smelter is situated (Cr 2147 and 193 mg/kg, respectively; Ni 2356 and 264 mg/kg). These values are clearly lower than those encountered around the smelter. Average total Cr and Ni concentrations in soils around the smelter are 3117 and 1243 mg/kg, respectively. The highest concentrations of Cr (up to 2.3 wt.%), were recorded in samples taken near the smelting compartment within the industrial plant and next to the slags clearly indicating that the smelter forms a point source of Cr contamination. The Cr / Fe ratio is the best indicator to differentiate non-polluted (Cr / Fe Serpentinite soil: 130–390; Pliocene soils: < 130) from polluted areas (> 390 smelting nearby of the slags).Cr and Ni values for local backgrounds in stream and overbank sediments were taken in the Mat river 6 km upstream and to the east of the smelter (268 and 430 mg/kg for Cr, and 306 and 604 mg/kg for Ni, respectively). Equivalent sediments taken from the Zalli i Germanit river, which drains the smelter area are respectively 816 and 1126 mg/kg for Cr and 1115 and 1185 mg/kg for Ni.Dust samples, taken from the lofts of houses up to 2 km from the smelter, display high concentrations of Cr, Ni and Zn (average contents of 2899, 436 and 902 mg/kg, respectively). The later concentrations in the dust samples have been confirmed by mineralogical analysis where Cr-bearing mineral phases such as ferrochromium and chromium oxides, clearly relate to the activity of the smelter. Consequently, atmospheric deposition of dust particles forms a serious problem and can also be responsible for the elevated contents encountered in soil samples around the smelter.All these data show that the degree of contamination caused by industrial activity of the Burrel Cr-smelter is severe, although no Cr(VI) was detected in soil water extractions nor in the surface or groundwater where concentrations were < 0.01 mg/kg.  相似文献   

西秦岭关子镇蛇绿混杂岩的地球化学和锆石SHRIMP U-Pb年龄   总被引：3，自引：2，他引：3  

李王晔李曙光  裴先治张国伟 《岩石学报》2007,23(11):2836-2844

西秦岭沿天水武山断裂带产出的关子镇蛇绿混杂岩由变玄武岩、变中-基性深成岩浆岩以及少量蛇纹岩组成。变玄武岩具有平坦或轻稀土略亏损的稀土配分型式((La/Yb)_N=0.63～1.24),且不存在Nb、Ta和Ti的负异常,表明它们形成于洋中脊环境。变中-基性深成岩浆岩包含两种类型:类型Ⅰ显示轻稀土富集((La/Yb)_N>2.2)、具有显著Nb负异常((La/Nb)_N>2.4)的特征,类似于岛弧火山岩;类型Ⅱ显示轻稀土亏损到略富集((La/Yb)_N=0.44～1.38)、无显著Nb负异常((La/Nb)_N<1.5),这些特征与上述变玄武岩类似,表明它们也是关子镇蛇绿岩的组成部分。蛇绿岩中辉长岩和闪长岩(该闪长岩属"大洋斜长花岗岩类")样品的锆石SHRIMP U-Pb年龄分别为534±9Ma和517±8Ma,这反映关子镇蛇绿岩可能为早-中寒武世古洋壳残片。由于西秦岭的天水武山断裂带是东秦岭商丹断裂带的西延并共同被认为是华北和华南陆块之间的主缝合线,上述年龄对理解该带及古秦岭洋的演化提供了重要制约。  相似文献   

西藏改则地区拉果错蛇绿岩地球化学特征及成因   总被引：11，自引：3，他引：11  

王保弟许继峰  曾庆高康志强陈建林  董彦辉 《岩石学报》2007,23(6):1521-1530

拉果错蛇绿岩位于西藏改则县南侧,是班公湖-怒江缝合带南侧蛇绿岩带中发育最完整的蛇绿岩之一,可能形成晚侏罗世—早白垩世,主要由地幔橄榄岩、堆晶岩、枕状熔岩、岩墙、斜长花岗岩及放射虫硅质岩等构造单元组成。微量元分析结果表明该蛇绿岩中的中基性岩富集 Sr、Rb 等大离子亲石元素,亏损 Nb、Ta 等高场强元素,具有岛弧型火山岩的特点其在稀土元素球粒陨石标准化配分图解中主要显示平坦型曲线,它们可能是由消减板片流体交代的地幔楔源区的部分熔,形成。拉果错蛇绿岩可能形成于弧间盆地环境,代表了班公湖-怒江缝合带南侧弧-弧碰撞的产物。  相似文献   

西藏丁青弧前蛇绿岩的地球化学特征   总被引：9，自引：4，他引：9  

刘文斌  钱青等 《岩石学报》2002,18(3):392-400

丁青蛇绿岩位于班化湖－丁青－怒江蛇绿岩带的东段，其地幔岩出露规模是该带中最大的。本文报道的丁青蛇绿岩主要由地幔橄榄岩、堆晶岩、辉长岩和斜长花岗岩组成。蛇绿岩剖面上覆硅岩中的放射虫化石是早株罗世和晚三叠世诺利克期的，中侏罗统砂岩和砾岩不整合覆盖在蛇绿岩之上，由此确定丁青蛇绿岩是晚三叠－早侏罗世的，在中株罗世之前侵位，丁青蛇绿岩属于玻安岩系，玻安岩的特点是富Si、Mg和大离子亲石元素（LILE），贫高场强元素（Ti、P、Zr、Y、Yb和Nb）。丁青蛇绿岩的堆晶岩、辉长岩和辉绿岩均具“U”型REE分布，暗示丁青玻安岩是由于亏损的地幔源岩和来自消减带的水和流体两组分的混合形成的。丁青玻安岩的地球化学特征类似西太平洋第三纪玻安岩，而明显不同于MORB的地球化学性质， 表明丁青玻安岩应当形成于洋内岛弧的弧前环境，属于弧前蛇绿岩。  相似文献   

Age of the metamorphic sole of the Papuan Ultramafic Belt ophiolite, Papua New Guinea     

Wilfred Y. Lus  Ian McDougall  Hugh L. Davies 《Tectonophysics》2004,392(1-4):85

The Papuan Ultramafic Belt (PUB) ophiolite is former oceanic crust and upper mantle emplaced onto continental crust in Papua New Guinea (PNG) in a zone of general convergence between the Pacific and Australian plates. The metamorphic sole beneath the ophiolite is best exposed in the Musa–Kumusi divide and comprises a 40- to 300-m-thick body of granulite and amphibolite facies rocks. Geochronological studies on the metamorphic sole, using amphiboles from the granulites and amphibolites, yield measured K–Ar ages ranging from 65.0±0.7 to 57.2±0.6 Ma and average ⁴⁰Ar–³⁹Ar direct total fusion ages ranging from 67.0±0.7 to 59.5±0.2 Ma. Five of the six ⁴⁰Ar–³⁹Ar plateau ages, derived from age spectra, lie between 58.6±0.2 and 57.8±0.2 Ma, with an overall mean age of 58.3±0.4 Ma. The large spread in measured K–Ar and ⁴⁰Ar–³⁹Ar total fusion ages is thought to be caused by the presence of variable amounts of excess argon. The mean plateau age for five samples of 58.3±0.4 Ma is interpreted to mark the time of cooling of the metamorphic sole following peak metamorphism. We suggest that the development of the metamorphic sole and emplacement of the PUB ophiolite onto the PNG crust occurred in a relatively short time interval in the Paleocene.  相似文献