Evidence for a Widespread Tethyan Upper Mantle with Indian-Ocean-Type Isotopic Characteristics   总被引：21，自引：2，他引：21  

ZHANG  S.-Q.; MAHONEY  J. J.; MO  X.-X.; GHAZI  A. M.; MILANI  L.; CRAWFORD  A. J.; GUO  T.-Y.; ZHAO  Z.-D. 《Journal of Petrology》2005,46(4):829-858

The mantle sources of Tethyan basalts and gabbros from Iran,Tibet, the eastern Himalayas, the seafloor off Australia, andpossibly Albania were isotopically similar to those of present-dayIndian Ocean ridges and hotspots. Alteration-resistant incompatibleelement compositions of many samples resemble those of ocean-ridgebasalts, although ocean-island-like compositions are also present.Indian-Ocean-type mantle was widespread beneath the Neotethysin the Jurassic and Early Cretaceous, and present beneath atleast parts of the Paleotethys as long ago as the Early Carboniferous.The mantle beneath the Indian Ocean today thus may be largely‘inherited’ Tethyan mantle. Although some of theTethyan rocks may have formed in intra-oceanic back-arcs orfore-arcs, contamination of the asthenosphere by material subductedshortly before magmatism cannot be a general explanation fortheir Indian-Ocean-ridge-like low-²⁰⁶Pb/²⁰⁴Pb signatures. Supplyof low-²⁰⁶Pb/²⁰⁴Pb material to the asthenosphere via plumesis not supported by either present-day Indian Ocean hotspotsor the ocean-island-like Tethyan rocks. Old continental lowercrust or lithospheric mantle, including accreted, little-dehydratedmarine sedimentary material, provides a potential low-²⁰⁶Pb/²⁰⁴Pbreservoir only if sufficient amounts of such material can beintroduced into the asthenosphere over time. Anciently subductedmarine sediment is a possible low-²⁰⁶Pb/²⁰⁴Pb source only ifthe large increase of U/Pb that occurs during subduction-relateddewatering is somehow avoided. Fluxing of low-U/Pb fluids directlyinto the asthenosphere during ancient dewatering and introductionof ancient pyroxenitic lower-crustal restite or basaltic lower-arccrust into the asthenosphere provide two other means of creatingTethyan–Indian Ocean mantle, but these mechanisms, too,have potentially significant problems. KEY WORDS: Indian Ocean; mantle geochemical domains; ophiolites; Tethyan Ocean  相似文献   

安徽大别山蛇绿岩特征及其形成的大地构造环境     

徐贵忠 《吉林大学学报(地球科学版)》1989,(2)

在安徽境内大别群中出露一系列镁铁质和超镁铁质岩体,属于“肢解的蛇绿岩”。与大别群建造应属同一造山期产物。它们可能在中元古代末期,因洋壳海域的岩石圈断块沿华北断块南部的大陆边缘的深海沟向北快速俯冲消减,遭到强烈挤压破碎而侵位到大别群不同构造层位中。  相似文献   

新疆西准噶尔地区两类蛇绿岩的地质特征及其成因研究   总被引：5，自引：0，他引：5  

郝梓国  王希斌  鲍佩声  彭根永  金远新 《岩石矿物学杂志》1989,8(4):299-310

本文将西准噶尔地区蛇绿岩分为两类:一类是变质橄榄岩 橄长岩 辉长岩岩石组合(简称PTG系列);另一类则是变质橄榄岩 辉石岩 辉长岩岩石组合(简称PPG系列)。前者以达拉布特、和布克赛尔蛇绿岩带为代表,后者以唐巴勒、玛依勒山蛇绿岩带为代表。PTG系列遵循富Al的演化趋势,而PPG系列则遵循富Ca的演化趋势;从而造成两类蛇绿岩之间在岩石组合、矿物学、岩石化学、稀土元素等地球化学以及所含铬铁矿床的种属上均有明显的差异。 两类蛇绿岩中变质橄榄岩的成因机制是上地幔岩部分熔融,两者之间的差异则是由部分熔融程度决定的。而壳层岩石(指堆积杂岩、岩墙杂岩、熔岩)则是由岩浆结晶作用形成的;堆积杂岩中出现辉石岩 辉长岩和橄长岩 辉长岩的不同岩石组合则与堆积岩岩浆房出露的深度和氧化状态有关。  相似文献   

四川盐边元古代蛇绿岩中辉石的成因矿物学及其大地构造意义   总被引：14，自引：0，他引：14  

孙传敏 《矿物岩石》1994,14(3):1-15

本文用电子探针分析了岩浆型残余辉石的化学成分，建立了辉石组分之间的相关关系和定量的类质同象交换式，并讨论了母岩浆成分、结晶条件（压力、冷凝速度）对辉石成分的影响。深成岩和火山岩中辉石的标型元素含量和相关参数十分相近，说明深成─火山岩系为同源岩浆成因。尽管一些火山岩样品中辉石的Ａｌ，Ｔｉ因快速冷凝而富集，但总体化学成分仍明显显示拉斑玄武岩特征，与世界上典型的显生宙蛇绿岩熔岩及现代洋中脊玄武岩中的辉石相似，但与岛弧有关的火山岩明显不同。这说明。盐边元古代蛇绿岩很可能形成于一个继大陆裂谷之后的海洋扩张环境。本文提供的成因矿物学资料有助于理解和重建扬子板块西缘元古代造山带的地质历史。  相似文献   

Tectonic control of bioalteration in modern and ancient oceanic crust as evidenced by carbon isotopes     

Harald  Furnes  Yildirim  Dilek  Karlis  Muehlenbachs Neil R.  Banerjee 《Island Arc》2006,15(1):143-155

Abstract We review the carbon‐isotope data for finely disseminated carbonates from bioaltered, glassy pillow rims of basaltic lava flows from in situ slow‐ and intermediate‐spreading oceanic crust of the central Atlantic Ocean (CAO) and the Costa Rica Rift (CRR). The δ¹³C values of the bioaltered glassy samples from the CAO show a large range, between ?17 and +3‰ (Vienna Peedee belemnite standard), whereas those from the CRR define a much narrower range, between ?17‰ and ?7‰. This variation can be interpreted as the product of different microbial metabolisms during microbial alteration of the glass. In the present study, the generally low δ¹³C values (less than ?7‰) are attributed to carbonate precipitated from microbially produced CO₂ during oxidation of organic matter. Positive δ¹³C values >0‰ likely result from lithotrophic utilization of CO₂ by methanogenic Archaea that produce CH₄ from H₂ and CO₂. High production of H₂ at the slow‐spreading CAO crust may be a consequence of fault‐bounded, high‐level serpentinized peridotites near or on the sea floor, in contrast to the CRR crust, which exhibits a layer‐cake pseudostratigraphy with much less faulting and supposedly less H₂ production. A comparison of the δ¹³C data from glassy pillow margins in two ophiolites interpreted to have formed at different spreading rates supports this interpretation. The Jurassic Mirdita ophiolite complex in Albania shows a structural architecture similar to that of the slow‐spreading CAO crust, with a similar range in δ¹³C values of biogenic carbonates. The Late Ordvician Solund–Stavfjord ophiolite complex in western Norway exhibits structural and geochemical evidence for evolution at an intermediate‐spreading mid‐ocean ridge and displays δ¹³C signatures in biogenic carbonates similar to those of the CRR. Based on the results of this comparative study, it is tentatively concluded that the spreading rate‐dependent tectonic evolution of oceanic lithosphere has a significant control on the evolution of microbial life and hence on the δ¹³C biosignatures preserved in disseminated biogenic carbonates in glassy, bioaltered lavas.  相似文献   

东准噶尔扎河坝超高压变质成因石英菱镁岩的^40Ar／^39Ar同位素年代学信息及地质意义   总被引：2，自引：4，他引：2  

牛贺才 单强张海祥  于学元 《岩石学报》2007,23(7):1627-1634

在扎河坝-阿尔曼泰蛇绿岩岩块内分布着高压-超高压成因的二辉橄榄岩、石榴辉石岩、石英菱镁岩及榴闪岩。石英菱镁岩内多硅白云母的 Si(pfu)值均大于3.35,最高可达3.77,是典型高压-超高压成因的矿物。石英菱镁岩及其围岩蛇纹石化二辉橄榄岩的 K_2O 含量极低,且多硅白云母的 Na/(Na K)比值小于0.04,这些地球化学特征显示,扎河坝多硅白云母不应含有过剩 Ar,是一个理想的~(40)Ar/~(39)Ar 定年对象。精确的~(40)Ar/~(39)Ar 年代学研究结果表明,扎河坝石英菱镁岩中多硅白云母的~(40)Ar/~(39)Ar 同位素年龄为281.6±2.5Ma。而矿物化学特征表明,扎河坝石英菱镁岩中的多硅白云母曾经历了退变质作用的改造,因此,它代表的应该是超高压变质石英菱镁岩的折返年龄。多硅白云母的~(40)Ar/~(39)Ar 年代学研究结果表明,扎河坝-阿尔曼泰蛇绿混杂岩内超高压石英菱镁岩的折返事件应发生在早二叠世。  相似文献   

Suprasubduction zone ophiolite formation along the periphery of Mesozoic Gondwana   总被引：2，自引：0，他引：2  

Yildirim  Harald  Minella 《Gondwana Research》2007,11(4):453-475

Neotethyan suprasubduction zone ophiolites represent anomalous oceanic crust developed in older host basins during trench rollback cycles and later entrapped in orogenic belts as a result first of trench-passive margin and then continent–continent collisions. The Middle Jurassic Mirdita zone ophiolites in northern Albania constitute a critical transition between the dominantly mid-ocean ridge basalt (MORB)-related Early Jurassic Alpine–Apennine ophiolites in the west and supra-subduction zone (SSZ)-generated Cretaceous Eastern Mediterranean ophiolites in the east. The previously recognized Western- and Eastern-type ophiolites in the Mirdita zone display significant differences in their internal structure and pseudostratigraphy, but their geochemical affinities are more gradational in contrast to the earlier claims that these ophiolites may have formed in different tectonic settings at different times. Crosscutting relations of dike intrusions in the Eastern-type ophiolites indicate changes in the chemistry of magmatic plumbing systems from basaltic to andesitic, dacitic, rhyodacitic, and boninitic compositions through time and from west to east. The chemostratigraphy of the extrusive sequence in the Western-type ophiolites shows that the MORB-like tholeiitic rocks display a significant decrease in their TiO₂ contents and Zr concentrations stratigraphically upward, although their ε_Nd(T) values (+ 7.3 to + 6.9) show minor variation. The basaltic andesites in the upper 100 m of the Western extrusive sequence have island arc tholeiite (IAT)-like chemical characteristics (low-Ti, lower HFSE and HREE distribution, significant LREE depletion and higher Co, Ni, and Cr contents) that signify increased subduction influence in magma/melt evolution. The Eastern-type extrusive rocks range in composition from basaltic andesite to andesite, dacite and rhyodacite stratigraphically upward mimicking the temporal changes in the sheeted dikes, and they display constant Zr ( 50 ppm) but significantly varying Cr contents. The TiO₂ contents of their pyroxenes are < 0.3 wt.%, and their ε_Nd(T) values decrease from + 6.5 in the lower parts to  + 3.1 in the uppermost section of the sequence. Farther east in the extrusive sequence the youngest boninitic lavas and dikes have ε_Nd(T) values between − 1.4 and − 4.0. These chemical variations through time point to a mantle source increasingly contaminated by subduction-derived aqueous fluids and sediments, which were incorporated into the melt column beneath an extending protoarc–forearc region. Slab retreat and sinking played a major role in establishing asthenospheric upwelling and corner flow beneath the forearc mantle that in turn facilitated shallow partial melting of highly depleted harzburgitic peridotites, producing boninitic magmas. This chemical progression in the Mirdita zone ophiolite volcanism is similar to the temporal variations in magma chemistry documented from very young intraoceanic arcs built on recently generated backarc crust (i.e., South Sandwich arc). The Western and Eastern-type ophiolites in the Mirdita zone are therefore all subduction-related with the subduction zone influence in the lavas increasing stratigraphically upward as well as eastwards, suggesting a west-dipping slab geometry. The Mirdita zone and the Western Hellenic ophiolites in the Balkans were produced within a marginal basin that had evolved between the Apulian and Pelagonian microcontinents, and were subsequently emplaced onto their passive margins diachronously through different collisional processes.  相似文献   

Mantle flow patterns and magma chambers at ocean ridges: Evidence from the Oman ophiolite     

A. Nicolas  F. Boudier  G. Ceuleneer 《Marine Geophysical Researches》1988,9(4):293-310

As a result of an extensive program of structural mapping in the ultramafic section of the Oman ophiolite, maps of mantle flow below the spreading center of origin have been drawn. They reveal a mantle diapiric system in which the uppermost mantle flow diverges from diapirs 10–15 km across, which could have been spaced by an average distance of 50 km. Some diapirs could have been located off-axis. The rotation of flow lines in the diapirs occurs within the few hundred meters of the transition zone separating the mantle and crustal formations. The importance of this zone is stressed. The structure of the layered gabbros of the crustal unit in most places reflects a large magmatic flow induced by the solid state flow in the underlying peridotites. The magmatic foliation of the gabbros steepens upsection and becomes parallel to the sheeted dike attitude. A new model of a tent-shaped magma chamber is derived from these structural data.  相似文献   

Geochemistry of the Jurassic Mirdita Ophiolite (Albania) and the MORB to SSZ evolution of a marginal basin oceanic crust   总被引：7，自引：0，他引：7  

Yildirim Dilek  Harald Furnes  Minella Shallo 《Lithos》2008,100(1-4):174-209

The Middle Jurassic Mirdita Ophiolite in northern Albania is part of an ophiolite belt occurring between the Apulian and Pelagonian subcontinents in the Balkan Peninsula. The upper mantle and crustal units of the Mirdita Ophiolite show major changes in thickness, rock types, and chemical compositions from west to east as a result of its complex evolution in a suprasubduction zone (SSZ) environment. The  3–4-km-thick Western Mirdita Ophiolite (WMO) includes lherzolite–harzburgite, plagioclase–lherzolite, plagioclase–dunite in its upper mantle units and a plutonic complex composed of olivine gabbro, troctolite, ferrogabbro, and gabbro. These peridotites and gabbroic rocks are overlain directly by a  600-m-thick extrusive sequence containing basaltic pillow lavas and hyaloclastites. Sheeted dikes are rare in the WMO. The  12-km-thick Eastern Mirdita Ophiolite (EMO) includes tectonized harzburgite and dunite with extensive chromite deposits, as well as ultramafic cumulates including olivine clinopyroxenite, wehrlite, olivine websterite, and dunite forming a transitional Moho with the overlying lower crustal section. The plutonic rocks are made of pyroxenite, gabbronorite, gabbro, amphibole gabbro, diorite, quartz diorite, and plagiogranite. A well-developed sheeted dike complex has mutually intrusive relations with the underlying isotropic gabbros and plagiogranites and feeds into the overlying pillow lavas. Dike compositions change from older basalt to basaltic andesite, andesite, dacite, quartz diorite, to late-stage andesitic and boninitic dikes as constrained by crosscutting relations. The  1.1-km-thick extrusive sequence comprises basaltic and basaltic andesitic pillow lavas in the lower 700 m, and andesitic, dacitic and rhyodacitic massive sheet flows in the upper 400 m. Rare boninitic dikes and lavas occur as the youngest igneous products within the EMO. The basaltic and basaltic andesitic rocks of the WMO extrusive sequence display MORB affinities with Ti and Zr contents decreasing upsection (TiO₂ = 3.5–0.5%, Zr = 300–50 ppm), while _Nd(T) (+ 8 to + 6.5) varies little. These magmas were derived from partial melting of fertile MORB-type mantle. Fractional crystallization was important in the evolution of WMO magmas. The low Ti and HREE abundances and Cs and Ba enrichments in the uppermost basaltic andesites may indicate an increased subduction influence in the evolution of the late-stage WMO magmas. Basaltic andesites in the lower 700 m of the EMO volcanic sequence have lower TiO₂ ( 0.5%) and Zr ( 50 ppm) contents but _Nd(T) values (+ 7 to + 6.5) are similar to those of the WMO lavas. These rocks show variable enrichment in subduction-enriched incompatible elements (Cs, Ba, Th, U, LREE). The basaltic andesites through dacites and boninites within the upper 400 meters of EMO lavas show low TiO₂ ( 0.8–0.3%) and _Nd(T) (+ 6.5 to + 3.0). The mantle source of these rocks was variably enriched in Th by melts derived from subducted sediments as indicated by the large variations in Ba, K, and Pb contents. EMO boninitic dikes and lavas and some gabbroic intrusions with negative _{Nd (T)} values (− 1.4 and − 4.0, respectively) suggest that these magmas were produced from partial melting of previously depleted, ultra-refractory mantle. The MORB to SSZ transition (from west to east and stratigraphically upwards in the Mirdita Ophiolite and the progression of the _Nd(T) values from + 8.0 to − 4.0 towards the east resulted from an eastward shift in protoarc–forearc magmatism, keeping pace with slab rollback in this direction. The mantle flow above the retreating slab and in the arc-wedge corner played a major role in the evolution of the melting column, in which melt generation, aggregation/mixing and differentiation occurred at all levels of the sub-arc/forearc mantle. The SSZ Mirdita Ophiolite evolved during the intra-oceanic collapse and closure of the Pindos marginal basin, which had a protracted tectonic history involving seafloor spreading, protoarc rifting, and trench-continent collision.  相似文献   

Volcanic facies analysis of a subaqueous basalt lava-flow complex at Hruškovec,NW Croatia — Evidence of advanced rifting in the Tethyan domain     

Ladislav A. Palinkaš  Vladimir Bermanec  Sibila Borojević Šoštarić  Tea Kolar-Jurkovšek  Sabina Strmić Palinkaš  Ferenc Molnar  Goran Kniewald 《Journal of Volcanology and Geothermal Research》2008

The Hruškovec quarry of basaltoid rocks is situated on the northwestern slopes of Mt. Kalnik, within the Zagorje–Mid-Transdanubian zone, a part of the North-western Dinarides. The basaltoids are inter-bedded with radiolarites of the Middle and Upper Triassic age (Langobardian, Carnian–Norian). Spilites, altered diabases and meta-basalts form part of Triassic volcanic-sedimentary sequence, made of sandstones, shales, micritic limestone, altered vitric tuffs and radiolarian cherts, incorporated tectonically into the Jurassic–Cretaceous mélange.  相似文献