Sulfide-rich dunite within a thick Moho transition zone of the northern Oman ophiolite : Implications for the origin of Cyprus-type sulfide deposits.
Sulfide-rich dunite within a thick Moho transition zone of the northern Oman ophiolite : Implications for the origin of Cyprus-type sulfide deposits.
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阿曼北部蛇绿岩厚层莫霍面过渡带内富含硫化物的纯橄榄岩：对塞浦路斯型硫化物矿床起源的影响。
DOI：
10.1016/j.lithos.2012.11.024
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发表时间：
2013
期刊：
影响因子：
3.5
通讯作者：
Norikatsu Akizawa
中科院分区：
文献类型：
--
作者：
Hironori Negishi;Shoji Arai;Hisayoshi Yurimoto;Shoichi Ito;Satoko Ishimaru;Akihiro Tamura;Norikatsu Akizawa
特殊的岩质，部分是石灰石，含有高达3vol。在阿曼北部沿Wadi Thuqbah蛇绿岩发现了来自厚（~1000m） Moho过渡带（MTZ）的%硫化物。我们讨论了它们与地表附近塞浦路斯型块状硫化物矿床形成的相关性。野外观测表明，富硫化物的MTZ泥质岩为晚侵入成因。硫化物与磁铁矿形成复合颗粒，形成角状碎屑，被磁铁矿包裹或切割。硫化物部分由均质磁黄铁矿和磁黄铁矿与镍黄铁矿的蠕状共生组成。斜辉石中的硫化物包裹体由磁黄铁矿和镍黄铁矿泡组成，不含磁铁矿。富硫化物白云石中的橄榄石具有低NiO含量（0.1 ~ 0.3wt.%）而高Fo值（~91）的特点，因此它们不属于普通无硫化物MTZ白云石-韦氏石的Fo - NiO趋势。这种低镍橄榄石是从高镁岩浆中析出的，岩浆中分离出富镍硫化物熔体。高温单硫化物固溶体低温（<200℃）亚固溶形成镍黄铁矿-磁黄铁矿共生体。橄榄石在蛇纹石化过程中释放出的铁生成磁铁矿，并与硫化物结合形成复合晶粒。硫化物的原位S同位素比值（δ34S=0.7 ~ 2.8）略高于地幔值，但在海洋岛弧（如马里亚纳）岩浆的范围内。δ34S值低于来自海水和与morb有关的硫化物（如TAG （Trans-Atlantic Geotraverse）矿床）的δ34S值。同一地区地壳剖面的塞浦路斯型块状硫化物矿床（Aarja）的S同位素比值与Thuqbah富硫化物的溶质/韦氏岩中硫化物的S同位素比值相似，表明两者具有遗传联系。Aarja硫化物矿床形成于V2火山岩内，由于高温海水环流，岩浆相对富硫且离轴成因。图克巴富硫化物白云岩可能代表了在离脊岩浆-热液体系中形成的阿尔加塞浦路斯型块状硫化物矿床的火成岩根。
Peculiar dunites, in part wehrlitic, that contain up to 3vol.% sulfides from a thick (~1000m) Moho transition zone (MTZ) are found along Wadi Thuqbah in the northern Oman ophiolite. We discuss their relevance to the formation of Cyprus-type massive sulfide deposits near the surface. Field observations suggest that the sulfide-rich MTZ dunites are of late-intrusive origin. The sulfides form composite grains with magnetite and form angular clasts, which are enclosed or cut by magnetite. The sulfide part is composed of homogeneous pyrrhotite and vermicular intergrowth of pyrrhotite and pentlandite. Sulfide inclusions in clinopyroxene comprise pyrrhotite with pentlandite blebs, free of magnetite. Olivines in the sulfide-rich dunite characteristically show low NiO contents (0.1–0.3wt.%) relative to a high Fo value (~91), and as such they do not lie on a Fo–NiO trend of ordinary sulfide-free MTZ dunites–wehrlites. This low-Ni olivine was precipitated from a high-Mg magma that had segregated Ni-rich sulfide melts. The pentlandite–pyrrhotite intergrowth was formed by subsolidus exsolution at low temperatures (<200°C) from high-temperature mono-sulfide solid solution. Iron released from olivine during serpentinization produced magnetite, which was combined with the sulfides to form the composite grains. In-situ S isotope ratios of the sulfides (δ34S=0.7–2.8) are slightly higher than mantle values but lie within the range for magmas from oceanic island arcs, such as the Marianas. The δ34S are lower than those for sulfate from seawater and MORB-related sulfides, such as TAG (Trans-Atlantic Geotraverse) deposits. One of the Cyprus type massive sulfide deposits (Aarja) from the crustal section of the same area shows similar S isotope ratios to the sulfides in the Thuqbah sulfide-rich dunites/wehrlites, indicating their genetic linkage. The Aarja sulfide deposit was formed within the V2 lavas, which are relatively sulfur-rich and of an off-axis origin, as a result of high-temperature seawater circulation. The Thuqbah sulfide-rich dunite possibly represents an igneous root of the Cyprus-type massive sulfide deposit of Aarja formed in an off-ridge magmatic-hydrothermal system.