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首页> 外文期刊>Geochemistry International >Primary Magmas of Uralian Alaskan-Type Ultramafic Complexes:Geochemical Constraints Deduced from Mineral Compositions
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Primary Magmas of Uralian Alaskan-Type Ultramafic Complexes:Geochemical Constraints Deduced from Mineral Compositions

机译：乌拉尔阿拉斯加型超镁铁质复合物的初生岩浆：从矿物成分推导的地球化学约束。

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摘要

The association of plutonic dunites and olivine-clinopyroxene ultramafic rocks is known to occur in the Urals in two types of settings:(1)differentiated gabbro-ultramafic intrusions of the Alaskan type,which are spatially restricted to Paleozoic island-arc complexes of the Tagil zone(Uralian Platinum Belt)and(2)the layered series of some ophiolitic complexes,which are related to Paleozoic zones of suprasubduction spreading.Data newly obtained on the geochemistry of clinopyroxene in the dunites,considered together with literature data on the chemistry of spinel,are used to characterize the composition of the melt that coexisted with the plutonic ultramafics.The dunite-wehrlite-clinopyroxenite plutonic complexes in the Urals(of both ophiolitic and Alaskan types)are proved to have been produced by primitive suprasubduction-zone magmas.Compared with MOR basalts,these magmas were variably depleted in HFSE and HREE and enriched in LILE and LREE.Among the known geochemical types of plutonic ultramafics in subduction environments,the ultramafic complexes of the Uralian Platinum Belt(Alaskan type)are noted for the strongest enrichment of their primary magmas in LILE and LREE.The primary magmas of ultramafic rocks in the Platinum Belt had high Mg#(no less than 78-82),low Al_2O_3 contents(10-12.5 wt %),and moderately elevated contents of TiO_2(0.4-1.0 wt %).The most probable analogues of these primary magmas were the melts that gave rise to high-K and calc-alka-line volcanic series in island arcs.
机译：已知在乌拉尔有两种类型的背景发生了深成双辉岩和橄榄石-斜辉石超镁铁质岩的结合：（1）阿拉斯加类型的辉长岩-超音波侵入体，在空间上仅限于塔吉尔的古生代岛弧复合体区（乌拉尔白金带）和（2）与超俯冲展布的古生代区有关的一些蛇绿岩复合物的层状序列。关于二叠纪斜辉石地球化学的最新数据，以及有关尖晶石化学的文献资料被用来表征与古生代超镁铁质共存的熔体成分。事实证明，乌拉尔的榴辉岩-辉绿岩-斜辉石-辉石岩复合体是由超俯冲带岩浆形成的。在含MOR玄武岩的情况下，这些岩浆的HFSE和HREE含量不同，富含LILE和LREE。在俯冲环境中的岩浆岩层中，乌拉尔铂金带（阿拉斯加型）的超镁铁质复合物以其在LILE和LREE的原生岩浆最富集而著称。铂金带中超镁铁质岩层的原生岩浆Mg＃高78-82），较低的Al_2O_3含量（10-12.5 wt％）和适度提高的TiO_2含量（0.4-1.0 wt％）。这些原生岩浆最可能的类似物是产生高K和钙的熔体岛弧中的碱性火山系列。

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