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首页> 外文期刊>Journal of Asian earth sciences >Petrotectonic significance of the chemistry of chromite in the ultramafic-mafic complexes of Pakistan
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Petrotectonic significance of the chemistry of chromite in the ultramafic-mafic complexes of Pakistan

机译：巴基斯坦超镁铁质-镁铁质复合物中铬铁矿化学的岩石构造学意义

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The suture zones, which border the Indian craton in Pakistan are characterized by several large mafic-ultramafic complexes. From south to north these include: (1) Bela, (2) Muslimbagh-Zhob valley, (3) Waziristan, (4) Dargai (Skhakot-Qila), (5) Shangla-Mingora, (6) Jijal, and (7) Sapat. Besides these, there is the huge (300x ≤ 40 km) Chilas mafic-ultramafic complex in the Cretaceous Kohistan magmatic arc. The Sapat, Jijal, Shangla, and Dargai (Skhakot-Qila) complexes are distributed along the Indus suture. The Waziristan, Zhob valley and Bela complexes lie along the suture on the western margin of the Indian plate. All these complexes were emplaced during late Cretaceous-Paleocene time at ca. ～65 Ma. These complexes largely consist of ultramafic and mafic plutonic rocks (ranging from dunite and peridotite to gabbro). The mafic-ultramafic rocks of the Sapat, Chilas and Jijal complexes are generally well layered and appear to be mainly cumulates. In addition to cumulate plutonic rocks, the remaining five complexes also contain abundant residual peridotites, sheeted dykes, a variety of lava flows (locally pillowed), and associated pelagic sediments. Disseminated and segregated chromite occurs in all the complexes. On the basis of the chromium number [Cr#= 100 X Cr/(Cr + Al)] of their chromite, the complexes can be divided into three groups: (1) the Sapat and Jijal complexes contain chromites with Cr# > 60; (2) the Shangla-Mingora, Dargai (Skhakot-Qila), Waziristan, Muslimbagh-Zhob and Bela rocks contain chromites that display a wide range of composition with Cr varying from 15 to 90; and (3) rocks of the Chilas complex are characterized by low-Cr chromites (Cr# mostly < 60). The chromite compositions appear to indicate different tectonic settings for the origin of the complexes under consideration. Those with high Cr chromite belong to an island arc type tectonic setting. Opinion differs on the origin of the group (2) chromite-bearing complexes; they may well be of complex origin with components, which originated in different tectonic settings. The Chilas complex of group (3) contains low Cr chromite similar to oceanic rocks supporting the idea that it is related to rifting within an island arc setting.
机译：与巴基斯坦印度克拉通接壤的缝合带的特征是几个大型铁镁质-超音波复合体。从南到北包括：（1）贝拉（2），穆斯林巴格-霍布河谷（3）Waziristan，（4）达尔盖（Skhakot-Qila），（5）尚拉-明戈拉，（6）贾加勒和（7）萨帕特。除此之外，在白垩纪科伊斯坦岩浆弧中还有一个巨大的（300x≤40 km）Chilas镁铁质-超镁铁质复合体。 Sapat，Jijal，Shangla和Dargai（Skhakot-Qila）复合物沿印度河缝线分布。瓦济里斯坦（Waziristan），霍布山谷（Zhob）谷和贝拉（Bela）复合体位于印度板块西缘的缝合线上。所有这些复合物都在白垩纪-古新世晚期（大约在）被安置。 〜65马这些复合物主要由超镁铁质和镁铁质深成岩组成（从榴辉岩和橄榄岩到辉长岩）。 Sapat，Chilas和Jijal复合体的镁铁质-超镁铁质岩石通常分层良好，并且似乎主要是堆积的。除了堆积的深成岩外，其余五个复合体还包含大量的残留橄榄岩，片状堤坝，各种熔岩流（局部枕状）以及相关的浮游沉积物。在所有的配合物中都发生了散布和分离的亚铬酸盐。根据亚铬酸盐的铬数[Cr＃= 100 X Cr /（Cr + Al）]，可将络合物分为三类：（1）Sapat和Jijal络合物含有Cr＃> 60的亚铬酸盐； （2）上拉—明戈拉，达盖（Skhakot-Qila），瓦济里斯坦，穆斯林巴格-霍布和贝拉岩石含有铬铁矿，其铬的组成范围很广，铬含量从15到90不等； （3）奇拉斯复合岩的特征是低铬亚铬酸盐（Cr＃大多<60）。亚铬酸盐组成似乎表明所考虑的络合物的起源具有不同的构造背景。高铬铬铁矿的那些属于岛弧型构造环境。关于（2）含铬铁矿的络合物的起源有不同的看法。它们很可能起源于具有复杂构造成分的复杂成分。组（3）的Chilas配合物包含与海洋岩石相似的低铬亚铬酸盐，支持了这种想法与在岛弧环境中裂谷有关。

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