Clinopyroxenite dykes within a banded unit in the basal mantle section of the northern part of the Oman ophiolite: A record of the latest deep-seated magmatism.
Clinopyroxenite dykes within a banded unit in the basal mantle section of the northern part of the Oman ophiolite: A record of the latest deep-seated magmatism.
复制标题
阿曼蛇绿岩北部基底地幔部分带状单元内的单斜辉石岩脉：最新深层岩浆作用的记录。
DOI：
10.1016/j.lithos.2017.09.022
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发表时间：
2017
期刊：
影响因子：
3.5
通讯作者：
A.
中科院分区：
文献类型：
--
作者：
Ishimaru;S.;Arai;S. and Tamura;A.
我们在阿曼蛇绿岩北部变质底最上部的苏梅尼地区的带状方辉橄榄岩块中发现了单斜辉石岩脉。岩脉清晰地切割了方辉橄榄岩的变形结构并包含其碎片，表明岩脉是在蛇绿岩仰冲过程中形成的。岩脉中单斜辉石的 Mg# [= Mg / (Mg + 总 Fe)] 范围为 0.81 至 0.91，并且在接近方辉橄榄岩碎片处增加至 0.93。方辉橄榄岩碎片中的地幔矿物通过与形成岩脉的岩浆相互作用而发生化学改变，与未改变的方辉橄榄岩相比，产生了较低的单斜辉石和尖晶石 Mg#，以及较高的 TiO2 含量的尖晶石。这些地球化学特征表明，斜辉石岩脉是源自相对较深的富含轻稀土元素（LREE）的原始岩浆的堆积物，具有类似洋岛玄武岩（OIB）的亲和力，在地球化学上类似于山脊外的V3熔岩。将这些数据与地质观测相结合表明，单斜辉石岩脉代表了 V3 熔岩的根系。我们对单斜辉石岩脉的分析证明了 V3 岩浆的外部性质，它是从外部添加到切片海洋岩石圈中的。 V3 岩浆很可能经历了深层的单斜辉石结晶，并且在到达地表的过程中与地幔橄榄岩的相互作用有限。苏美尼单斜辉石岩的产状方式（即埋入由石榴石角闪岩包围的带状方辉橄榄岩块中）与阿曼蛇绿岩下方由于“俯冲板片”断裂和随后热软流圈地幔的渗透而产生的类 OIB 岩浆（V3 熔岩）一致。这一观点与阿曼蛇绿岩中 V3 相关岩石的有限分布是一致的。在蛇绿岩仰冲过程中产生这种类似 OIB 的岩浆并不罕见，尤其是在年轻而炎热的海洋岩石圈俯冲过程中。
We found clinopyroxenite dykes in a banded harzburgite block within the Sumeini area in the uppermost part of the metamorphic sole of the northern part of the Oman ophiolite. The dykes clearly cut the deformational structure of the harzburgite and contain its fragments, indicating dyke formation during obduction of the ophiolite. The Mg# [= Mg / (Mg + total Fe)] of clinopyroxenes in the dykes ranges from 0.81 to 0.91, and increases up to 0.93 proximal to harzburgite fragments. Mantle minerals in the harzburgite fragments were modified chemically through interaction with the magma that formed the dyke, yielding lower clinopyroxene and spinel Mg#, and spinels with higher TiO2contents than those in the unaltered harzburgite. These geochemical features indicate that the clinopyroxenite dykes are cumulates derived from a relatively deep-seated primitive magma enriched in light rare earth elements (LREE) with an ocean island basalt (OIB)-like affinity, geochemically similar to the V3 lavas of an off-ridge origin. Combining these data with geological observations suggests that the clinopyroxenite dykes represent root system of the V3 lavas. Our analyses of the clinopyroxenite dykes testify to the external nature of the V3 magmas, which was added to the sliced oceanic lithosphere from the outside. It is likely that the V3 magma underwent deep-seated crystallization of clinopyroxene and had limited interaction with mantle peridotite en route to the surface. The mode of occurrence of the Sumeini clinopyroxenites (i.e., emplaced into a banded harzburgite block surrounded by garnet amphibolite) is consistent with the generation of OIB-like magmas (V3 lava) beneath the Oman ophiolite resulting from the break-off of the “subducting slab” and subsequent infiltration of hot asthenospheric mantle. This view is consistent with the limited distribution of V3-related rocks in the Oman ophiolite. The production of such OIB-like magmas during ophiolite obduction is not a rare event, especially during the subduction of young and hot oceanic lithosphere.