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Geochemical characteristics of mafic intrusive rocks from the Naga Hills Ophiolite, north-east India: Constraints on petrogenesis and tectonic setting
Geological Journal ( IF 1.8 ) Pub Date : 2022-08-22 , DOI: 10.1002/gj.4567
Mohammed Faruque Hussain 1 , Ajoy Dey 1, 2
Affiliation  

The Naga Hills Ophiolite (NHO) of Late Jurassic to Eocene age is one of the well-exposed domains of Tethyan ophiolites, located in the northern margin of the Indo-Myanmar Orogenic Belt, north-east India. It is composed of suites of tectonite peridotite and cumulative ultramafic, mafic intrusive-extrusive rocks, felsic intrusive, radiolarian, and marine pelagic sediments. The mafic intrusives of the NHO exhibit rhythmic to cryptic layering and isotropic in nature. Based on their mineralogy, the mafic intrusives are identified as gabbro, gabbronorite, hornblende gabbro, and olivine gabbro. The gabbros are adcumulate and mesocumulate and essentially composed of plagioclase feldspar, clinopyroxene, orthopyroxene, hornblende, with minor olivine, serpentine, chlorite, and magnetite. These mafic intrusive rocks show affinity to tholeiitic parental magma and fractionated trends in the multi-elemental diagram, with negative anomalies at Zr, P, Ce and positive anomalies at Sr, Nb, and Ti suggesting that the magmatism was influenced by subduction zone components. The majority of the samples represent light rare earth elements (LREE) depletion (LaN/SmN = 0.28–0.86), except two samples that display LREE enrichment (LaN/SmN = 2.11–3.03), with negligible negative Eu anomaly. Petrogenetic modelling suggests 5%–20% partial melting of a depleted mid-ocean ridge basalt-type mantle source, within the spinel lherzolite stability field, as well as low degree partial melting (<10%) of an enriched mantle source probably metasomatized by sediment-melt from a subducted slab. Therefore, based on mineralogical and geochemical data, we propose that the mafic intrusive of the NHO were generated in the intra-oceanic arc system within the Neotethys Ocean with the active participation of possible wet basaltic melt from spinel-lherzolite source-mantle, subsequently modified by melts derived from sediments in a subduction zone.

中文翻译:

印度东北部 Naga Hills 蛇绿岩基性侵入岩的地球化学特征:对岩石成因和构造背景的制约

晚侏罗世至始新世的那加山蛇绿岩 (NHO) 是特提斯蛇绿岩的出露区之一,位于印度东北部印缅造山带北缘。它由构造岩、橄榄岩和累积的超镁铁质、镁铁质侵入-喷出岩、长英质侵入岩、放射虫和海洋远洋沉积物组成。NHO 的镁铁质侵入岩在自然界中表现出有节奏到隐蔽的分层和各向同性。根据矿物学,镁铁质侵入岩被确定为辉长岩、辉长岩、角闪岩辉长岩和橄榄石辉长岩。辉长岩呈堆积状和中堆积状,主要由斜长石、斜辉石、斜辉石、角闪石以及少量橄榄石、蛇纹石、绿泥石和磁铁矿组成。这些镁铁质侵入岩显示出与拉斑长质母岩浆的亲和力以及多元素图中的分异趋势,Zr、P、Ce 负异常,Sr、Nb 和 Ti 正异常,表明岩浆活动受俯冲带成分的影响。大多数样品代表轻稀土元素 (LREE) 耗尽 (LaN /Sm N  = 0.28–0.86),除了显示 LREE 富集的两个样本 (La N /Sm N = 2.11–3.03),负 Eu 异常可忽略不计。岩石成因模型表明,在尖晶石二辉橄榄岩稳定区内,贫化的大洋中脊玄武岩型地幔源有 5%–20% 的部分熔融,以及可能由来自俯冲板块的沉积物熔体。因此,基于矿物学和地球化学数据,我们提出 NHO 的镁铁质侵入体是在新特提斯洋内的洋内弧系统中产生的,可能来自尖晶石-二辉橄榄石源-地幔的湿玄武岩熔体的积极参与,随后被改造来自俯冲带沉积物的熔体。
更新日期:2022-08-22
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