Mineral chemistry, whole-rock compositions, and petrogenesis of leg 176 gabbros: Data and discussion
Mineral chemistry, whole-rock compositions, and petrogenesis of leg 176 gabbros: Data and discussion
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DOI：
10.2973/odp.proc.sr.176.011.2002
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发表时间：
2002
期刊：
影响因子：
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通讯作者：
Y. Niu;T. Gilmore;S. Mackie;A. Greig;W. Bach
中科院分区：
文献类型：
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作者：
Y. Niu;T. Gilmore;S. Mackie;A. Greig;W. Bach
我们报告矿物化学，全岩主要元素组成，并在第176航次期间钻探和选择的735 B孔样品的微量元素分析。我们讨论了这些数据，连同腿176船载数据和腿118样品数据从文献中，在原生火成岩成因。尽管在给定的样品中矿物成分变化，但735 B孔辉长岩的主要成分矿物显示出良好的化学平衡，如橄榄石、单斜辉石和斜方辉石的Mg#（= Mg/[Mg+ Fe 2 +]）与斜长石的An（=Ca/[Ca+Na]）之间的显著相关性所示。这表明，橄榄岩中的橄榄石+斜长石、辉长岩中的斜长石+单斜辉石、橄榄辉长岩中的斜长石+单斜辉石+橄榄石、辉长岩中的斜长石+单斜辉石+橄榄石+斜方辉石等矿物组合都是从各自的母体熔体中共沉淀出来的。铁钛氧化物（钛铁矿和钛磁铁矿），这是普遍存在于大多数这些岩石，是不是在化学平衡与橄榄石，单斜辉石，斜长石，但沉淀后在较低的温度。一些样品中的弥散氧化物可能是从富Fe-Ti熔体中析出的。沿着剪切带/区集中的氧化物可能标志着由于压实或压滤而从累积序列中排出的熔体聚结/输送区。735 B号体孔为堆积物。735 B孔中最原始的橄榄石（Fo = 0.842）表明，735 B孔岩性的最原始熔体母体必须具有Mg# ≤ 0.637，这明显低于735 B孔的Mg# = 0.714。
We report mineral chemistry, whole-rock major element compositions, and trace element analyses on Hole 735B samples drilled and selected during Leg 176. We discuss these data, together with Leg 176 shipboard data and Leg 118 sample data from the literature, in terms of primary igneous petrogenesis. Despite mineral compositional variation in a given sample, major constituent minerals in Hole 735B gabbroic rocks display good chemical equilibrium as shown by significant correlations among Mg# (= Mg/[Mg+Fe2+]) of olivine, clinopyroxene, and orthopyroxene and An (=Ca/[Ca+Na]) of plagioclase. This indicates that the mineral assemblages olivine + plagioclase in troctolite, plagioclase + clinopyroxene in gabbro, plagioclases + clinopyroxene + olivine in olivine gabbro, and plagioclase + clinopyroxene + olivine + orthopyroxene in gabbronorite, and so on, have all coprecipitated from their respective parental melts. Fe-Ti oxides (ilmenite and titanomagnetite), which are ubiquitous in most of these rocks, are not in chemical equilibrium with olivine, clinopyroxene, and plagioclase, but precipitated later at lower temperatures. Disseminated oxides in some samples may have precipitated from trapped Fe-Ti–rich melts. Oxides that concentrate along shear bands/zones may mark zones of melt coalescence/transport expelled from the cumulate sequence as a result of compaction or filter pressing. Bulk Hole 735B is of cumulate composition. The most primitive olivine, with Fo = 0.842, in Hole 735B suggests that the most primitive melt parental to Hole 735B lithologies must have Mg# ≤ 0.637, which is significantly less than Mg# = 0.714 of bulk Hole 735B.