Melt extraction and reaction in the forearc mantle: Constraints from trace elements and isotope geochemistry of ultra-refractory peridotites of the New Caledonia Peridotite Nappe
Melt extraction and reaction in the forearc mantle: Constraints from trace elements and isotope geochemistry of ultra-refractory peridotites of the New Caledonia Peridotite Nappe
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弧前地幔中的熔体萃取和反应：新喀里多尼亚橄榄岩推覆体超难熔橄榄岩微量元素和同位素地球化学的制约
DOI：
10.1016/j.lithos.2020.105882
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发表时间：
2020-11
期刊：
影响因子：
3.5
通讯作者：
Wei Lin
中科院分区：
文献类型：
--
作者：
Yang Xu;Chuan-Zhou Liu;Wei Lin
弧前地幔普遍经历了高度的部分熔融和普遍的熔融岩反应。新喀里多尼亚蛇绿岩（橄榄岩推覆体）的大型超基性地块为研究弧前地幔内部的过程提供了机会。本研究选取了三个地块（即梅茅崖、Ouassë Bay、Massif du Sud）的辉锌矿、灰锌矿和韦氏石样品。橄榄岩中Al2O3（0.10 ~ 0.78 wt%）和CaO （0.21 ~ 0.58 wt%）含量较低，而橄榄石Fo（90.8 ~ 92.5）和尖晶石Cr#（0.55 ~ 0.74）含量较高。这表明它们经历了高度的部分熔融，导致原生斜辉石完全消耗。测量了正辉石中微量元素，以限制新喀里多尼亚哈兹伯尔岩的演化。结果表明：正映石中重稀土元素（HREE）含量低；它们的Yb含量是球粒陨石的0.04 ~ 0.39倍，可以用枯竭的MORB地幔（DMM）源的~25 ~ 30%的分数熔融来模拟。正辉石中轻、中稀土元素（lree和mree）和大离子亲石元素（LILEs）也表现出不同程度的富集，暗示了后期交代作用。CaO含量高（9.02 ~ 9.75 wt%）， Al2O3含量低（1.59 ~ 1.60 wt%）。他们已经耗尽了Sr-Nd-Hf同位素组成，与新喀里多尼亚CE-boninites相似，并在MORB场内绘制。websterites和dunites的187os /188Os比值（0.12348-0.13067）与深海橄榄岩和新喀里多尼亚harzburgites的比值（0.1203-0.1534）相当。黑土岩、泥质岩和威氏岩的全岩和矿物地球化学组成和模拟表明，新喀里多尼亚橄榄岩至少经历了两个阶段的部分熔融和与各种迁移熔体的反应。此外，我们还证明了正辉石中微量元素可以用于区分不同构造背景下的超难熔碳酸盐。
The forearc mantle has generally experienced high degrees of partial melting and pervasive melt-rock reactions. Large ultramafic massifs of the New Caledonia ophiolite (Peridotite Nappe) provide opportunities for studying processes within the forearc mantle. Samples of harzburgite, dunite and websterite from three massifs (i.e., Me Maoya, Ouassë Bay, Massif du Sud) have been selected in this study. The peridotites have low contents of Al2O3(0.10–0.78 wt%) and CaO (0.21–0.58 wt%), but high olivine Fo (90.8–92.5) and spinel Cr# (0.55–0.74) values. This indicates that they have experienced high degrees of partial melting, resulting in the complete consumption of primary clinopyroxene. Trace elements of orthopyroxenes have been measured to constrain the evolution of the New Caledonia harzburgites. Results show that orthopyroxenes have low contents of heavy rare earth element (HREE); their Yb contents are 0.04–0.39 times of chondrites, which can be modeled by ~25–30% of fractional melting of a depleted MORB mantle (DMM) source. The orthopyroxenes also show variable enrichment of light and middle rare earth elements (LREEs and MREEs) and large ion lithophile elements (LILEs), implying late-stage metasomatism. The websterites have high CaO (9.02–9.75 wt%) but low Al2O3(1.59–1.60 wt%) contents. They have depleted Sr-Nd-Hf isotope compositions similar to that of New Caledonia CE-boninites and plot within the MORB field. Both websterites and dunites have187Os/188Os ratios (0.12348–0.13067) comparable to that of abyssal peridotites and the New Caledonia harzburgites (0.1203–0.1534). Geochemical compositions and modeling of whole-rock and minerals of harzburgites, dunites and websterites suggest that the New Caledonia peridotites have experienced at least two-stage partial melting and reactions with various migrating melts. Moreover, we also demonstrated that trace element of orthopyroxenes can be applied to discriminate ultra-refractory harzburgites from different tectonic settings.
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