Petrogenesis of Eocene mafic and felsic magmas in the New Caledonia ophiolite: geochemistry and geochronology constraints
Petrogenesis of Eocene mafic and felsic magmas in the New Caledonia ophiolite: geochemistry and geochronology constraints
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新喀里多尼亚蛇绿岩始新世镁铁质和长英质岩浆的岩石成因：地球化学和地质年代学限制
DOI：
10.1080/00206814.2021.1978111
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发表时间：
2021-09
影响因子：
2.6
通讯作者：
Wei Lin
中科院分区：
文献类型：
--
作者：
Yang Xu;Chuan-Zhou Liu;Xue-Fa Shi;Wei Lin
新喀里多尼亚蛇绿岩（橄榄岩推覆体）中的长英质和镁铁质侵入体记录了俯冲过程中岩浆演化的重要信息。对橄榄岩推覆体中辉长岩/闪长岩样品进行了系统的岩石学、年代学和地球化学研究，探讨了其成因。辉长岩主要由斜长石、单斜辉石和角闪石组成。大多数单斜辉石蚀变为角闪石或阳起石，而一些角闪石的高Al 2 O3（> 8wt%）和低SiO2（<46wt%）含量是岩浆成因的。这表明辉长岩是从含水熔体中结晶出来的。辉长岩具有亏损的Sr-Nd-Hf同位素组成，表明辉长岩的母岩浆可能来自亏损的MORB型地幔（DMM）软流圈。辉长岩锆石的δ 18 O值为+4.74 ~+6.63‰，略高于类地幔锆石的δ 18 O值（+5.3 ± 0.6‰），表明其成因中有俯冲流体的参与。闪长岩主要由钠长石（An 1 -4）和透闪石组成。新喀里多尼亚蛇绿岩中的长英质脉岩，包括花岗岩类、高镁长英质脉岩和闪长岩，均为大洋斜长花岗岩。极低的TiO 2含量、Yb和SiO2含量的大致负相关性、斜长花岗岩和镁铁质岩石的稀土配分模式以及锆石的成分表明，斜长花岗岩不是MORB分离结晶的产物，而是由镁铁质原岩的水化熔融作用形成的。闪长锆石呈核边结构。边缘和岩芯的U-Pb年龄相同，分别为54.6 ± 0.9 Ma和54.6 ± 0.6 Ma，根据明显更老的日期，没有发现古老的继承岩芯。结果表明，辉长岩/闪长岩的锆石U-Pb年龄约为55 Ma，辉长岩的钛铁矿U-Pb年龄约为53 Ma，比新喀里多尼亚玻安岩的年龄（51-47 Ma）老。因此，新喀里多尼亚蛇绿岩在俯冲开始期间的岩浆演化已被重建。
ABSTRACT Both felsic and mafic intrusions occur in mantle peridotites of the New Caledonia ophiolite (Peridotite Nappe) and record important information regarding the magmatic evolution during subduction initiation. A systematic petrological, geochronological and geochemical study on gabbro/diorite samples from the Peridotite Nappe is performed to explore their petrogenesis. The gabbro is mainly composed of plagioclase, clinopyroxene and amphibole. Most clinopyroxene have been altered to hornblende or actinolite, whereas some amphibole with high Al2O3 (>8 wt%) and low SiO2 (<46 wt%) contents are of a magmatic origin. This suggests that the gabbro crystallized from hydrous melts. The gabbro shows depleted Sr-Nd-Hf isotope compositions, suggesting that the parental magma of the gabbro could have been derived from the depleted MORB-type mantle (DMM) asthenosphere. The gabbro zircon have δ18O values of +4.74-+6.63‰, which are slightly higher than the mantle-like δ18O values of +5.3 ± 0.6‰, indicating the involvement of subduction-related fluids in their genesis. The diorite mainly consists of albite (An1-4) and tremolite. The felsic dikes within the New Caledonia ophiolite, including granitoids, high-Mg felsic dikes and diorites, are oceanic plagiogranites. Extremely low TiO2 contents, roughly negative correlation of Yb and SiO2 contents, REE patterns of plagiogranites and mafic rocks, and compositions of zircon suggest that the plagiogranites were not products of fractional crystallization of MORB but were generated by hydrous melting of mafic protoliths. The diorite zircon show core-rim textures. Both rims and cores yield identical U-Pb ages of 54.6 ± 0.9 Ma vs 54.6 ± 0.6 Ma, and no old inherited cores were identified based on significantly older dates. Our studies show zircon U-Pb ages of ~55 Ma for the gabbro/diorite and titanite U-Pb age of ~53 Ma for the gabbro, which are older than the New Caledonia CE-boninites (51–47 Ma). Therefore, the magmatic evolution of the New Caledonia ophiolite during subduction initiation has been reconstructed.
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影响因子：
4.2
作者：
C. Spandler;D. Rubatto;J. Hermann
通讯作者：
C. Spandler;D. Rubatto;J. Hermann
影响因子：
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Cassian Pirard;J. Hermann;H. O’Neill
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3.5
作者：
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通讯作者：
A. Secchiari;A. Montanini;D. Bosch;P. Macera;Dominique Cluzel