Abstract
The Mersin ophiolite, Turkey, is of typical arc type based on geochemistry of crustal rocks without any signs of mid-ocean ridge (MOR) affinity. We examined its ultramafic rocks to reveal sub-arc mantle processes. Mantle peridotites, poor in clinopyroxene (<1.0 vol.%), show high Fo content of olivine (90–92) and Cr# [=Cr/(Cr + Al) atomic ratio] (=0.62–0.77) of chromian spinel. NiO content of olivine is occasionally high (up to 0.5 wt.%) in the harzburgite. Moho-transition zone (MTZ) dunite is also highly depleted, i.e., spinel is high Cr# (0.78–0.89), clinopyroxene is poor in HREE, and olivine is high Fo (up to 92), but relatively low in NiO (0.1–0.4 wt.%). The harzburgite is residue after high-degree mantle melting, possibly assisted by slab-derived fluid. The high-Ni character of olivine suggests secondary metasomatic formation of olivine-replacing orthopyroxene although replacement textures are unclear. The MTZ dunite is of replacive origin, resulted from interaction between Mg-rich melt released from harzburgite diapir and another harzburgite at the diapir roof. The MTZ dunite is the very place that produced the boninitic and replacive dunite. The MTZ is thicker (>1 km) in Mersin than in MOR-related ophiolite (mostly < 500 m), and this is one of the features of arc-type ophiolite.
Highlights
The mantle wedge is the very place where both magmatism and metasomatism are active, and is considered to be complicated in petrologic nature (e.g., [1])
We found wehrlite at a few outcrops in Moho-transition zone (MTZ) (Table 1), and its mineral assemblage is the same as that in the Layered Ultramafic (LU) rocks
The Cr# of chromian spinel is an indicator of degree of partial melting for residual spinel peridotite or primary melt composition for cumulative ultramafics and volcanic rocks (e.g., [49,50,51])
Summary
The mantle wedge is the very place where both magmatism and metasomatism are active, and is considered to be complicated in petrologic nature (e.g., [1]). Minerals 2018, 8, 464 ones experienced switch of tectonic arc [4,5,6] They may exhibit various degrees of superposition of island-arc rocks on precursor oceanic rocks [4,7]. We expect that the mantle section of the in Turkey (e.g., [8]) for our study because its crustal rocks, except for alkaline basalt showing preMersin ophiolite ophiolitefeature has recorded mantle-wedge to production of the [9], mostlyvarious show island-arc charactersprocesses without anyrelated sign of MORB affinity [9,10]. That the mantle section of the Mersin ophiolite has recorded various mantle-wedge processes related to production of the arc-type crustal rocks upsection
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