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Decoding of Mantle Processes in the Mersin Ophiolite, Turkey, of End-Member Arc Type: Location of the Boninite Magma Generation

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Decoding of Mantle Processes in the Mersin Ophiolite, Turkey, of End-Member Arc Type: Location of the Boninite Magma Generation minerals Article Decoding of Mantle Processes in the Mersin Ophiolite, Turkey, of End-Member Arc Type: Location of the Boninite Magma Generation Satoko Ishimaru 1,*, Yuji Saikawa 1, Makoto Miura 2,3, Osman Parlak 4,5 and Shoji Arai 2 1 Department of Earth and Environmental Science, Faculty of Advanced Science and Technology, Kumamoto University, 2-39-1 Kurokami, Chuo-ku, Kumamoto 860-8555, Japan; [email protected] 2 Department of Earth Sciences, Kanazawa University, Kakuma, Kanazawa 920-1192, Japan; [email protected] (M.M.); [email protected] (S.A.) 3 GIA Godo Kaisha, 4-19-9 Taito, Taito-ku, Tokyo 110-0016, Japan 4 Jeoloji Mühendisli˘giBolümü,˘ Çukurova Üniversitesi, TR-01330 Adana, Turkey; [email protected] 5 State Key Laboratory of Geological Processes and Mineral Resources, Center for Global Tectonics, School of Earth Sciences, China University of Geosciences, Wuhan 430074, China * Correspondence: [email protected]; Tel.: +81-96-342-3471 Received: 4 September 2018; Accepted: 15 October 2018; Published: 18 October 2018 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. Keywords: arc-type ophiolite; mantle wedge; partial melting; metasomatism; peridotite-melt reaction; boninite; Mersin; Turkey 1. Introduction 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]). It is quite important to accumulate petrologic data for our better understanding of the mantle wedge. Mantle peridotite xenoliths from current island arcs have been a good source of information about the mantle wedge because of the absence of serpentinization, but their small sizes (<1 m across) and fragmentary nature lead to a serious disadvantage in terms of spatial resolution of mantle processes. The mantle section of ophiolites of arc origin may provide us with information to delineate details of the mantle wedge processes because of its greater exposure. For example, the Oman ophiolite has a mantle section of ~500 km in length [2]. However, ophiolites have various origins (e.g., [3]), and therefore, we should carefully select ophiolites for the purpose of investigation of the mantle wedge process. Typical ophiolites including the Tethyan Minerals 2018, 8, 464; doi:10.3390/min8100464 www.mdpi.com/journal/minerals Minerals 2018, 8, 464 2 of 33 ones experiencedMinerals 2017, 7 switch, x FOR PEER oftectonic REVIEW setting of formation from a mid-ocean ridge to an island2 of 33 arc [4–6]. They may exhibit various degrees of superposition of island-arc rocks on precursor oceanic rocks [4,7]. We selectedophiolites the including Mersin ophiolite,the Tethyan oneones ofexperienced Neothetyan switch ophiolites of tectonic setting in Turkey of formation (e.g., [from8]) for a mid- our study becauseocean its crustal ridge to rocks, an island except arc [4–6]. for alkalineThey may basalt exhibit showing various degrees pre-ophiolite of superposition feature of [ 9island-arc], mostly show rocks on precursor oceanic rocks [4,7]. We selected the Mersin ophiolite, one of Neothetyan ophiolites island-arcin Turkey characters (e.g., without[8]) for our any study sign because of MORB its crustal affinity rocks, [9,10 except]. We for expect alkaline that basalt the mantle showing section pre- of the Mersinophiolite feature has recorded [9], mostly various show island-arc mantle-wedge characters processeswithout any related sign of MORB to production affinity [9,10]. of the We arc-type crustal rocksexpect upsection.that the mantle section of the Mersin ophiolite has recorded various mantle-wedge processes related to production of the arc-type crustal rocks upsection. 2. Geological Setting 2. Geological Setting 2.1. Regional Geology 2.1. Regional Geology Anatolia (Asia Minor) is subdivided into EW-trending belts from North to South, namely Anatolia (Asia Minor) is subdivided into EW-trending belts from North to South, namely the the Pontides,Pontides, the the Anatolides, Anatolides, the Taurides and and Southeast Southeast Anatolian Anatolian Border Border Folds Folds[11] (Figure [11] (Figure1a). 1a). OphiolitesOphiolites and related and related metamorphic metamorphic rocks rocks in in Turkey Turkey define define severalseveral suture suture zones zones that that resulted resulted from from the closurethe of theclosure Neotethyan of the Neotethyan oceanic oceanic basins basins between between the the Eurasian Eurasian and and Afro-ArabianAfro-Arabian plates plates during during the Triassicthe to MioceneTriassic to period. Miocene From period. North From toNorth South, to So theseuth, these suture suture zones zones are are named: named: (a) (a) The The Intra-Pontide, Intra- (b) the Izmir-Ankara-Erzincan;˙Pontide, (b) the İzmir-Ankara-Erzincan; (c) the Inner (c) Tauride;the Inner Tauride; and (d) and the (d) SE the Anatolian SE Anatolian suture suture zones zones [12 –25]. [12–25]. Figure 1.Figure(a) Distributions 1. (a) Distributions of Neotethyan of Neotethyan ophiolites ophiolites and and mmélangesélanges in in Turkey. Turkey. Modified Modified after after Parlak Parlak [8]. [8]. (b) Simplified geological map of the Mersin ophiolite [8]. R1 and R2 are routes for taking samples (b) Simplified geological map of the Mersin ophiolite [8]. R1 and R2 are routes for taking samples for for this study and the details are in Figure 2. this study and the details are in Figure2. The ophiolites of Southern Turkey are located along two lineaments, namely the Assylian suture Thezone ophiolites and the ofTauride Southern belt (Figure Turkey 1a). are The located Tauride along ophiolites two lineaments, are characterized namely by dismembered the Assylian suture zone andophiolitic the Tauride units, namely belt (Figure the Lycian,1a). Tekirova, The Tauride Beysehir-Hoyran, ophiolites Alihoca, are characterized Mersin, Pozanti-Karsanti, by dismembered ophioliticPinarbasi, units, namelyand Divrigi the ophiolites Lycian, Tekirova,[8,12,19,26–28]. Beysehir-Hoyran, The Tauride ophiolites Alihoca, mainly Mersin, consist Pozanti-Karsanti, of three Pinarbasi,tectonic and Divrigiunits, they ophiolites are, in ascending [8,12,19 order,,26–28 ophiolitic]. The Tauride mélange, ophiolites sub-ophiolitic mainly metamorphic consist ofsole, three and tectonic oceanic lithospheric remnants [8]. units, they are, in ascending order, ophiolitic mélange, sub-ophiolitic metamorphic sole, and oceanic The Mersin ophiolite is situated in the Southern flank of the Tauride platform and located lithosphericapproximately remnants 30 [km8]. NW of Mersin town in Southern Turkey (Figure 1a). It is exposed in an area of The60 Mersinkm long–25 ophiolite km wide is and situated displays inan theapproximately Southern 6 flankkm-thick of crust-mantle the Tauride section platform (Figure and 1b). located approximatelyThe Mersin 30 ophiolite km NW shows of Mersin a good town ophiolitic in Southern sequence except Turkey for (Figure the absence1a). Itof issheeted exposed dykes, in and an area of 60 km long–25the stratigraphy km wide is as and follows displays from bottom an approximately to top: Mantle tectonites 6 km-thick with crust-mantle an underlying metamorphic section (Figure 1b). The Mersin ophiolite shows a good ophiolitic sequence except for the absence of sheeted dykes, and the stratigraphy is as follows from bottom to top: Mantle tectonites with an underlying metamorphic sole, ultramafic–mafic cumulates, and effusive rocks [29]. The mantle tectonites are highly serpentinized along the contact with sole amphibolite or the Mersin mélange, and exhibit foliation characterized Minerals 2018, 8, 464 3 of 33 by alteration of dunite and orthopyroxenite bands [29]. We observed a dunite-dominant zone with Minerals 2017, 7, x FOR PEER REVIEW 3 of 33 chromitite layering and pods between tectonized peridotite and ultramafic-mafic cumulative rocks showingsole, layering ultramafic–mafic (Figure2)[ cumulates,30]. We defineand effusive this dunite-dominant rocks [29]. The zonemantle as tectonites the Moho-transition are highly zone, which isserpentinized mainly composed along the of contact dunite with with sole minor amphibol amountite or the of wehrliteMersin mélange, [31]. This and Moho-transitionexhibit foliation zone dunite changescharacterized to ultramafic by alteration cumulates,
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