NDLI: Physiognomy and timing of metasomatism in the southern Vourinos ultramafic suite, NW Greece: a chronicle of consecutive episodes of melt extraction and stagnation in the Neotethyan lithospheric mantle

Content Provider	Springer Nature Link
Author	Kapsiotis, Argyrios N.
Copyright Year	2015
Abstract	The southern Vourinos massif, located in the Hellenides orogenic belt, forms part of the mantle section of the homonymous Neotethyan ophiolite complex in the NW Greek mainland. The southern domain of the massif is comprised voluminous and strained peridotite outcrops with variable pyroxene and olivine modal abundances, ranging from harzburgite (sensu stricto) to olivine-rich harzburgite and fine- to coarse-grained dunite. These peridotites are intruded by a complex network of undeformed websterite to olivine-rich websterite dykes. The peridotite lithologies are characterized by high Cr# [=Cr/(Cr + Al)] values in Cr-spinel (0.54–0.80), elevated Mg# [=Mg/(Mg + Fe2+)] ratios in olivine (0.91–0.94), poor Al2O3 content in clinopyroxene (up to 1.85 wt%) and very low bulk-rock abundances of Al2O3 (up to 0.66 wt%), CaO (up to 0.84 wt%), V (up to 45 ppm), Sc (up to 11 ppm) and REE, which are suggestive of their strongly depleted nature. They also display a wide range of fO2 values that vary between the fayalite–magnetite–quartz (FMQ-2) and FMQ+1 buffers, signifying their genesis under anoxic to oxidizing conditions. Simple batch and fractional melting models cannot satisfactorily explain their ultradepleted composition, whereas whole-rock Ni/Yb versus Yb systematics can be simulated by up to 27 % closed-system, non-modal, dynamic melting of a primitive mantle source, implying their multifarious origin in a progressively changing, in space and time, geotectonic setting. Chromian spinel chemistry (Cr# vs. TiO2) provides evidence for two consecutive melt–peridotite interaction events pertaining to patent metasomatism. The first incident is related to the release of IAT melts from the deep parts of the southern Vourinos mantle segment, which reacted with harzburgites transforming them into olivine-rich harzburgites and replacive dunites, whereas mixing of different pulses of IAT melts with distinct SiO2 activities generated heterogeneously deformed, cumulitic dunites. The second event is linked to the genesis of MORB/IAT magmas that originally invaded harzburgites. The MORB/IAT melts, although intensely reactive at the stage of harzburgite impregnation, lost their ability to react and stagnated in the peridotite groundmass as they approached the conceivable boundary with olivine-rich harzburgite. Microtextural observations and compositional data support that the interstitial, unstrained clinopyroxene ± olivine aggregates recognized in the harzburgite varieties represent intergranular melt blebs that ‘chilled’ in the mantle during an episode of rapid lithosphere exhumation. This is further corroborated by the absence of lavas with MORB/IAT geochemical affinities from the Vourinos extrusive sequence. Microstructural features of websterite veins suggest that their genesis cannot be ascribed to the melts that penetrated the peridotites that cross cut. In contrast, they retain marks of olivine assimilation from the wall rocks that was facilitated by interaction with olivine-undersaturated, arc-derived tholeiitic melts released at a late phase from the ultradepleted southern Vourinos mantle suite.
Starting Page	983
Ending Page	1013
Page Count	31
File Format	PDF
ISSN	14373254
Journal	International Journal of Earth Sciences
Volume Number	105
Issue Number	3
e-ISSN	14373262
Language	English
Publisher	Springer Berlin Heidelberg
Publisher Date	2015-06-09
Publisher Place	Berlin, Heidelberg
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Peridotites Partial melting Melt–rock interaction Melt stagnation Ophiolites Geology Geophysics/Geodesy Sedimentology Structural Geology Mineral Resources Geochemistry
Content Type	Text
Resource Type	Article
Subject	Earth and Planetary Sciences

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