Multiple episodes of melting, depletion, and enrichment of the Tethyan mantle: Petrogenesis of the peridotites and chromitites in the Jurassic Skenderbeu massif, Mirdita ophiolite, Albania

Abstract

The Jurassic Mirdita ophiolite in Albania displays a structural-geochemical transition from a mid-ocean ridge-type (MOR) oceanic lithosphere in the west to a suprasubduction zone (SSZ) type in the east across an ~30-km-wide fossil Tethyan oceanic domain. We investigated the upper mantle peridotites of the Skenderbeu massif, situated at this transition within the ophiolite, to document the geochemical fingerprint of the inferred tectonic switch. The peridotites comprise harzburgites and dunites with podiform chromitite deposits. We present new whole-rock major element, trace element, rare earth element (REE), and platinum group element chemistry to evaluate their mantle melt evolution and petrogenesis. Harzburgites have high average CaO, Al 2 O 3 , and REE contents, and contain Al-rich pyroxene and spinel with lower Cr contents. Dunites have low average CaO, Al 2 O 3 , and REE values, and contain Al-poor clinopyroxene and high-Cr spinel. Modeling of trace element compositions of the harzburgites suggests as much as ~10%-15% melting, whereas the trace element compositions of the dunites indicate ~20%-25% melting. The harzburgites and dunites and chromitites represent, respectively, the products of low-degree partial melting in a MOR setting, and the products of high-degree partial melting and refertilization in a forearc mantle. The harzburgites resulted from rock-melt interactions between ascending melts and residual peridotites beneath a MOR, whereas the dunites and the high-Cr chromitites formed as a result of interactions between boninitic melts and mantle peridotites in a mantle wedge. The Skenderbeu mantle units thus constitute a geochemical-petrological archive of a transition from MOR to SSZ melt evolution in space and time within the same ocean basin.

Ophiolites, diamonds, and ultrahigh-pressure minerals: New discoveries and concepts on upper mantle petrogenesis

“…Dunites and chromitites are, however, the products of partial melting of subduction metasomatized, highly depleted harzburgites and their reactions with boninitic melts in later stages of subduction initiation magmatism. These findings reported by Wu et al (2018) are consistent with the time-progressive melt evolution patterns of the upper mantle peridotites in the Mirdita ophiolite farther north (as presented by Saccani et al, 2018), and in some other Tethyan ophiolites (Dilek and Furnes, 2009).…”

“…Therefore, they do not necessarily represent the melt products evolved in different tectonic environments at different times. Wu et al (2018) document the nature of melting, depletion, and enrichment processes experienced by the upper mantle peridotites of the Skenderbeu ophiolite in northern Albania. The massif consists of, from bottom to top, harzburgites with lenses of dunite and podiform and disseminated chromitites, lherzolite, and plagioclase lherzolite representing the upper mantle peridotites.…”

“…The Skenderbeu ophiolite is lacking a sheeted dike complex and plutonic rocks, and its extrusive rocks are unconformably overlain by a supraophiolitic mélange (Shallo and Dilek, 2003). Using new mineral chemistry, whole-rock, trace element, and platinum group element (PGE) geochemistry data from the harzburgites, dunites, and chromitites, Wu et al (2018) show that these upper mantle units record significantly different degrees of partial melting and rock-melt interactions during the evolution of the Skenderbeu massif. Trace element modeling indicates that harzburgites formed as a result of ~10%-15% low-degree partial melting of an already depleted MORB mantle.…”

Mineralogy, geochemistry, and melt evolution of the Kalaymyo peridotite massif in the Indo-Myanmar Ranges (western Myanmar), and tectonic implications

“…Most of the previous studies in the Indo-Myanmar ophiolites and these existing tectonic models for their evolution are almost entirely based on the geochemistry and geochronology of www.gsapubs.org | Volume 10 | Number 1 | LITHOSPHERE crustal rocks. The peridotite suites in these ophiolites have been largely untouched, although recent systematic geochemical, petrological, and structural studies of upper mantle peridotites in many ophiolites around the world have provided significant clues for their melt evolution and tectonic setting of their igneous construction (e.g., Pearce et al, 2000;Zhou et al, 2005;Arai et al, 2007;Dilek et al, 2007Dilek et al, , 2008Dilek and Furnes, 2009;Dilek and Thy, 2009;Liu et al, 2010;Dai et al, 2011;Uysal et al, 2012;Dokuz et al, 2015;Saccani et al, 2017;Wu et al, 2017).…”

Diamond in Oceanic Peridotites and Chromitites: Evidence for Deep Recycled Mantle in the Global Ophiolite Record

“…The above-mentioned diamond-bearing ophiolites represent remnants of the eastern Mesozoic Tethyan oceanic lithosphere. New publications show that diamonds also occur in chromitites in the Pozanti-Karsanti ophiolite of Turkey, and in the Mirdita ophiolite of Albania in the western Tethyan zone (Lian et al, 2017;Xiong et al, 2017;Wu et al, 2018). Similar diamonds and associated minerals have also reported from Paleozoic ophiolitic chromitites of Central Asian Orogenic Belt of China and the Ray-Iz ophiolite in the Polar Urals, Russia (Yang et al, 2015a, b;Tian et al, 2015;Huang et al, 2015).…”