Petrogenetic Implications for Ophiolite Ultramafic Bodies from Lokris and Beotia (Central Greece) Based on Chemistry of Their Cr-spinels

Abstract

Cr-spinels from ultramafic rocks from Lokris (Megaplatanos and Tragana), and Beotia (Ypato and Alyki) ophiolitic occurrences were studied. These rocks comprise principally harzburgite with minor dunite. Small amounts of clinopyroxene-rich harzburgite and lherzolite have been observed along with the harzburgite in Alyki. The Cr# in the studied spinels displays a wide variability. The spinels hosted in harzburgite and cpx-rich harzburgite display low Cr# (<0.6), typical for oceanic (including back-arc basins) ophiolites, whereas the spinels hosted in dunite with Cr# (>0.6) characterize arc-related ophiolitic sequences. Cr-spinels from Alyki indicate a moderate fertile character and are analogous to those from abyssal peridotites. The dunitic and harzburgitic spinel-olivine pairs are consistent with a Supra-Subduction Zone origin. The relatively large range in spinel Cr# and Mg# may have been resulted from a wide range of degrees of mantle melting during the evolution of the host peridotites.

Major and Trace-Element Chemistry of Cr-Spinel in Upper Mantle Xenoliths from East Antarctica

“…Overall, we have defined studied upper mantle xenoliths as the residues of 6-12% (Yuzhnoe body) and 8-16% (Severnoe body) of mantle melting (see below). [18,24]. Symbols are as in Figure 9.…”

“…Spinel is a common phase in mantle rocks and is mostly represented by its Cr-rich variety (e.g., [18][19][20] and references therein). Spinel is volumetrically a minor mineral in the upper mantle xenoliths, but it is one of the most stable mantle minerals resistant to the secondary alterations, particularly when compared to other upper mantle minerals [18][19][20][21][22][23]. However, Cr-spinel can be modified by cryptic metasomatism through fluid (melt) to rock interaction [19,22,24].…”

“…The present work was based on the xenolith samples previously studied for bulk rock, rock-forming mineral and sulfide geochemistry [2][3][4]7,16]. Spinel is a common phase in mantle rocks and is mostly represented by its Cr-rich variety (e.g., [18][19][20] and references therein). Spinel is volumetrically a minor mineral in the upper mantle xenoliths, but it is one of the most stable mantle minerals resistant to the secondary alterations, particularly when compared to other upper mantle minerals [18][19][20][21][22][23].…”

Mineral chemistry and geochemistry of serpentinites from the Bianmagou ophiolite in the North Qilian Belt, NW China: Implications for protoliths, melt extractions, and melt/fluid metasomatism

“…The residual spinels from the Bianmagou serpentinites (Table S3 (Khedr, Arai, Python, & Tamura, 2014;Pomonis & Magganas, 2017;Section 5.3.2). Moreover, the spinels contain a small proportion of minor elements, such as TiO 2 (up to 0.10 wt%), NiO (0.03-0.17 wt%), and MnO (0.20-0.33 wt%).…”

Mineralogical Evidence for Partial Melting and Melt-Rock Interaction Processes in the Mantle Peridotites of Edessa Ophiolite (North Greece)

“…Spinel-group minerals have a wide range of compositions reflecting a residual or secondary origin and are normally resistant to serpentinisation, thus they are commonly used as petrogenetic and geotectonic indicators. Their chemical composition depends on the petrogenesis (crystallisation from melt, residue after partial melting) and physical conditions (temperature, pressure, oxygen fugacity) of their host peridotites [24][25][26][27][28][29][30][31]. Additionally, the degree of partial melting can be calculated using the chemical composition of unaltered spinel-group minerals.…”