Crustal diopsidites from the northern Oman ophiolite: Evidence for hydrothermal circulation through suboceanic Moho

Abstract

This paper details a new discovery of anorthite -bearing diopsidites (= anorthite diopsidites) from the lowermost crust along Wadi Fizh in the northern Oman ophiolite. The anorthite diopsidites occur as networks within layered gabbros 50 m above the gabbro/peridotite boundary, and are mainly composed of high -Mg diopsidic clinopyroxenes and anorthites with various amounts of uvarovite. They are intermediate in mineral chemical characteristics between the crustal gabbros and the diopsidites, and interpreted as an interaction product between hightemperature Ca -rich hydrothermal fluids and peridotites within the mantle section. The anorthite diopsidites were probably formed by interaction between the fluids involved in diopsidization within the mantle section and the layered gabbro. The fluids responsible for the formation of the anorthite diopsidite were also Ca -rich and carried Cr to form uvarovite from the underlying mantle section. High -temperature hydrothermal circulation plays an important role in the transportation of elements, e.g., Ca and Cr, from the upper mantle to the lower crust across the Moho in the ocean floor.

Subduction initiation for the formation of high-Cr chromitites in the Kop ophiolite, NE Turkey

“…Instead, their major element compositions largely overlap those hydrothermal diopsides from the northern Oman ophiolite ( Fig. 5B; Akizawa et al, 2011;Python et al, 2007aPython et al, , 2007b, possibly suggesting they were produced by Ca-rich fluids at high temperature conditions (over 900°C; Python et al, 2007a).…”

“…6C). However, the diopsides in the diospidites from the mantle part of Oman ophiolite display remarkable positive anomalies of Sr (average δ Sr 4.66) and Eu (average δ Eu 5.22) (Akizawa et al, 2011;Python et al, 2007b), which are not found for the dispersed clinopyroxenes. Compared with clinopyroxenes from different backgrounds, the clinopyroxenes in this study is more similar to those from the subduction zones or subcontinental lithospheric mantle, which are commonly featured by the enrichment of LILE and depletion of HFSE (Bizimis et al, 2000;Bodinier and Godard, 2007;Xu et al, 2000).…”

“…The lack of orthopyroxenes in the hydrothermal diopsidites of Oman ophiolite indicates that orthopyroxenes were unstable in the diopside related hydrothermal processes (Akizawa et al, 2011;Python et al, 2007b). As a result, the pyroxenite veins should be formed in disparate chemical environments from those dispersed clinopyroxenes.…”

“…All these differences above corroborate the vein-type clinopyroxenes were supposed to be magmatic in origin. Leterrier et al (1982), Parman et al (2003), Bloomer and Hawkins (1987), Sobolev and Danyushevsky (1994) and Akizawa et al (2011). Olivine grains in the Kop14-18 (cpx-harzburgite) have an average Fo value of 91.8, and the Cr# values of magnesiochromite grains range from 28.7 to 39.2. These results are comparable to the typical mantle harzburgite that have experienced about 15-20% partial melting (Fig.…”

Clinopyroxenites (diopsidites) and metabasites from the East Sarmatian Orogen, East European Craton

“…This feature is taken to indicate that the vein clinopyroxenites are products of residual melt after the crystallization of abyssal peridotites. The genesis of rodingites as well as the related diopsidites is explained by extreme Ca-metasomatism of gabbroic massifs and dykes in contact with ultramafic oceanic lithospheric mantle Bach and Klein, 2009;Akizawa et al, 2011). Kelemen et al, 1995;Suhr et al, 2003), where the pyroxenes reflect the composition of percolating melts.…”