Geochemical characterization and petrogenesis of intermediate to silicic rocks in ophiolites: A global synthesis

Abstract

We present a global synthesis of the geochemistry of intermediate to silicic intrusive and volcanic rocks from 149 Phanerozoic to Archean ophiolites, and evaluate models for their genesis during the development of oceanic crust in different tectonic environments. Our synthesis shows that the evolved rocks in subduction-unrelated, Rift/Continental Margin ophiolites are predominantly basaltic andesite and andesite, whereas MOR type (mid-ocean ridge) ophiolites exhibit nearly equal proportions of basaltic andesite/andesite and rhyodacite and Plume/MOR type ophiolites are characterized by rhyolites. Intermediate to silicic volcanic units in the Backarc subgroup of subduction-related ophiolites are characterized by similar amounts of basaltic andesite/andesite and rhyodacite, whereas in the Backarc to Forearc, Forearc, and Volcanic Arc subgroups they are mainly basaltic andesite/andesite. The Zr, Nb and La contents of the intermediate to silicic rocks in subduction-related ophiolites are significantly lower than those of their counterparts in subduction-unrelated ophiolites. Intermediate to silicic rocks in Rift/Continental Margin and Plume/MOR type ophiolites are generally LREE-enriched, whereas those in the MOR type vary from LREE-depleted to LREE-enriched. The Backarc and Backarc to Forearc types are similar to the MOR type; silicic rocks of the Forearc and Volcanic Arc types are generally LREE-enriched. Nb, Sr, Eu, and Ti exhibit negative anomalies of varying magnitudes in multi-element diagrams. Our modeling based on the La-SiO 2 proxies of Brophy (2009) suggests that the main process in the formation of the majority of the intermediate to silicic rocks in both subduction-unrelated and subduction-related ophiolites is partial melting of basaltic and/or gabbroic rocks beneath the spreading centers, whereas a minor volume in subduction-related ophiolites are adakites that resulted from partial melting of the subducting slab. Silicic to intermediate rocks in Plume/MOR type ophiolites appear to be generated by fractional crystallization of basaltic melt. The incompatible, non-conservative elements, such as Ba and Th, are weakly to strongly enriched in subduction-related ophiolites as a result of shallow to deep enrichment associated with subduction zone processes.

Origin and Age Determination of the Neotethys Meliata Basin Ophiolite Fragments in the Late Jurassic–Early Cretaceous Accretionary Wedge Mélange (Inner Western Carpathians, Slovakia)

“…The abyssal type harzburgites in the Jaklovce Unit ophiolite complex, having a character of weakly depleted harzburgites are consistent with the marginal basin with the subduction-unrelated mantle rocks [7,[90][91][92][93][94]. They are also typical of the mantle portion of the ophiolitic complexes [93,94] from the passive margins reported by [129], and which evolved during rift-drift and seafloor spreading [130]. Moreover, the rodingite dykes cross-cutting serpentinized harzburgites may already have formed on the ocean floor [92].…”

The lawsonite-glaucophane blueschists of Elba Island (Italy)

“…10b) indicates MORB affinity. In order to confirm the MORB typology, several discrimination diagrams (Furnes and Dilek, 2017; Xia and Li, 2019 and references therein) were considered ( Fig. 10c-g).…”

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

“…This study establishes a well-constrained spatial-temporal evolution of ophiolitic magmas beneath a forearc spreading center, and provides a realistic petrogenetic template for suprasubduction zone (SSZ) oceanic crust formation in a forearc setting that was driven by slab-rollback processes (Dilek and Thy, 2009). One of the most significant implications of the results of this study is that extrusive rocks ranging in compositions and age from N-MORB to IATB and boninites, which are commonly found in many ophiolites around the world (Furnes and Dilek, 2017), can be genetically related through subduction-related, time-progressive melting, depletion, and enrichment events in the upper mantle within the same SSZ tectonic setting. Therefore, they do not necessarily represent the melt products evolved in different tectonic environments at different times.…”