Origin of arc magmatic signature: A temperature-dependent process for trace element (re)-mobilization in subduction zones

Abstract

Serpentinite is a major carrier of fluid-mobile elements in subduction zones, which influences the geochemical signature of arc magmatism (e.g. high abundances of Li, Ba, Sr, B, As, Mo and Pb). Based on results from Neoproterozoic serpentinites in the Arabian-Nubian Shield, we herein report the role of antigorite in the transportation of fluid-mobile elements (FME) and light rare earth elements (LREE) from the subducted slab to arc-related magma during subduction. The serpentinites contain two generations of antigorites: the older generation is coarse-grained, formed at a temperature range of 165–250 °C and is enriched in Li, Rb, Ba and Cs, whereas the younger generation is finer-grained, formed at higher temperature conditions (425–475 °C) and has high concentrations of B, As, Sb, Mo, Pb, Sr and LREE. Magnesite, on the other hand, remains stable at sub-arc depths beyond the stability field of both antigorites, and represents a potential reservoir of FME and LREE for deeper mantle melts. Magnesite has high FME and LREE absorbing capacity (over 50–60%) higher than serpentine phases. Temperature is the main controlling factor for stability of these minerals and therefore the release of these elements from subducted slabs into arc magmatism. As the liberation of these elements varies along the length of the slab, the resulting cross-arc geochemical variation trend can help to determine the subduction polarity of ancient arcs.

Cr-spinel records metasomatism not petrogenesis of mantle rocks

“…7) and fluid-mobile elements (FME) in those rocks 14 . Generally, migration of aqueous fluids/melts from a subducting slab enriches the overlying mantle with incompatible elements (i.e., FME) and water, yielding metasomatized sub-arc mantle 22,23 .…”

Plume–MOR decoupling and the timing of India–Eurasia collision

“…The onset of India–Eurasia collision led to quiescence in the Neotethys closure activity, and low spreading rates along the Indian Ocean ridges 18 , thus causing deceleration in the northward drift of the Indian plate 91 , 92 . The subduction zones influenced the mantle by recycling crustal materials, including sediments 69 , 93 , hence modifying the asthenosphere mantle 94 , then recycling it back into MORs 94 , 95 , and into arc magmatism 93 . A group of microcontinental blocks existed between India and Eurasia before the closure of the Neo-Tethys 96 , this is a common phenomenon at many continental margins 97 , and was induced by mantle plume 98 , 99 .…”