Late Neoproterozoic proto-arc ocean crust in the Dariv Range, Western Mongolia: a supra-subduction zone end-member ophiolite

Abstract

An unusual late Neoproterozoic (c. 572 Ma) ophiolite is exposed in the Dariv Range (western Mongolia), which contains intermediate to acidic lavas and sheeted dykes, and an igneous layered complex consisting of gabbro-norites, websterites, orthopyroxenites and dunites underlain by serpentinized mantle harzburgites. Based on the compositions of the crustal units and the crystallization sequences in the mafic and ultramafic cumulates we conclude that the entire oceanic crust, including the cumulates, was made from arc magmas with boninitic characteristics. The Dariv rocks bear a strong resemblance to rocks recovered from the modern Izu-Bonin-Mariana fore-arc, a fragment of proto-arc oceanic basement, and we propose that the Dariv Ophiolite originated in a similar tectonic setting. A metamorphic complex consisting of amphibolite-to granulite-facies metasedimentary and meta-igneous rocks was thrust over the ophiolite. This metamorphic complex probably represents a Cambrian arc. Thrusting started before 514.7 AE 7.6 Ma as constrained by new sensitive high-resolution ion microprobe U-Pb zircon analyses from a syn-to post-tectonic diorite. The Dariv Ophiolite is a type-example of a proto-arc ophiolite, a special class of supra-subduction zone ophiolites.

Making continental crust: origin of Devonian orthogneisses from SE Mongolian Altai

“…While ages of c. 430-440 Ma are not known from the Tseel and adjacent terranes (Tab. 1), ages of c. 510-530 Ma correspond well with those of magmatic rocks in the Lake Zone (e. g. Dijkstra et al 2006;Hrdličková et al 2010;Rudnev et al 2012Rudnev et al , 2013Jian et al 2014). Moreover, the age of ~740 Ma resembles that known from coarse-grained orthogneiss of the Zamtyn Nuruu range, also in the Lake Zone (Demoux et al 2009b;Hanžl et al 2014) Therefore, the lower-middle crust underlying the studied region seems to have an affinity to the Neoproterozoic rocks of the Lake Zone.…”

The Dehshir ophiolite (central Iran): Geochemical constraints on the origin and evolution of the Inner Zagros ophiolite belt

“…The higher content of CaO and Al 2 O 3 in some clinopyroxene-bearing harzburgites may be due to the percolation of and reaction with basaltic melt, as is seen for some abyssal peridotites (e.g., Dijkstra et al, 2006;Pagé et al, 2008). Because spinel composition is widely accepted for characterizing the geotectonic setting and petrogenesis of peridotites (e.g., Dick and Bullen, 1984;Rahgo shay, 1986;Rollinson, 2005), we compared peridotite spinel compositions (Cr# = [100Cr/Cr + Al] versus Mg#) from both inner and typical outer (Neyriz) ophiolite belts (Fig.…”

Precambrian crystalline basement in southern Mongolia as revealed by SHRIMP zircon dating

“…The accretion of these portions of oceanic lithosphere onto Precambrian crystalline massifs likely occurred in late Cambrian time and was accompanied by widespread magmatism and regional metamorphism. A minimum time for the accretion of the Bayannor ophiolite within the Dariv Metamorphic Complex is given by the intrusion of an undeformed quartz diorite at 515 ± 8 Ma (SHRIMP zircon age; Dijkstra et al 2006). A phase of high-grade metamorphism in this complex is moreover recorded at 499 ± 3 Ma by a U-Pb zircon age for a hypersthene-garnet granulite (Kozakov et al 2002) and may reflect accretion of the ophiolitic sequence onto the crystalline basement.…”