Geochemistry and tectonic environment of the Dagzhuka ophiolite in the Yarlung-Zangbo suture zone, Tibet.

Abstract

The Cretaceous Dagzhuka ophiolite lies in the middle segment of the Yarlung-Zangbo suture zone, Tibet, and has a well-preserved ophiolitic section including a mantle sequence, cumulate complex, diabase dyke swarm and basaltic lavas. Compared to the primitive mantle, tectonized peridotites in the Dagzhuka ophiolite are depleted in Al, Ca, Ti and high field strength elements, but relatively enriched in large ion lithophile elements (Rb, Ba, Th). They have U-shaped, chondrite-normalized REE patterns suggesting an early stage of depletion by partial melting, followed by enrichment from slab-derived fluids. These features support a model in which the mantle peridotites at Dagzhuka formed in a forearc setting. The diabases and basalts are low-K tholeiites depleted in LREE, with compositions similar to N-MORB. However, these rocks are strongly depleted in Nb and Ta but enriched in Th and Rb, features characteristic of island arc lavas. Thus, the Dagzhuka ophiolite is believed to have formed in a supra-subduction zone environment, possibly a fore-arc basin.ophiolite has a well-preserved lithologic sequence ranging from mantle peridotite at the base to pillow lava at the top and thus provides an ideal environment in which to study the evolution of the Tethyan ocean basin (Nicolas et al., 1981;Girardeau et al., 1985;Wang et al., 1987).Although the ophiolite has been studied extensively, there is no agreement as to its origin or tectonic setting. For example, Girardeau et al. (1985) suggested that it formed at mid-oceanic ridge whereas Wang et al. (1999) favored formation in a small, multi-stage oceanic basin. Here we report the results of extensive field and laboratory studies over the past decade and present a new interpretation of the ophiolite. New major and trace element data place important constraints on the tectonic setting of the Dagzhuka ophiolite and suggest that it formed in a supra-subduction zone environment.

Helium and neon isotopic compositions in the ophiolites from the Yarlung Zangbo River, Southwestern China: The information from deep mantle

“…Much evidence indicates that the Yarlung Zangbo River ophiolites formed possibly in an island-arc tectonic environment [1,22,64,65] , and the boninites might be related to subduction in island-arc tectonic belt that were found along the Yarlung Zangbo River suture zone [66] . However, we would not deny the view that plume might occur during the formation of the Neo-Tethys Ocean.…”

Platinum-group elemental geochemistry of mafic and ultramafic rocks from the Xigaze ophiolite, southern Tibet

“…The geochemistry of its volcanic sequence suggests a two-stage formation -initial formation at a mid-ocean ridge followed by modification in a suprasubduction zone environment Xia et al, 2003). Xia et al (2003) showed that the peridotites in the Dazhuka section underwent an early stage of depletion due to high degrees of partial melting and a later stage of metasomatism. Analyses of PGEs in the basalts, diabases and mantle peridotites from the Xigaze ophiolite may yield further insights into the magmatic processes that produced the ophiolite and the mantle metasomatism.…”

SHRIMP dating of the Bangong Lake SSZ-type ophiolite: Constraints on the closure time of ocean in the Bangong Lake-Nujiang River, northwestern Tibet

“…In the Tibet Plateau, the Yarlung Zangbo River in southern Tibet and the Bangong Lake-Nujiang River in northern Tibet are the well-preserved Neo-Tethyan ophiolitic belts [21] . Although there is a consensus on the petrogenesis and emplaced time of the Yarlung Zangbo River ophiolites, most researchers have been agreed that the Yarlung Zangbo River ophiolite formed in the suprasubduction zone environment [17,19,[22][23][24] , and was emplaced on the south margin of the Lhasa block during 80-90 Ma [19] . There exits a controversy over the age of the Yarlung Zangbo River ophiolite considered to have formed in the SSZ environment.…”