Petrogenesis of the Kangjinla peridotite in the Luobusa ophiolite, Southern Tibet

Surprises from the top of the mantle transition zone

“…These very large samples were then treated using industrial scale mineral separation processes to recover the very small volumes of mineral inclusions from the chromitite. An exceptional 1-ton sample from Luobusa yielded about 1000 grains of diamond (Xu et al, 2011) but normally the diamond occurrence in chromitites is much smaller and is about 0.03 grammes per ton (30 ppb). Four different mineral separation techniques are used to separate the minerals into up to 13 different groups on the basis of their physical properties.…”

Timing of Secondary Hydrothermal Alteration of the Luobusa Chromitites Constrained by Ar/Ar Dating of Chrome Chlorites

“…These studies include: major and trace elemental and/or isotopic compositions of different textural chromitites and their host peridotites (e.g., [1][2][3][4][5][6][7][8]), and unusual ultrahigh-pressure (UHP), highly reduced and crustally derived minerals found either in situ or as separates in the chromitites and peridotites (e.g., [9][10][11][12][13][14][15][16][17][18][19][20][21]). [42]), and the distribution of magmatism on the Lhasa terrane (modified from Chung et al [43]).…”

“…The chromitites were initially thought to have bearing on the formation and evolution of the ophiolite. The Luobusa ophiolite originated at a mid-ocean ridge spreading center at 177 ± 31 Ma and was later modified by supra-subduction zone (SSZ) magmatism at 120 ± 10 Ma involving an intra-oceanic subduction system [5][6][7]41,53,54]. However, the presence of ultrahigh-pressure (UHP) and highly reduced minerals such as diamond, coesite, and native elements, initially found in the chromitites but more recently also in their host peridotites, requires additional processes or models to outline the genesis of the chromitites (e.g., [4,10,11,13,[17][18][19][20][55][56][57]).…”

Mineralogy, Petrology and Geochemistry of Peridotites from the Northern Ophiolititc Sub‐belt, Western Yarlung Zangbo Suture Zone, Tibet

“…Peridotites are usually considered to be the solid residues of oceanic upper mantle left behind after varied degree of mantle meting and crust-mantle segregation (Aldanmaz et al, 2009). Thus, geochemical data on the peridotites and their constituent minerals record important information on mantle melting, melt extraction and melt/fluid-rock interaction in the upper mantle and contribute to our understanding of the origin and tectonic setting of ophiolitic rocks (Kelemen et al, 1992;Niu, 2004;Parkinson and Pearce, 1998;Xu et al, 2011). LREE-enriched (U-shaped or spoon-shaped) chondrite-normalized REE patterns are widespread in worldwide ophiolitic mantle peridotites.…”

“…As the ophiolites provide important constraints for reconstruction of the geodynamic evolution of the Neo-Tethyan Ocean, and record significant events during the period of India-Asia collision, large numbers of studies have been carried out on the Yarlung Zangbo suture zone. However, previous studies of this ophiolitic belt mainly focused on the eastern and central segments (Malpas et al, 2003;Xu et al, 2011;Yamamoto et al, 2013;Yang et al, 2007), and the southern ophiolitic subbelt of the western segment (Miller et al, 2003;Liu et al, 2013). Because of the absence of data on the ophiolitic rocks of the northern sub-belt, the tectonic setting of the northern sub-belt ophiolite and the relationship between the northern and southern sub-belt remain ambiguous.…”