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Durham University

Department of Earth Sciences

Profile

Publication details for Professor Yaoling Niu

Song, S.G., Niu, Yaoling, Zhang, L.F. & Bucher, K. (2009). The Luliangshan garnet peridotite massif of the North Qaidam UHPM belt, NW China - a review of its origin and metamorphic evolution. Journal of Metamorphic Geology 27(9): 621-638.

Author(s) from Durham

Abstract

The Luliangshan garnet peridotite massif is an ultramafic complex in the North Qaidam UHPM belt,
NW China. The strongly layered complex comprising garnet-bearing dunite, garnet-harzburgite,
garnet-lherzolite and garnet-pyroxenite and garnet-free dunite, occurs together with eclogite embedded
in various continental gneisses. The geological setting, the internal structure, bulk-composition, rare
earth elements, isotopic and mineral composition data show that the garnet peridotite derives from a
middle Ordovician Alaskan-type layered sub-arc cumulate intrusion of ascending mantle wedge melts.
An abyssal peridotite protolith can be excluded. During the Ordovician-Silurian continental collision,
thickening and foundering, the Luliangshan peridotite complex was exposed to ultrahigh pressures
(UHP) reaching 5.5 GPa possibly >6 GPa at temperatures of 900 C (perhaps up to 1000 C)
corresponding to a depth of 200 km. The extreme pressure conditions have been derived from
thermobarometry using mineral compositions of the garnet peridotite assemblages, but they are
supported by a wealth of decompression-induced mineral exsolutions in UHP minerals and by diamond
inclusion in zircon. The Luliangshan garnet peridotite has experienced four stages of retrograde
overprint during exhumation that lasted into the Devonian: (i) decompression-induced unmixing of the
UHP minerals; (ii) garnet kelyphitisation; (iii) amphibole overprinting and (iv) serpentinization.
Hydrous minerals occurring within peak metamorphic assemblage represent pseudo-inclusions, that is
reaction products of reactions related to various stages of decompression and cooling rather than
prograde inclusions during porphyroblast growth.r彋