Modification of subcontinental lithospheric mantle in SE China

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Abstract

Studies of mantle-derived xenoliths are important for understanding
the composition of the subcontinental lithospheric mantle
(SCLM), its evolution through time, and continental
dynamics. The removal or modification of the older lithospheric
mantle beneath eastern China is interpreted to be mainly a Mesozoic
process. However, the mechanism and timing of lithospheric
thinning in eastern China have not been clearly documented.
Our recent work, focussing on peridotites with no volatilebearing
phases, reveals other evidence of metasomatism and provides
more constraints for identifying the metasomatic agent(s).
In situ Re–Os isotopic data for sulfides in mantle xenoliths
from eastern China show a wide range in Os isotopic composition,
reflecting the complexity of mantle events. The data suggest the
widespread presence of Proterozoic mantle, which has been
repeatedly flushed with sulfur-bearing metasomatic fluids since
Proterozoic time.
Detailed compositional profile analysed by electron microprobe
show that primary olivine and clinopyroxene have higher
mg numbers (0.89–0.91), while neoblast olivine and clinopyroxene
have lower mg numbers (0.65–0.88). No significant zoning has
been found for spinel and orthopyroxene, but olivine has very distinctive
composition zoning with mg number decreasing from 0.90
to 0.73 from core to rim. Feldspar- and carbonate-bearing peridotites,
rare in other perodotite xenoliths worldwide, have been
identified. The feldspar occurs as interstitial material, but typically
forms fine-grained aggregates made up of secondary olivine,
plagioclase, clinopyroxene and very small grains of Cr-rich spinel,
ilmenite. Feldspar is relative rich in titanium (0.15–0.46% TiO2).
The formation of feldspar is inferred to be due to the reaction:
sp + opx + cpx + fluid = fs + ol and indicates that the most
recent metasomatic process was related to infiltration of an alkali-
rich fluid into the peridotites.
Original languageEnglish
Pages (from-to)A713-A713
Number of pages1
JournalGeochimica et Cosmochimica Acta
Volume70
Issue number18 supplement
DOIs
Publication statusPublished - 2006
EventGoldschmidt Conference (16th : 2006) - Melbourne, Australia
Duration: 27 Aug 20061 Sep 2006

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