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Genesis of Young Lithospheric Mantle in Southeastern China: an LAM-ICPMS Trace Element Study |
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| Authors: | XU XISHENG; OREILLY SUZANNE Y; GRIFFIN WL; ZHOU XINMIN |
| Institution: | 1DEPARTMENT OF EARTH SCIENCES, NANJING UNIVERSITY, NANJING 210093, P.R. CHINA 2GEMOC NATIONAL KEY CENTRE, DEPARTMENT OF EARTH AND PLANETARY SCIENCES, MACQUARIE UNIVERSITY, SYDNEY, N.S.W. 2109, AUSTRALIA 3CSIRO EXPLORATION AND MINING, NORTH RYDE, SYDNEY, N.S.W. 2113, AUSTRALIA |
| Abstract: | Geological and geophysical evidence indicates that at least100 km of Archaean to Proterozoic lithospheric mantle has beenremoved from beneath large areas of eastern and southeasternChina during late Mesozoic to Cenozoic time. Mantle-derivedxenoliths in Tertiary basalts from several localities acrossthis region have been studied by X-ray fluorescence, electronmicroprobe and laser ablation microprobe–inductively coupledplasma-mass spectrometry to characterize this thinner lithosphere.Trace element patterns of clinopyroxenes in the peridotitesfrom southeastern China can be divided into four groups: fertilegarnet lherzolites, fertile spinel (± garnet) lherzolites,and depleted and enriched peridotites. The addition of Nb, Sr,light rare earth elements, but not of Ti and Zr, suggests ametasomatizing agent containing both H2O and CO2. This studyalso demonstrates that the negative Ti anomaly commonly observedin clinopyroxene from mantle peridotites cannot be balancedby the Ti in coexisting orthopyroxene, but can be explainedby small degrees of partial melting, using appropriate distributioncoefficients. Most of the peridotites from southeastern China,whether spinel or garnet facies, are highly fertile in termsof Al2O3 and CaO contents and mg-number; many resemble commonlyused primitive mantle compositions. Modelling of trace elementpatterns in clinopyroxene indicates that most spinel and garnetperidotites from the Nushan, Mingxi and Niutoushan localitiesexperienced less than 5%, and many less than 2%, partial melting.A few depleted spinel peridotites from Nushan, and all spinelperidotites from Mingxi, require 10–25% fractional partialmelting; almost all spinel peridotites from the Qilin localityshow evidence of higher degrees (6–25%) of fractionalpartial melting. At both Nushan and Mingxi, the more depletedcompositions occur in the upper part of the lithospheric mantle,which now is |
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