HR: 1330h
AN: V22B-0587 [PDF]
TI: Comparison on geochemistry of minerals in garnet peridotites from Paleozoic and Neogene xenoliths and
from Triassic UHP terrane to constrain the lithospheric evolution of east China
AU: * Zheng, J
EM: jpzheng2003@yahoo.com
AF: Faculty of Earth Sciences, China University of Geosciences, Wuhan, 430074
China
AU: * Zheng, J
EM: jpzheng2003@yahoo.com
AF: Department of Geological and Environmental Sciences, Stanford University, Stanfore, CA 94305 United States
AU: * Zheng, J
EM: jpzheng2003@yahoo.com
AF: GEMOC ARC National Key Centre, Department of Earth and Planetary Sciences, Macquarie University,
Sydney, NSW 2109
Australia
AU: Griffin, W
EM: bill.griffin@mq.edu.au
AF: GEMOC ARC National Key Centre, Department of Earth and Planetary Sciences, Macquarie University,
Sydney, NSW 2109
Australia
AU: Griffin, W
EM: bill.griffin@mq.edu.au
AF: CSIRO Exploration and Mining, North Ryde, Sydney, NSW1067
Australia
AU: Zhang, R
EM: zhang@pangea.stanford.edu
AF: Department of Geological and Environmental Sciences, Stanford University, Stanfore, CA 94305 United States
AU: Liou, J
EM: liou@pangea.stanford.edu
AF: Department of Geological and Environmental Sciences, Stanford University, Stanfore, CA 94305 United States
AU: O'Reilly, S
EM: sue.oreilly@mq.edu.au
AF: GEMOC ARC National Key Centre, Department of Earth and Planetary Sciences, Macquarie University,
Sydney, NSW 2109
Australia
AB:
Major and trace element data of minerals in garnet peridotite xenoliths from early Paleozoic (457-500 Ma) and Neogene (16-18
Ma) volcanics within the North China Craton are compared with those from tectonically exhumed Triassic Sulu ultra-high
pressure (UHP) terrane along its southern margin. Estimated P-T conditions of the Paleozoic and Neogene garnet peridotite
xenoliths reflect different geotherms corresponding to surface heat flow of $\sim$40 mW/m$^{2}$ (Paleozoic) and $\sim$80
mW/m$^{2}$ (Neogene). Paleozoic peridotite xenoliths are compositionally similar to cratonic mantle; they have high Mg number
in olivine (mean 92.7), Cr number in garnet (mean 27.6), and Ni and La/Yb (19-25) in clinopyroxene (Cpx). They have low
Al$_{2}$O$_{3}$, TiO$_{2}$, HREE and Y in Cpx, low Y/Ga in garnet (0.33-1.34), and show LREE-enriched pattern of Cpx. Neogene
peridotite xenoliths represent a more fertile mantle with low Mg number in olivine (mean 89.5), Cr number in garnet (mean
3.5), and La/Yb (2.5-3.3) in Cpx. They have high Al$_{2}$O$_{3}$, TiO$_{2}$, HREE and Y in Cpx, and high Y/Ga in garnet
(8.45-20.7), and show flat REE pattern of Cpx. The differences suggest that the buoyant refractory lithospheric keel present
beneath the eastern part of the North China Craton in Paleozoic time was largely replaced by younger and hotter fertile
lithospheric mantle during late Paleozoic-Paleogene time. The Triassic Sulu UHP peridotites have lower Mg number in olivine
(91.5?0_673?0_6981.0) and garnet (73.2-82.0), Cr number in garnet (1.9-18.3), and Al$_{2}$O$_{3}$ of orthopyroxene
(0.15-0.34) than the Paleozoic xenoliths. Cpx in the peridotites contains very low HREE (0.02-0.29 ppm) and incompatible
trace elements (except Sr), displays sinusoidal to LREE-enriched patterns with La/Yb of 80.3-143 and exhibits distinctly
negative Nb, Zr and Ti anomalies. Garnets have low REE and strongly negative Ce anomalies ($\delta$ Ce=0.24-0.56), and Y,
Cr$_{2}$O$_{3}$, Nd/Y and Sc/Y are typical of highly to moderately refractory mantle. The UHP peridotites are interpreted
having evolved from Paleozoic-like protoliths through interaction with crust-derived carbonatitic and silicate melt/fluids,
before UHP metamorphism. Exhumation of the Sulu UHP rocks may have occurred in an extensional regime allowing the
asthenospheric upwelling. Peridotites sampled by Neogene basalts represent the newly accreted lithosphere derived from
cooling of the upwelling asthenospheric mantle in Jurassic-Cretaceous and Paleogene time.
DE: 1744 Tectonophysics
DE: 8102 Continental contractional orogenic belts
DE: 8120 Dynamics of lithosphere and mantle--general
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting