Melt-peridotite interactions; links between garnet pyroxenite and high-Mg# signature of continental crust

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doi: 10.1016/j.epsl.2005.02.034
Authors:Liu Yongsheng; Gao, S.; Lee, C. T. A.; Hu, S.; Liu, X.; Yuan, H.
Author Affiliations:Primary:
China University of Geosciences, National Key Laboratory of Geological Processes and Mineral Resources, Wuhan, China
Northwest University, China
Rice University, United States
Volume Title:Earth and Planetary Science Letters
Source:Earth and Planetary Science Letters, 234(1-2), p.39-57. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0012-821X
Publication Date:2005
Note:In English. 70 refs.; illus., incl. 1 plate, 2 tables, geol. sketch map
Summary:Abundant lherzolite, garnet pyroxenite and granulite xenoliths are found in the Neogene Hannuoba basalt of the North China craton. Garnet pyroxenites generally occur as veins/layers in spinel lherzolites. There is a gradual decrease in olivine and an increase in orthopyroxene mode going from the lherzolite to the pyroxenite, suggesting that orthopyroxene may be forming at the expense of olivine. Garnet pyroxenites are enriched in the highly incompatible elements (e.g., Rb, K, Na, Sr, Ba, Nb and Ta) but have high and uniform Ni contents and Mg#s (83-90). This set of geochemical observations is paradoxical because the enrichments in highly incompatible elements signify derivation from a melt having either an evolved character or a significant fluid component, but the high Ni contents and high Mgsuggest a much more primitive origin. A somewhat similar paradox is observed in the granulite xenoliths. Many of the granulite xenoliths have intermediate compositions, characterized by SiO2>50 wt.%, high Al2O3, Na2O, and Sr contents, low Y and heavy rare-earth contents, and high Sr/Y, La/Yb and Na2O/K2O ratios. However, these intermediate granulites have unusually high Mg#s (54-71) and high Ni (21-147 ppm) contents for their SiO2 contents and would otherwise suggest that these granulites are more primitive than their SiO2 contents indicate. It has been hypothesized that continuous melt-rock reaction between a silicic melt and ultramafic country rock (lherzolite) can convert olivine to orthopyroxene, ultimately resulting in the formation of a high Mg# garnet pyroxenite, similar to what is seen in the Hannuoba garnet pyroxenite composite xenoliths. In addition, silicic melts that have reacted with mantle peridotite would be predicted to have anomalously high Mg#s and Ni contents (due to the strong buffering capacity of peridotite for Mg and Ni), producing melts having compositions similar to the intermediate-mafic granulite xenoliths in this study. It is thus possible that the Hannuoba garnet pyroxenites and intermediate-mafic granulites share a common petrogenetic origin. Such a link is further supported by the fact that the rare-earth element abundance patterns of melts calculated to be in equilibrium with the garnet pyroxenites roughly coincide with that of the intermediate granulites. It is concluded that the Hannuoba garnet pyroxenite-bearing composite xenoliths may present the first physical evidence for the hypothesized melt-rock reaction necessary for generating evolved magmas with high Mg# and hence, high-Mg# andesitic signature of the continental crust. Abstract Copyright (2005) Elsevier, B.V. [G.L.B.]
Sections:Geochemistry; Petrology
Subsections:Igneous rocks; Metamorphism: regional, dynamic
Subjects:Absolute age; Alkaline earth metals; Basalts; Cenozoic; Chemical composition; Chemical ratios; Continental crust; Crust; Dates; Enrichment; Garnet pyroxenite; Geochemistry; Granulites; ICP mass spectra; Igneous rocks; Inclusions; Isotope ratios; Isotopes; Lherzolite; Magmas; Magmatism; Magnesium; Major elements; Mass spectra; Melts; Metals; Metamorphic rocks; Neogene; Nesosilicates; Orthosilicates; P-T-t paths; Peridotites; Petrography; Plutonic rocks; Pyroxenite; Silicate melts; Silicates; Spectra; Sr-87/Sr-86; Stable isotopes; Strontium; Tertiary; Textures; Trace elements; U/Pb; Ultramafics; Volcanic rocks; Water-rock interaction; X-ray fluorescence spectra; Xenoliths; Zircon; Zircon group; Asia; China; Far East; North China Platform; Hannuoba China
Coordinates:N404500 N410000 E1150000 E1141500
Abstract Numbers:05M/2604
Record ID:2006020306
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands
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