Lower crustal evolution under central Arizona: Sr, Nd and Pb isotopic and geochemical evidence from the mafic xenoliths of Camp Creek

Details Lower crustal evolution under central Arizona: Sr, Nd and Pb isotopic and geochemical evidence from the mafic xenoliths of Camp Creek Lower crustal evolution under central Arizona: Sr, Nd and Pb isotopic and geochemical evidence from the mafic xenoliths of Camp Creek

Sep 1988

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1988e%26psl..90...26e&link_type=abstract

Earth and Planetary Science Letters, Volume 90, Issue 1, p. 26-40.

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28

Scientific paper

Oligocene potassic volcanism at the Camp Creek area, Arizona has sampled the lower crust by bringing mafic granulite, amphibolite and garnet-bearing pyroxenite (eclogite) xenoliths to the surface. Xenolith geobarometry records metamorphic pressures of approximately 10 kbar and temperatures of 650-900°C. Whole-rock Sr and Nd isotopic compositions correlate roughly with xenolith metamorphic mineral assemblages: higher temperature eclogites have 87Sr/86Sr ranging from 0.7066 to 0.7080 and ɛNd of -2 to -5.8 while lower temperature amphibolites have 87Sr/86Sr of 0.7074 to 0.7082 and ɛNd of -6 to -9. Sr and Nd isotopic compositions of mineral separates reflect, in some xenoliths, intermineral diffusion up to the time of latite eruption and limited exchange with the host latite. Pb isotopic compositions of the xenoliths show little mineralogical dependence and overlap the field for normal MORB. These data suggest that lower-crustal metamorphism has significantly affected the Sr and Nd isotope evolution of the eclogites but has had little effect on their Pb isotope systematics.
For xenoliths closer to igneous bulk compositions (i.e. not enriched in metamorphic garnet and pyroxene), Nd depleted mantle model ages range from 1.2 to 1.9 Ga, in agreement with the Pb-Pb array ``age'' of 1.1 +/- 0.6 Ga. This is interpreted as dating the separation of the lower crust from the mantle during the Proterozoic crust-building event in this area. Similar Nd model ages for nearby Cenozoic and Mesozoic granitoids suggest that the type of mafic lower crust represented by the Camp Creek xenoliths may be a suitable source for younger plutonics in the area.

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