期刊
EARTH AND PLANETARY SCIENCE LETTERS
卷 301, 期 3-4, 页码 493-501出版社
ELSEVIER
DOI: 10.1016/j.epsl.2010.11.031
关键词
Tanzanian Craton; thermochronology; lower crust; feldspar; anti-perthite; LA-MC-ICP-MS
资金
- National Science Foundation [EAR0337255]
- National Geographic Society [7836-05]
- Directorate For Geosciences
- Division Of Earth Sciences [0739006] Funding Source: National Science Foundation
Common and radiogenic Pb isotopic compositions of plagioclase and anti-perthitic feldspars from granulite-facies lower crustal xenoliths from the Labait Volcano on the eastern margin of the Tanzanian Craton have been measured via laser ablation MC-ICP-MS. Common Pb in plagioclase and a single stage Pb evolution model indicate that the lower crust of the Tanzanian Craton was extracted from mantle having a U-238/Pb-204 of 8.1 +/- 0.3 and a Th-232/U-238 of 4.3 +/- 0.1 at 2.71 +/- 0.09 Ga (all uncertainties are 2 sigma). Since 2.4 Ga, some orthoclase domains within anti-perthites have evolved with a maximum U-238/Pb-204 of 6 and Th-232/U-238 of 4.3. The spread in Pb isotopic composition in the anti-perthitic feldspars yields single crystal Pb-Pb isochrons of similar to 2.4 Ga, within uncertainty of U-Pb zircon ages from the same sample suite. The Pb isotopic heterogeneities imply that these granulites resided at temperatures <600 degrees C in the lower crust of the Tanzanian Craton from ca. 2.4 Ga to the present. In concert with the chemistry of surface samples, mantle xenoliths, and lower crustal xenoliths, our data imply that the cratonic lithosphere in Tanzania formed ca. similar to 2.7 Ga, in a convergent margin setting, and has remained undisturbed since 2.7 Ga. (C) 2010 Elsevier B.V. All rights reserved.
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