Samarium-neodymium data on two late Proterozoic ophiolites of Saudi Arabia and implications for crustal and mantle evolution |
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Authors: | Stefan Claesson John S Pallister Mitsunobu Tatsumoto |
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Institution: | (1) U.S. Geological Survey, Denver Federal Center, 80225 Denver, CO, USA;(2) Present address: Laboratoriet för isotopgeologi, Naturhistoriska riksmuseet, Box 50 007, S-104 05 Stockholm, Sweden |
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Abstract: | Whole-rock and mineral samples from the Jabal al Wask and Jabal Ess ophiolites, northwestern Saudi Arabia, yield Sm-Nd isochron ages of 743+24 Ma and 782±38 Ma, respectively. These formation ages, which provide maximum limits for possible obduction ages, are in broad but not precise agreement with the previously known geologic history of the Arabian Shield. They indicate that the ophiolitic rocks are roughly coeval with nearby volcanic and plutonic rocks, supporting a back-arc origin for the two ophiolites. We suggest that the Jabal al Wask and Jabal Ess ophiolites were parts of the same northeast-southwest trending ophiolite belt, now offset along the Najd fault system. Initial Nd values range from +6.6 to+ 7.6, indicating derivation from a mantle source that has been LIL-depleted for at least 2 Ga. Reported Nd values from the Arabian Shield that are lower than this suggest the presence of older, reworked continental crust. |
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