Magma genesis during early stages of lithospheric extension: Great Basin of western North America
Conference
·
· Geological Society of America, Abstracts with Programs; (United States)
OSTI ID:5099338
- Rice Univ., Houston, TX (United States). Dept. of Geology Geophysics
Models for extension-related magmatism based on decompression melting of asthenosphere mantle are in conflict with geological and geochemical observations in the Great Basin. First, assuming a dry'' peridotite source, a substantial lag time (ca. 20 Ma) between onset of extension and first manifestations of magmatism is predicted, whereas magmatism was syn-extensional over a large part of the eastern Great Basin. Second, a gradual increase in magmatic intensity with time is predicted, whereas the observed pattern is characterized by voluminous early volcanism and diminishing melt production with time. Third, the models predict initially deep magma production ([approximately] 80 km) followed by progressive shoaling of the magma production zone. In contrast, compositions of the magmas suggest significant involvement of shallower lithospheric sources (incl. crust) in the earliest magmas, and dominance of deeper asthenospheric sources only in the latest Cenozoic, particularly in the southern portion of the Great Basin -- i.e. a duality of mantle sources. The authors suggest that melting of mafic lithologies within lithospheric mantle is physically plausible and can account for many aspects of early extensional magmatism. Only after lithospheric stretching nears [approximately] 100% does asthenospheric mantle become a dominant source of Great Basin basaltic magmas. There is no need to invoke a plume heat source. This model is tested by comparing the thermo-mechanical behavior of extending lithosphere with phase equilibria results for mafic compositions.
- OSTI ID:
- 5099338
- Report Number(s):
- CONF-9305259--
- Conference Information:
- Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 25:5
- Country of Publication:
- United States
- Language:
- English
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