Other
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006e%26psl.252..260s&link_type=abstract
Earth and Planetary Science Letters, Volume 252, Issue 3-4, p. 260-274.
Other
7
Scientific paper
Rhyolite lavas and xenoliths from the Salton Sea geothermal field (Southern California) provide insights into crustal compositions and processes during continental rupture and incipient formation of oceanic crust. Salton Buttes rhyolite lavas contain xenoliths that include granophyres, fine-grained altered rhyolites (“felsite”), and amphibole-bearing basalts. Zircon is present in lavas and xenoliths, surprisingly even in the basaltic xenoliths, where it occurs in plagioclase-rich regions interpreted as pockets of crystallized partial melt. Zircons in the xenoliths are exclusively Late Pleistocene Holocene in age and lack evidence for inheritance. U Th isochron ages are: 20.5- 1.2+ 1.2 ka (granophyres), 18.3- 3.5+ 3.6 ka (felsite), 30.1- 12.4+ 14.1 ka and 9.2- 6.6+ 7.0 ka (basalts; all errors 1σ). The dominant zircon population in the rhyolite lavas yielded U Th ages between ˜ 18 and 10 ka, with few pre-Quaternary xenocrysts present. δ18Ozircon values are lower than typical crustal basement values, thus ruling out rhyolite genesis by melting of continental crust. Moreover, δ18Ozircon values are ˜ 0.5 1.0‰ lower than compositions achievable by zircon crystallization from residual melt in equilibrium with unaltered mid-ocean ridge basalt, suggesting that basaltic crust and silicic plutons in the subsurface of the Salton Sea geothermal field isotopically exchanged with meteoric waters. This is evidence for deep-reaching hydrothermal circulation and indicates rhyolite genesis by episodic remelting of altered basalts instead of fractional crystallization of unaltered basaltic magma.
Schmitt Axel K.
Vazquez Jose Alberto
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