The age of Lathrop Wells volcanic center: An {sup 40}Ar/{sup 39}Ar dating investigation
- New Mexico Bureau of Mines and Mineral Resources, New Mexico Institute of Mining and Technology, Socorro (United States)
- Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, New Mexico (United States)
- Department of Energy, Environmental Management Division, Los Alamos National Laboratory, Las Vegas, Nevada (United States)
The {sup 40}Ar/{sup 39}Ar age spectrum analyses of basalt whole rock and partially degassed sanidine xenocrysts for the Lathrop Wells volcanic center, Nevada, yield eruption ages of 77.3{plus_minus}6.0 and 76.6{plus_minus}4.9; ka (2{sigma}) for the Ql{sub 1} and Ql{sub 2} flows, respectively. Basaltic samples were analyzed in four to six replicate runs and yield normally distributed plateau ages. Miocene ash flow tuff xenoliths were collected from the basaltic units with the majority of samples coming from the Ql{sub 2}. The sanidines from the Ql{sub 2} xenoliths yielded apparent plateau ages (n=10) ranging from 69{plus_minus}17 to 309{plus_minus}11; ka with a strong cluster (n=6) at {approximately}77 ka. Because the diffusion dimension of sanidine is approximated by the physical crystal size, cracking of the sanidine following the development of an argon concentration profile may result in complex argon age spectra. Experimental studies exploring the natural and laboratory argon systematics of degassed sanidine reveal that crystal breakage and HF acid etching lead to anomalously old apparent ages. These new ages for the Ql{sub 1} and Ql{sub 2} flows are analytically indistinguishable and agree well with published eruption ages determined by {sup 3}He and {sup 36}Cl cosmogenic surface exposure dating methods. We conclude that the Ql{sub 1} and Ql{sub 2} flows are temporally equivalent. Additionally, the agreement between our eruption ages for these units and the published 76{plus_minus}20; ka [{ital Zreda} {ital et al.}, 1993] {sup 36}Cl exposure age for the Lathrop Wells scoria cone (Qs{sub 3}) suggests that the cone may be temporally equivalent to the Ql{sub 1} and Ql{sub 2} flows. We believe the simplest and most reasonable interpretation is that the volcanic center is monogenetic. {copyright} 1999 American Geophysical Union
- OSTI ID:
- 328584
- Journal Information:
- Journal of Geophysical Research, Vol. 104, Issue B1; Other Information: PBD: Jan 1999
- Country of Publication:
- United States
- Language:
- English
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