Stratigraphy and geochemistry of volcanic rocks in the Lava Mountains, California: Implications for the Miocene development of the Garlock fault

Abstract

Volcanism in the Lava Mountains occurred between 11.7 and 5.8 Ma and was contemporaneous with sinistral motion on the Garlock fault. Volcanic rocks, equivalent in age and chemistry to those in the Lava Mountains, crop out 40 km to the southwest in the El Paso Mountains across the Garlock fault. Three chemical groups of volcanic rocks erupted in the Lava Mountains over a period of 5 m.y. These are (1) andesite of Summit Diggings, Almond Mountain volcanic section, and Lava Mountains Andesite, (2) basalt of Teagle Wash, and (3) tuffs in the northeastern Lava Mountains and dacite in the Summit Range. Volcanic rocks of each group have distinctive chemical signatures useful for correlation of units across the Garlock fault. Our work demonstrated that tuffs in the Almond Mountain volcanic section may be equivalent to a tuff in member 5 of the Miocene Dove Spring Formation, El Paso Mountains. The basalt of Teagle Wash probably correlates with basalt flows in member 4, and tuffs in the northeast Lava Mountains may be equivalent to tuff of member 2. Correlation of these units across the Garlock fault implies that the Lava Mountains were situated south of the El Paso Mountains between 10.3 and 11.6 Ma and that 32–40 km of offset occurred on the Garlock fault in 10.4 m.y., resulting in a displacement rate of 3.1 to 3.8 mm/yr. Projecting this rate to the total offset of 64 km on the Garlock suggests that left-lateral slip began at ca. 16.4 Ma. Smith, E.I., Sanchez, A., Keenan, D.L., and Monastero, F.C., 2002, Stratigraphy and geochemistry of volcanic rocks in the Lava Mountains, California: Implications for the Miocene development of the Garlock fault, in Glazner, A.F., Walker, J.D., and Bartley, J.M., eds., Geologic Evolution of the Mojave Desert and Southwestern Basin and Range: Boulder, Colorado, Geological Society of America Memoir 195, p. 151–160. Data Repository item 2002### contains additional material related to this article. INTRODUCTION The Lava Mountains lie just south of the active Garlock fault, a major continental strike-slip fault that separates the southwestern Basin and Range to the north from the Mojave block to the south. The fault extends 250 km from the San Andreas fault to the Avawatz Mountains just south of Death Valley (Fig. 1). Total sinistral displacement on the Garlock fault is 64 km (Smith, 1962; Smith and Ketner, 1970; Davis and Burchfiel, 1973; Monastero et al., 1997). Estimates of the initiation of faulting vary from 10 to 9 Ma (Burbank and Whistler, 1987; Loomis and Burbank, 1988) to after 17 Ma (Monastero et al., 1997). Faulting continued to the present with a minimum of 18 km of displacement occurring across the central Garlock E.I. Smith et al. 152 Figure 1. Geologic map of the Lava Mountains and neighboring Summit Range and Black Hills modified from Smith (1964), Dibblee (1967), and Keenan (2000). WLMV—Western Lava Mountains Volcano. Inset map of California shows the following locations: GF—Garlock fault, SA—San Andreas fault, LM—Lava Mountains, EC—Eagle Crags volcanic field, EP—El Paso Mountains, and CR—Coso Range. Box indicates area covered by Figure 3. EC