Field trip no. 7 from “Geologic Excursions to the Rocky Mountains and Beyond,” field trip guidebook of the 1996 Annual Meeting of the Geological Society of America. (SP-44 has the complete set.) 36 pages. Digital PDF download. OF-96-04-07D
From the Introduction:
The 23- to 13-Ma Caliente and 17- to 12-Ma Kane Springs Wash caldera complexes, the youngest of a series of major silicic magmatic centers that erupted progressively from northerly to southerly locations in the eastern part of the Basin and Range province during the Oligocene and Miocene, recorded synchronous magmatism and extensional tectonism. The northernmost and older of the two, the Caliente caldera complex, experienced two episodes of extension synchronous with magmatism. As Caliente eruptive products evolved from calc-alkaline magmas (23-17 Ma) to more alkaline bimodal high-silica rhyolitic magmas (15.5-13 Ma), and local basalt flows (12 Ma) outside the caldera complex, the main episode of extension in the Caliente area resulted in north-northwest-striking, right-oblique- and dip-slip faults, subordinate conjugate north-northeast-striking, left-oblique- and dip-slip faults, and concurrent tilting and counter-clockwise vertical-axis rotation.
The younger extensional episode (post-12 Ma) in the Caliente area, characterized mostly by north-striking basin-range normal faults, postdated volcanic rocks in the Caliente area, although basalts of the same age are present in other parts of the Basin and Range. The younger of the two caldera complexes, the Kane Springs Wash, reached its peralkaline and volumetric eruptive climax at about 14.5 Ma during the greatest rate of extension, as measured by progressive tilting of strata along listric growth faults. Extensional tectonism in the Kane Wash area was heterogeneous in distribution, degree, style, and timing and included common north-northwest-striking, right-oblique-slip faults, north-northeast-striking, left-lateral strike-slip and oblique-slip faults, north-northeast- to north-striking, steeply dipping normal faults, magmatic dilation in calderas, and sparse west-dipping low-angle normal faults.
Although drier peralkaline Kane Springs Wash magmatism caused no significant mineralization, wetter calc-alkaline to alkaline Caliente magmatism formed several economic mineral deposits, the most significant of which were developed in the late 19th- and early 20th-century Ferguson (Delamar) mining district.