Relation of peralkaline magmatism to heterogeneous extension during the middle Miocene, southeastern Nevada

Abstract

Volcanism migrated southward in the northern Basin and Range province in the Oligocene and early Miocene to produce voluminous calcalkaline silicic ash flow tuffs. Alkaline volcanism became dominant by middle Miocene (17–14 Ma) as smaller volumes of rhyolite‐trachyte‐basalt suites were erupted from the relatively small Kane Springs Wash caldera complex including the Narrow Canyon, Boulder Canyon, and Kane Springs Wash calderas in southeastern Nevada. Only minor extension affected the Kane Wash area before the end of calcalkaline activity, but extension expressed by rate of progressive stratal tilt peaked (15–13.5 Ma) with peralkaline magmatism (14.7–14.4 Ma). Variations in distribution, degree, style, and timing of deformation demonstrate heterogeneous extension in the Kane Wash area. Only minor extension and tilting persisted post‐middle Miocene (<12 Ma). All major eruptive sources overlap domains of rapid extension. Most of the eruptive volumes from the two oldest calderas of the complex apparently pooled within their calderas, creating outflow deficits. Denudation faulting associated with magmatic tumescence may have followed preexisting active extensional fault systems to unload magma chambers, thus triggering eruptions into structural depressions. Evolution of alkaline magmas is demonstrated by progressive increases in peralkalinity and high field strength elements such as Zr, Y, and Nb. Nd, Pb, and Sr isotopic compositions provide evidence that significantly less crustal interaction affected middle Miocene peralkaline magmas than pre‐middle Miocene calcalkaline magmas. εNd values are −5 to −7 for peralkaline magmas and −7 to −11 for calcalkaline magmas; 208Pb/204Pb ratios are 38.2–38.6 for peralkaline magmas and 38.5–38.9 for calcalkaline magmas. Regional cooling, short duration of magmatism, small volumes of magma, and local extension caused less crustal interaction in peralkaline Kane Wash magmas than in earlier magmas. North of the Kane Wash area, older more voluminous calcalkaline magmas intruded hotter crust for a longer period and thus interacted with the crust to a greater degree in spite of synvolcanic extension.

Generation of Late Cretaceous silicic rocks in SE China: Age, major element and numerical simulation constraints

“…When compared with other large rhyolite provinces (Fig. 5b), e.g., the northern Basin and Range, W United States (Scott et al, 1995), the Yellowstone Plateau, Idaho (Bindeman and Valley, 2001), and the Taupo Volcanic Zone (Brown et al, 1998;Sutton et al, 2000), no any rhyolites from these provinces possess such high peraluminosity comparable with the SP rhyolites in the SCMB. Even the well-known SP rocks, such as Himalaya leucogranites (including Manaslu) (Vidal et al, 1982;Searle et al, 1997;Guillot and Le Fort, 1995), the peraluminosity is far less than these SP rhyolites.…”

“…(b) Other rhyolites from silicic large igneous provinces (SLIPs) and typical SP rocks. (1 and 2) northern Basin and Range rhyolites (Scott et al, 1995); (3) Low-d 18 O Yellowstone rhyolites (Bindeman and Valley, 2001); (4 and 5) the Oruanui rhyolites (Sutton et al, 2000) and Whakamaru ignimbrites (Brown et al, 1998) in the Taupo Volcanic Zone; and (6) representative SP rocks of leucogranites in Himalaya (Searle et al, 1997) in which the black dots are the averaged Manaslu leucogranites of various types (Vidal et al, 1982;Guillot and Le Fort, 1995). Shaded areas are same as in (a).…”

A mantle melting profile across the Basin and Range, SW USA

“…One of the most extensively studied regions of continental extension is the Basin and Range (B&R) province, where recent work has focused on structure of the upper mantle [Humphreys andDueker, 1994a, 1994b;Zandt et al, 1995;Jones and Phinney, 1998;Wernicke, 1992;Jones et al, 1992;Savage and Sheehan, 2000;Humphreys, 1995;Humphreys et al, 2000;Lowry et al, 2000]. It is generally accepted that the lithosphere has been thinned during the past 15 Myr and that Cenozoic volcanism is related to extension [e.g., Wernicke, 1992;Wernicke et al, 1988;Gans and Bohrson, 1998;Best and Christiansen, 1991;Scott et al, 1995;Jones, 1987;Hawkesworth et al, 1995;Zandt et al, 1995;Walker and Coleman, 1991;Walker et al, 1995]. Despite the general association between extension and volcanism, it has been difficult to constrain the depth and extent of mantle melting that leads to B&R basaltic magmatism.…”

Basin and Range volcanism as a passive response to extensional tectonics

“…7C). Strain rates along most of this trend are unknown, but at the southern terminus of the region (at Kane Springs Wash), Scott et al (1995) found that the time of peak extension rate, at 15-13.5 Ma, coincided with the eruption of peralkaline (i.e, high K-index) rocks at 14.4 Ma. These spacetime coincidences indicate that K-index may be a powerful tool for gauging the timing of extensional faulting where stratigraphic or structural information is insuffi cient.…”