Slab-rollback ignimbrite flareups in the southern Great Basin and other Cenozoic American arcs: A distinct style of arc volcanism

Abstract

In continental-margin subduction zones, basalt magmas spawned in the mantle interact with the crust to produce a broad spectrum of volcanic arc associations. A distinct style of very voluminous arc volcanism develops far inland on thick crust over periods of 10-20 m.y. and involves relatively infrequent caldera-forming explosive eruptions of dominantly calc-alkaline rhyolite, dacite, and trachydacite with repose times of 10 4-10 6 yr. Volumes of individual eruptions are large (10 2-10 3 km 3), and nested super-eruptions of thousands of cubic kilometers are common. Calderas are as much as 60-75 km in diameter, and surrounding individual ignimbrite outflow sheets extend outward as much as 150 km, blanketing upwards of 10 5 km 2. Little or no basalt is extruded, whereas andesitic differentiates coeval with silicic ignimbrites range from minor to dominant in relative volume. A common feature in these flareups is essentially nonextending, thick, inland crust overlying a subducting oceanic plate with transverse tears that rolled back to a steeper dip from a previously flat configuration. Lithospheric delamination is locally possible. Large volumes of basalt that provide heat and mass for silicic magma generation in the crust form by fluid fluxing of the growing mantle wedge overlying the steepening dehydrating slab and from asthenospheric decompression. Variations in the mantle input, together with variations in crustal thickness, temperature, and composition, modulate the expression of the flareups. As a consequence of the high flux of mantle-derived magma into the thick crust, geotherms become elevated, and the brittle-ductile transition can rise to depths as shallow as 7 km. At this transition, diapirically rising magmas from a melting, assimilation, storage, and homogenization (MASH) zone are blocked and spread laterally into discoid chambers that grow until a thermomechanical threshold is attained, triggering climactic eruption and caldera collapse. This ignimbrite flareup style of continental arc volcanism is exemplified by the mid-Cenozoic southern Great Basin ignimbrite province; other examples include the contemporaneous Southern Rocky Mountain, Mogollon-Datil, vast Sierra Madre Occidental volcanic fields, and the late Cenozoic Altiplano-Puna volcanic complex in the Central Andes. Rhyolitic and trachydacitic ignimbrites typically have erupted, but where the crust was predominantly felsic, prewarmed, and orogenically thickened, well-developed MASH zones have spawned multiple super-eruptions of phenocryst-rich dacite, or monotonous intermediates, and smaller volumes of calc-alkaline rhyolite ignimbrite. In the Great Basin, eruptions of dry, hot trachydacite magma followed the monotonous intermediates. Partial melting in thinner crust with a major mafic component yielded more alkalic rhyolite and related trachydacite.

Geology and evolution of the McDermitt caldera, northern Nevada and southeastern Oregon, western USA

“…Intrinsic variables such as peralkalinity and inferred high temperature strongly encouraged the intense rheomorphism shown by the McDermitt Tuff and most strongly peralkaline tuffs, but seem to have had little influence on caldera character. Note: From this study, Mahood (1984), Swanson and McDowell (1984), McIntosh et al (1992), Christiansen (2001), Christiansen (2005), Lipman (2007), Christiansen and McCurry (2008), Lipman and McIntosh (2008), Bonnichsen et al (2008), John et al (2008), McDowell and McIntosh (2012), Henry and John (2013), Ellis et al (2013), Best et al (2013aBest et al ( , 2013bBest et al ( , 2016, and Lipman and Bachmann (2015).…”

“…Comparisons are made with strongly peralkaline calderas, for which erupted tuffs have peralkalinity indices >1.1 to 2.0 (Mahood, 1984), and with calderas of the ignimbrite flareup of western North America. The ignimbrite flareup formed a semicontinuous belt of ignimbrites and source calderas from the Great Basin of the United States to the southern end of the Sierra Madre Occidental in Mexico (Swanson and McDowell, 1984;Ferrari et al, 2007;McDowell and McIntosh, 2012;Henry et al, 2012b;Best et al, 2013aBest et al, , 2016. Overall understanding of the geometry, evolution, and geotectonic setting of calderas is based heavily on study of the ignimbrite flareup, particularly in the United States (Table 7; Lipman, 1984Lipman, , 2007Best et al, 2013aBest et al, , 2013bBest et al, , 2016Henry and John, 2013;Lipman and Bachmann, 2015).…”

“…The Eocene rocks are part of the Eocene-Oligocene southwestward sweep of magmatism across the Great Basin, probably resulting from rollback of the shallow Laramide slab (Humphreys, 1995;Henry and John, 2013;Best et al, 2016). Late Eocene intermediate volcanic rocks crop out throughout northern Nevada (Fig.…”

Surface uplift in the Central Andes driven by growth of the Altiplano Puna Magma Body

“…Although the sill-like radial geometry of the APMB differs from the elongate geometry of the Sierran batholith, magmatism during the peak APVC flare-up focused within a relatively narrow NNW-SSE zone akin to most arc-related batholiths3536. Furthermore, the APVC is only one component of a much more extensive ignimbrite province that spans the Central Andean arc and therefore may be considered analogously to the SNB3738.…”

Incremental growth of an upper crustal, A-type pluton, Argentina: Evidence of a re-used magma pathway

“…Subsequently, the SBU magmas were able to ascend in a pre-heated pathway allowing it to gradually change into batches with vertically elongated visco-elastic diapirs (e.g., Paterson and Vernon, 1995;Paterson, 1999, del Potro et al, 2013;Best et al, 2016) (Fig. 14c).…”