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

Abstract

The McDermitt caldera (western USA) is commonly considered the point of origin of the Yellowstone hotspot, yet until now no geologic map existed of the caldera and its geology and development were incompletely documented. We developed a comprehensive geologic framework through detailed and re connaissance geologic mapping, extensive petrographic and chemical analy sis, and highprecision Eruption of the McDermitt Tuff generated the irregularly keyholeshaped, 40 × 30-22 km McDermitt caldera. Collapse occurred mostly along a narrow ringfault zone of discrete faults with variable downwarp into the caldera be tween faults. Minor parallel faults locally widen the zone to as much as 6 km. We find no evidence that the McDermitt caldera consists of multiple nested calderas, as previously postulated. Total collapse was no more than ~1 km, and total erupted volume was ~1000 km 3 , of which 50%-85% is intracaldera tuff. Uncertainties in these estimates arise because an intracaldera tuff section is exposed only along the western edge of the caldera, and outflow tuff is not completely mapped. Megabreccia and mesobreccia are common in intracal dera tuff in the complete section. Intracaldera tuff is strongly rheomorphic, scrambling the compositional zoning, which is locally better preserved in out flow sections. However, outflow tuff is also strongly rheomorphic where it was deposited over steep topography.The caldera underwent postcollapse resurgent uplift driven by intrusion of icelandite magma, which also erupted from two major vents and as wide spread lavas. Major igneous activity around the McDermitt caldera lasted from before 16.7 to 16.1 Ma, although minor highalumina olivine tholeiite lavas were emplaced ca. 14.9 Ma in the youngest recognized igneous activity.Tuffaceous sediments as much as 210 m thick filled the caldera, although whether deposition preceded, followed, or spanned resurgence is unresolved. Although formed during regional extension, the caldera is cut only at its west ern and eastern margins by much younger, highangle normal faults that re sulted in gentle (~10°) eastward tilting of the caldera.Numerous hydrothermal systems probably related to caldera magmatism and focused along caldera structures produced Hg, Zrrich U (some along the western caldera ring fracture dated as 16.3 Ma), Ga, and minor Au mineral ization. Lithium deposits formed throughout the intracaldera tuffaceous sedi ments, probably ca. 14.9 Ma.Silicic central Snake River Plain, which also erupted voluminous rhyolitic tuffs. How ever, the Snake River Plain ignimbrites are metaluminous and homogeneous in bulk chemistry, with plagioclase, sanidine, and minor quartz as common phenocrysts, and rarely contain pumice or lithics.

Evidence for Cyclical Fractional Crystallization, Recharge, and Assimilation in Basalts of the Kimama Drill Core, Central Snake River Plain, Idaho: 5.5-Million-Years of Petrogenesis in a Mid-crustal Sill Complex

“…The region contains a record of continuous bimodal volcanism extending over 17 Ma Coble and Mahood, 2012;Henry et al, 2017) to the present, and documents the migration of timetransgressive rhyolitic volcanism from the Bruneau-Jarbidge volcanic center (circa 12 Ma) to its present location beneath the Yellowstone Plateau (Pierce and Morgan, 1992;Anders et al, 2009). Interaction between the mantle hotspot and overlying continental lithosphere has resulted in large rhyolite calderaforming eruptions, followed by eruption of smaller basaltic shield volcanoes (Bonnichsen et al, 2008;Christiansen and McCurry, 2008;McCurry and Rodgers, 2009).…”

The three-stage petrochemical evolution of the Steens Basalt (southeast Oregon, USA) compared to large igneous provinces and layered mafic intrusions

“…Regional rhyolite volcanism associated with the CRBG has been recently recognized (Coble and Mahood, 2012;Benson and Mahood, 2016;Benson et al, 2017;Streck et al, 2015Streck et al, , 2016. It begins after the earliest Steens Basalt eruptions (16.69 Ma near McDermitt Caldera; Henry et al, 2017) and continues until at least 15 Ma. This suggests an important role for crustal staging and assimilation in the CRBG.…”

Lithium-Rich Claystone in the McDermitt Caldera, Nevada, USA: Geologic, Mineralogical, and Geochemical Characteristics and Possible Origin

“…The samples included both hand samples of core and bulk samples from intervals 0.3 to 2.6 m thick that were previously chemically analyzed for Lithium Nevada during deposit evaluation. The XRD analysis was also [19][20][21][22][23][24][25][26][27][28][29][30][31][32]. CA-California; ID-Idaho; MT-Montana; NV-Nevada; OR-Oregon; UT-Utah; WA-Washington; WY-Wyoming.…”

“…1000 km 3 of the 16.39 ± 0.02 Ma (n = 3) McDermitt Tuff which is strongly zoned from peralkaline, aphyric, high-SiO 2 rhyolite (comendite) to metaluminous, abundantly anorthoclase-phyric, trachydacite or Fe-rich andesite (icelandite) ( Table 1) [19]. The caldera is one of several that formed during the initial development of the Yellowstone hotspot and Columbia River basalt volcanism in northern Nevada and southeastern Oregon (Figure 1) [19][20][21][22]. 14.87 ± 0.05 Ma: Formation of diagenetic K-feldspar in Li-rich zone at Thacker Pass.…”

“…In contrast, Li clay deposits, such as though occurring in the McDermitt caldera, are called "sediment-hosted deposits" [4] or "unusual lithium deposits" [2] and interpreted to represent "less than 3% of global lithium resources" [4]. These deposits are also characterized as "hectorite deposits" [2][3][4] [19][20][21][22][23][24][25][26][27][28][29][30][31][32]. CA-California; ID-Idaho; MT-Montana; NV-Nevada; OR-Oregon; UT-Utah; WA-Washington; WY-Wyoming.…”