Evidence for 600 year‐old basalt and magma mixing at Inyo Craters Volcanic Chain, Long Valley Caldera, California

Bailey, Roger C.; Suemnicht, Gene A.

doi:10.1029/jb095ib13p21441

Cited by 28 publications

(5 citation statements)

References 21 publications

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“…Sample Gua7 is included as part of the volcanic front although it comes from Cerro Quemado, a Holocene dome complex slightly (5 km) “behind” one of the large stratovolcanoes (Santa María) defining the front [ Conway et al , 1992]. Gua7 has abundant fine‐grained mafic inclusions which are interpreted as blobs of mafic, possibly hybrid, magma quenched in their more silicic host [ Eichelberger , 1980; Bacon and Metz , 1984; Bacon , 1986; Koyaguchi , 1986; Grove and Donnelly‐Nolan , 1986; Linneman and Myers , 1990; Varga et al , 1990; Nakada et al , 1994; Feeley and Dungan , 1996; Clynne , 1999; Murphy et al , 2000; Saito et al , 2002]. We attempted to completely exclude these inclusions from the powdered sample, but were probably unsuccessful (see below).…”

Section: Samples and Analytical Techniquesmentioning

confidence: 99%

U‐series disequilibria in Guatemalan lavas, crustal contamination, and implications for magma genesis along the Central American subduction zone

Walker¹,

Mickelson²,

Thomas³

et al. 2007

J. Geophys. Res.

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Th excess in Guatemalan mafic samples, on the other hand, is crustal contamination, consistent with the relatively high Th/Nb and low Ba/Th ratios in these samples. We suspect, however, that crustal contamination only exerts a sizable control over the U-series disequilibrium of mafic magmas in Guatemala, and not elsewhere along the Central American volcanic front. This agrees with previously published trace element and isotopic evidence that throughout Central America, with the exception of Guatemala, mafic magmas are largely uncontaminated by crustal material.

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Section: Samples and Analytical Techniquesmentioning

confidence: 99%

U‐series disequilibria in Guatemalan lavas, crustal contamination, and implications for magma genesis along the Central American subduction zone

Walker¹,

Mickelson²,

Thomas³

et al. 2007

J. Geophys. Res.

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“…Bacon [1985] has reported mafic magmatic inclusions in the rhyolite at Mono Craters, and Varga et al [1988] have reported similar inclusions in the coarsely porphyritic rhyolite at Deadman and Glass Creek domes. One of the end-members is the low-Ba, high-silica rhyolites.…”

Section: Respectively the Qmodel Calculated Mafic End-member (Sementioning

confidence: 99%

Petrology and emplacement dynamics of intrusive and extrusive rhyolites of Obsidian Dome, Inyo Craters Volcanic Chain, eastern California

Vogel¹,

Eichelberger²,

Younker³

et al. 1989

J. Geophys. Res.

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Drilling at Obsidian Dome has provided continuous core samples of the distal and proximal portions of Obsidian Dome, its conduit, and an associated feeder dike. Both the dome and conduit are chemically and mineralogically zoned and consist of a finely porphyritic, high‐Ba, low‐silica rhyolite occurring in the basal portion of the dome and margins of the conduit and a finely porphyritic, low‐Ba, higher‐silica rhyolite occurring in the upper portion of the dome and center of the conduit. The high‐Ba rhyolite contains two distinct phenocrysts assemblages with two distinct compositions and represents mingled magmas. The low‐Ba rhyolite in the dome and conduit contains significantly fewer disequilibrium phenocrysts and is only slightly mingled. The dike, sampled at 600 m depth, as well as a related tephra fall from Obsidian Dome vent, are entirely low‐Ba rhyolite that contain no evidence of magma mingling. End‐members of the mingled magma, calculated using two different methods, are a 63% silica end‐member and a silicic end‐member identical in composition to the dike and tephra fall from Obsidian Dome vent. This silicic end‐member was the first magma emplaced in the dike and comprised much or all of the first magma vented to the surface during formation of the Obsidian Dome vent when eruption rates were high. Magma mingling of mafic and rhyolite magmas occurred during formation of the conduit. A comparison of the magma types at Obsidian Dome with the other 600‐year‐old magma types in the Inyo chain demonstrates that the finely porphyritic rhyolites at Obsidian Dome are similar to the finely porphyritic rhyolites at the other domes. All of these originated by mingling of two end‐members. The coarsely porphyritic rhyolites that occur at Glass Creek and Deadman domes are distinctly different from the finely porphyritic rhyolites. The two rhyolites can not be related by any fractionation scheme and could not have been in thermal or chemical equilibrium with each other. These observations require considerable heterogeneity in the Inyo Domes magmatic system. Two possible interpretations of the chemical variation and emplacement sequence are explored. In the first interpretation the chemical patterns observed in the surface and subsurface samples at Obsidian Dome are explained by differential draw‐up of magma from a stratified dikelike reservoir. This differential draw‐up is the result of changing flow rates during the course of the eruption. When the magma initially vented to the surface during the main part of the explosive phase, flow rates were very high, and the deepest layer of the reservoir was drawn into the conduit where magma mingling occurred. During the subsequent effusive phase, flow rates were low, draw‐up depths were reduced, and only magma from the uppermost layer in the reservoir erupted, only slightly contaminated by earlier hybrid magma drawn up. Similar processes most likely occurred at the other Inyo domes; however, the low‐Ba rhyolite was less abundant, and highly viscous, coarsely prophyritic rhyolite ...

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“…Compositionally, the mid-fourteenth century Inyo eruption was extraordinarily complex (Sampson and Cameron, 1987;Vogel et al, 1989). As summarized in Hildreth (2004), at least four discrete magmas were confl uent during the eruption: (1) crystal-poor rhyolite like that of Mono Craters; (2) crystal-rich Long Valley rhyolite like that of the 100 ka west moat domes; (3) trachydacite like that of the 42-27 ka chain of fl ows and domes (unit dnw) on the northwest margin of the caldera; and (4) andesitic magmatic inclusions (~60% SiO 2 ) found quenched in two of the 1350 CE fl ows (Varga et al, 1990). The compositional and petrographic similarity of the crystal-rich component to the nearby Long Valley rhyolite of Deer Mountain was pointed out by Sampson and Cameron (1987).…”

Section: Post-mammoth Inyo Chainmentioning

confidence: 99%

Mammoth Mountain and its mafic periphery--A late Quaternary volcanic field in eastern California

et al. 2014

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The trachydacite complex of Mammoth Mountain and an array of contemporaneous mafi c volcanoes in its periphery together form a discrete late Pleistocene magmatic system that is thermally and compositionally independent of the adjacent subalkaline Long Valley system (California, USA). The Mammoth system fi rst erupted ca. 230 ka, last erupted ca. 8 ka, and remains restless and potentially active. Magmas of the Mammoth system extruded through Mesozoic plutonic rocks of the Sierra Nevada batholith and extensive remnants of its prebatholith wall rocks. All of the many mafi c and silicic vents of the Mammoth system are west or southwest of the structural boundary of Long Valley caldera; none is inboard of the caldera's buried ring-fault zone, and only one Mammoth-related vent is within the zone. Mammoth Mountain has sometimes been called part of the Inyo volcanic chain, an ascription we regard inappropriate and misleading. The scattered vent array of the Mammoth system, 10 × 20 km wide, is unrelated to the range-front fault zone, and its broad nonlinear footprint ignores both Long Valley caldera and the younger Mono-Inyo range-front vent alignment. Moreover, the Mammoth Mountain dome complex (63%-71% SiO 2 ; 8.0%-10.5% alkalies) ended its period of eruptive activity (100-50 ka) long before Holocene inception of Inyo volcanism. Here we describe 25 silicic eruptive units that built Mammoth Mountain and 37 peripheral units, which include 13 basalts, 15 mafi c andesites, 6 andesites, and 3 dacites. Chemical data are appended for nearly 900 samples, as are paleomagnetic data for ~150 sites drilled. The 40 Ar/ 39 Ar dates (230-16 ka) are given for most units, and all exposed units are younger than ca. 190 ka. Nearly all are mildly alkaline, in contrast to the voluminous subalkaline rhyolites of the contiguous long-lived Long Valley magma system. Glaciated remnants of Neogene mafi c and trachydacitic lavas (9.1-2.6 Ma) are scattered near Mammoth Mountain, but Quaternary equivalents older than ca. 230 ka are absent. The wide area of late Quaternary Mammoth magmatism remained amagmatic during the long interval (2.2-0.3 Ma) of nearby Long Valley rhyolitic eruptions. Recent Unrest Geophysical unrest beneath Mammoth Mountain and in adjacent parts of the Sierra Nevada and Long Valley caldera has generated concern among residents, stakeholders, and geoscientists since at least 1980, when 4 magnitude 6 earthquakes shook the area. Extensive monitoring for three decades has documented numerous earthquake swarms, ground uplift and deformation, changes in hydrothermal systems, and emission of magmatic CO 2 at several sites semiencircling

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Evidence for 600 year‐old basalt and magma mixing at Inyo Craters Volcanic Chain, Long Valley Caldera, California

Cited by 28 publications

References 21 publications

U‐series disequilibria in Guatemalan lavas, crustal contamination, and implications for magma genesis along the Central American subduction zone

U‐series disequilibria in Guatemalan lavas, crustal contamination, and implications for magma genesis along the Central American subduction zone

Petrology and emplacement dynamics of intrusive and extrusive rhyolites of Obsidian Dome, Inyo Craters Volcanic Chain, eastern California

Mammoth Mountain and its mafic periphery--A late Quaternary volcanic field in eastern California

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