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Gold butte crustal section, South Virgin Mountains, Nevada
Author(s) -
Fryxell Joan E.,
Salton Gillian G.,
Selverstone Jane,
Wernicke Brian
Publication year - 1992
Publication title -
tectonics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.465
H-Index - 134
eISSN - 1944-9194
pISSN - 0278-7407
DOI - 10.1029/92tc00457
Subject(s) - geology , unconformity , proterozoic , butte , geochemistry , gneiss , phenocryst , metamorphism , sedimentary rock , dome (geology) , denudation , metamorphic rock , paleontology , petrology , tectonics , volcanic rock , volcano
The Gold Butte block consists of a complex of Proterozoic medium‐ to high‐grade metamorphic and plutonic rocks, unconformably overlain by steeply east dipping Paleozoic sedimentary rocks on its east side. This complex is one of the largest continuous exposures of crystalline rocks in the southwestern United States that lie structurally beneath a steeply tilted section of Phanerozoic strata, and it may represent part of an intact Proterozoic‐Miocene crustal section reaching paleodepths of approximately 15 km. The section was exposed during tectonic denudation in Miocene time (at about 15 Ma) and lies directly adjacent to the Colorado Plateau to the east. Proterozoic and Tertiary geological features support the hypothesis that the block represents a relatively intact crustal section. A large exposure of Proterozoic rapakivi granite, the Gold Butte Granite (circa 1.45 Ga), crops out over most of the crystalline complex and displays strong zoning in phenocryst abundance, which increases toward the top of a 10‐ to 12‐km‐thick magma chamber. The wallrocks of the granite are predominantly garnet‐bearing gneisses (circa 1.7 Ga), which display increasing pressures of final equilibration westward away from the basal Phanerozoic unconformity. Thermobarometry of gneisses immediately beneath the unconformity indicate pressures of 2–3 kbar, whereas those 12–13 km west of the unconformity yield pressures of 5–6 kbar, suggesting the crustal section was established by 1.7 Ga. The style of deformation displayed by denudation structures also varies from east to west, with brittle faulting only in eastern portions of the block and retrograde metamorphism, mylonitization, and chlorite brecciation of the garnet gneiss observed in western areas.