Geology of the Telescope Peak Quadrangle, California and Late Mesozoic Regional Metamorphism, Death Valley Area, California

Geology;Geochemistry

Labotka, Theodore Charles ; Albee, Arden Leroy

University:California Institute of Technology

Department:Geological and Planetary Sciences

关键词: Geology;    Geochemistry;   

Others  :  https://thesis.library.caltech.edu/11139/29/Labotka_TC_1978.pdf

美国|英语

来源: Caltech THESIS

【 摘 要 】

The Telescope Peak Quadrangle lies in the central Panamint Mountains which form the western boundary of Death Valley, California. The oldest rocks in the quadrangle consist of an 1800 m.y. complex of augen gneiss, quartzofeldspathic gneiss, and muscovite-biotite schist.These rocks were intruded approximately 1400 m.y. ago by porphyritic quartz monzonite in the World Beater Dome area. The earlier Precambrian rocks are unconformably overlain by the later Precambrian Pahrump Group. The Pahrump Group is comprised of the Crystal Spring Formation, Beck Spring Dolomite, and Kingston Peak Formation. These formations show variations in thicknesses and lithologies within thequadrangle which indicate that the Pahrump Group was deposited in a dynamic environment. The lithologies and thicknesses of the Crystal Spring Formation and Beck Spring Dolomite indicate that most of the quadrangle was underlain by a platform of earlier Precambrian basement which stood above sea level in the World Beater Dome area (World Beater Island) and which dropped off into deeper water nearTuber Canyon. The distribution of locally derived conglomerates in the lower Kingston Peak Formation and the presence of a local unconformity at the base indicate that at the end of Beck Spring Dolomite deposition, World Beater Island and adjacent areas to the north were uplifted, and the lower Kingston Peak Formation was deposited in eastern and western basins separated by the uplift. Continued deposition buried the uplift, and upper units in the Kingston Peak Formation include diamictite which grades northward into fine-grained greywacke, pillow basalt inter bedded in the diamictite, micaceous limestone, conglomerate, and argillite. The Pahrump Group is unconformably overlain by later Precambrian Noonday Dolomite, Johnnie Formation, Stirling Quartzite and Cambrian and Precambrian Wood Canyon Formation. The rocks were regionally metamorphosed at low pressure and intruded by leucocratic, muscovite-bearing granite about 80 m.y.ago. Folding occurred after this metamorphism and a north-northwest-trending anticline and World Beater Dome were formed. Retrograde metamorphism accompanied the folding event. Subsequently, low-angle normal faults developed, the Miocene Little Chief stock was intruded, large masses of monolithologic breccia formed, and the Panamint Mountainswere uplifted along the Panamint Valley fault zone.

Regional metamorphic terrains in the Panamint Mountains and in the Funeral Mountains show marked differences in the physical conditions attained during metamorphism. The Panamint Mountains exhibit low pressure regional metamorphism, and the characteristic assemblages developed in pelitic schists are andalusite + staurolite + biotiteand andalusite + cordierite + biotite. Isograds based on the appearance of sillimanite in pelitic rocks and tremolite and diopside in calcareous rocks indicate a westward increase in metamorphic grade toward an 80 m.y. muscovite granite pluton. A higher pressure metamorphicterrain was developed in the Funeral Mountains, and mineralassemblages in pelitic rocks are characterized.by the presence of kyanite. Garnet, staurolite, and kyanite isograds have been delineated and show that the grade increases toward the structual culmination of the Funeral Mountains, Migmatites occur in the highest grade area (sillimanite + garnet + biotite +muscovite + quartz), and the metasedimentary sequence was intruded by muscovite granite. The reaction chloritoid -> staurolite + garnet + chlorite is recorded in the Funeral Mountains, but in the Panamint Mountains the coexistence of chloritoid + biotite indicates that the garnet + chlorite join became unstable prior to the breakdown of chloritoid. Microprobe data on coexisting mineral assemblages, chemographic analysis of mineral facies in pelitic schists, and available experimental data indicate that the extremes in physical conditions attained during metamorphism were ~3 kb, ~600°C in the Panamint Mountains and ~8.5 kb, ~700°C in the Funeral Mountains. The sequence of tectonic and metamorphic events in the two areas is similar, but the facies series represent greatly different P/T gradients.

Assemblages in calciferous schist from the low pressure environment in the Panamint Mountains are characterized by quartz + epidote + calcic amphibole + chlorite + biotite in the trernolite zone and by quartz + epidote + calcic amphibole + garnet + biotite, quartz + epidote + diopside + calcic amphibole, and quartz + epidote + diopside + grossular in the diopside zone. Muscovite or microcline are common additional phases. Assemblages which occur in quartz + epidote + muscovite or quartz + epidote + microcline rocks are potentially useful for delineation of metamorphic grade and distinction between lower and higher pressure facies series. The compositions of calcic amphiboles formed in a low pressure environment generally fall in the series tremolite-pargasite and are related to the continuous break down of epidote and chlorite.