Replacement of Clinopyroxene by Amphibole in Metavolcanic Rocks and Metamorphism of the Slate Creek Complex, Northern Sierra Nevada, California PDF Download

Author: Timothy Jay Fagan
Publisher:
ISBN:
Category :
Languages : en
Pages : 1164

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Author: Paul C. Bateman
Publisher:
ISBN:
Category : Batholiths
Languages : en
Pages : 218

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A study of the structure, composition, and pre-Tertiary history of the Sierra Nevada batholith in the Mariposa 1 by 2 quadrangle.

Author: Cordell Durrell
Publisher:
ISBN:
Category : Geology
Languages : en
Pages : 142

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Author: Jesse Socorro Chadwick
Publisher:
ISBN:
Category : Folds (Geology)
Languages : en
Pages : 202

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Structural analysis, bedrock mapping, and quantitative thermobarometry reveal a protracted metamorphic history for the multiple lithologies present in the Jerome Rock Lakes area of the Spanish Peaks, located in the northern Madison Range, southwest Montana. Volumetrically-dominant quartzofeldspathic gneisses are primarily of the tonalite-trondhjemite-granodiorite (TTG) suite and record multiple episodes of high-temperature deformation. Coarse-grained hornblende in association with K feldspar-bearing leucosome indicates locally vapor-present melting. Clinopyroxene-bearing metabasic enclaves in the quartzofeldspathic gneisses record the subsolidus hydration of clinopyroxene porphyroclasts to hornblende and subsequent dehydration melting of hornblende in the transitional granulite facies to produce garnet coronae and clinopyroxene neoblasts under vapor-absent conditions. Variably migmatized garnet-sillimanite schists record amphibolite facies metamorphism at ca. 5.5 kbar and 640 oC, with extensive melt production via melting of biotite. Inclusions of staurolite in kyanite-bearing metaquartzite are inferred to indicate the presence of modern thicknesses of continental crust and a geothermal gradient similar to Phanerozoic values. Infrequent layers containing tschermakitic amphibole layers may represent the residuum of vapor-present melting of biotite and indicate local variation in the activity of water. Migmatized garnet amphibolites record peak upper-amphibolite to transitional granulite facies metamorphism at ca. 10 kbar and 800 oC. A clockwise P-T path of Alpine character is proposed for the lithologies of the Jerome Rock Lakes area, with peak pressures in the kyanite field attained before peak temperatures, followed by rapid, steeply adiabatic to isothermal decompression. Early isoclinal folds developed during prograde metamorphism and were rotated into the regional foliation. Progressive deformation resulted in the formation of later isoclinal folds coplanar with foliation. Peak temperatures were attained after cessation of deformation, indicated by undeformed leucosomes. A second episode of deformation produced outcrop-scale parallel folds trending north-south. The Precambrian tectonic history of the northern Madison Range is inferred to have terminated in a continental collision with northwest-southeast directed shortening that produced steeply-dipping, NNE-trending regional foliation. This style is generally consistent with that observed elsewhere in the Spanish Peaks and in the Tobacco Root Range, generated by the ca. 1.7 Ga collision of western North America with the Medicine Hat craton.

Author: Robert S. Hildebrand
Publisher: Geological Society of America
ISBN: 0813724953
Category : Science
Languages : en
Pages : 182

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"In this well-illustrated book, Hildebrand expands upon his model for the development of the North American Cordillera detailed in Special paper 457. Starting with an overview of Cordilleran geology he goes on to provide an in depth look at how the Rubian ribbon continent was assembled. He integrates the complex geology of the Cordillera into an actualistic model involving arc magmatism, arc-continent collision, slab failure magmatism, and transcurrent motion in both Rubia and the western North American margin. While much of the focus is on the assembly of the Rubian ribbon continent, Hildebrand explores its interactions with North America during the Sevier and Laramide events and concludes that North America was the lower plate in both"--Provided by publisher.

Author: Peter Schiffman
Publisher:
ISBN:
Category : Igneous rocks
Languages : en
Pages : 0

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Author: Jesslyn Kathleen Starnes
Publisher:
ISBN: 9781321364026
Category :
Languages : en
Pages :

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The Franciscan complex of coastal California is considered the world's type locality for subduction processes and consists of metamorphosed fragments of oceanic crust from a down-going plate as well as metamorphosed sedimentary rocks deposited in or near an oceanic trench above the down-going slab. Although it has been intensely studied for decades, several key questions remain unresolved: When did subduction begin? Was subduction continuous or episodic? Along what P-T paths were Franciscan rocks metamorphosed? This study presents new U-Pb zircon ages from two distinct populations of zircon in a garnet amphibolite that is interpreted as a retrograded eclogite. U-Pb analyses of zircon analyzed in-situ within garnet porphyroblasts yielded a weighted mean 206Pb/238U age of 175.6 ± 4 Ma whereas zircon separated from the matrix of the sample yielded 159.5 ± 4 Ma. The latter is similar to ages of high-grade blocks throughout the Franciscan whereas the former suggests Franciscan subduction began at least 16 Ma earlier. The data suggest that subduction and associated metamorphic processes have been continuous from ~180 Ma to at least 133 Ma. Petrological data demonstrate that this garnet amphibolite block progressed along a clock-wise P-T path, from eclogite facies to amphibolite facies, with a subsequent blueschist facies overprint. The two populations of zircon yield individual grain ages that range from ~133 to ~208 Ma, but statistical tests and trace element analyses of the zircon demonstrate that the two populations are distinct and must represent different stages in the metamorphic history of the amphibolite. Geochemical analyses of the zircon, along with textural relationships and Lu-Hf age of the garnet porphyroblasts, imply that the eclogite facies metamorphism was coeval with, or perhaps even older than the oldest zircon population, while the amphibolite facies metamorphism overlapped with the matrix zircon growth. This study also demonstrated the viability of dating very small (

Author: Robert S. Hildebrand
Publisher: Geological Society of America
ISBN: 0813725321
Category : Nature
Languages : en
Pages : 123

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In this Special Paper, Hildebrand and Whalen present a big-picture, paradigm-busting synthesis that examines the tectonic setting, temporal relations, and geochemistry of many plutons within Cretaceous batholithic terranes of the North American Cordillera. In addition to their compelling tectonic synthesis, they argue that most of the batholiths are not products of arc magmatism as commonly believed, but instead were formed by slab failure during and after collision. They show that slab window and Precambrian TTG suites share many geochemical similarities with Cretaceous slab failure rocks. Geochemical and isotopic data indicate that the slab failure magmas were derived dominantly from the mantle and thus have been one of the largest contributors to growth of continental crust. The authors also note that slab failure plutons emplaced into the epizone are commonly associated with Cu-Au porphyries, as well as Li-Cs-Ta pegmatites.

Author: John Allan Bradford
Publisher:
ISBN:
Category : Geology
Languages : en
Pages : 108

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The Midway-Cassiar project area covers approximately 3,000 sq km in the Cassiar Mountains of northern British Columbia, between the Dease River and the Yukon border near Rancheria. This study began in 1986 as one of several regional mapping projects to produce detailed geological maps of the area. This report describes the history of exploration and mining in the area and previous geological work; general geology; structural geology and metamorphism; and economic geology.

Author: Adam M. Booth
Publisher: Geological Society of America
ISBN: 0813700620
Category : Science
Languages : en
Pages :

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