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Warren Hamilton

Publications and source records attributed to Warren Hamilton.

16 recordsLinked to original sources
USGS1983

Correlation of metamorphosed Paleozoic strata of the southeastern Mojave Desert region, California and Arizona

Isolated outcrops of deformed, regionally metamorphosed Paleozoic strata are scattered within the southeastern Mojave Desert region of California and western Arizona. These strata unconformably overlie a basement of Proterozoic crystalline rocks and are overlain in turn by metamorphosed Mesozoic sedimentary rocks. The strata can be correlated lithostratigraphically with the classic cratonal Paleozoic section of the western Grand Canyon, Arizona, and with nonmetamorphosed Paleozoic sections transitional between cratonal and miogeoclinal in the Ship, Marble, and Providence Mountains, California. The strata evidently were once continuous with Paleozoic epicontinental strata exposed throughout the southern Great Basin and Colorado Plateau. Outcrops of Paleozoic strata and of the underlying Proterozoic basement in the southeastern Mojave Desert region define a terrane that has been disrupted by Mesozoic thrust faults and by Tertiary detachment faults but that nevertheless retain a gross paleogeographic coherence. This coherent terrane extends at least as far west and southwest as the Big Maria, Palen, and Calumet Mountains, and possibly beyond to include Paleozoic exposures in the San Bernardino Mountains and near Victorville. Poorly understood tectonic boundaries separate the area of paleogeographic coherence from known or suspected allochthonous terranes in the western Mojave Desert and the eastern Transverse Ranges.

Arizona, California↗
USGS1979

Dynamics of the Continental Crust: suggestions for U.S. Geological Survey research in the 1980's

Crustal dynamics--the study of the movement of mass and energy within, into, and out of the Earth's crust--encompasses most efforts of earth science, either directly or as background and support. A new international program is being formulated to promote cooperative development of the concepts required to solve proliferating problems created by intensifying human use and misuse of the land and its resources. A tentative title suggested by the U.S. Geodynamics Committee for this program for the decade of the 1980's is "Crustal Dynamics: A Framework for Resources." The needs are pressing at both the national and international levels. Many reasons cited for undertaking this international program are akin to the justifications for forming, maintaining, or enlarging governmental geological surveys. Thus, the U.S. Geological Survey has an obligation to participate in the Crustal Dynamics Program to meet its expanding responsibilities to serve the nation effectively. A U.S. Geological Survey workshop was convened near Denver on September 20-23, 1978, to consider appropriate roles that might be played in the Crustal Dynamics decade. Some 60 Survey geologists, geophysicists, geochemists, and hydrologists participated. Principal questions addressed were: 1) What are the major earth-science problems that should be investigated during the next decade? 2) What are their implications to society? 3) What competence can be brought to bear on these problems and what further competence and tools need to be developed? 4) What roles are appropriate for the USGS within the broader national and international earth-science communities? This report presents some responses to these questions. Readers may recognize some defects. The report was prepared by several committees and its sections remain uneven despite editing. Insufficient time was available for either lengthy consideration or discussions, and no opportunity was provided for communication with colleagues in other organizations. The report is not a finished proposal for USGS participation in the Crustal Dynamics program, but rather is intended as a basis for further discussion and consideration both within the organization and with colleagues in other institutions and organizations, toward formulation of a viable program.

Open-File Report↗
USGS1969

Mesozoic California and the underflow of Pacific mantle

The Mesozoic evolution of California is interpreted as dominated by the underflow of oceanic mantle beneath the continental margin. Underflow during part of Late Cretaceous time of more than 2000 km of the eastern Pacific plate seems required by the marine magnetic data. Correspondingly, varied oceanic environments—abyssal hill, island arc, trench, oceanic crust, and upper mantle, perhaps also continental rise and abyssal plain—appear to be represented in the eugeosynclinal terranes of California. The rock juxtapositions accord with the concept that these materials were scraped off against the continent as the oceanic plate slid beneath it along Mesozoic Benioff seismic zones, which are now seen as serpentine belts separating profoundly different rock assemblages. The chaotic Franciscan Formation of coastal California consists of deep-ocean Late Jurassic to Late Cretaceous sedimentary, volcanic, crustal, and mantle materials. As open-ocean abyssal oozes and the oceanic crust beneath them were swept into the Benioff-zone trench at the continental margin, they were covered by terrigenous clastic sediments, and the entire complex was carried beneath the correlative continental-shelf and continental-slope deposits (Great Valley sequence) and the older Mesozoic complexes. The other eugeosynclinal terranes of California can be interpreted, albeit with less confidence, in similar terms of underflow of Pacific mantle. In the Klamath Mountains and northern Sierra Nevada, for example, Ordovician and Silurian ocean-floor materials, overlain by or juxtaposed against an Upper Silurian to Permian island arc, were swept in first to the continent, along with a large fragment of oceanic crust and mantle and another fragment of an old orogenic belt. This debris was followed by Permian and Triassic ocean-floor deposits. Late Triassic and Jurassic volcanic products from stocks and batholiths forming in the welded complexes lapped across both landward and oceanward sides of the region. Reversal of Cenozoic extension, strike-slip faulting, and volcanic crustal growth in the western United States reveals a Cretaceous tectonic pattern strikingly like the modern pattern of the Andes, so the paleotectonic setting of North America can be inferred from the South American present. The Mesozoic batholiths of North America, like the late Cenozoic volcanic belt of the central Andes, are products of the same rapid motion of oceanic plates that carried oceanic sediments against the continent to form eugeosynclinal terranes. Magmas generated in the Benioff zones formed the batholiths and the volcanic fields which initially capped them.

California↗
USGS1967

Tectonics of Antarctica

Antarctica consists of large and wholly continental east Antarctica and smaller west Antarctica which would form large and small islands, even after isostatic rebound, if its ice cap were melted. Most of east Antarctica is a Precambrian Shield, in much of which charnockites are characteristic. The high Transantarctic Mountains, along the Ross and Weddell Seas, largely follow a geosyncline of Upper Precambrian sedimentary rocks that were deformed, metamorphosed and intruded by granitic rocks during Late Cambrian or Early Ordovician time. The rocks of the orogen were peneplained, then covered by thin and mostly continental Devonian-Jurassic sediments, which were intruded by Jurassic diabase sheets and overlain by plateau-forming tholeiites. Late Cenozoic doming and block-faulting have raised the present high mountains. Northeastern Victoria Land, the end of the Transantarctic Mountains south of New Zealand, preserves part of a Middle Paleozoic orogen. Clastic strata laid unconformably upon the Lower Paleozoic plutonic complex were metamorphosed at low grade, highly deformed and intruded by Late Devonian or Early Carboniferous granodiorites. The overlying Triassic continental sedimentary rocks have been broadly folded and normal-faulted. Interior west Antarctica is composed of miogeosynclinal clastic and subordinate carbonate rocks which span the Paleozoic Era and which were deformed, metamorphosed at generally low grade, and intruded by granitic rocks during Early Mesozoic time and possibly during other times also. Patterns of orogenic belts, if systematic, cannot yet be defined; but fragmentation and rotation of crustal blocks by oroclinal folding and strike-slip faulting can be suggested. The Ellsworth Mountains, for example, consist of Cambrian-Permian metasedimentary rocks that strike northward toward the noncorrelative and latitudinally striking Mesozoic terrane of the Antarctic Peninsula in one direction and southward toward that of the Lower Paleozoic: terrane of the Transantarctic Mountains in the other; the three regions may be separated by great strike-slip faults. The Antarctic Peninsula in west Antarctica, south of South America, consists of metavolcanic and metasedimentary rocks intruded by Late Cretaceous quartz diorite. The pre-granitic rocks are of Jurassic and Early Cretaceous ages wherever they have been dated by fossils, although some crystalline complexes may be older. The S-shape of the peninsula may represent oroclinal bending within Cenozoic time as part of a motion system in which a narrow continental bridge between South America and Antarctica was deformed and ruptured. Perhaps this bridge lagged behind as the larger continental plates drifted into the Pacific Ocean Basin.

Tectonophysics↗
USGS1963

Overlapping of late mesozoic orogens in western Idaho

Early formed rocks of the border zone of the Idaho batholith are thrust westward over the low-grade metavolcanic rocks of the Seven Devils Mountains. Late intrusions of the border zone cut out upper plate rocks and contact-metamorphose lower plate rocks. Granitic intrusions in the Seven Devils complex are metamorphosed near the border zone of the Idaho batholith. Such relationships are interpreted in the light of a regional synthesis to indicate the overlapping and oblique truncation of the eastern part of a belt deformed largely during Jurassic time by the western part of a tectonic belt active during early stages of the middle Cretaceous events that produced the Idaho batholith.

Idaho↗
USGS1962

Late cenozoic structure of west-central Idaho

The massive Salmon River Mountains of interior Idaho are bounded on the west by a belt 30 miles wide of post-Miocene, west-tilted normal-fault blocks and west-dipping monoclines. The belt is coincident with the western border zone of the middle Cretaceous Idaho batholith, as it extends from the west edge of the massive interior of the batholith to about the western limit of the border zone of gneisses and schists. West of this belt is the Columbia Plateau province of irregular domal and anticlinal uplifts and northwest-trending normal faults. These structures are superimposed upon east- to northeast-trending, low-grade metamorphic rocks intruded by semi-concordant stocks and small batholiths, products largely of Late Jurassic (?) orogeny. The Idaho batholith has been little deformed, and its border-zone rocks of intermediate competence are broken by concordant structures. Young structures cut directly across the relatively incompetent rocks of the older orogen to the west. The mountains flanking the Snake River and Salmon River canyons are higher than those farther away, suggesting that local isostatic uplift may be compensating for their erosion.

Idaho↗
USGS1961

Origin of the Gulf of California

The probable cumulative Late Cretaceous and Cenozoic right-lateral strike-slip displacement along the San Andreas fault in central California is 350 miles. The San Andreas and the allied faults into which it branches southward trend longitudinally into the Gulf of California , and the seismicity of the region indicates that the fault system follows the length of the Gulf and enters the Pacific basin south of Baja California . Crustal structure of most of the Gulf is of oceanic type, so that an origin by structural depression of continental rocks is not possible. Tectonic styles north and south of Los Angeles differ greatly. To the north, the Coast Ranges expose thick Upper Cretaceous and Cenozoic sedimentary rocks that were deposited in local basins and deformed tightly and repeatedly. To the south, in the Peninsular Ranges and Baja California , correlative rocks are thin and show little compressive deformation. The California batholith of mid-Cretaceous age and allied crystalline rocks form the basement of Baja California , southwestern Arizona, and northwestern Sonora and probably extend along the coast of mainland Mexico; the Gulf apparently bisects the crystalline belt longitudinally. These features suggest that Baja California initially lay 300 miles to the southeast, against the continental-margin bulge of Jalisco. The Gulf of California may be a pull-apart feature caused by strike-slip displacement plus up to 100 miles of cross-strike separation of the continental plate, subcontinental materials having welled up into the rift gap. The strike-slip motion has a tensional component across the continental margin south of Los Angeles but a compressional component to the north.

Gulf of California↗
USGS1958

Geology of the north half of the Mt. Abbot quadrangle, Sierra Nevada, California

The north half of the 15-minute Mt. Abbot quadrangle lies across the crest of the Sierra Nevada. The Cretaceous granitic rocks that underlie most of the area form eight large discordant plutons that range from quartz diorite to alaskite; the largest pluton is coarse prophyritic quartz monzonite. Pre-batholithic metasedimentary and metavolcanic rocks and metagabbro and metadiorite are minor. The porphyritic quartz monzonite sent gently dipping dikes as much as 200 feet thick into its walls. These dikes in places make up more than half the height of exposed contact zones. A broad border zone of protoclastic flaser gneiss was formed in part of the pluton and in the adjacent wall rocks and dikes. A contact between granodiorite and calcareous metasedimentary rocks swarms with dark inclusions. Their origin, puzzling in most places, is here clearly due to progressive hybridization of calc-silicate xenoliths; the changes take place within a few tens of yards of the contact. The xenoliths were amphibolitized concentrically and reconstituted to typical dark-inclusion texture and mineralogy and were drawn out from blocky xenoliths into spindle shapes. Elsewhere, large irregular xenoliths of metadiorite were assimilated by alaskite. Within the resulting complex is a thick series of alaskite flow layers crowded with xenocrysts showing graded “bedding”. All the granitic plutons were intrusive; assimilation of mafic wall rocks by felsic magmas may have caused much of the diversity.

California↗