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Intrusive rocks of the Holden and Lucerne quadrangles, Washington— The relation of depth zones, composition, textures, and emplacement of plutons
The core of the northern Cascade Range in Washington consists of Precambrian and upper Paleozoic metamorphic rocks cut by numerous plutons, ranging in age from early Triassic to Miocene. The older plutons have been eroded to catazonal depths, whereas subvolcanic rocks are exposed in the youngest plutons. The Holden and Lucerne quadrangles span a -sizeable and representative part of this core. The oldest of the formations mapped in these quadrangles is the Swakane Biotite Gneiss, which was shown on the quadrangle maps as Cretaceous and older in age. The Swakane has yielded a middle Paleozoic metamorphic age, and also contains evidence of zircon inherited from some parent material more than 1,650 m.y. old. In this report, the Swakane is assigned an early Paleozoic or older age. It consists mostly of biotite gneiss, but interlayered with it are scattered layers and lenses of hornblende schist and gneiss, clinozoisite-epidote gneiss, and quartzite. Thickness of the Swakane is many thousands of meters, and the base is not exposed. The biotite gneiss is probably derived from a pile of siliceous volcanic rocks containing scattered sedimentary beds and basalt flows. Overlying the Swakane is a thick sequence of eugeosynclinal upper Paleozoic rocks metamorphosed to amphibolite grade. The sequence includes quartzite and thin layers of marble, hornblende schist and gneiss, graphitic schist, and smaller amounts of schist and gneiss of widely varying compositions. The layers have been tightly and complexly folded, and, in places, probably had been thrust over the overlying Swakane prior to metamorphism. Youngest of the supracrustal rocks in the area are shale, arkosic sandstone, and conglomerate of the Paleocene Swauk Formation. These rocks are preserved in the Chiwaukum graben, a major structural element of the region. Of uncertain age, but possibly as old as any of the intrusive rocks in the area, are small masses of ultramafic rocks, now almost completely altered to serpentine. These occur either as included irregular masses in later intrusives or as tectonically emplaced lenses in metamorphic rocks. Also of uncertain age but probably much younger, perhaps as young as Eocene, are larger masses of hornblendite and hornblende periodotite that grade into hornblende gabbro. These are exposed on the surface and in the underground workings of the Holden mine. Oldest of the granitoid intrusives are the narrow, nearly concordant Dumbell Mountain plutons, having a radiometric age of about 220 m.y. They consist of gneissic hornblende-quartz diorite and quartz diorite gneiss. Most contacts consist of lit-par-lit zones, but some are gradational or more rarely sharp. The plutons are typically catazonal. Closely resembling the Dumbell Mountain plutons in outcrop appearance, but differing considerably in composition, are the Bearcat Ridge plutons. These consist of gneissic quartz diorite and granodiorite. The Bearcat Ridge plutons are not in contact with older dated plutons, but because their textural and structural characteristics so closely resemble those of the Dumbell Mountain plutons, they are considered to be the same age. Their composition, however, is suggestive of a much younger age. Cutting the Dumbell Mountain plutons is the Leroy Creek pluton, consisting of gneissic biotite-quartz diorite and trondjhemite. The gneissic foliation in the Leroy Creek is characterized by a strong and pervasive swirling. Cutting both the Dumbell Mountain and Leroy Creek plutons are the almost dikelike Seven-fingered Jack plutons. These range in composition from gabbro to quartz diorite; associated with them are contact complexes of highly varied rocks characterized by gabbro and coarse-grained hornblendite. Most of the rocks are gneissic, but some are massive and structureless. Dikes, sills, small stocks, and irregular clots of leucocratic quartz diorite and granodiorite are abundant in the Swakane Biotite Gneiss and are locally abundant in the Seven-fingered Jack and other plutons. Although the leucocratic rocks vary little in appearance or composition, some, particularly those in the Swakane, were formed by metamorphic segregation, whereas the others are probably felsic differentiates of intrusive rocks. The Tenpeak and White Mountain plutons are closely similar and are probably connected at depth. Rocks of the Tenpeak are more varied and range in composition from gabbro to granodiorite; quartz diorite is not only most common in the Tenpeak, but also constitutes, by far, the greatest bulk of the White Mountain pluton. Much of the rock in both plutons is somewhat gneissic, but some is nongneissic. The north end of the White Mountain pluton is bordered by a contact complex similar to those associated with the Seven-fingered Jack and other plutons in the area. Maximum potassium/argon ages determined on hornblende from the Tenpeak are about 90 m.y. Probably somewhat younger than the Tenpeak and White Mountain plutons is the Sulphur Mountain pluton. Only a small part of the pluton extends into the Holden quadrangle, and here the rocks are gneissic granodiorite. The High Pass and Buck Creek plutons are tabular, somewhat silllike masses of granodioritic and quartz dioritic composition. Rocks in the Buck Creek pluton are entirely gneissic, whereas rocks only near the contacts or in the thinner parts of the High Pass are gneissic. In most places, the contacts of both plutons consist of lit-par-lit zones, but numerous dikes of the High Pass are present in the host rocks, especially the Sulphur Mountain pluton. The Riddle Peaks pluton consists of layered and unlayered hornblende gabbro. Inasmuch as the pluton is cut on all sides by later intrusive rocks, its age relative to older plutons is not known, but it is almost certainly pre-Tertiary. Much of the gabbro is rhythmically layered, but some is unlayered or only vaguely layered. In places, thick sheets of unlayered gabbro alternate with equally thick sheets of rhythmically layered gabbro. The rock is mostly fresh and unaltered or recrystallized. No pseudosedimentary structures other than the gravity-stratified rhythmic layers were seen. The Cardinal Peak pluton has a core consisting largely of granodiorite and quartz diorite and a rim of contact complexes containing large amounts of gabbro and coarse-grained hornblendite. The northern part of the intrusive is highly protoclastic throughout and contains numerous spindle- and canoe-shaped masses a third of a meter to several meters across and a few meters to several tens of meters long that are either partly or completely enveloped by rinds of fine-grained protoclastic material. These masses seem to have behaved as roller bearings during intrusion of the partly crystalline magma.
Tertiary volcanic rocks and uranium in the Thomas Range and northern Drum Mountains, Juab County, Utah
The Thomas Range and northern Drum Mountains have a history of volcanism, faulting, and mineralization that began about 42 m.y. (million years) ago. Volcanic activity and mineralization in the area can be divided into three stages according to the time-related occurrence of rock types, trace-element associations, and chemical composition of mineral deposits. Compositions of volcanic rocks changed abruptly from rhyodacite-quartz latite (42-39 m.y. ago) to rhyolite (38-32 m.y. ago) to alkali rhyolite (21 and 6-7 m.y. ago); these stages correspond to periods of chalcophile and siderophile metal mineralization, no mineralization(?), and lithophile metal mineralization, respectively. Angular unconformities record episodes of cauldron collapse and block faulting between the stages of volcanic activity and mineralization. The youngest angular unconformity formed between 21 and 7 m.y. ago during basin-and-range faulting. Early rhyodacite-quartz latite volcanism from composite volcanoes and fissures produced flows, breccias, and ash-flow tuff of the Drum Mountains Rhyodacite and Mt. Laird Tuff. Eruption of the Mt. Laird Tuff about 39 m.y. ago from an area north of Joy townsite was accompanied by collapse of the Thomas caldera. Part of the roof of the magma chamber did not collapse, or the magma was resurgent, as is indicated by porphyry dikes and plugs in the Drum Mountains. Chalcophile and siderophile metal mineralization, resulting in deposits of copper, gold, and manganese, accompanied early volcanism. Te middle stage of volcanic activity was characterized by explosive eruption of rhyolitic ash-flow tuffs and collapse of the Dugway Valley cauldron. Eruption of the Joy Tuff 38 m.y. ago was accompanied by subsidence of this cauldron and was followed by collapse and sliding of Paleozoic rocks from the west wall of the cauldron. Landslides in The Dell were covered by the Dell Tuff, erupted 32 m.y. ago from an unknown source to the east. An ash flow of the Needles Range(?) Formation was erupted 30-31 m.y. ago from an unknown source. Mineralization probably did not occur during the rhyolitic stage of volcanism. The last stage of volcanism was contemporaneous with basin-and-range faulting and was characterized by explosive eruption of ash and pumice, forming stratified tuff, and by quiet eruption of alkali rhyolite as viscous flows and domes. The first episode of alkali rhyolite volcanism deposited the beryllium tuff and porphyritic rhyolite members of the Spor Mountain Formation 21 m.y. ago. After a period of block faulting, the stratified tuff and alkali rhyolite of the Topaz Mountain Rhyolite were erupted 6-7 m.y. ago along faults and fault intersections. Erosion of Spor Mountain, as well as explosive eruptions through dolomite, provided abundant dolomite detritus to the beryllium tuff member. The alkali rhyolite of both formations is fluorine rich, as is evident from abundant topaz, and contains anomalous amounts of lithophile metals. Alkali rhyolite volcanism was accompanied by lithophile metal mineralization which deposited fluorite, beryllium, and uranium. The structure of the area is dominated by the Thomas caldera and the younger Dugway Valley cauldron, which is nested within the Thomas caldera; the Thomas caldera is surrounded by a rim of Paleozoic rocks at Spor Mountain and Paleozoic to Precambrian rocks in the Drum Mountains. The Joy fault and Dell fault system mark the ring-fracture zone of the Thomas caldera. These structural features began to form about 39 m.y. ago during eruption of the Mt. Laird Tuff and caldera subsidence. The Dugway Valley cauldron sank along a series of steplike normal faults southeast of Topaz Mountain in response to collapse of the magma chamber of the Joy Tuff. Caldera structure was modified by block faulting between 21 and 7 m.y. ago, the time of widespread extensional faulting in the Basin and Range Province. Vents erupted alkali rhyolite 6-7 m.y. ago along basin-and-range faults.
Upper Cretaceous subsurface stratigraphy and structure of coastal Georgia and South Carolina
Upper Cretaceous subsurface stratigraphy and structure of coastal Georgia and South Carolina is based on the study of 24 wells along two transects, one extending across the seaward-dipping sedimentary basin termed the 'Southeast Georgia Embayment' northeastward to the crest of the Cape Fear Arch, and the other alined east-west, parallel to the basin axis and including the COST GE-l well on the Outer Continental Shelf. A new biostratigraphic analysis, using calcareous nannofossils, of the Fripp Island, S.C., well and reinterpretations of the Clubhouse Crossroads corehole 1, South Carolina, and other wells in South Carolina, Georgia, and northernmost Florida have made possible the comparison and reevaluation of stratigraphic interpretations of the region made by G. S. Gohn and others in 1978 and 1980 and by P. M. Brown and others in 1979. The present study indicates that within the Upper Cretaceous section the stratigraphic units formerly assigned a Cenomanian (Eaglefordian and Woodbinian) age are Coniacian (Austinian) and Turonian (Eaglefordian) in age. A previously described hiatus encompassing Coniacian and Turonian time is not present. More likely, a hiatus is probably present in the upper Turonian, and major gaps in the record are present within the Cenomanian and between the Upper Cretaceous and the pre-Cretaceous basement. After an erosional episode in Cenomanian time that affected the section beneath eastern Georgia and South Carolina, Upper Cretaceous marine clastic and carbonate rocks were deposited on a regionally subsiding margin that extended to the present Blake Escarpment. In contrast, during Cenozoic time, especially in the Eocene, subsidence and sedimentation rates were uneven across the margin. A thick progradational sequence of carbonate rocks accumulated in the Southeast Georgia Embayment and also built the present Continental Shelf, whereas farther offshore a much thinner layer of sediments was deposited on the Blake Plateau. There is no general agreement on the exact placement of the Cenomanian-Turonian boundary in Europe or the United States Western Interior, and the widespread Sciponoceras gracile ammonite zone represents an interval of equivocal age between accepted Cenomanian and Turonian strata. The extinction of the foraminifer genus Rotalipora took place within the Sciporwceras gracile zone; it is used here to identify the Cenomanian-Turonian boundary. Pollen zone IV (Complexiopollis-Atlantopollis assemblage zone) is an important and widespread biostratigraphic unit characterized by a distinctive spore and pollen flora. It is consistently associated with lower Turonian calcareous nannofossils on the Atlantic continental margin; these nannofossil assemblages are also present in pollen zone IV, in strata that encompass the Sciponoceras gracile zone and the lower part of the Mytiloides labiatus zone in the Gulf Coastal Plain at Dallas, Tex.
Seismic intensities of earthquakes of conterminous United States– Their prediction and interpretation
No abstract available.
Cenozoic block uplifts in east-central Idaho and southwest Montana
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Petrologic and structural studies in the northwestern Sierra Nevada, California
No abstract available.
The oilspill risk analysis model of the U. S. Geological Survey
The U.S. Geological Survey has developed an oilspill risk analysis model to aid in estimating the environmental hazards of developing oil resources in Outer Continental Shelf (OCS) lease areas. The large, computerized model analyzes the probability of spill occurrence, as well as the likely paths or trajectories of spills in relation to the locations of recreational and biological resources which may be vulnerable. The analytical methodology can easily incorporate estimates of weathering rates , slick dispersion, and possible mitigating effects of cleanup. The probability of spill occurrence is estimated from information on the anticipated level of oil production and method of route of transport. Spill movement is modeled in Monte Carlo fashion with a sample of 500 spills per season, each transported by monthly surface current vectors and wind velocities sampled from 3-hour wind transition matrices. Transition matrices are based on historic wind records grouped in 41 wind velocity classes, and are constructed seasonally for up to six wind stations. Locations and monthly vulnerabilities of up to 31 categories of environmental resources are digitized within an 800,000 square kilometer study area. Model output includes tables of conditional impact probabilities (that is, the probability of hitting a target, given that a spill has occurred), as well as probability distributions for oilspills occurring and contacting environmental resources within preselected vulnerability time horizons. (USGS)
Tertiary marine pelecypods of California and Baja California; Nuculidae through Malleidae
No abstract available.
Tertiary marine pelecypods of California and Baja California; Propeamussiidae and Pectinidae
No abstract available.
Tertiary marine pelecypods of California and Baja California; Plicatulidae to Ostreidae
No abstract available.
Tertiary marine pelecypods of California and Baja California; Lucinidae through Chamidae
No abstract available.
Tertiary marine pelecypods of California and Baja California: Erycinidae through Carditidae
No abstract available.
A superpower system for the region between Boston and Washington
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Environmental geology of the Front Range urban corridor and vicinity, Colorado, with a section on physical properties and performance characteristics of surficial deposits and rock units in the Greater Denver area
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The central Virginia volcanic-plutonic belt: An island arc of Cambrian(?) age
Pre-Ordovician, probable Early Cambrian metavolcanic and somewhat younger meta-intrusive rocks form a linear belt in the central Virginia Piedmont. On the basis of the geologic and geochemical features of these rocks in the Fredericksburg area, and insofar as this area is representative of the entire belt, it is concluded that this belt constitutes an ancient island-arc sequence. The westernmost Chopawamsic Formation consists of a tholeiitic island-arc suite and associated calcalkaline metavolcanic rocks. Prior to Upper Ordovician time, low-potassic tonalitic plutons of plagiogranitic (pretectonic) and trondhjemitic (late-tectonic) affinities were intruded into the Chopawamsic terrane. The tholeiitic amphibolites of the Ta River Metamorphic Suite are considered to be an eastern, oceanward facies of the Chopawamsic Formation. The James Run Formation of Maryland is probably a northern lateral equivalent of the central Virginia volcanic-plutonic belt. It may have formed as part of the ancient Virginia belt or along a penecontemporaneous but independent volcanic arc. The metavolcanic rocks and associated plutons of the Carolina slate belt in the southeast Piedmont are considered to have formed independently of the central Virginia volcanic-plutonic belt and perhaps in a different tectonic environment.
Middle and upper Paleozoic granitic rocks in the Piedmont near Fredericksburg, Virginia; geochronology
No abstract available.