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Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

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At least 649 records · Page 36Linked to original sources
USGS1974

Tectonic significance of the Kodiak-Bowie seamount chain, northeastern Pacific

The hypothesis of a fixed melting spot reference frame (M) for relative plate motion is tested in the northeastern Pacific Ocean, where the Kodiak-Bowie seamount chain intersects the northern triple junction between the Pacific, American, and Juan de Fuca plates. Available age determinations on Kodiak and Giacomini Seamounts provide an estimated average rate of volcanic propagation along the chain of 6.5 cm per yr and allow estimates of plate movements relative to the melting spot. The inferred motion of the American plate relative to M is close to that observed along the Yellowstone-Snake River Plain volcanic trend and broadly supports the concept of a fixed melting spot reference frame. However, the convex northward curvature of the Kodiak-Bowie chain and of several chains to the south does not support the hypothesis. The lack of parallelism between these seamounts and the Hawaiian chain suggests slow relative movement between the Kodiak-Bowie and Hawaiian melting spots.

Geology↗
USGS1971

Palynology, age, and correlation of the Wanship Formation and their implications for the tectonic history of northeastern Utah

Although never formally introduced, the stratigraphic name Wanship Formation has become entrenched in the literature; recently, misunderstanding of its age and correlation has led to invalid interpretations of the structural evolution of northeastern Utah . The basal Wanship conglomerate has been erroneously correlated with a conglomerate within the Frontier Formation at Coalville. The Coalville section has been dated as Cenomanian-Coniacian. The Wanship Formation at its "type locality" is Campanian-Maestrichtian in age , as determined by its palynomorph content, and is not correlative with the Coalville section. The Wanship is correlative with the lower Evanston Formation . Recognition of these relationships obviates the need for a hypothesized episode of folding and faulting during middle Cretaceous time in northeastern Utah .

Utah↗
USGS1980

Late Wisconsin and Holocene tectonic stability of the United States mid-Atlantic coastal region

Deposits that formed in the intertidal zone during sea-level rise 12,000 to 9,000 yr ago have undergone very little differential vertical deformation in the area between New York City and South Carolina. The lack of north-south vertical deformation contrasts with tide-gauge and with precise leveling measurements that have been used to indicate that considerable differential vertical movement is occurring along the coast. Probably, present rates of deformation cannot be extrapolated to early Holocene. Depths of dated in-place intertidal deposits and estimates that suggest the U.S. mid-Atlantic shelf was downwarped during Holocene glacio-isostatic adjustment are used to indicate that eustatic sea levels were not substantially below 30 m depth about 12,000 yr B.P.

Geology↗
USGS1987

Cretaceous age of the upper part of the McCoy Mountains Formation, southeastern California and southwestern Arizona, and its tectonic significance: reconciliation of paleobotanical and paleomagnetic evidence.

The upper part of the 7-km-thick McCoy Mountains Formation in southeastern California contains fossil angiosperm wood that closely resembles the genus Paraphyllanthoxylon , which is known only from strata of late Early Cretaceous and younger age. This wood, in conjunction with geologic field relations, supports previous interpretations that the upper part of the McCoy Mountains Formation is of late Early Cretaceous and/or Late Cretaceous age, in contrast to a more recent interpretation that the entire formation is of Jurassic age. Alternatives are therefore needed to the recent hypothesis that deposition, deformation, and metamorphism of the McCoy Mountains Formation were related to movement on the Jurassic Mojave-Sonora megashear.

Geology↗
USGS1992

Depositional and tectonic framework of the rift basins of Lake Baikal from multichannel seismic data

Recent multichannel seismic reflection data from Lake Baikal, located in a large, active, continental rift in central Asia, image three major stratigraphic units totalling 3.5 to 7.5 km thick in four subbasins. A major change in rift deposition and faulting between the oldest and middle-rift units probably corresponds to the change from slow to fast rifting. A brief comparison of the basins of Lake Baikal with those of the East African rift system highlights differences in structural style that can be explained by differences in age and evolution of the surrounding basement rocks. -from Authors

Lake Baikal↗
USGS1996

Tectonic model explaining divergent contraction directions along the Cascadia subduction margin, Washington

Differential motion across the central Cascadia subduction boundary in Washington results in a complex pattern of folds and faults within the shelf and onshore parts of the accretionary margin. Faults and folds above a coastal, north-northwest–trending thrust system provide evidence of ongoing subduction-related contraction. South of this coastal thrust system many fold axes and thrust faults trend east-northeast, in the direction of convergence. These structures are not consistent with a simple subduction system undergoing northeastward convergence. This deformation, adjacent to the boundary between the subduction complex and the Siletz terrane, may be driven by relative convergence between the northward-translating Siletz terrane and the subduction complex. The regional pattern of modern uplift rates is consistent with ongoing north-south contraction across this boundary and the north-south compressional stress field in the area.

Geology↗
USGS2001

Huge, CO2-charged debris-flow deposits and tectonic sagging in the northern plains of Mars

The northern plains of Mars contain a vast deposit, covering one-sixth of the planet, that apparently resulted in extensive lithospheric deformation. The center of the deposit may be as much as 2–3 km thick. The deposit has lobate margins consistent with the flow of fluidized debris for hundreds to thousands of kilometers derived from highland and high-plains sources. The deposit surface lowers inward by ∼900 m in places and is locally bordered by a bulge ∼300 m high. Similar deformation accompanied development of Pleistocene ice sheets on Earth. The lack of burial of a large inlier of older terrain and the response time of the mantle to the loading require that the deposit was emplaced in <1000 yr, assuming that the deposit was originally flat. We account for what may have been the largest catastrophic erosional and/or depositional event in solar system history by invoking pore-filling subsurface CO 2 as an active agent in the processes of source-rock collapse and debris flow.

Geology↗
USGS2007

Precambrian accretionary history and phanerozoic structures-A unified explanation for the tectonic architecture of the nebraska region, USA

The Phanerozoic history in Nebraska and adjacent regions contains many patterns of structure and stratigraphy that can be directly related to the history of the Precambrian basement rocks of the area. A process is proposed that explains the southward growth of North America during the period 1.8-1.6 Ga. A series of families of accretionary events during the Proterozoic emplaced sutures that remained as fundamental basement weak zones. These zones were rejuvenated in response to a variety of continental stress events that occurred during the Phanerozoic. By combining the knowledge of basement history with the history of rejuvenation during the Phanerozoic, both the details of Proterozoic accretionary growth and an explanation for the patterns of Phanerozoic structure and stratigraphy is provided. ?? 2007 The Geological Society of America. All rights reserved.

Conference Paper↗
USGS2007

The Pennsylvanian-early permian bird spring carbonate shelf, Southeastern California: Fusulinid biostratigraphy, paleogeographic evolution, and tectonic implications

The Bird Spring Shelf in southeastern California, along with coeval turbidite basins to the west, records a complex history of late Paleozoic sedimentation, sea-level changes, and deformation along the western North American continental margin. We herein establish detailed correlations between deposits of the shelf and the flanking basins, which we then use to reconstruct the depositional history, paleogeography, and deformational history, including Early Permian emplacement of the regionally significant Last Chance allochthon. These correlations are based on fusulinid faunas, which are numerous both on the shelf and in the adjoining basins.

Special Paper of the Geological Society of America↗
USGS2008

Magmatism and tectonics in a tilted crustal section through a continental arc, eastern Transverse Ranges and southern Mojave Desert

This field guide describes a two-and-one-half day transect, from east to west across southern California, from the Colorado River to the San Andreas fault. Recent geochronologic results for rocks along the transect indicate the spatial and temporal relationships between subarc and retroarc shortening and Cordilleran arc magmatism. The transect begins in the Jurassic(?) and Cretaceous Maria retroarc fold-and-thrust belt, and continues westward and structurally downward into the Triassic to Cretaceous magmatic arc. At the deepest structural levels exposed in the southwestern part of the transect, the lower crust of the Mesozoic arc has been replaced during underthrusting by the Maastrichtian and/or Paleocene Orocopia schist.

Arizona, California↗
USGS2010

Ordovician volcanic-arc terrane in the Central Appalachian Piedmont of Maryland and Virginia: SHRIMP U-Pb geochronology, field relations, and tectonic significance

U-Pb zircon geochronology and field relations provide insights into metavolcanic and associated rocks in the Central Appalachian Piedmont of Maryland and northern Virginia. Ordovician ages were determined for volcanic-arc rocks of the James Run Formation (Churchville Gneiss Member, 458 ± 4 Ma; Carroll Gneiss Member, 462 ± 4 Ma), Relay Felsite (458 ± 4 Ma), Chopawamsic Formation (453 ± 4 Ma), and a Quantico Formation volcaniclastic layer (448 ± 4 Ma). A previously dated first phase of volcanism in the Chopawamsic Formation was followed by the second phase dated here. The latter suggests a possible source for contemporaneous volcanic-ash beds throughout eastern North America. Dates from the Chopawamsic and Quantico Formations constrain the transition from arc volcanism to successor-basin sedimentation. Ordovician metatonalites of the Franklinville (462 ± 5 Ma) and Perry Hall (461 ± 5 Ma) plutons are contemporaneous with the James Run Formation, whereas granitoids of the Bynum Run (434 ± 4 Ma) and Prince William Forest (434 ± 8 Ma) plutons indicate an Early Silurian plutonic event. The Popes Head Formation yielded Mesoproterozoic (1.0–1.25 Ga, 1.5–1.8 Ga) detrital zircons, and metamorphosed sedimentary mélange of the Sykesville Formation yielded Mesoproterozoic (1.0–1.8 Ga) detrital zircons plus a minor Archean (2.6 Ga) component. A few euhedral zircons (ca. 479 Ma) in the Sykesville Formation may be from granitic seams related to the Dalecarlia Intrusive Suite. A Potomac orogeny in the Central Appalachian Piedmont is not required, but the earliest Taconic orogenesis remains poorly constrained.

Maryland, Virginia↗
USGS2010

A chronicle of Miocene extension near the Colorado Plateau-Basin and Range boundary, southern White Hills, northwestern Arizona: Paleogeographic and tectonic implications

In northwestern Arizona, the high-standing, relatively unextended Colorado Plateau abruptly gives way across a system of major west-dipping normal faults to a highly extended part of the Basin and Range province known as the northern Colorado River extensional corridor. The transition from unextended to highly extended upper crust is unusually sharp within this region, contrasting with a broad transition zone elsewhere. The southern White Hills lie near the eastern margin of the extensional corridor in northwestern Arizona and contain a large east-tilted half graben that chronicles Miocene extension and constrains the timing of structural demarcation between the Colorado Plateau and Basin and Range province during Neogene time. This growth-fault basin is bounded on the east by the west-dipping Cyclopic and Cerbat Mountains fault zones. Greater tilts in the hanging walls suggest that these faults have listric geometries. The stratigraphy in the half graben consists of Miocene vol canic rocks intercalated with an eastward-thickening wedge of synextensional fanglomerates. Tilts in the Miocene units decrease up section from ~75° to 5°. Recent 40 Ar/ 39 Ar dating (11 new dates) of variably tilted volcanic rocks in the growth-fault basin and regional relations constrain the timing of east-west extension between ca. 16.6 and <9 Ma, with peak extension from ca. 16.6 to 15.2 Ma. Capping 8.7 Ma basalts are tilted 5°–10° and record the waning stages of extension. Thus, the sharp boundary between the Colorado Plateau and Basin and Range began developing by ca. 16.5 Ma and has changed little since ca. 9 Ma. Major extension and basin development significantly lowered base level within the extensional corridor and induced headward erosion into the western margin of the Colorado Plateau, which ultimately facilitated development of the western Grand Canyon. Abundant clasts of 1.7 Ga megacrystic granite in the eastward-thickening fanglomerates within the growth-fault basin suggest a partial provenance from the Garnet Mountain area along or near the western margin of the Colorado Plateau beginning as early as ca. 16 Ma and continuing to ca. 9 Ma.

Arizona↗
USGS2012

Igneous activity, metamorphism, and deformation in the Mount Rogers area of SW Virginia and NW North Carolina: A geologic record of Precambrian tectonic evolution of the southern Blue Ridge Province

Mesoproterozoic basement in the vicinity of Mount Rogers is characterized by considerable lithologic variability, including major map units composed of gneiss, amphibolite, migmatite, meta-quartz monzodiorite and various types of granitoid. SHRIMP U-Pb geochronology and field mapping indicate that basement units define four types of occurrences, including (1) xenoliths of ca. 1.33 to ≥1.18 Ga age, (2) an early magmatic suite including meta-granitoids of ca. 1185–1140 Ma age that enclose or locally intrude the xenoliths, (3) metasedimentary rocks represented by layered granofels and biotite schist whose protoliths were likely deposited on the older meta-granitoids, and (4) a late magmatic suite composed of younger, ca. 1075–1030 Ma intrusive rocks of variable chemical composition that intruded the older rocks. The magmatic protolith of granofels constituting part of a layered, map-scale xenolith crystallized at ca. 1327 Ma, indicating that the lithology represents the oldest, intact crust presently recognized in the southern Appalachians. SHRIMP U-Pb data indicate that periods of regional Mesoproterozoic metamorphism occurred at 1170–1140 and 1070–1020 Ma. The near synchroneity in timing of regional metamorphism and magmatism suggests that magmas were emplaced into crust that was likely at near-solidus temperatures and that melts might have contributed to the regional heat budget. Much of the area is cut by numerous, generally east- to northeast-striking Paleozoic fault zones characterized by variable degrees of ductile deformation and recrystallization. These high-strain fault zones dismember the terrane, resulting in juxtaposition of units and transformation of basement lithologies to quartz- and mica-rich tectonites with protomylonitic and mylonitic textures. Mineral assemblages developed within such zones indicate that deformation and recrystallization likely occurred at greenschist-facies conditions at ca. 340 Ma.

North Carolina, Virginia↗
USGS2014

Geophysical framework of the Peninsular Ranges batholith—Implications for tectonic evolution and neotectonics

The crustal structure of the Peninsular Ranges batholith can be divided geophysically into two parts: (1) a western mafic part that is dense, magnetic, and characterized by relatively high seismic velocities (>6.25 km/s), low heat flow (<60 mW/m 2 ), and relatively sparse seismicity, and (2) an eastern, more felsic part that is less dense, weakly magnetic, and characterized by lower seismic velocities (<6.25 km/s), high heat flow (>60 mW/m 2 ), and abundant microseismicity. Potential-field modeling indicates that the dense, mafic part of the batholith extends to depths of at least 20 km and likely to the Moho. The magnetic anomalies of the western part of the batholith extend south beyond the spatially extensive exposures of the batholith to the tip of the Baja California peninsula, which suggests that the mafic part of the batholith projects beneath Cenozoic volcanic cover another 400 km. The linearity and undisrupted nature of the magnetic belt of anomalies suggest that the western part of the batholith has behaved as a rigid block since emplacement of the batholith. The batholith may have influenced not only the development of the Gulf of California oblique rift, but also strike-slip faulting along its northern margin, and transtensional faulting along its western margin, likely because it is thermally and mechanically more resistant to deformation than the surrounding crust.

California↗
USGS2014

U-Pb zircon geochronology of plutonism in the northern Peninsular Ranges batholith, southern California: Implications for the Late Cretaceous tectonic evolution of southern California

Utilizing both sensitive high-resolution ion microprobe (SHRIMP) and conventional isotope dilution–thermal ionization mass spectrometry (ID-TIMS) methods, crystallization and/or emplacement ages have been obtained for a suite of Cretaceous intermediate-composition plutonic samples collected along a roughly E-W–trending traverse through the northern Peninsular Ranges batholith. Previously noted petrologic, mineralogic, and textural differences delineated four major zonations from west to east and raised the need for detailed geochemical and isotopic work. U-Pb zircon geochronology establishes that these zonations are essentially temporally separate. Mean 206 Pb/ 238 U ages date the three older zones from west to east at 126–107 Ma, 107–98 Ma, and 98–91 Ma. Despite petrologic differences, a relatively smooth progression of magmatism is seen from west to east. A fourth zone is defined by magmatism at ca. 85 Ma, which represents emplacement of deeper-level plutons east of the Eastern Peninsular Ranges mylonite zone in an allochthonous thrust sheet in the northeastern Peninsular Ranges batholith. The age data presented here differ slightly from those presented in earlier work for similar rocks exposed across the middle and southern portions of the Peninsular Ranges batholith in that our data define a relatively smooth progression of magmatism from west to east, and that the transition from western-type to eastern-type plutonism is interpreted to have occurred at ca. 98 Ma and not at ca. 105 Ma. The progressive involvement of older crustal components in the enrichment of eastern Peninsular Ranges batholith–type magma sources is documented by the occurrence of Proterozoic zircon inheritance within samples of the eastern part of the batholith.

Book chapter↗