USGS Science⌕ Search

SEARCH · USGS Science

Results for “Evolution”

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

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 775 records · Page 43Linked to original sources
USGS1986

Tectonic evolution of Northwest California and Southwest Oregon

Tectonostratigraphic terrances in northwest California and southwest Oregon record a complex history of subduction, collision, and transform faulting. During the late Jurassic Nevadan orogeny, the Elder Creek-Snow Camp and western Klamath terranes were imbricated during collision of an island-arc system with the continental margin. Subsequent collisions are recorded in the Pickett Peak (Early Cretaceous) and Yolla Bolly (middle Cretaceous) terranes.

California, Oregon↗
USGS2016

Geochemistry, petrologic evolution, and ore deposits of the Miocene Bodie Hills Volcanic Field, California and Nevada

The southern segment of the ancestral Cascades magmatic arc includes numerous volcanic fields; among these, the Bodie Hills volcanic field (BHVF), astride the California-Nevada border north of Mono Lake, is one of the largest (>700 km2) and most well studied. Episodic magmatism in the BHVF spanned about 9 million years between about 15 and 6 Ma; magmatic output was greatest between ca. 15.0 to 12.6 Ma and ca. 9.9 to 8.0 Ma. About two dozen contiguous and coalescing eruptive centers above middle- to shallow-crustal-level reservoirs generated several trachyandesite stratovolcanoes and numerous silicic trachyandesite to rhyolite flow dome complexes whose compositional variations are consistent with fractionation of observed phenocryst phases. BHVF rocks have high-potassium calc-alkaline compositions consistent with generation of subduction-related continental margin arc magmas beneath thick continental crust. Radiogenic isotope ratios in BHVF rocks vary considerably but suggest somewhat enriched, crustal sources; isotopic ratios for some of the more primitive units are consistent with more depleted, mantle sources. Neither age nor whole-rock compositions of BHVF rocks are well correlated with isotopic variations. Textures and compositions of phenocrysts in BHVF rocks are in accord with the associated magma reservoirs evolving via open-system behavior. Reservoir recharge and subsequent incomplete homogenization are evidenced by the broad compositional diversity characteristic of many BHVF eruptive units. Significant compositional diversity among the products of coeval eruptive centers further suggests that centers responsible for BHVF magmatism were underlain by small, discrete, compositionally distinct, and closely spaced reservoirs. Volcanic rocks of the BHVF host quartz-adularia and quartz-alunite epithermal gold-silver deposits, from which about 3.4 Moz. of gold and 28 Moz. of silver have been produced. The volcanic rocks and contained deposits are broadly coeval, which suggests that the associated magmas are the sources of heat, fluids, and metals involved in deposit genesis. Characteristics of the quartz-adularia deposits are consistent with derivation from near-neutral pH fluids at ≤250 °C, whereas those of the quartz-alunite systems require more acidic, oxidized, and sulfur-rich fluids at temperatures <250 °C. Economically viable precious metal accumulations are in fault-hosted vein deposits in the Bodie and Aurora districts. Circulation of hydrothermal fluids through permeable pyroclastic deposits but lacking prominent structural conduits resulted in large areas of altered but unmineralized rock.

California, Nevada↗
USGS1994

Ontogeny and evolution of salinity tolerance in anadromous salmonids: Hormones and heterochrony

Use of estuaries and oceans by salmonids varies greatly, from no use in nonanadromous species, to movement toward the sea soon after hatching and emergence in some Pacific salmon. This variation is accompanied by large differences in the ontogeny of salinity tolerance among salmonids. Some species acquire increased salinity tolerance early in development, whereas others develop this characteristic much later, indicating there is a heterochrony (change in timing) in the development of salinity tolerance in salmonids. The basic physiological mechanisms for ion regulation in seawater (such as increased gill chloride cells, gill Na + ,K + -ATPase activity, membrane permeability, and drinking rate) are common to all salmonids. What determines the differences in salinity tolerance among the salmonids is not the basic mechanisms for salt secretion but the environmental and ontogenetic control of these mechanisms. In salmonids such as pink and chum salmon that enter seawater soon after emergence, acclimation to seawater may be controlled largely by internal (ontogenetic) information. In smolting salmonids that acquire increased salinity tolerance 1–2 yr after hatching, photoperiod is the dominant environmental cue. In nonsmolting species that migrate 2–3 yr after hatching, salinity itself may be the primary stimulus for salt secretory mechanisms. Physiological changes triggered by developmental and environmental cues are mediated by endocrine factors. Treatments with cortisol, growth hormone, and insulin-like growth factor I have been shown to increase seawater tolerance of salmonids, whereas prolactin is inhibitory. Differences in developmental patterns of endocrine activity (such as secretion, binding proteins, and receptors) are hypothesized to be responsible for the differences in timing (heterochrony) of increased salinity tolerance among and within salmonid species.

Estuaries↗
USGS1986

Demography, environmental uncertainty, and the evolution of mate desertion in the snail kite

The Snail Kite (Rostrhamus sociabilis), an endangered hawk, has a unique mating system in Florida (Beissinger and Snyder 1987): when food is abundant, males or females desert their mates at nearly equal frequency (ambisexual mate desertion) in the midst of a nesting cycle. I examined the demographic and environmental constraints selecting for a clutch size that permits one parent to desert, yet optimizes the number of offspring produced by each parent. Demographic studies, conducted from 1979—1983, indicated that kites have (1) a very high nest failure rate (° = 68%) due most often to unstable nest sites and predation, (2) a variable nesting season (5—10 mo/yr), (3) an early age of first reproduction for a bird this size (10 mo), (4) a high degree of iteroparity (double and potentially triple clutching within a season), and (5) unstable populations. Both nesting success and population size were directly related to Everglades water levels and resultant snail densities. Kites responded to large annual changes in food abundance, not by adjusting clutch size but by deserting their mates and presumably attempting to renest. Kite demographic traits appear to be adaptations to or results of an uncertain environment. Based on 67 yr of Everglades water levels, environmental predictability, measured by spectral analysis and Colwell's (1974) index, was low and influenced by water management regimes: (1) water levels were lowered, (2) annual variation in levels increased and annual cycles became stronger, (3) the period length of long—term drought—flood cycles shifted from 10 or more yr toward 5 yr, and (4) levels became a less predictive cue for favorable nesting conditions. A potential evolutionary pathway from biparental care to mate desertion in Snail Kites is proposed. It is unlikely that mate desertion evolved solely from a context of conflict between the sexes, because kite nesting success is so low that it is probably maladaptive for a parent to desert and jeopardize the survival of any of its first brood. Instead, mate desertion behavior probably evolved in response to a smaller average clutch size; this would allow females to be highly iteroparous and avoid the costs of overinvestment, and should be strongly favored in a highly uncertain environment. Analysis of clutches in museum collections suggests that an apparent decline in clutch size may have occurred in Florida during the past century. The potential for ambisexual mate desertion to occur in other vertebrates is during the past century. The potential for ambisexual mate desertion to occur in other vertebrates is examined.

Ecology↗
USGS2016

Reevaluating the age of the Walden Creek Group and the kinematic evolution of the western Blue Ridge, southern Appalachians

An integrated synthesis of existing datasets (detailed geologic mapping, geochronologic, paleontologic, geophysical) with new paleontologic and geochemical investigations of rocks previously interpreted as part of the Neoproterozoic Walden Creek Group in southeastern Tennessee suggest a necessary reevaluation of the kinematics and structural architecture of the Blue Ridge Foothills. The western Blue Ridge of Tennessee, North Carolina, and Georgia is composed of numerous northwest-directed early and late Paleozoic thrust sheets, which record pronounced variation in stratigraphic/structural architecture and timing of metamorphism. The detailed spatial, temporal, and kinematic relationships of these rocks have remained controversial. Two fault blocks that are structurally isolated between the Great Smoky and Miller Cove-Greenbrier thrust sheets, here designated the Maggies Mill and Citico thrust sheets, contain Late Ordovician-Devonian conodonts and stable isotope chemostratigraphic signatures consistent with a mid-Paleozoic age. Geochemical and paleontological analyses of Walden Creek Group rocks northwest and southeast of these two thrust sheets, however, are more consistent with a Late Neoproterozoic (550&ndash;545 Ma) depositional age. Consequently, the structural juxtaposition of mid-Paleozoic rocks within a demonstrably Neoproterozoic-Cambrian succession between the Great Smoky and Miller Cove-Greenbrier thrust sheets suggests that a simple foreland-propagating thrust sequence model is not applicable in the Blue Ridge Foothills. We propose that these younger rocks were deposited landward of the Ocoee Supergroup, and were subsequently plucked from the Great Smoky fault footwall as a horse, and breached through the Great Smoky thrust sheet during Alleghanian emplacement of that structure.

North Carolina, Tennessee↗
USGS2006

Cenozoic tectonic evolution of the basin and range province in northwestern Nevada

A regional synthesis of new and existing geologic and thermochronologic data document late Cretaceous - early Cenozoic regional erosion, Oligocene - Miocene volcanism, and subsequent late Miocene extension of the Basin and Range Province in northwestern Nevada and northeastern California. Across an ???220-km-wide region between the Santa Rosa and Warner Ranges, conformable sequences of 35 to 15 Ma volcanic rocks are cut by only a single generation of high-angle normal faults that accommodated ???23 km of total east-west extension (???12%). Fission-track, (U-Th)/He, geologic, and structural data from the Pine Forest Range show that faulting there began at 11 to 12 Ma, progressed at a relatively constant rate until at least 3 Ma, and has continued until near the present time. Extension in the Santa Rosa Range to the east took place during the same interval, although the post-6 Ma part of this history is less well constrained. Less complete constraints from adjacent ranges permit a similar timing for faulting, and we infer that extensional faulting in northwestern Nevada began everywhere at 12 Ma and has continued up to the present. Faulting in the Warner Range in northeastern California can only be constrained to have begun between 14 and 3 Ma, but may represent westward migration of Basin and Range extension during the Pliocene. Compared to the many parts of the Basin and Range in central and southern Nevada, extension in northwestern Nevada began more recently, is of lesser total magnitude, and was accommodated entirely by high-angle normal faults. Fission-track data document Late Cretaceous unroofing of Cretaceous (115 - 100 Ma) granitic basement rocks in northwestern Nevada, followed by a long period of relative tectonic quiescence that persisted through Oligocene and Miocene volcanism until the onset of Basin and Range extension at ???12 Ma. The low magnitude of extension (12%) and early Tertiary stability suggest that the modern ???31 km thick crust in northwestern Nevada was only slightly thicker (???35 km) prior to extension at 12 Ma, and was no thicker than ???38 km in the Late Cretaceous. This stands in contrast to other parts of the Basin and Range, where the crust was thickened to at least 45 to 50 km by Cretaceous thrusting and subsequently thinned to ???30 km by large magnitude (>50%) extension.

American Journal of Science↗
USGS1986

The Center Pond pluton: The restite of the story (phase separation and melt evolution in granitoid genesis)

The Center Pond pluton is a calc-alkaline post-tectonic Acadian body intruding chlorite grade Silurian metasediments of E-central Maine. Mapping and petrographic work reveal that the pluton contains 5 igneous rock types; quartz diorite, hornblende-biotite granodiorite, biotite granite, porphyritic granite, and aplitic granite. The linearity of major and trace element trends and Rb-Sr isotope systematics indicate that partial melting and unmixing of a single mafic or intermediate metaigneous rock to restite (residual phases in equilibrium with the melting event at depth) and near-eutectic minimum melt may account for much of the observed geochemical variation within the Center Pond pluton. Major and trace element trends rule out fractional crystallization as a model for Center Pond. -from Authors

Maine↗
USGS2004

U-Pb zircon constraints on the tectonic evolution of southeastern Tibet, Namche Barwa area

The eastern syntaxis of the Himalayas is expressed in the crust as a pronounced southward bend in the orogen. The change in strike of geologic features coincides with the high topography of the Namche Barwa region, the exposure of granulite-grade metamorphic rocks, and a 180-degree bend in the Yalu Tsangpo. We have conducted a geochronologic and geochemical investigation of several suites of granitoids collected from the Namche Barwa massif and subjacent terranes of southeastern Tibet, ranging from cm-scale dikes and sills to larger, outcrop-scale intrusions. U-Pb SHRIMP-RG zircon ages establish at least five magmatic episodes: ∼400 to 500 Ma, ∼120 Ma, 40 to 70 Ma, 18 to 25 Ma, and 3 to 10 Ma . These episodes broadly correlate to spatial patterns in sample localities, as follows: 400 to 500 Ma ages occur in zircon cores collected from within the massif proper; ∼120 Ma granites, related to early Gangdese arc plutonism, are primarily located northeast of Namche Barwa; later (40-70 Ma) Gangdese activity is expressed in granites west of Namche Barwa. 18 to 25 Ma granites occur both along the suture zone west of Gyala Peri, and directly north of Namche Barwa along the area of the Jiali fault zone, and are attributed both to shearing within the Jiali fault zone and to an early Miocene Gangdese Thrust event. Exceptionally young (<10 Ma) zircon ages are clustered near the core of the massif, along the Yalu Tsangpo gorge. Trace-element geochemical data indicates the presence of both fluid-present and fluid absent melts, with a fluid-absent (decompression) melting regime dominating near the core of Namche Barwa.

Tibet↗