York Mountains Research Articles

Low-temperature thermochronologic constraints on the kinematic history and spatial extent of the Eastern California shear zone

The Stateline fault system is a 200-km-long zone of active right-lateral shear along the California-Nevada border, United States. Recent identification of 30 ± 4 km of dextral offset since 13.1 Ma on the southern segment of the fault requires significant displacement to extend farther south than has been commonly considered in the past. However, major structures exposed where the fault projects to the south reveal predominantly dip-slip extensional faulting, suggesting that displacement is transferred into substantial northwest-oriented extension in eastern Ivanpah Valley. New (U-Th)/He apatite data from Proterozoic orthogneiss in the southern McCullough Range and northern New York Mountains support this model by recording dates as young as 5 ± 1 Ma in the structurally deepest parts of the footwalls to the range-bounding normal faults. This age is distinctly younger than both the ages of regional extension in surrounding areas and the youngest (U-Th)/He apatite dates reported from the immediately adjacent Colorado River extensional corridor. Late Miocene–Pliocene extension in Ivanpah Valley, contemporaneous with that elsewhere in the Eastern California shear zone, provides an independent line of support that the eastern margin of the Eastern California shear zone extends to the California-Nevada border. If this age marks the onset of deformation on the State-line system, then long-term slip rates on the southern segment may be as high as 5 mm/yr, significantly higher than the present-day estimate of 0.9 mm/yr derived from geodetic observations across the northern segment of this fault system.

Dike swarms on Seward Peninsula, Alaska, and their implications for the kinematics of Cretaceous extension in the Bering Strait region

Late Cretaceous dike swarms on Seward Peninsula, northwestern Alaska, represent the youngest local manifestation of a ~115–75 Ma magmatic event in the Bering Strait region. Magmatism accompanied and followed high-grade metamorphism and ductile deformation. A Late Cretaceous extensional tectonic setting for the region is suggested by the thickness and seismic-reflection characteristics of the crust, regional basin development, formation of high-strain tectonites with subhorizontal foliations, bimodal magmatism, and dike swarms. The orientation of the dike swarms is used to address the kinematics of extension. A diabase dike swarm in the Kigluaik Mountains consists of dikes that strike northeast (040°) and dip steeply. Phenocrysts include plagioclase, clinopyroxene, orthopyroxene, and hornblende. Geochemical data indicate that SiO2 ranges from 48% to 56%, and K2O from 1.2% to 4.0%. The dikes are geochemically similar to the mafic to intermediate root of the 90 Ma Kigluaik pluton. Sr- and Nd-isotope data show that initial 87Sr/86Sr ranges from 0.7070 to 0.7077 and initial εNd ranges from –0.85 to –2.90. Field relations and 40Ar/39Ar geochronology bracket the dike ages between 90 and 84 Ma. Diabase dikes in the York Mountains are associated with normal faults that strike east–west to east-northeast. Dikes in the Bendeleben Mountains are both mafic and felsic, but their orientations are unknown. Alkalic dikes in the Darby Mountains strike 030°–050°, similar to those in the Kigluaik Mountains. Regional relationships including the orientation of dikes, normal faults, mineral stretching lineations, and other shear-sense indicators suggest that between 110 and 90 Ma extension on Seward Peninsula was generally oriented north–south to north-northwest–south-southeast.

A new Late Ordovician microdomatid gastropod genus from Seville, south west Spain, with a revision of Ordovician Microdomatoidea

A new microdomatid gastropod, Eopagodea sevillana gen. and sp. nov., is described from the Late Ordovician (pre-Hirnantian Ashgill) limestones of Seville, Ossa Morena Zone, Spain. Palaeozoic microdomatids lived in shallow-water environments and were restricted to warm-water regions. Occurrence of microdomatid gastropods in the pre-Hirnantian Ashgill limestones of the Cerrón del Hornillo syncline (Ossa Morena Zone, Spain) is interpreted as an example of an influx of warm-water faunal elements into the otherwise cool to cold climate of the Mediterranean region during a short-termed, pre-Hirnantian increase of palaeotemperatures. The Late Ordovician microdomatid genus Daidia Wilson, 1951, is revised and two new Late Ordovician (Ashgill) subspecies of Daidia cerithioides (Salter, 1859) are described: Daidia cerithioides sewardensis n. subsp. from the Don River area of the York Mountains, Seward Peninsula, western Alaska, and Daidia cerithioides wilsonae n. subsp. from the Little East Lake Formation of northwestern Maine.

The Age and Origin of the Little Diomede Island Upland Surface

Geomorphology and projected uplift rates indicate that the upland surface of Little Diomede Island may represent a high sea level stand that occurred 2.6 million years ago in the Bering Strait. The 350-363 m upland surface of the island could be correlative with the York terrace, an uplifted marine terrace previously recognized on the southern flanks of the York Mountains, Seward Peninsula. The modern surface of Little Diomede Island is composed of a cryoplanation terrace enclosing a central blockfield and rimmed with tors. Beryllium-l0 cosmogenic isotope analysis of two tors and three outcrops from the upper surface indicate the island has been under the influence of a subaerial periglacial environment at least for the last 36 000 years (MIS 3) and probably for 254 000 (MIS 7/8). Unequivocal evidence does not exist to support glaciation of Little Diomede Island.

Fossil spring deposits in the southern Great Basin and their implications for changes in water-table levels near Yucca Mountain, Nevada, during Quaternary time

Research Article| February 01, 1995 Fossil spring deposits in the southern Great Basin and their implications for changes in water-table levels near Yucca Mountain, Nevada, during Quaternary time Jay Quade; Jay Quade 1Department of Geosciences/Desert Laboratory, University of Arizona, Tucson, Arizona 85721 Search for other works by this author on: GSW Google Scholar Martin D. Mifflin; Martin D. Mifflin 2Mifflin and Associates, Inc., 3230 East Flamingo Road, Suite 205, Las Vegas, Nevada 89121 Search for other works by this author on: GSW Google Scholar William L. Pratt; William L. Pratt 3Museum of Natural History, University of Nevada at Las Vegas, Las Vegas, Nevada 89154 Search for other works by this author on: GSW Google Scholar William McCoy; William McCoy 4Department of Geology and Geophysics, University of Massachusetts at Amherst, Amherst, Massachusetts 01003 Search for other works by this author on: GSW Google Scholar Lloyd Burckle Lloyd Burckle 5Lamont-Doherty Geological Observatory, Palisades, New York 10964 Search for other works by this author on: GSW Google Scholar GSA Bulletin (1995) 107 (2): 213–230. https://doi.org/10.1130/0016-7606(1995)107<0213:FSDITS>2.3.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Jay Quade, Martin D. Mifflin, William L. Pratt, William McCoy, Lloyd Burckle; Fossil spring deposits in the southern Great Basin and their implications for changes in water-table levels near Yucca Mountain, Nevada, during Quaternary time. GSA Bulletin 1995;; 107 (2): 213–230. doi: https://doi.org/10.1130/0016-7606(1995)107<0213:FSDITS>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Fossil spring deposits are common in the southern Great Basin, and their distribution provides important constraints on the hydrologic response of the regional water table to climate change. This information is crucial, because the proposed high-level nuclear waste repository at Yucca Mountain will be located ∼200–400 m above the modern water table. Water tables will rise in response to a future return to glacial climates, but the magnitude of the change—and the consequences for radionuclide travel times and overall repository integrity—are key uncertainties. Increased recharge during past pluvial periods in the Spring Mountains and Sheep Range caused water tables to rise and ground water to discharge over broad expanses of the Las Vegas Valley system, and in nearby Pahrump, Sandy, and Coyote Springs Valleys. In contrast, other valleys in the region contain only small areas of Pleistocene discharge resulting from local damming of ground water by faults that cut valley alluvium. In these instances, which include the Valley Wells area, and Piute and northern Coyote Springs Valleys, smaller ranges such as the Clark and New York Mountains supplied the moisture. The change in water-table levels since the last full glacial period varies between and within valleys, from as little as 10 m in several areas to 95 m in the Coyote Springs Valley. At Yucca Mountain, the water table has probably changed by ≤115 m in response to climate change.The spring deposits and the mollusk faunas found with them, often misinterpreted as lacustrine in origin, share many essential features with active spring systems in northeast Nevada. Deposits associated with discharge mainly consist of pale brown silt and sand that is entrapped by dense stands of phreatophytes covering valley bottoms when water tables are high. Pale green mud, containing a mix of aquatic, semiaquatic, and moist terrestrial mollusks, accumulates in wet meadows and marshes associated directly with spring discharge.The record in subbasins of the Las Vegas Valley system is dominated by late Wisconsin–age sediments, although pond sediments and alluvium belonging to at least one older (pre-Wisconsin?) pluvial period are also locally exposed. Deposits from two even earlier episodes of spring discharge, both of which also occurred during Rancholabrean time (10 to <450 ka), are exposed in the Pahrump, Chicago, Piute, and Coyote Springs Valleys, and in the Valley Wells. The records from the Pahrump and Coyote Springs Valleys are especially well exposed and likely extend back to at least early Pleistocene time. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Paleomagnetism and tectonic rotation of the lower Miocene Peach Springs Tuff: Colorado Plateau, Arizona, to Barstow, California

We have determined remanent magnetization directions of the lower Miocene Peach Springs Tuff at 41 localities in western Arizona and southeastern California. An unusual northeast and shallow magnetization direction confirms the proposed geologic correlation of isolated outcrops of the tuff from the Colorado Plateau to Barstow, California, a distance of 350 km. The Peach Springs Tuff was apparently emplaced as a single cooling unit about 18 or 19 Ma and is now exposed in 4 tectonic provinces west of the Plateau, including the Transition Zone, Basin and Range, Colorado River extensional corridor, and central Mojave Desert strike-slip zone. As such, the tuff is an ideal stratigraphic and structural marker for paleomagnetic assessment of regional variations in tectonic rotations about vertical axes. From 4 sites on the stable Colorado Plateau, we have determined a reference direction of remanent magnetization (I = 36.4°, D = 33.0°, α 95 = 3.4°) that we interpret as a representation of the ambient magnetic field at the time of eruption. A steeper direction of magnetization (I = 54.8°, D = 22.5°, α 95 = 2.3°) was observed at Kingman where the tuff is more than 100 m thick, and similar directions were determined at 7 other thick exposures of the Peach Springs Tuff. The steeper component is presumably a later-stage magnetization acquired after prolonged cooling of the ignimbrite. When compared to the Plateau reference direction, tilt-corrected directions from 3 of 6 sites in the central Mojave strike-slip zone show localized rotations up to 13° in the vicinity of strike-slip faults. The other three sites show no significant rotations with respect to the Colorado Plateau. Both clockwise and counterclockwise rotations were measured, and no systematic regional pattern is evident. Our results do not support kinematic models which require consistent rotation of large regions to accommodate the cumulative displacement of major post-middle Miocene strike-slip faults in the central Mojave Desert. Most of our sites in the Transition Zone and Basin and Range province have had no significant rotation, although small counterclockwise rotation in the McCullough and New York Mountains may be related to sinistral shear along en echelon faults southwest of the Lake Mead shear zone. The larger rotations occur in the Colorado River extensional corridor, where 8 of 14 sites show rotations ranging from 37° clockwise to 51° counterclockwise. These rotations occur in allochthonous tilt blocks which have been transported northeastward above the Chemehuevi-Whipple Mountains detachment fault. Upper-plate blocks within 1 km of the exposed detachment unexpectedly show no significant rotation. From this relation, we infer that rotations are accommodated along numerous low-angle faults at higher structural levels above the detachment surface.

Ecology of gall-forming Lepidoptera onTetradymia: III. Within-plant horizontal and vertical distribution

does not appear. First page follows. Introduction Gall insects differ from most other herbivorous insects in that they must remain in one place, chosen soon after eclosion, until adulthood. In a sense, the outcome of the ecological “game” is completely determined by the player’s first “move.” The organism’s phyletic heritage, like rules written eons in the past, sets the constraints for a life style at once specialist, cryptic, and sessile. Zweigelt (1930 in(Mani, 1964) argued that gall formation is advantageous for a plant in that it localizes the parasite in time and space, and forces it to extreme specialization. Explanations for observed distributions of Gnorimoschema tetradymiella Busck 1903 and Scrobipalpa n. sp. gelechiid moths among Tetradymia stenolepis Greene 1885 (Asteraceae) host plants were sought in (Hartman (1983b)). The horizontal distribution of Scrobipalpa n. sp. leaf galls and G. tetradymiella stem galls within individual T. stenolepis was similarly studied to elicit patterns among plants, elevations, and years. A subsidiary objective was to identify the environmental processes governing these patterns in the New York Mountains, California (for description of study area see (Hartman, 1983b). Vertical distribution was studied to determine the effect of leaf and stem gall densities on gall height. Correlative objectives included finding how T. stenolepis foliage distribution and quality were related to each other, and to gall height. Horizontal distribution: Gall location among quadrants Agricultural entomologists interested in obtaining accurate infestation estimates often note that insect density varies within a tree according to the cardinal points. Directional insolation, wind, and water flow create differential growth rates and vegetation quality among plant sectors (Friedrick, 1951 in(Dean, 1959); (Ebeling, 1950). Pattern-skewing (also called sector or quad bias) of galls on Tetradymia in the New York Mountains was explained as either: 1) Gall insect behavior biasing one or more gall crops toward a particular quad, or 2) gall attrition from animal browse, weather, and shedding of plant parts being least in this quad. Wind patterns were analyzed to test the former alternative. Moth orientation to host-plant olfactory cues or mating pheromones requires stable, low-velocity breezes to maintain integrity of the aerial trail and/or continuous emission by a pheromone source (Farkas and Shorey, 1972); (Kaae and Shorey, 1972); (Sower, Kaae, and Shorey, 1973). Gall formation was investigated in terms of new galls being either distributed nearly evenly over the compass points, or concentrated in one or two sectors. Under concentration, the same sector may be chosen every year due to extrinsic environmental influences (termed “bias-clumping,” in the sense of a consistent skewing) or the insect may be innately aggregative, but with sectors varying between plants and between years (termed “random-clumping”). Old galls, subject the longest to animal browse, weather, and shedding of plant parts were examined for attrition effects. Three patterns were identified: 1) Loss from a random sector, independent of gall density; 2) loss which was greatest where gall density was highest; and 3) loss which was dispersed evenly over all plant sectors. Animal browse produces

Distribution Ecology of Haplopappus and Chrysothamnus in the Mojave Desert. I. Niche Position and Niche Shifts on North-Facing Granitic Slopes

The close systematic affinities between the composite genera Haplopappus and Chrysothamnus, including different points of contact with “intergeneric” hybrids, are reviewed. The Mohave Desert has several shrubby representatives of each genus, and at census sites from the east-central New York Mountains to buttes at the extreme western end of the desert, north-facing granitic slopes at the foothills of mountain ranges support four Haplopappus species (H. cuneatus. H. laricifolius, H. linearifolias and H. cooperi) and one Chrysothamnus (C. teretifolius). These five species occupy “distributional niches” represented as ranges and areas of dominance on the habitat plane of slope angle and proportion of rocks in the substrate. Central desert sites have four species (excluding C. teretifolius); peripheral desert sites always include C. teretifolius rather than H. laricifolius and support two to four species depending on the size and isolation of the suitable habitat area. Species may occupy different positions on the habitat gradient depending on species number at the site, moisture availability, and in particular competition from other species. C. teretifolius appears to be favored when population turnover rates are high, either in disturbed sites or on natural islands of habitat.

DISTRIBUTION ECOLOGY OF HAPLOPAPPUS AND CHRYSOTHAMNUS IN THE MOJAVE DESERT. I. NICHE POSITION AND NICHE SHIFTS ON NORTH‐FACING GRANITIC SLOPES

The close systematic affinities between the composite genera Haplopappus and Chrysothamnus, including different points of contact with “intergeneric” hybrids, are reviewed. The Mohave Desert has several shrubby representatives of each genus, and at census sites from the east‐central New York Mountains to buttes at the extreme western end of the desert, north‐facing granitic slopes at the foothills of mountain ranges support four Haplopappus species (H. cuneatus. H. laricifolius, H. linearifolias and H. cooperi) and one Chrysothamnus (C. teretifolius). These five species occupy “distributional niches” represented as ranges and areas of dominance on the habitat plane of slope angle and proportion of rocks in the substrate. Central desert sites have four species (excluding C. teretifolius); peripheral desert sites always include C. teretifolius rather than H. laricifolius and support two to four species depending on the size and isolation of the suitable habitat area. Species may occupy different positions on the habitat gradient depending on species number at the site, moisture availability, and in particular competition from other species. C. teretifolius appears to be favored when population turnover rates are high, either in disturbed sites or on natural islands of habitat.

Epithermal beryllium deposits in water-laid tuff, western Utah

Epithermal beryllium deposits in western Utah have distinctive geological and geochemical associations that provide guides to exploration for new resources of beryllium and associated metals. Beryllium deposits at Spor Mountain and the Honeycomb Hills are uniquely associated with topaz-bearing rhyolite of Late Tertiary age and are restricted to porous water-laid tuff and breccia that contains carbonate clasts. The beryllium deposits are near both local and regional faults that probably provided conduits for mineralizing fluids.The beryllium deposits contain sizable but uneconomic concentrations of fluorite, lithium (in smectite), manganese oxides, zinc (in smectite and manganese oxides), and uranium, as well as many trace elements. Distinctive zones of argillic and feldspathic alteration enclose the beryllium deposits and generally are parallel to the original stratification of the host tuff. Anomalous concentrations of fluorine, beryllium, cesium, lithium, gallium, niobium, and yttrium occur in relatively unmineralized tuff nearby; these elements form extensive but discontinuous halos around the Spor Mountain beryllium and fluorspar district.The mineralized areas at Spor Mountain and the Honeycomb Hills may be the tops of extensive altered zones that contain deep ore deposits. Anomalous molybdenum, lead, tin, and tungsten in beryllium deposits at Spor Mountain may indicate such leakage. Consideration of possible zonation of ore deposits suggests that if ore deposits do exist at depth, they are in greisens, banded tactites, and medium to high temperature veins similar to the tin-beryllium deposits in the York Mountains of Alaska.

Geology of the Sagamore Canyon–Slaughterhouse Spring area, New York Mountains, California

More than 2,000 m of Paleozoic and Mesozoic rocks are present in the Sagamore Canyon–Slaughterhouse Spring area, New York Mountains, California. Although recrystallized to marble, the rocks can be subdivided into formations typical of platform units east of the Cordilleran geosyncline. These formations range from the Cambrian Tapeats Sandstone, which rests unconformably on Precambrian crystalline rocks, to the Upper Mississippian–Pennsylvanian–Permian(?) Bird Spring Formation. A calc-silicate and quartzite unit unconformably overlies the Bird Spring and is tentatively correlated with the Triassic Moenkopi Formation. Mesozoic siliceous metavolcanic and metasedimentary rocks unconformably overlie the Moenkopi(?). Precambrian crystalline rocks, Paleozoic marble, and Mesozoic(?) calc-silicate rocks and quartzite are thrust eastward over Mesozoic metavolcanic and metasedimentary rocks. The allochthon is structurally complex; it consists of structures belonging to at least 10 deformational events. Correlation of these deformational events with better-dated events in the Clark Mountains suggests that both early and late Mesozoic folding, thrusting, and high-angle faulting affected the allochthonous rocks. All folds and thrust faults are intruded by a Late Cretaceous pluton (K-Ar dated at 71.7 ± 0.8 m.y. B.P). Regionally, allochthonous rocks of the New York Mountains probably are in the easternmost thrust plate of the Cordilleran fold and thrust belt, which is in a position analogous to that of the Keystone thrust plate farther north. The thrust plate contains Precambrian crystalline rocks and platform Paleozoic rocks and includes structures of probably both early and late Mesozoic age. These relationships demonstrate the complete crosscutting of the Paleozoic geosyncline by Mesozoic structures. The high-angle Slaughterhouse fault juxtaposes autochthonous Precambrian crystalline rocks and deformed and intruded Paleozoic and Mesozoic rocks. Structural relations in adjacent areas suggest that this fault can be traced more than 45 km, but no rocks can be matched across it. We speculate that the fault has strike-slip displacement and may represent a Mesozoic strike-slip fault associated with Mesozoic subduction and arc magmatism.