USGS Science⌕ Search

Geology topics

K.S. Kellogg

Publications and source records attributed to K.S. Kellogg.

At least 19 recordsLinked to original sources
USGS2012

Root zone of the late Proterozoic Salma caldera, northeastern Arabian Shield, Kingdom of Saudi Arabia

The eroded root of the late Proterozoic Salma caldera crops out in a striking, roughly elliptical feature, about 27 km long and 22 km wide, near the northeastern edge of the Arabian Shield. The caldera is genetically part of an elongate alkalic granitic massif (Jabal Salma) that extends 35 km from the caldera to the southwest. Comenditic ash flow tuff and lava(?) of the caldera fill, probably more than 1 km thick, are the oldest recognized rocks of the caldera complex. These rocks were erupted during caldera collapse associated with the rapid evacuation of the upper, mildly peralkalic part of a zoned magma reservoir. Within the caldera fill, a massive, lithic-rich intracaldera rhyolite, probably a lava in excess of 1 km thick, is overlain by a layered ash flow sequence. Numerous megabreccia blocks, probably derived from the caldera wall, occur in the massive rhyolite. Open folds in the layered volcanic rocks may be due to high-temperature slumping of the rocks toward the center of the caldera following collapse. Later peralkalic granite that intruded the caldera ring fracture zone occurs in an arcuate pattern outside the area of exposed caldera fill. After caldera collapse, metaluminous to peraluminous magma rose beneath the caldera at approximately 580 Ma and solidified as biotite alkali granite, rim syenogranite, and late, high-level granophyre. Rare earth element abundances indicate that the layered rhyolite tuff, peralkalic granite, and granophyre are chemically more evolved than the biotite alkali granite and rim syenogranite. The granophyre intruded the caldera fill as a dome-shaped body composed of numerous sheetlike masses. Granophyric texture resulted from rapid pressure release and quenching accompanying the intrusion of each sheet. Maximum penetration of the granophyre into overlying rocks occurred in the central region and along the west side of the caldera, where the caldera fill volcanic rocks have been removed by erosion. No apparent structural doming of the exposed volcanic rocks along the east side of the caldera took place; the layered ash flows commonly dip steeply toward the center of the caldera. Postemplacement deformation and metamorphism of the caldera are minimal. Small-displacement strike-slip faults cut the complex, which is tilted to the northeast by no more than about 2°.

Journal of Geophysical Research Solid Earth↗
USGS2007

New 40Ar/39Ar age determinations and paleomagnetic results bearing on the tectonic and magmatic history of the northern Madison Range and Madison Valley region, southwestern Montana, U.S.A

Detailed 40Ar/39Ar dating and paleomagnetic analysis of dacite porphyry sills and dikes that intrude Cretaceous sedimentary rocks in the northern Madison Range in southwestern Montana show that Laramide shortening was essentially complete by ???69 Ma. A negative paleomagnetic fold test indicates that Laramide folding occurred before cooling of the dacite sills and dikes at ???69 Ma. Laramide deformation began synchronous with deposition of the Livingston Formation rocks at ???79 Ma. These results are consistent with previous observations in the region that show the onset of Laramide deformation in the northern Rocky Mountains becoming progressively younger toward the east. 40Ar/39Ar dating of additional igneous rocks in the northern Madison Valley and around Norris, Montana better define post-Laramide tectonomagmatic events in the region, including Eocene-Oligocene volcanism and Basin and Range crustal extension. Dates from three rhyolitic intrusions near Red Mountain are between 48.71 ?? 0.18 Ma and 49.42 ?? 0.18 Ma, similar to the dates from basal silicic flows of the Virginia City volcanic field (part of the southwest Montana volcanic province), suggesting that the Red Mountain intrusions may have been the sources for some of the early extrusive rocks. Magmatism in the Virginia City volcanic field became generally more mafic with time, and a ???30-Ma basalt flow near Norris is considered a late, outlying member of the volcanic field. A tuff along the east side of the Madison Valley half graben yielded a early middle Miocene date (16.2 ?? 0.19 Ma), suggesting that accelerated crustal extension and associated rapid basin sedimentation probably began in the early Miocene, slightly earlier than previous estimates.

Rocky Mountain Geology↗
USGS2005

Taking apart the Big Pine fault: Redefining a major structural feature in southern California

New mapping along the Big Pine fault trend in southern California indicates that this structural alignment is actually three separate faults, which exhibit different geometries, slip histories, and senses of offset since Miocene time. The easternmost fault, along the north side of Lockwood Valley, exhibits left-lateral reverse Quaternary displacement but was a north dipping normal fault in late Oligocene to early Miocene time. The eastern Big Pine fault that bounds the southern edge of the Cuyama Badlands is a south dipping reverse fault that is continuous with the San Guillermo fault. The western segment of the Big Pine fault trend is a north dipping thrust fault continuous with the Pine Mountain fault and delineates the northern boundary of the rotated western Transverse Ranges terrane. This redefinition of the Big Pine fault differs greatly from the previous interpretation and significantly alters regional tectonic models and seismic risk estimates. The outcome of this study also demonstrates that basic geologic mapping is still needed to support the development of geologic models. Copyright 2005 by the American Geophysical Union.

Tectonics↗
USGS2005

Pliocene transpressional modification of depositional basins by convergent thrusting adjacent to the "Big Bend" of the San Andreas fault: An example from Lockwood Valley, southern California

The "Big Bend" of the San Andreas fault in the western Transverse Ranges of southern California is a left stepping flexure in the dextral fault system and has long been recognized as a zone of relatively high transpression compared to adjacent regions. The Lockwood Valley region, just south of the Big Bend, underwent a profound change in early Pliocene time (???5 Ma) from basin deposition to contraction, accompanied by widespread folding and thrusting. This change followed the recently determined initiation of opening of the northern Gulf of California and movement along the southern San Andreas fault at about 6.1 Ma, with the concomitant formation of the Big Bend. Lockwood Valley occupies a 6-km-wide, fault-bounded structural basin in which converging blocks of Paleoproterozoic and Cretaceous crystalline basement and upper Oligocene and lower Miocene sedimentary rocks (Plush Ranch Formation) were thrust over Miocene and Pliocene basin-fill sedimentary rocks (in ascending order, Caliente Formation, Lockwood Clay, and Quatal Formation). All the pre-Quatal sedimentary rocks and most of the Pliocene Quatal Formation were deposited during a mid-Tertiary period of regional transtension in a crustal block that underwent little clockwise vertical-axis rotation as compared to crustal blocks to the south. Ensuing Pliocene and Quaternary transpression in the Big Bend region began during deposition of the poorly dated Quatal Formation and was marked by four converging thrust systems, which decreased the areal extent of the sedimentary basin and formed the present Lockwood Valley structural basin. None of the thrusts appears presently active. Estimated shortening across the center of the basin was about 30 percent. The fortnerly defined eastern Big Pine fault, now interpreted to be two separate, oppositely directed, contractional reverse or thrust faults, marks the northwestern structural boundary of Lockwood Valley. The complex geometry of the Lockwood Valley basin is similar to other Tertiary structural basins in southern California, such those that underlie Cuyama Valley, the Ridge basin, and the east Ventura basin.

Tectonics↗
USGS2003

The mesoproterozoic Beaverhead impact structure and its tectonic setting, Montana-Idaho: 40Ar/39 and U-Pb isotopic constraints

New 40Ar/39Ar and uranium-lead (U-Pb) zircon data from the Beaverhead impact structure, first identified by extensive shatter coning of Proterozoic quartzite and gneiss from the Beaverhead Mountains near the Montana-Idaho border, indicate that the structure formed at or after 900 Ma. The 40Ar/39Ar age spectra from fine-grained muscovite and biotite from a breccia zone in high-grade gneiss show significant argon loss but yield dates for highest-temperature steps that cluster between 899 and 908 Ma. The dated minerals probably formed by recrystallization of impact glass, so on both geologic and isotopic grounds, the dates probably represent the minimum age of impact. U-Pb data for zircons from the same breccia are strongly discordant and yield an upper intercept apparent age of 2464 ?? 56 Ma and a lower intercept apparent age of 779 ?? 69 Ma. Another brecciated gneiss about 7 km to the northeast that does not contain secondary mica does contain zircons that yield a concordant apparent age of 2455 ?? 9 Ma. Nearby gneiss that neither is brecciated nor contains shatter cones yields an apparent age of 2451 ?? 46 Ma. The 40Ar/39Ar results constrain the age of the shatter-coned quartzite and indicate that it is >900 Ma and possibly correlative with the Gunsight Formation of the Mesoproterozoic Lemhi Group. The upper intercept U-Pb age of ???2450 Ma from all three dated samples also shows that the Paleoproterozoic basement rocks of the area are among the youngest in the mostly Archean Wyoming province of North America. The impact site lies near the margin of the province, along the northeast-trending Great Falls tectonic zone, and the relatively young crustal age may reflect Early Proterozoic marginal accretion.

Journal of Geology↗
USGS2001

Tectonic controls on large landslide complex: Williams Fork Mountains near Dillon, Colorado

An extensive (~ 25 km2) landslide complex covers a large area on the west side of the Williams Fork Mountains in central Colorado. The complex is deeply weathered and incised, and in most places geomorphic evidence of sliding (breakaways, hummocky topography, transverse ridges, and lobate distal zones) are no longer visible, indicating that the main mass of the slide has long been inactive. However, localized Holocene reactivation of the landslide deposits is common above the timberline (at about 3300 m) and locally at lower elevations. Clasts within the complex, as long as several tens of meters, are entirely of crystalline basement (Proterozoic gneiss and granitic rocks) from the hanging wall of the Laramide (Late Cretaceous to Early Tertiary), west-directed Williams Range thrust, which forms the western structural boundary of the Colorado Front Range. Late Cretaceous shale and sandstone compose most footwall rocks. The crystalline hanging-wall rocks are pervasively fractured or shattered, and alteration to clay minerals is locally well developed. Sackung structures (trenches or small-scale grabens and upslope-facing scarps) are common near the rounded crest of the range, suggesting gravitational spreading of the fractured rocks and oversteepening of the mountain flanks. Late Tertiary and Quaternary incision of the Blue River Valley, just west of the Williams Fork Mountains, contributed to the oversteepening. Major landslide movement is suspected during periods of deglaciation when abundant meltwater increased pore-water pressure in bedrock fractures. A fault-flexure model for the development of the widespread fracturing and weakening of the Proterozoic basement proposes that the surface of the Williams Range thrust contains a concave-downward flexure, the axis of which coincides approximately with the contact in the footwall between Proterozoic basement and mostly Cretaceous rocks. Movement of brittle, hanging-wall rocks through the flexure during Laramide deformation pervasively fractured the hanging-wall rocks. ?? 2001 Elsevier Science B.V. All rights reserved.

Geomorphology↗
USGS1999

Neogene basins of the northern Rio Grande rift: Partitioning and asymmetry inherited from Laramide and older uplifts

Three asymmetric Neogene basins in the northern Rio Grande rift of New Mexico and Colorado - the San Luis basin, the upper Arkansas River graben, and the Blue River graben - are tilted toward large flanking normal faults and lie astride the similarly asymmetric Late Cretaceous-early Tertiary (Laramide) San Juan-San Luis, Sawatch, and Front Range-Gore Range uplifts, respectively. The steep, thrust-faulted side of each uplift is on the same side as the down-rotated side of each of the Neogene basins. In addition, the direction of stratal tilt changes northward across the Villa Grove accommodation zone from east in the San Luis basin to west in the upper Arkansas River graben. This accommodation zone coincides approximately with the northward change from the east-directed San Juan-San Luis uplift to the west-directed Sawatch uplift. These observations, supported by seismic-reflection studies across the San Luis basin and studies of several other superimposed pairs of rift basins and Laramide uplifts, suggest that the basin-bounding normal faults are listric and merge at depth with the older thrusts, which are also listric and root into the crust at about 15-16 km. The Blue River graben is complicated by lack of basin fill and a thrust history along the west side of the Gore Range that is at least as old as late Paleozoic. Nonetheless, the Neogene valley is demonstrably tilted west and lies astride an overall west-directed thrust system, similar to other thrust-and-basin relationships in the northern Rio Grande rift.

Tectonophysics↗
USGS1986

Geology and tin-greisen mineralization of the Akash granite, northern Arabian Shield

The western margin of the postorogenic Akash granite, 30 km E of Ha'il in the northern Arabian Shield, is greisenized and contains anomalous concentrations of Sn. The pluton intrudes metamorphic and intrusive rocks, and crops out as a 10 by 15 km elliptical body with its long axis oriented N. It consists predominantly of metaluminous alkali-feldspar granite or syenogranite, with accessory biotite and muscovite, and traces of fluorite. Greisenization extends discontinuously in a zone at least 3 km long parallel to the western contact, and along E-trending hematitic quartz veins for more than 2 km from the contact. The veins occupy fractures that were probably conduits for ascending mineralizing fluids. Within about 20 m of the contact, they are enclosed in quartz—white mica greisen containing hematite, fluorite, and locally, topaz and cassiterite. Composite chip samples from the greisenized zone have an average Sn content of 710 ppm, and a maximum of 1600 ppm. Anomalous values for Zn, Fe, Mn, Mo, Bi and Cu also occur, but none of the samples contain detectable W. Three samples of hematitic quartz averaged 126 ppm Sn, and one contained 200 ppm W.

Journal of African Earth Sciences↗
USGS1985

The Salma Caldera complex, northeastern Arabian Shield, Kingdom of Saudi Arabia

The upper Proterozoic Salma caldera is genetically part of an elongate alkali granitic massif, Jabal Salma. Comenditic ash-flow tuffs, the oldest recognized rocks of the caldera complex, were erupted during caldera collapse associated with the rapid evacuation of the upper, mildly peralkaline part of a zoned magma reservoir. Within the tuff sequence, a massive, lithic-rich intracaldera tuff containing megabreccia blocks is overlain by a layered ash-flow sequence. Later peralkaline granite intruded the caldera ring fracture zone. Metaluminous to peraluminous magma rose beneath the caldera approximately 580 Ma ago and solidified as biotite alkali-feldspar granite, syenogranite, and granophyre. No apparent structural doming of the exposed volcanic rocks along the east side of the caldera took place, and post- emplacement deformation and metamorphism of the caldera are minimal.

Open-File Report↗
USGS1984

Reconnaissance geology of the Qufar Quadrangle, sheet 27/41 D, Kingdom of Saudi Arabia

The Qufar quadrangle, south of the city of Ha' il in the northern Arabian Shield is underlain by late Proterozoic granitic and dioritic rocks and two volcano-sedimentary sequences. Phanerozoic rocks include a few outcrops of the Cambrian and Ordovician Saq Sandstone and small remnants of Miocene basalt flows and plugs. The oldest rocks in the quadrangle comprise the Nuf formation, a layered sequence of submarine, tholeiitic metabasalt and meta-andesite, and interbedded metagraywacke and marble. The Nuf formation may correlate with rocks mapped as Halaban or Hulayfah group (approximately 780-720 Ma old) to the south of the quadrangle. Cogenetic subvolcanic rocks include gabbro and diorite. Voluminous plutonic rocks of approximately monzogranite composition intruded and dismembered the Nuf formation, gabbro, and diorite, which were simultaneously metamorphosed and internally deformed. Metamorphism of the Nuf formation was variable, but generally' upper greenstone-facies assemblages were produced. Following a period of extensive erosion, the Hadn formation, dacitic to rhyolitic ignimbrite and flow breccia, and interbedded subgraywacke, arkose, and minor conglomerate was deposited. The Hadn formation may be a continental equivalent of the Murdama group, which is mapped to the south of the quadrangle and is approximately 650 to 610 Ma old. Numerous plutons, predominantly monzogranite, but ranging from gabbro to alkali-feldspar granite, post-date the Hadn formation. Of these, the Malayhah granite is particularly noteworthy because it has a broad zone of cataclasis along the western and southern border. Country rock within several kilometers of the western contact is also highly sheared, predominantly along northerly trends. Locally, a melange of several rock types was produced. Contact metamorphism to garnet-amphibolite hornfels facies occurred at this time, and may be responsible for the formation of small sub-economic magnetite lenses interlayered with some of the marbles of the Nuf formation. In the northern part of the quadrangle, southeast dipping imbricate thrust faults probably closely post-date the emplacement of the Mulayhah granite. These thrusts were followed in time by predominantly northeast-trending high-angle faults. The last major plutonic event in the area is the intrusion of the alkalic granite complexes at Jabal Aja and Jabal Sal ma about 580 Ma ago. Of particular note is a per alkalic border facies of the Jabal Aja complex that is associated with pegmatites enriched in thorium, niobium, and rare-earth elements.

Open-File Report↗