Preliminary geologic map and cross sections of the Tetons Quadrangle and adjacent part of the Observation Knoll Quadrangle, Beaver and Iron counties, Utah (original) (raw)
Related papers
Open-file report /, 1979
Unconsolldated, poorly sorted stream, fan, slope-wash, and talus deposits. The unit includes detritus of the unit Tbrt as talus aprons around The Tetons and as a mantle on a pediment between The Tetons and Jockey Road. Total thickness probably does not exceed 40 m FORMATION OF BLAWN WASH (MIOCENE) Rhyolite member of the Tetons Light-gray, pink, lavender, or brown porphyritic rhyolite flows and shallow intrusions with only a few small (<1 mm) phenocrysts of smokey quartz, sanidine, and plagioclase in a microcrystalline matrix. Generally flow layered and locally spherulitic and lithophysal with topaz and rare fluorite in vugs. Sanidine from the intrusive rhyolite south of the Staats mine has a K-Ar age of 20 m.y. (Lindsey and Osmonson, 1978) Rhyolite member of Pink Knolls Flows and shallow intrusive plugs and dikes of gray to brown strongly porphyritic rhyolite; locally vitrophyric. Phenocrysts of quartz, sanidine, plagioclase, and lesser biotite comprise as much as one-third of the rock. Phenocrysts range widely in size, and within individual outcrops, sanidine and quartz range from small crystals to prominent phenocrysts as much as 3 cm and 1 cm across, respectively Tuff member A sequence of light-colored, generally loosely consolidated, vitric-lithic ash-flow and minor air-fall tuffs with intervening beds of stratified water-lain tuffs, volcanic sandstones, and conglomerates. The topaz rhyolite at The Tetons is underlain by a strongly welded ash-flow tuff with collapsed pumice lenses of black or brown glass. Tuffs in the unit contain less than 10 percent phenocrysts of quartz, plagioclase, sanidine, and biotite and have abundant pumice lapilli. Fragments of the Lund Tuff Member as much as 25 cm across are typically present, and are especially common in the epiclastic beds. Scattered fragments of Lund are commonly the only indication of the unit beneath poorly exposed slopes. The unit appears to be comprised of locally derived material, in part representing the precursory explosive facies of younger rhyolite flows and intrusions. Possibly as much as 300 m of this unit is exposed in Blawn Wash Mafic flow member Gray lava flow with phenocrysts of augite and labradorite; weathers brown with red liesegang bands; zeolite amygdules. In these and adjacent quadrangles the unit ranges from 55 to 60 weight percent Si02 and 2.4 to 4.0 K 0 0. Thickness 200 m
Journal of Geophysical Research, 1990
Ma rhyolite lava and precursory non-welded tuff that form the Spor Mountain Formation in west-central Utah. The mafic inclusions are not lithic inclusions; no comparable volcanic unit was present at the surface when the Spor Mountain Formation erupted. Mineral and bulk compositions preclude liquid immiscibility. The mafic inclusions show clear morphologic and textural effects of magma mingling shortly before eruption of the rhyolite. Globular inclusions from both units are vesicular, phenocryst-poor, plagioclase-sanidine-clinopyroxeneorthopyroxene-magnetite-ilmenite latites and trachytes with quench temperatures of about 1000°C. Although overlapping in SiO 2 , TiO 2 , Zr, and Hf concentrations, inclusions from the underlying tuff lack negative Eu anomalies and are enriched in P 2 O 5 , K 2 O, A1 2 O 3 , Sr, Pb, Cr, and Ni whereas those hosted in the overlying lava have small negative Eu anomalies and two-fold enrichments in Fe 2 O 3 , MnO, HREE, Y, Ta, Th, Rb, and Cs. The most reasonable explanation for the differences between the two sets of inclusions lies in selective chemical exchange between the rhyolite lava and the mafic inclusions after eruption. Limited mechanical mixing occurred after the inclusions solidified and became chemically modified. The textures of the inclusions in the lavas and the elements selectively mobilized in the inclusions imply that vapor-phase transport occurred in this low-pressure volcanic environment. If such substantial variations in inclusion compositions can arise during what must have been a short period of time before chemical reactions were halted by rapid cooling, it seems unlikely that the compositions of mafic inclusions formed by magma mingling in slowly cooled granites preserve their original compositions, mineralogies, or information about their ultimate sources. Using the compositions of such chemically modified inclusions as end-members for mixing calculations may lead to erroneous results regarding the significance of magma mixing in plutonic rocks. CHRISTIANSEN AND VENCHIARUTTI LIMITS ON INFERENCES FROM INCLUSIONS 17,719 the Great Basin, the northern part of the Basin and Range province. The Cenozoic volcanic history of the Great Basin was reviewed by Best et ah [1989] and of the area around Spor Mountain by Lindsey [1982] and Shawe [1972]. Cenozoic magmatism in the northern Great Basin began about 42 Ma with the emplacement of a calc-alkaline sequence of intermediate-composition lavas, ash flows, and small intrusions. The oldest volcanic rocks near Spor Mountain consist of dacitic to andesitic lavas, agglomerates, and ash flow tuffs. The Drum Mountain Rhyodacite, a prominent member of this association, erupted to form a stratovolcano with peripheral lava flows. Lindsey [1982] reports a fission track age on zircon of 42 Ma for this unit. At 38 Ma (Joy Tuff) and again at 32 Ma (Dell Tuff) rhyolitic ash flows were erupted. Most of the tuffs are found only as relatively thin remnants of intracaldera deposits. After an 11 m. y. lull in magmatic activity in the region, the 21 Ma Spor Mountain Formation erupted on the western margin of the Caldera complex [Lindsey, 1982]. Scattered eruptions of rhyolite and basalt to basaltic andesite lavas occurred in this part of the eastern Great Basin after about 10 Ma, including the eruption of the Topaz Mountain Rhyolite in the adjacent Thomas Range and Keg Mountains. High-angle block faulting typical of Basin and Range extension formed between 21 and 7 Ma. The rhyolites of the Spor Mountain Formation take their name from Spor Mountain which is a block of tilted and intricately faulted lower and middle Paleozoic sedimentary rocks composed chiefly of carbonates (Figure 1). Numerous, relatively small plugs, dikes, and breccia pipes of Spor Mountain Formation rhyolite intruded the sedimentary sequence. Post eruption basin-and-range faulting has complicated the structure making it difficult to estimate the number of vents involved. Lindsey [1979] identified at least 11 vents, including breccia pipes. Eruptions of the Spor Mountain Formation commenced with emplacement of a series of ignimbrites, pyroclastic fall deposits, and pyroclastic surge deposits, and ended with extrusion of rhyolite lavas over the tuff [Bikun, 1980]. The tephra deposits and local accumulations of tuffaceous sandstone and conglomerate have been mapped as the beryllium tuff member of the Spor Mountain Formation [Lindsey, 1979]. The pyroclastic rocks overlie Paleozoic sedimentary rocks, the Drum Mountain Rhyodacite, and the fluvial sediments of the Spor Mountain Formation mentioned above. The upper part of the tuff was hydrothermally altered and mineralized (Be-U-F-Li-Mn) by fluids trapped beneath the impermeable lava cap [Lindsey, 1977; Burt and Sheridan, 1981]. Alteration mineral assemblages in the tuff include smectite resulting from incomplete argillization of glass, local sericite, and secondary potassium feldspar [Lindsey, 1977]. The tephra reaches a thickness of almost 100 m; a central welded zone is developed in thick sections [Williams, 1963] and basal zones at a few localities (D. A. Lindsey, written communication, 1989). The tuff contains lithic inclusions of sedimentary rocks entrained as the pyroclastic material moved through the vent. Especially in the upper 10 m of the tuff, carbonate lithic inclusions were altered to colorful nodules of silica minerals, fluorite, clay, manganese oxides, and bertrandite during mineralization of the tuff.
Open-file report /, 1992
Hill-slope deposits Boulder to sand-sized rock fragments that have weathered out from bedrock or alluvium, moved downslope through creep and slopewash, and accumulated on hill slopes. Two types of hill-slope deposits have been mapped, but the hill-slope deposits in most areas have not been distinguished from the underlying bedrock. Qt Talus (Holocene)-Hill-slope deposits of angular fragments of rhyolite derived from the rhyolite lava-flows member of the Blawn Formation (Tbr) in south-central part of map area and from andesite lava flows (Ta) along western edge. Rock fragments range from sand-size to boulders 1 m in diameter. Matrix is generally coarse sand, but locally there is no matrix. Thickness less than 5 m Qc Gravelly colluvium (Holocene and late and middle Pleistocene)~Hill-slope deposits of unsorted, unstratified, subrounded to subangular, light-gray to reddish-brown volcanic pebbles, cobbles and boulders as large as 50 cm in a matrix of reddish-brown angular sand. Consists of a thin mantle of debris eroded from older alluvial deposits (QTf, Qpl, Qp2, Qsl, Qs2) and transported down hill slopes chiefly by creep. Generally overlies early Pleistocene and Pliocene fan alluvium (QTf) and Tertiary lacustrine basin-fill deposits (Te). Older deposits have a calcic soil horizon with laminated calcium carbonate in the upper part. The laminations parallel the hill slope. Calcium carbonate cements the oldest colluvium and completely fills interstices to 1 m depth. Thickness less than 5 m Stream deposits Silt, sand, and gravel that fill channels and form floodplains and terraces along Meadow Valley Wash and minor streams Qal Alluvium of ephemeral streams (Holocene) Channel and floodplain alluvium of small, ephemeral streams. Very pale brown (10YR 7/3) pebbly sand, moderately bedded and poorly sorted, intercalated with lenticular beds of channel-cross-bedded, sandy, pebbly, cobble gravel. Unit also includes alluvium and colluvium in small fans along valley sides. Maximum thickness about 3 m Qsa Floodplain and channel alluvium of Meadow Wash (Holocene)-Floodplain deposits are interbedded very pale brown (10YR 7/3) pebbly sand, gray
Preliminary geologic map of the Parowan Quadrangle, Iron County, Utah
Open-File Report, 1993
Qac Alluvium and colluvium undivided (Holocene)-Pebbles, cobbles, and boulders in a silt and sand matrix. Poorly sorted. Composed of locally derived material deposited along streams, bordering flood plains, and local depressions. Estimated maximum thickness 5 m Of a Fan alluvium (Holocene) In Parowan Valley deposits are composed of poorly sorted pebbles, cobbles, and lesser amounts of boulders supported by silty sand matrix. Unit includes well rounded clasts derived from conglomerate beds of the Grand Castle (Tgc), Claron (Tc), and Brian Head (Tbh) formations. Approximate thickness 20 m QTfa Basin-fill deposit (late Pleistocene-Tertiary) Shown in cross section only. Includes basin-fill alluvial deposits approximately 470 m thick Qt Terrace alluvium (late Pleistocene)-Medium to coarse sand and pebbly to bouldery gravel. Found in the upper part of First Left Hand Canyon. Clasts are predominantly from Baldhills Member of Isom Formation (Tib) and also may have been eroded from landslide debris (QTli) hi Yankee Meadows. Estimated maximum thickness 20 m Qbw Trachy-basalt lava flows of Water Canyon (middle Pleistocene)-Black to darkgray, dense to vesicular, olivine-clinopyroxene bearing flows. Quartz xenocrysts common. Vent is located hi Water Canyon approximately 3 km east from eastern edge of Parowan Valley where flows fill a paleovalley. K-Ar whole rock date of lava is 0.45 ±0.04 Ma (Fleck and others, 1975). Table 1 shows chemical analysis and CIPW normative analysis. Thickness about 120m Qbwc Cinder cone of vent area-Composed of grayish-red scoria approximately 90 m thick Qbwd Feeder dike for basalt lava flows-Dark gray dense olivine-clinopyroxene bearing. Width about 2 m Qbh Breccia and basaltic dike of Second Hand Canyon (Pleistocene?)-Breccia and dikes are located hi Second Left Hand Canyon west of Henderson Hill. Breccia contains predominantly angular fragments of Claron Formation, Grand Castle Formation (?), cinder blocks of mafic rock, and sparse Needles Range Group rocks and Isom Formation hi a gray matrix. The breccia and dike may represent a vent complex. Approximate thickness 60 m Qdh Basaltic dikes Dikes are medium gray and fine grained, and contain olivine and clinopyroxene phenocrysts, rare quartz xenocrysts(?) and rare sandstone xenoliths. Dikes intrude the breccia and parallel mapped faults. Exposure may represent remnants of a vent breccia with feeder dike (roots of a cinder cone) Qp Pediment alluvium (middle? Pleistocene) Poorly sorted deposit composed of subangular pebbles, cobbles, and sparse boulders of Tertiary volcanic rocks, and Tertiary-Cretaceous sedimentary rocks hi a silty sand matrix. Deposited as thin veneers on fan-shaped surfaces. Estimated thickness 3-12 m
1981
The Topopah Spring Member of the Paintbrush Tuff and the Lithic-rich tuff are two Tertiary volcanic units that occur in cores from drill holes UE25a-l and USW-Gl at Yucca Moun¬ tain, Nevada. Recently they have been suggested as possibly suitable for the permanent storage of high-level radioactive waste. This report augments earlier petrologic characteriza¬ tion of these units. The Topopah Spring Member (approximately 350 m thick) has two compound cooling units. The upper, thinner unit is densely welded to vitrophyric. The lower unit ranges from norwelded to vitrophyric, and its nonwelded base is exten¬ sively zeolitized to clinoptilolite and mordenite. Heulandite occurs as fracture fill in the overlying vitrophyric part, but zeolites are absent above that vitrophyre. Here primary devitrification plus vapor-phase crystallization dominate the mineralogy. Vapor-phase effects are especially prominent between the two vitrophyres in both cores and in¬ clude numerous large lithophysal cavities throughout most of this moderately to densely welded tuff. The Lithic-rich tuff extends from 1203 to 1506 m in the USW-Gl drill core. It is nonwelded to partly welded but is well indurated due to pervasive intergrowths of authigenic minerals. Thesr phases are analcime, albite, alkali feld¬ spar, sericite, chlorite and quartz. The transition from analcime to secondary albite corresponds to Iijima's zeolite Zone IV boundary, and this boundary appears in USW-Gl at 1326 m. However, analcime remains as a prominent phase through most of the Lithic-rich tuff. Further work is necessary to assess the suitability of either of these horizons for a waste repository. In the Topopah Spring Member, both mechanical and hydrologic proper¬ ties of the thick lithophysal zone must be studied, as well as the complete sequence of fracture fill. For both units, zeolite and clay mineral stabilities need to be investigated.
Geology of the Intermountain West, 2020
Two types of breccia are found in the Mississippian Leadville Limestone, Paradox Basin, southeastern Utah: (1) breccia associated with karstification and (2) breccia created by natural hydrofracturing, i.e., “autobreccia.” Breccia associated with sediment-filled cavities is relatively common throughout the upper one-third of the Leadville Limestone in Lisbon and other Paradox Basin oil and gas fields. These cavities and/or cracks are related to karstification of exposed Leadville during Late Mississippian time. Infilling of cavities by detrital carbonate and siliciclastic sediment occurred before deposition of the Pennsylvanian Molas Formation or Hermosa Group. Transported material consists of poorly sorted detrital quartz grains, chert fragments, and clasts of carbonate and clay. Carbonate muds infilling karst cavities are very finely crystalline non-porous dolomites. Post-burial brecciation, caused by natural hydrofracturing, is also quite common within Leadville reservoirs at Lisbon and other fields. Brecciation created an explosive-looking, pulverized rock, an “autobreccia” as opposed to a collapse breccia. Clasts within autobreccias remained in place or moved very little. Dolomite clasts are commonly surrounded by solution-enlarged fractures partially filled with coarse rhombic and late saddle dolomites. Areas between clasts exhibit good intercrystalline porosity and microporosity or are filled by dolomite cements. Intense pyrobitumen lining of pores was concurrent with, or took place shortly after, brecciation. The presence of zebra dolomites and zebra vugs attest to high temperatures associated with natural hydrofracturing. Rimmed microstructures or stair-step fractures are present, reflecting shear and explosive fluid expulsion from the buildup of pore pressure. Abundant pyrobitumen makes porous breccias and dolomites look like black “shales.” Post-burial breccias are associated with the best reservoir development at Lisbon field. Outcrop analogs for both breccia types are present in the stratigraphically equivalent Mississippian section along the south flank of the Uinta Mountains in northeastern Utah. Based on field observations, a key component for autobrecciation is the presence of an underlying aquifer that serves as a conduit for hydrothermal fluids. Large volumes of water throughput are required to produce brecciation and the amount, type, and generations of dolomite present at Lisbon field. We propose a model where convection cells bounded by basement-rooted faults transfer heat and fluids possibly from crystalline basement, Pennsylvanian evaporites, and Oligocene igneous complexes. Post-burial brecciation often results in the formation of large, diagenetic hydrocarbon traps.
2017
Thin fallout tuffs in the Duchesne River Formation in the Uinta Basin, Utah are evidence that volcanism was active in northern Nevada and Utah in the late Eocene. The Uinta Basin is a sedimentary basin that formed during the Laramide orogeny. Ponded lakes of various salinity filled and emptied and during the late Eocene the northern rim was dominated by a wetland/floodplain depositional setting. Most of the tuffs have rhyolitic mineral assemblages including quartz, biotite, sanidine, and allanite. Rhyolitic glass shards were also found in one of the ash beds. Biotite compositions have Fe/(Fe+Mg) ratios typical of calc-alkaline igneous rocks and clusters of biotite compositions suggest 3 or 4 volcanic events. Sanidine compositions from five samples grouped at Or73 and Or79. Only one sample had plagioclase with compositions ranging between An22-An49. Some beds also contained accessory phases of titanite, apatite, and zircon. Whole rock compositions of the altered volcanic ash beds indicate these tuffs underwent post-emplacement argillic alteration, typical of a wetland/floodplain depositional setting. Immobile element ratios and abundances, such as Zr/Nb and Y are typical of a subduction zone tectonic setting and rhyolitic composition. 40 Ar/ 39 Ar ages constrain the timing of volcanism. One plagioclase and one sanidine separate from two different tuff beds yielded ages of 39.47 ± 0.16 Ma and 39.36± 0.15 Ma respectively. These dates, along with the compositional data seem to limit the eruptive source for these fallout tuffs to the northeast Nevada volcanic field. These new ages, along with previously published ages in the Bishop Conglomerate which unconformably overlies the Duchesne River Formation, constrain the timing of two uplift periods of the Uinta Mountains at 39 Ma and 34 Ma. Finally, the ages also date the fauna of the Duchesnean Land Mammal Age to be about 39.4 Ma as opposed to less precise earlier estimates that placed it between 42 and 33 Ma.