Isotopic Ages of Igneous Intrusions in Southeastern Utah: Evidence for a Mid-Cenozoic Reno-San Juan Magmatic Zone (original) (raw)
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Central Utahdiverse …, 2007
The late Cenozoic transition from subduction-related to extension-related volcanism is recorded in the Soldiers Pass volcanic field of the southern Lake Mountains, north-central Utah. The Soldiers Pass Formation (new formal name) is a Paleogene (35-33 Ma) suite of intermediate to silicic volcanic rocks interstratified with and overlain by lake and hot-spring deposits. In ascending order, its volcanic units include the trachydacite tuff member, Chimney Rock Pass Tuff Member, breccia member, and andesite member. Nearly horizontal lake and hot-spring deposits (White Knoll Member) are interlayered with and cap the volcanic strata. The volcanic rocks are very high-K, magnesian rocks with large negative Nb anomalies on normalized trace-element diagrams. Mineral compositions show they crystallized at high oxygen and water fugacities. Magma mixing is evidenced by high concentrations of compatible elements in the intermediate composition rocks, plagioclase and sanidine compositions and textures, and disequilibrium mineral assemblages. In short, the Paleogene suite has the characteristics of magmas formed at continental subduction zones. There is no structural evidence of extension during the eruption of the Paleogene suite.
The record of Middle Jurassic volcanism in the Carmel and Temple Cap Formations of southwestern Utah
… Society of America …, 2001
Jurassic Temple Cap and Carmel Formations in southwestern Utah record a pulse of active arc-related volcanism between 166 and 171 Ma. A second pulse between 148 and 155 Ma has previously been documented in the Upper Jurassic Morrison Formation. Volcanic and volcaniclastic rocks of these same ages have also been identified closer to or within the arc in California in the Inyo Mountains, the Cowhole Mountains, the Palen Mountains, and the central Mojave Desert. The upper part of the volcaniclastic Mount Wrightson Formation and the strata of Cobre Ridge in southern Arizona are ca. 170 Ma in age and appear to be time correlative with the Middle Jurassic formations in southwestern Utah.
Basement complexes in the Wasatch fault, Utah, provide new limits on crustal accretion
New and reinterpreted isotopic data for crystalline rocks exposed in the Wasatch Range require a reevaluation of Precambrian crustal boundaries in Utah. Crystalline rocks of the Santaquin Complex underwent metamorphism prior to ca. 1670 Ma, consistent with Sr and Nd isotope data. Mafic to intermediate rocks have major element, trace element, and isotope ratios indicative of derivation in an arc accreted to the Archean craton in Proterozoic time, requiring the crustal suture to be north of the Santaquin Complex. Farther north, the Farmington Canyon Complex has been considered Archean based on published Nd model ages and discordant U/Pb zircon ages. However, Nd model ages and zircons could be inherited from sedimentary protoliths. U/Pb and electron microprobe ages of monazite have a mode at 1650 to 1700 Ma, concordant with the Santaquin Complex, and lack inheritance. We propose that the Farmington Canyon Complex was first cratonized from Archeanderived sediments in the Proterozoic, requiring a crustal suture to be north of it as well. Accretion ages of arc terranes in southeastern Wyoming are ϳ60-100 m.y. older than in Utah. Thus, a serious reevaluation of basement architecture in Utah is needed and a previously unrecognized temporal complexity of accretion is indicated.
Cenozoic paleogeographic evolution of the Elko Basin and surrounding region, northeast Nevada
Geosphere, 2016
Geologic mapping, supported by 40 Ar/ 39 Ar and U-Pb geochronology and geochemistry of sedimentary and volcanic rocks, reveals the details of the Cenozoic depositional and tectonic history of the eastern Piñon Range and central Huntington Valley in the north-central Basin and Range Province, Nevada (USA). Cretaceous to Miocene supracrustal successions were studied in detail in order to compare the geologic evolution of the upper crust near the Ruby Mountains-East Humboldt Range (RMEH) metamorphic core complex (MCC) with the magmatic, metamorphic, and defor ma tional history of the deep crust in the developing MCC. During the well-documented Late Cretaceous-Oligo cene history of partial melting and infrastructure development within the RMEH, surface deposits in Huntington Valley reflect general tectonic quiescence, with evidence for the development of the shallow Elko Basin, minor extension, and eruption of southward-younging ignimbrite flare-up volcanism. Thin, discontinuous successions of Cretaceous-early Cenozoic sedimentary strata were locally blanketed by rhyo dacite ignimbrites, domes, and subvolcanic intrusions of the Robinson Mountain volcanic field between 38.5 and 36.8 Ma. This magmatic event represents the first local expression of Cenozoic volcanism linked to the ignimbrite flare-up, and its onset occurred slightly after a renewal of partial melting in the RMEH beginning ca. 42 Ma. The volcanic section was subsequently tilted ~10°-15° west before ca. 33.9 ± 0.4 Ma. Although melting continued at depth in the RMEH until after 30 Ma, there was no eruption of volcanic rocks after Robinson Mountain volcanism. An additional ≥10°-15° of westward tilting occurred between 31.1 ± 0.3 Ma and ca. 24.4 Ma, as bracketed by the 31 Ma tuff of Hackwood Ranch (which was probably erupted from a distant caldera) and an angular unconformity beneath the overlying Miocene Humboldt Formation. Neither of these tilting events and unconformities appears to represent significant (>~1 km each) extension, but they could be surface expressions of magmatism, metamorphism, and crustal flow at depth. The Humboldt Formation includes >2000 m of sediment deposited mostly between ca. 16 and 12 Ma, with deposition lasting until at least ca. 8.2 Ma. Humboldt Formation sedi ments thicken eastward, toward the west-dipping fault that bounds the RMEH, and are interpreted as a basin that developed in the hanging wall of this fault system. Motion on this normal fault system led to the exhumation of metamorphic and igneous rocks of the core complex ~10 m.y. after the documented cessation of partial melting, high-temperature metamorphism, and intrusion of granitoids into the deep crust ca. 29 Ma. Metamorphic clasts and a detrital zircon signature thought to represent RMEH provenance are first detected in 14.2 Ma or younger sediments.
Potassium-Argon Geochronometry of Mesozoic Igneous Rocks in Nevada, Utah, and Southern California
Geological Society of America Bulletin, 1973
K-Ar dates for 123 mineral separates from 91 samples of granitic rocks, and 3 samples of Orocopia and Vitrefax Schist from Nevada, western Utah, the Mojave Desert, the Colorado Desert, and the northern and eastern Peninsular Ranges of southern California, range in age from 218 to 19 m.y.; however, most of the dates lie between 160 and 50 m.y. A majority of the hornblende and muscovite dates are nearly concordant with, but generally a few m.y. older than, coexisting biotite dates; some are highly discordant. The oldest plutons gave Late Triassic to Early Jurassic dates (El Paso and San Bernardino Mountains, 218 to 194 m.y.). Jurassic igneous activity reached a culmination slightly before 150 m.y. ago over a large area in northern Nevada and western Utah and supplied ash to the Morrison Formation of the Colorado Plateau. Several plutons of the northeastern Mojave Desert yielded similar dates. A similar major culmination of Mesozoic pluton emplacement in early and middle Late Cretaceous time is represented by scattered plutons in Nevada and probably by most of the plutons in the Peninsular Ranges and southern deserts of California. Earliest Tertiary dates were obtained from far-southeastern California (50 to 66 m.y.). Most dates in the Cordilleran batholith belt of the Southwest, which parallels the edge of the late Mesozoic continent, are between 160 and 75 m.y. and are essentially coeval with metamorphism in the parallel high-pressure, low-temperature Franciscan belt to the west (approximately 150 to 75 m.y.). About 75 m.y. ago, this pattern abruptly changed to a Laramide one with abundant 75 to 50 m.y. dates in a belt running through southern Arizona into southeastern California at a high angle to the edge of the continent. Only very sparse dates of this-age are found in Nevada. Abundant Laramide dates are not encountered again until the Idaho, Boulder, and Coast Range batholiths. These important changes in Cordilleran tectonics may be effects of a change from dominantly dip-slip subduction during Franciscan time to dominantly northnortheast strike-slip subduction during Laramide time. Furthermore, the initiation of rifting of eastern North America in Triassic time, changes in spreading rate, and reorientation of spreading directions in the Atlantic Ocean appear to correlate with the beginning of widespread pluton emplacement in western North America, changes in the rate of magma generation in the Cordillera, and shifts of the Cordilleran tectonic pattern, respectively, during Mesozoic time.
Earth-Science Reviews, 2019
The Great Basin of the western United States, the northern component of the Basin and Range Province, is a region of Cenozoic lithospheric extension with multiple periods and types of igneous activity. The composition and volume of Cenozoic magmas reflect a complex interaction between mantle-derived magmas and highly diverse crust, where both mantle sources and magmatic processes were modulated by tectonic environment. The Fish Creek Mountains in north-central Nevada underwent multiple igneous events ranging from ca. 40 Ma to 1 Ma that span all of the complex Cenozoic tectono-magmatic episodes of the Great Basin. The Fish Creek Mountains, therefore, is an ideal location to evaluate the different sources and processes involved in magma generation. Many plutons were emplaced in the region between about 40 and 38 Ma, several of which host base and precious metal deposits. Between 36 and 33 Ma, lava fields and calderas of the 37-19 Ma Ignimbrite Flare-up were emplaced. Both these and the preceding plutons resulted from southwestward rollback of the Farallon plate beneath North America during by far the most voluminous phase of Cenozoic magmatism. The lavas range from rare basalt and basaltic andesite to andesite, dacite, and rhyolite, have continental arc-like incompatible element patterns, and high initial 87 Sr/ 86 Sr d lithospheric mantle source combined with minor crustal component. Ignimbrites of the 34.4 Ma Cove Mine
Limited extension during peak Tertiary volcanism, Great Basin of Nevada and Utah
Journal of Geophysical Research, 1991
The relative timing and magnitude of middle Tertiary extension and volcanism in the Great Basin (northern Basin and Range province) of the westem United States remain controversial. To constrain the timing, we present 31 stratigraphic sections from the central part of the province, together with data from other studies in the Great Basin. Especially significant in this record of regional paleogeographic and associated tectonic conditions are thick sections of many well-dated ash flow sheets emplaced during the period of the most voluminous, or peak, volcanic activity about 31-20 Ma. From these data we make the following conclusions: (1) Extension prior to the period of peak volcanism was apparently localized. (2) Extension during peak volcanism (the ignimbrite flareup) was minor and in places possibly related to magmatic processes in the shallow crust, rather than to regional tectonic processes. Angular unconformities and interbedded epiclastic deposits within sequences of volcanic rocks from 31 to about 22-20 Ma that would manifest synvolcanic faulting, tilting, and erosion are limited. In the Great Basin as a whole, major extension and peak volcanism correlate poorly in space as well as time. Essentially dip-slip faults cutting the entire conformable volcanic sequence are common in the Great Basin and indicate a widespread episode of extension after peakvolcanism. Southward sweeping Tertiary volcanism in the Great Basin reflects migration of the mantle magma supply that powered crustal magma systems. We suspect this migration was related to progressive southward foundering and steepening of dip of a subducting oceanic plate (after an earliest Tertiary near-horizontal configuration beneath the continental lithosphere) and consequent backflow of asthenospheric mantle into the widening wedge between the plates. In the northern Great Basin, where the sweep was rapid, we postulate that relatively small volumes of mantle-derived magma were inserted as dikes into the lower, locally extending crust which was unusually warm because of Mesozoic compressional thickening; crustal magma systems so powered were repeatedly tapped to feed modest volume eruptions of chiefly intermediate composition lava and minor silicic ash flow tuff. As the sweep stagnated in the central southern Great Basin, copious volumes of mafic magma were inserted into the crust, apparently mostly as extensive horizontal sheets, or sills, in a nonextending, uplifting crust in a state of nearly isotropic horizontal stress. These sills and the high mantle power input optimized crustal magma generation, creating huge volumes of silicic magma that vented as large volume ash flows, chiefly about 31-20 Ma. After about 22-20 Ma, the volcanic-capped plateau collapsed in a widespread network of north striking extensional faults as plate boundary compressive forces were overcome by spreading forces within the uplift. Eruption of lava again became the dominant mode of volcanism.
Late Cretaceous to Early Tertiary tectonostratigraphy of southwestern Utah
Museum of Northern Arizona Bulletin, v. 59, p. 181-188, 1993
The Upper Cretaceous to Paleogene sedimentary rocks of southwestern Utah record three temporally overlapping tectonic phases: 1) active Sevier-style thrust activity and foreland sedimentation; 2) cessation of thrust activity; and 3) active Laramide-style folding and intermontane sedimentation. The formations recording this tectonic evolution are, from oldest to youngest: the Iron Springs (and eastern equivalents), Kaiparowits, Canaan Peak, Grand Castle (new informal name), Pine Hollow, and Claron formations. Tbe Santonian to lower Campanian(?) upper part of the Iron Springs and mid-to-upper Campanian Kaiparowits formations represent synorogenic, fluvial sedimentation derived from the Sevier fold and thrust belt. The Iron Springs Formation received sediment from Precambrian to Upper Paleozoic strata exposed in the Wah Wah and Blue Mountain thrust sheets of southwestern Utah. The upper Campanian(?) to lower Paleocene Canaan Peak Formation was deposited in an east-to-northeast-directed, braided fluvial system. Petrographic and geochemical analysis of volcanic and siliceous clasts indicate that the Canaan Peak and Kaiparowits formations were derived from the Jurassic Deifonte Volcanics of southeastern California and the Mississippian Eleana Formation of southern Nevada. The early Paleocene Grand Castle formation represents an east- to southeast-flowing braided river system. Clast and sandstone lithologies indicate that the Grand Castle formation had the same provenance as the Iron Springs Formation. Conglomerate of the Grand Castle formation overlaps the easternmost Sevier thrust faults, suggesting a post-Sevier origin. The lower Pine Hollow Formation records active Laramide partition of the foreland basin associated with the development of the Johns Valley anticline and possibly the Circle Cliffs uplift. Fluvial, deltaic, and lacustrine deposits of the Claron Formation overlap paleotopographic highs of the Pine Hollow basin and indicate cessation of Laramide deformation by the middle Eocene.
2010
Volcanic stratigraphy and a kinematic analysis of NE-trending faults of Allens Ranch 7.5’ quadrangle, Utah County, Utah Adam P. McKean Department of Geological Sciences Master of Science The mineral resources of the Tintic Mining District are influenced by three major events in its geologic history; the Mesozoic Sevier Orogeny, Paleogene volcanism and Late Neogene Basin and Range extension. In this paper a detailed analysis of each these geologic events is presented to help us understand the structural host, mineralization and exhumation of the Tintic Mining District ore. A kinematic analysis of the faults was completed to determine the origin of NE-trending faults, Sevier Orogeny or Basin and Range extension, in the northern part of the East Tintic Mountains in Allens Ranch 7.5’ quadrangle, near the eastern margin of the Great Basin of central Utah. The structural history of the NE-trending faults found in the quadrangle was reconstructed to determine stress directions and fault ki...