scholarly journals Crustal thickening leading to exhumation of the Himalayan Metamorphic core of central Nepal: Insight from U-Pb Geochronology and40Ar/39Ar Thermochronology

Tectonics ◽  
2001 ◽  
Vol 20 (5) ◽  
pp. 729-747 ◽  
Author(s):  
Laurent Godin ◽  
Randall R. Parrish ◽  
Richard L. Brown ◽  
Kip V. Hodges
Keyword(s):  
Crustal Thickening ◽  
Central Nepal ◽  
Metamorphic Core

Accelerating exhumation in the Eocene North American Cordilleran hinterland: Implications from detrital zircon (U-Th)/(He-Pb) double dating

2019 ◽  
Vol 132 (1-2) ◽  
pp. 198-214 ◽  
Author(s):  
Andrew S. Canada ◽  
Elizabeth J. Cassel ◽  
Daniel F. Stockli ◽  
M. Elliot Smith ◽  
Brian R. Jicha ◽  
...  
Keyword(s):  
North American ◽  
Detrital Zircon ◽  
Sedimentary Basins ◽  
Metamorphic Core Complex ◽  
Crustal Thickening ◽  
Sediment Provenance ◽  
Core Complex ◽  
Extensional Faulting ◽  
Lag Times ◽  
Metamorphic Core

AbstractBasins in orogenic hinterlands are directly coupled to crustal thickening and extension through landscape processes and preserve records of deformation that are unavailable in footwall rocks. Following prolonged late Mesozoic–early Cenozoic crustal thickening and plateau construction, the hinterland of the Sevier orogen of western North America underwent late Cenozoic extension and formation of metamorphic core complexes. While the North American Cordillera is one of Earth’s best-studied orogens, estimates for the spatial and temporal patterns of initial extensional faulting differ greatly and thus limit understanding of potential drivers for deformation. We employed (U-Th)/(He-Pb) double dating of detrital zircon and (U-Th)/He thermochronology of detrital apatite from precisely dated Paleogene terrestrial strata to quantify the timing and magnitude of exhumation and explore the linkages between tectonic unroofing and basin evolution in northeastern Nevada. We determined sediment provenance and lag time evolution (i.e., the time between cooling and deposition, which is a measure of upper-crustal exhumation) during an 8 m.y. time span of deposition within the Eocene Elko Basin. Fluvial strata deposited between 49 and 45 Ma yielded Precambrian (U-Th)/He zircon cooling ages (ZHe) with 105–740 m.y. lag times dominated by unreset detrital ages, suggesting limited exhumation and Proterozoic through early Eocene sediment burial (<4–6 km) across the region. Minimum nonvolcanic detrital ZHe lag times decreased to <100 m.y. in 45–43 Ma strata and to <10 m.y. in 43–41 Ma strata, illustrating progressive and rapid hinterland unroofing in Eocene time. Detrital apatite (U-Th)/He ages present in ca. 44 and 39 Ma strata record Eocene cooling ages with 1–20 m.y. lag times. These data reflect acceleration of basement exhumation rates by >1 km/m.y., indicative of rapid, large-magnitude extensional faulting and metamorphic core complex formation. Contemporaneous with this acceleration of hinterland exhumation, syntectonic freshwater lakes developed in the hanging wall of the Ruby Mountains–East Humboldt Range metamorphic core complex at ca. 43 Ma. Volcanism driven by Farallon slab removal migrated southward across northeastern Nevada, resulting in voluminous rhyolitic eruptions at 41.5 and 40.1 Ma, and marking the abrupt end of fluvial and lacustrine deposition across much of the Elko Basin. Thermal and rheologic weakening of the lithosphere and/or partial slab removal likely initiated extensional deformation, rapidly unroofing deeper crustal levels. We attribute the observed acceleration in exhumation, expansion of sedimentary basins, and migrating volcanism across the middle Eocene to record the thermal and isostatic effects of Farallon slab rollback and subsequent removal of the lowermost mantle lithosphere.

scholarly journals Anatexis, cooling, and kinematics during orogenesis: Miocene development of the Himalayan metamorphic core, east-central Nepal

Geosphere ◽  
2016 ◽  
Vol 12 (5) ◽  
pp. 1575-1593 ◽  
Author(s):  
Kyle P. Larson ◽  
Dawn A. Kellett ◽  
John M. Cottle ◽  
Jess King ◽  
Graham Lederer ◽  
...  
Keyword(s):  
East Central ◽  
Central Nepal ◽  
Metamorphic Core

P–T–t path for the lower plate of the Eocene Tatla Lake metamorphic core complex, southwestern Intermontane Belt, British Columbia

1992 ◽  
Vol 29 (5) ◽  
pp. 972-983 ◽  
Author(s):  
R. M. Friedman
Keyword(s):  
British Columbia ◽  
Metamorphic Core Complex ◽  
Crustal Thickening ◽  
Lower Plate ◽  
Normal Faults ◽  
Low Grade ◽  
Core Complex ◽  
T Path ◽  
C 50 ◽  
Metamorphic Core

The Tatla Lake metamorphic complex (TLMC) is a metamorphic core complex located along the western edge of the Intermontane Belt in southwestern interior British Columbia. Low- to moderate-angle normal faults separate lower plate greenschist- and amphibolite-grade, highly strained, commonly mylonitic rocks from unstrained to weakly deformed strata of the upper plate. The lower plate is divided into a core of granoblastic gneiss and migmatitic tonalite and an overlying, 1–2.5+ km thick mylonitic package called the ductilely sheared assemblage (DSA). Amphibolite-grade metamorphism of the gneissic core (Mc) largely accompanied the development and folding of gneissic layering (ca. 107–79 Ma). Eocene (ca. 55–47 Ma) fabric and mineral assemblages in the DSA (Ms) obscure any earlier history. Three metamorphic zones are observed within southern DSA metapelites with increasing structural depth: chlorite–biotite, garnet–staurolite, and garnet–staurolite–kyanite–sillimanite. The middle zone is about 300 m thick; the latter zone is now about 4 km below low-grade upper plate rocks, indicating late- or post-Ds metamorphic omission. DSA P–T conditions are calculated with the garnet–biotite thermometer and garnet–Al2SiO5–quartz–plagioclase (GASP) and total Al in hornblende barometers. Southern DSA metapelites record Eocene Ms conditions of 480–619 °C (± 50 °C), generally increasing with depth. One sample gave a calculated P–T of 0.72 ± 0.15 GPa and 500 ± 50 °C. P–T data from this area suggest that up to 10 km of structural section may be missing. Zoned garnet (pre-Ds) core to rim GASP pressures of 0.70–0.36 ± 0.15 GPa, for an outcrop-sized pelitic xenolith within a Late Cretaceous tonalitic body (U–Pb: 71 Ma) in the northwestern DSA, record its ascent during pluton emplacement and subsequent Eocene tectonic uplift. A total Al in hornblende crystallization pressure of 0.54 ± 0.1 GPa was calculated for the surrounding body. Biotite and hornblende K–Ar dates of 53.4–45.6 Ma for DSA and gneissic core rocks record cooling of the lower plate through the 530–280 °C (± 40 °C) interval. Mc metamorphism in the gneissic core is thought to have developed in response to crustal thickening and compression, beneath a regional mid-Cretaceous thrust belt. Characteristics of Eocene Ms metamorphism in the DSA, such as truncated and thinned metamorphic zones, are consistent with development during extensional tectonic exhumation of the lower plate.

The P-T-t evolution of the exhumed Himalayan metamorphic core in the Likhu Khola region, East Central Nepal

2017 ◽  
Vol 35 (6) ◽  
pp. 663-693 ◽  
Author(s):  
S. Shrestha ◽  
K. P. Larson ◽  
C. Guilmette ◽  
M. A. Smit
Keyword(s):  
East Central ◽  
Central Nepal ◽  
Metamorphic Core

Diachronous deformation along the base of the Himalayan metamorphic core, west-central Nepal

2016 ◽  
Vol 128 (5-6) ◽  
pp. 860-878 ◽  
Author(s):  
Rohanna Gibson ◽  
Laurent Godin ◽  
Dawn A. Kellett ◽  
John M. Cottle ◽  
Douglas Archibald
Keyword(s):  
Central Nepal ◽  
West Central ◽  
Metamorphic Core

scholarly journals Jurassic–Cenozoic tectonics of the Pequop Mountains, NE Nevada, in the North American Cordillera hinterland

Geosphere ◽  
2021 ◽  
Author(s):  
Andrew V. Zuza ◽  
Christopher D. Henry ◽  
Seth Dee ◽  
Charles H. Thorman ◽  
Matthew T. Heizler
Keyword(s):  
North American ◽  
Late Jurassic ◽  
Metamorphic Core Complex ◽  
Crustal Thickening ◽  
Normal Faulting ◽  
Core Complex ◽  
The West ◽  
North American Cordillera ◽  
The North ◽  
Metamorphic Core

The Ruby Mountains–East Humboldt Range–Wood Hills–Pequop Mountains (REWP) metamorphic core complex, northeast Nevada, exposes a record of Mesozoic contraction and Cenozoic extension in the hinterland of the North American Cordillera. The timing, magnitude, and style of crustal thickening and succeeding crustal thinning have long been debated. The Pequop Mountains, comprising Neoproterozoic through Triassic strata, are the least deformed part of this composite metamorphic core complex, compared to the migmatitic and mylonitized ranges to the west, and provide the clearest field relationships for the Mesozoic–Cenozoic tectonic evolution. New field, structural, geochronologic, and thermochronological observations based on 1:24,000-scale geologic mapping of the northern Pequop Mountains provide insights into the multi-stage tectonic history of the REWP. Polyphase cooling and reheating of the middle-upper crust was tracked over the range of <100 °C to 450 °C via novel 40Ar/39Ar multi-diffusion domain modeling of muscovite and K-feldspar and apatite fission-track dating. Important new observations and interpretations include: (1) crosscutting field relationships show that most of the contractional deformation in this region occurred just prior to, or during, the Middle-Late Jurassic Elko orogeny (ca. 170–157 Ma), with negligible Cretaceous shortening; (2) temperature-depth data rule out deep burial of Paleozoic stratigraphy, thus refuting models that incorporate large cryptic overthrust sheets; (3) Jurassic, Cretaceous, and Eocene intrusions and associated thermal pulses metamorphosed the lower Paleozoic–Proterozoic rocks, and various thermochronometers record conductive cooling near original stratigraphic depths; (4) east-draining paleovalleys with ~1–1.5 km relief incised the region before ca. 41 Ma and were filled by 41–39.5 Ma volcanic rocks; and (5) low-angle normal faulting initiated after the Eocene, possibly as early as the late Oligocene, although basin-generating extension from high-angle normal faulting began in the middle Miocene. Observed Jurassic shortening is coeval with structures in the Luning-Fencemaker thrust belt to the west, and other strain documented across central-east Nevada and Utah, suggesting ~100 km Middle-Late Jurassic shortening across the Sierra Nevada retroarc. This phase of deformation correlates with terrane accretion in the Sierran forearc, increased North American–Farallon convergence rates, and enhanced Jurassic Sierran arc magmatism. Although spatially variable, the Cordilleran hinterland and the high plateau that developed across it (i.e., the hypothesized Nevadaplano) involved a dynamic pulsed evolution with significant phases of both Middle-Late Jurassic and Late Cretaceous contractional deformation. Collapse long postdated all of this contraction. This complex geologic history set the stage for the Carlin-type gold deposit at Long Canyon, located along the eastern flank of the Pequop Mountains, and may provide important clues for future exploration.

The Greater Himalayan Thrust Belt: Insight Into the Assembly of the Exhumed Himalayan Metamorphic Core, Modi Khola Valley, Central Nepal

Tectonics ◽  
2020 ◽  
Vol 39 (9) ◽  
Author(s):  
Sudip Shrestha ◽  
Kyle P. Larson ◽  
Aaron J. Martin ◽  
Carl Guilmette ◽  
Matthijs A. Smit ◽  
...  
Keyword(s):  
Thrust Belt ◽  
Central Nepal ◽  
Metamorphic Core ◽  
Insight Into

scholarly journals Geometry, kinematics, and magnitude of extension across the Thakkhola Graben, Central Nepal Himalaya

2021 ◽  
Vol 62 ◽  
pp. 1-17
Author(s):  
Thomas Baltz ◽  
Michael Murphy ◽  
Suoya Fan ◽  
Deepak Chamlagain
Keyword(s):  
Three Dimensional ◽  
Crustal Thickening ◽  
Timing Constraints ◽  
Geologic Mapping ◽  
Nepal Himalaya ◽  
Central Nepal ◽  
History Of ◽  
Extensional Structures ◽  
Parallel Extension ◽  
Thakkhola Graben

The Thakkhola Graben has been a region of geologic inquiry for many decades. Although it is widely viewed to be in a class of structures that are important in accommodating the three-dimensional strain within the Himalayan thrust wedge, we still lack a detailed understanding of the total finite strain accommodated by graben-bounding faults, as well as their shape and cross-cutting relationships with structures deeper in the thrust wedge. Using geologic mapping and structural analysis, we show that a suite of pre-extensional shortening structures is offset by normal-oblique faults bounding the Thakkhola Graben that we use to define a piercing line. We calculate these faults to have accommodated 8.7 kilometers of vertical thinning, 7.2 kilometers of arc-perpendicular shear, and only 2.2 kilometers of arc-parallel extension. The magnitude of arc-parallel extension is quite low compared to extensional structures to the west in the Gurla Mandhata-Humla region. The cross-cutting relationships established in this study and timing constraints determined by previous works are consistent with a structural history of crustal thickening leading to foreland propagation of the locus of arc-perpendicular shortening contemporaneous with hinterland extension.

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