scholarly journals Late Cretaceous upper-crustal thermal structure of the Sevier hinterland: Implications for the geodynamics of the Nevadaplano

Geosphere ◽  
2021 ◽  
Author(s):  
Nolan R. Blackford ◽  
Sean P. Long ◽  
Austin Stout ◽  
David W. Rodgers ◽  
C.M. Cooper ◽  
...  
Keyword(s):  
Late Cretaceous ◽  
Cross Sections ◽  
Thermal Field ◽  
Thermal Structure ◽  
Carbonaceous Material ◽  
Thermal Gradients ◽  
Field Gradients ◽  
Granitic Magmatism ◽  
Snake Range ◽  
Lower Crustal

Crustal temperature conditions can strongly influence the evolution of deformation during orogenesis. The Sevier hinterland plateau in Nevada and western Utah (“Nevadaplano”) experienced a Late Cretaceous episode of shallow-crustal metamorphism and granitic magmatism. Here, we investigate the thermal history of the Nevadaplano by measuring peak thermal field gradients attained in the upper 10–20 km of the crust along an east-west transect through nine ranges in eastern Nevada and western Utah, by integrating Raman spectroscopy of carbonaceous material thermometry and published conodont alteration indices with reconstructed cross sections. Thermal field gradients of 29 ± 3 °C/km were obtained in the House and Confusion Ranges in westernmost Utah. The Deep Creek, Schell Creek, and Egan Ranges in easternmost Nevada yielded elevated gradients of 49 ± 7 °C/km, 36 ± 3 °C/km, and 32 ± 6 °C/km, respectively. Moving westward, the White Pine, Butte, Pancake, and Fish Creek Ranges exhibit gradients typically between ~20–30 °C/km. The elevated thermal gradients in easternmost Nevada are interpreted to have been attained during ca. 70–90 Ma granitic magmatism and metamorphism and imply possible partial melting at ~18 km depths. Our data are compatible with published interpretations of Late Cretaceous lithospheric mantle delamination under the Sevier hinterland, which triggered lower-crustal anatexis and the resulting rise of granitic melts. The lack of evidence for structures that could have accommodated deep burial of rocks in the nearby Northern Snake Range metamorphic core complex, combined with thermal gradients from adjacent ranges that are ~1.5–3 times higher than those implied by thermobarometry in the Northern Snake Range, further highlights the debate over possible tectonic overpressure in Cordilleran core complexes. Cross-section retro-deformation defines 73.4 ± 4.6 km (76 ± 8%) of extension across eastern Nevada and 15 km of shortening in the Eastern Nevada fold belt.

scholarly journals Supplemental Material: Late Cretaceous upper-crustal thermal structure of the Sevier hinterland: Implications for the geodynamics of the Nevadaplano

2021 ◽  
Author(s):  
N.R. Blackford ◽  
et al.
Keyword(s):  
Late Cretaceous ◽  
Cross Sections ◽  
Thermal Structure ◽  
East Central ◽  
Crustal Thermal Structure

<div>Figure 7. Compilation of cross sections across east-central Nevada and western Utah (1:200,000 scale) with deformed cross sections in the top row (A) and restored cross sections in the bottom row (B). Translucent areas represent eroded rock above the modern surface (deformed cross sections) and above the Paleogene unconformity (restored cross sections).<br></div><div><br></div><div><br></div><div><br></div><div><br></div>

scholarly journals Supplemental Material: Late Cretaceous upper-crustal thermal structure of the Sevier hinterland: Implications for the geodynamics of the Nevadaplano

2021 ◽  
Author(s):  
N.R. Blackford ◽  
et al.
Keyword(s):  
Late Cretaceous ◽  
Cross Sections ◽  
Thermal Structure ◽  
East Central ◽  
Crustal Thermal Structure

<div>Figure 7. Compilation of cross sections across east-central Nevada and western Utah (1:200,000 scale) with deformed cross sections in the top row (A) and restored cross sections in the bottom row (B). Translucent areas represent eroded rock above the modern surface (deformed cross sections) and above the Paleogene unconformity (restored cross sections).<br></div><div><br></div><div><br></div><div><br></div><div><br></div>

Structural evolution in the Moine of northwest Scotland: a Caledonian linked thrust system?

1986 ◽  
Vol 123 (1) ◽  
pp. 1-11 ◽  
Author(s):  
Robert W. H. Butler
Keyword(s):  
Cross Sections ◽  
Lower Crust ◽  
Structural Evolution ◽  
Amphibolite Facies ◽  
Metamorphic Basement ◽  
Thrust System ◽  
Lower Crustal

AbstractA model is proposed whereby the Caledonian metamorphic basement-cover complex of northwest Scotland (the Moine) is considered as a linked thrust system. This system lies between the Moine thrust at its base and the Naver–Sgurr Beag slide at its top. Ductile fold and thrust zones, which developed at mid crustal levels at metamorphic grades from greenschist to amphibolite facies, are interpreted as decoupling from a detachment presently situated at relatively shallow depths. This model is illustrated by two preliminary balanced cross-sections. These imply shortening across the northwest Scottish Caledonides in excess of 130 km and probably over 200 km. When these structures are restored onto a crustal template a considerable quantity of lower crust is found to be required at depth. The most likely location for the lower crustal wedge is beneath the Grampian Highlands.

“Pipe-organ structures” in the Lee Formation (Pennsylvanian) of the central Appalachian Basin: animal or plant?

1992 ◽  
Vol 66 (1) ◽  
pp. 148-156 ◽  
Author(s):  
Donald R. Chesnut ◽  
James C. Cobb ◽  
Stephen F. Greb
Keyword(s):  
Cross Sections ◽  
Carbonaceous Material ◽  
Animal Origin ◽  
Pipe Organ ◽  
Cross Sectional ◽  
Thin Sections ◽  
Common Structure ◽  
Channel Form ◽  
The Individual ◽  
Vertical Tubes

A sequence of unusual vertical tubes, arranged in multiple groups, and each tube several meters high occurs in the Middlesboro Member of the Lee Formation (Lower Pennsylvanian). These structures are controversial with various interpretations suggesting either plant or animal origin. Observations supporting a plant origin include: 1) numerous C- and D-shaped, and multichambered tube cross sections are similar to fern and seed fern structures, 2) numerous membrane relicts loosely enclosing the tubes are similar to fern and seed fern tissues, 3) microscopic bundles are observed in cross-sectional thin sections, 4) presence of carbonaceous material and reported fecal pellets over a vertical distance in excess of 5 m are consistent with deteriorating plant material, not escape structures, 5) tubes are composed of casts and molds, but lack spreite or other features typical of escape structures, 6) tubes occur in clusters about one meter in diameter and are associated with coaly material at their base, which suggests that the clusters represent trees, 7) other trace fossils are absent in the enclosing sandstone, 8) tubes branch upward, which is a common structure in plants but unlikely in escape structures, 9) a coalified root structure was found at the base of the sandstone, and 10) all the tubes extend from the bottom of the sandstone to the top. The probability of burrowing animals escaping through as much as 8 m of sand with 100 percent survivorship is low.The structures may represent a stand of pteridosperms with each “tree” approximately 1–1.5 m in diameter. The individual pipe-organ structures represent aerial stems, shoots, and adventitious roots; each cluster of pipe-organ structures represents a single tree.Based upon sedimentologic features such as presence of 1) channel form, 2) scoured base, and 3) fining-upward sequence, we interpret the sandstone containing the pipe-organ structures to have been deposited in a sandy fluvial or tidal channel. The unidirectional cross-bed dips, poor sorting, occurrence only of very restrictive fauna and terrestrial flora, position of the sandstone above a possible floodplain facies, and lack of characteristic tidal structures suggest that the sandstone is more probably a sandy fluvial channel that may have minor tidal influence.

scholarly journals Lower-crustal rheology and thermal gradient in the Taiwan orogenic belt illuminated by the 1999 Chi-Chi earthquake

2019 ◽  
Vol 5 (2) ◽  
pp. eaav3287 ◽  
Author(s):  
Chi-Hsien Tang ◽  
Ya-Ju Hsu ◽  
Sylvain Barbot ◽  
James D. P. Moore ◽  
Wu-Lung Chang
Keyword(s):  
Tectonic Evolution ◽  
Laboratory Data ◽  
Orogenic Belt ◽  
Thermal Gradients ◽  
Short Term ◽  
Crustal Strength ◽  
Seismic Cycles ◽  
Natural Settings ◽  
Stress And Strain Rate ◽  
Lower Crustal

The strength of the lithosphere controls tectonic evolution and seismic cycles, but how rocks deform under stress in their natural settings is usually unclear. We constrain the rheological properties beneath the Taiwan orogenic belt using the stress perturbation following the 1999 Chi-Chi earthquake and fourteen-year postseismic geodetic observations. The evolution of stress and strain rate in the lower crust is best explained by a power-law Burgers rheology with rapid increases in effective viscosities from ~1017to ~1019Pa s within a year. The short-term modulation of the lower-crustal strength during the seismic cycle may alter the energy budget of mountain building. Incorporating the laboratory data and associated uncertainties, inferred thermal gradients suggest an eastward increase from 19.5±2.5°C/km in the Coastal Plain to 32±3°C/km in the Central Range. Geodetic observations may bridge the gap between laboratory and lithospheric scales to investigate crustal rheology and tectonic evolution.

scholarly journals Interplay of Cretaceous transpressional deformation and continental arc magmatism in a long-lived crustal boundary, central Fiordland, New Zealand

Geosphere ◽  
2020 ◽  
Vol 16 (5) ◽  
pp. 1225-1248
Author(s):  
Hannah J. Blatchford ◽  
Keith A. Klepeis ◽  
Joshua J. Schwartz ◽  
Richard Jongens ◽  
Rose E. Turnbull ◽  
...  
Keyword(s):  
New Zealand ◽  
Thermal Structure ◽  
Shear Zones ◽  
Arc Magmatism ◽  
Magmatic Arc ◽  
Continental Arcs ◽  
Metasedimentary Rocks ◽  
Spatio Temporal ◽  
Continental Magmatic Arc ◽  
Lower Crustal

Abstract Recovering the time-evolving relationship between arc magmatism and deformation, and the influence of anisotropies (inherited foliations, crustal-scale features, and thermal gradients), is critical for interpreting the location, timing, and geometry of transpressional structures in continental arcs. We investigated these themes of magma-deformation interactions and preexisting anisotropies within a middle- and lower-crustal section of Cretaceous arc crust coinciding with a Paleozoic boundary in central Fiordland, New Zealand. We present new structural mapping and results of Zr-in-titanite thermometry and U-Pb zircon and titanite geochronology from an Early Cretaceous batholith and its host rock. The data reveal how the expression of transpression in the middle and lower crust of a continental magmatic arc evolved during emplacement and crystallization of the ∼2300 km2 lower-crustal Western Fiordland Orthogneiss (WFO) batholith. Two structures within Fiordland’s architecture of transpressional shear zones are identified. The gently dipping Misty shear zone records syn-magmatic oblique-sinistral thrust motion between ca. 123 and ca. 118 Ma, along the lower-crustal WFO Misty Pluton margin. The subhorizontal South Adams Burn thrust records mid-crustal arc-normal shortening between ca. 114 and ca. 111 Ma. Both structures are localized within and reactivate a recently described &gt;10 km-wide Paleozoic crustal boundary, and show that deformation migrated upwards between ca. 118 and ca. 114 Ma. WFO emplacement and crystallization (mainly 118–115 Ma) coincided with elevated (&gt;750 °C) middle- and lower-crustal Zr-in-titanite temperatures and the onset of mid-crustal cooling at 5.9 ± 2.0 °C Ma−1 between ca. 118 and ca. 95 Ma. We suggest that reduced strength contrasts across lower-crustal pluton margins during crystallization caused deformation to migrate upwards into thermally weakened rocks of the mid-crust. The migration was accompanied by partitioning of deformation into domains of arc-normal shortening in Paleozoic metasedimentary rocks and domains that combined shortening and strike-slip deformation in crustal-scale subvertical, transpressional shear zones previously documented in Fiordland. U-Pb titanite dates indicate Carboniferous–Cretaceous (re)crystallization, consistent with reactivation of the inherited boundary. Our results show that spatio-temporal patterns of transpression are influenced by magma emplacement and crystallization and by the thermal structure of a reactivated boundary.

Modelling the thermal perturbation of the continental crust after intraplating of thick granitoid sheets: a comparison with the crustal sections in Calabria (Italy)

2002 ◽  
Vol 139 (6) ◽  
pp. 699-706 ◽  
Author(s):  
A. CAGGIANELLI ◽  
G. PROSSER
Keyword(s):  
Metamorphic Rocks ◽  
Thermal Gradients ◽  
Upper Crust ◽  
Mantle Lithosphere ◽  
Thermal Perturbation ◽  
Magma Intrusion ◽  
Lithosphere Thinning ◽  
Peak Metamorphism ◽  
Granitoid Emplacement ◽  
Lower Crustal

Thick granitoid sheets represent a considerable percentage of Palaeozoic crustal sections exposed in Calabria. High thermal gradients are recorded in upper and lower crustal regional metamorphic rocks lying at the roof and base of the granitoids. Ages of peak metamorphism and emplacement of granitoids are mostly overlapping, suggesting a connection between magma intrusion and low-pressure metamorphism. To analyse this relationship, thermal perturbation following granitoid emplacement has been modelled. The simulation indicates that, in the upper crust, the thermal perturbation is short-lived. In contrast, in the lower crust temperatures greater than 700°C are maintained for 12 Ma, explaining granulite formation, anatexis and the following nearly isobaric cooling. An even longer perturbation can be achieved introducing the effect of mantle lithosphere thinning into the model.

Zircon U–Pb ages, major and trace elements, and Hf isotope characteristics of the Tiantangzhai granites in the North Dabie orogen, Central China: tectonic implications

2013 ◽  
Vol 151 (5) ◽  
pp. 916-937 ◽  
Author(s):  
XIN DENG ◽  
KUNGUANG YANG ◽  
ALI POLAT ◽  
TIMOTHY M. KUSKY ◽  
KAIBIN WU
Keyword(s):  
Partial Melting ◽  
Eastern China ◽  
Major And Trace Elements ◽  
Central China ◽  
Dabie Orogen ◽  
Crustal Rocks ◽  
The North ◽  
Granitic Magmatism ◽  
Two Peaks ◽  
Lower Crustal

AbstractCretaceous granites are widespread in the North Dabie orogen, Central China, but their emplacement sequence and mechanism are poorly known. The Tiantangzhai Complex in the North Dabie Complex is the largest Cretaceous granitic suite consisting of six individual intrusions. In this study, zircon U–Pb ages are used to constrain the crystallization and protolith ages of these intrusions. The Shigujian granite is a syn-tectonic intrusion with an age of 141 Ma. This granite was emplaced under a compressional regime. Oscillatory rims of zircons have yielded two peaks at 137±1 Ma and 125±1 Ma. The 137±1 Ma peak represents the beginning of orogenic extension and tectonic collapse, whereas the 125±1 Ma peak represents widespread granitic magmatism. Zircon cores have yielded concordant ages between 812 and 804 Ma, which indicate a crystallization age for the protolith. The Tiantangzhai granites show relatively high Sr contents and high La/Yb and Sr/Y ratios. The Shigujian granite has positive Eu anomalies resulting from partial melting of a plagioclase-rich source in an over-thickened crust. Correspondingly, in situ Lu–Hf analyses from zircons yield high negative εHf(t) values from −24.8 to −26.6, with two-stage Hf model ages from 2748±34 to 2864±40 Ma, suggesting that the magmas were dominantly derived from partial melting of middle to lower crustal rocks. The Dabie orogen underwent pervasive NW–SE extension at the beginning of the early Cretaceous associated with subduction of the Palaeo-Pacific plate beneath eastern China.

The response of the thermal stratification of South Bay (Lake Huron) to climatic variability

1997 ◽  
Vol 54 (8) ◽  
pp. 1873-1882 ◽  
Author(s):  
J R King ◽  
B J Shuter ◽  
A P Zimmerman
Keyword(s):  
Thermal Structure ◽  
Climatic Variability ◽  
Warming Trend ◽  
Lake Huron ◽  
Thermal Gradients ◽  
Data Set ◽  
Mount Pinatubo ◽  
Recent Warming ◽  
Air Temperatures ◽  
Canonical Analyses

The 37-year record (1955-1992) of water temperature profiles and corresponding meteorology for South Bay (Lake Huron) provide an extensive empirical data set for the study of climate variability and corresponding alterations in lake thermal structure. Thermoclines became shallower over this period and epilimnetic temperatures increased. Canonical analyses correlated warm May-July air temperatures and high July-August solar radiation with warmer epilimnia, larger thermal gradients across the thermocline, and shallower thermoclines. Multivariate canonical scores indicate that these thermal responses have increased in parallel with the recent warming trend since the mid-1960s. Anomalous multivariate scores correspond to El Niño events, and an extreme low score corresponds to the Mount Pinatubo cooling effect of 1992.

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