To reactivate or not to reactivate—Nature and varied behavior of structural inheritance in the Proterozoic basement of the eastern Colorado Mineral Belt over 1.7 billion years of earth history

Caine, Jonathan Saul; Ridley, John; Wessel, Zachary R.

doi:10.1130/2010.0018(06)

Cited by 11 publications

(21 citation statements)

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“…Commonly cited evidence includes oblique slip on reverse faults that are misaligned with east‐northeast Laramide compression (Johnston & Yin, ; Neely & Erslev, ; Tindall & Davis, ), presence of inverted basin stratigraphy (Huntoon, ; Lawton, ; Marshak et al, ), and unfolded rocks below Phanerozoic cover strata (Bump, ). Even though some authors (Marshak et al, ; Timmons et al, ) claim that regional‐scale Laramide reverse faults formed through reactivation of regionally extensive Proterozoic fault systems, others claim that reactivation played at most only a local role (e.g., Caine et al, ). The latter is indicated by the independent and systematic change in Laramide reverse fault orientations within the Cordillera (Erslev & Koenig, ).…”

Section: Discussionmentioning

confidence: 99%

Discovery of Major Basement‐Cored Uplifts in the Northern Galiuro Mountains, Southeastern Arizona: Implications for Regional Laramide Deformation Style and Structural Evolution

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Seedorff

2018

Tectonics

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The Laramide orogeny is poorly understood in southeastern Arizona, largely because of complex structural overprinting by mid-Cenozoic extension that occurred over large areas. This study integrates new geological mapping with previous work, combined with structural reconstructions and forward modeling, to determine the primary structural style, timing, evolution, and kinematics of Laramide shortening in the northern Galiuro Mountains. Cenozoic normal faulting in the study area is minor and has only resulted in up to 13°of eastward tilting, as indicated by the gentle dips of synextensional strata. Detailed mapping has revealed newly identified reverse fault systems measuring at least 50 km in combined strike length. Each major fault strikes north-northwest, dips moderately to the west, places older rocks on younger, and has related fault-propagation folds. Once restored to their original orientation, reverse faults range in dip from 38°to 47°. These moderate dips of faults combined with related folds, the significant degree of basement involvement, and cover sequence lacking obvious penetrative deformation indicate that these faults are thick-skinned, basement-cored uplifts. Forward modeling and Cenozoic erosion surfaces suggest regionally extensive Laramide-age tilting to the west-southwest and gentle folding, possibly caused by a regional-scale reverse fault underlying the study area. These results are consistent with the interpretation that Laramide shortening in southeastern Arizona was primarily characterized by thick-skinned tectonics. Kinematic indicators, folded basement rocks, north-northwest strikes of reverse faults, and lack of evidence for basin inversion suggest that preexisting basement faults and fabrics had little or no effect on the subsequent structural evolution.Plain Language Summary The Late Cretaceous to early Eocene Laramide orogeny was a period of crustal shortening in the North American Cordillera that involved two different styles of reverse faulting. One style involves low-angle thrusts that typically slip parallel to bedding planes in layered rocks, whereas the other style involves faults that cut across bedding at moderate angles and continue downward through underlying crystalline basement rock. In southeastern Arizona, the style of Laramide shortening is debated and not well understood, in part because most of the region has undergone subsequent Cenozoic extension that has significantly rotated, dismembered, and buried most faults formed during Laramide crustal shortening. This study examines a newly discovered set of Laramide reverse faults that extend for more than 50 km along strike and that have only been affected by minor extension. Results from field mapping and structural modeling indicate that these faults are basement-involved, moderate-angle reverse faults. Because the upper crustal architecture across the region is largely consistent, the region as a whole may be characterized by moderate-angle reverse faults. Thus, nearby Laramide faults that have been previously interpr...

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Section: Discussionmentioning

confidence: 99%

Discovery of Major Basement‐Cored Uplifts in the Northern Galiuro Mountains, Southeastern Arizona: Implications for Regional Laramide Deformation Style and Structural Evolution

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Seedorff

2018

Tectonics

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“…Objective 1 will allow discrimination between the two end-member scenarios for halogen enrichment in discrete metamorphic strata discussed above, which can be used to inform decision-making and/or policy procedures for exploration for similar deposits elsewhere, and objective 2 will allow these mineralization events to be understood within the context of the current understanding of the geological evolution of the Colorado Front Range, specifically from the point-of-view of collisional orogenesis during the Proterozoic (cf. Jones and Connelly, 2006;Caine et al, 2010;Jones et al, 2010;Daniel et al, 2013).…”

Section: Project Aims and Motivationmentioning

confidence: 99%

Formation of Topaz-Enriched Gneiss in the East-Central Colorado Front Range via Crystallization of Mesoproterozoic Halogen-Rich Granitic Magmas

Cayes¹

2019

Geological Society of America Abstracts With Programs

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Metamorphic rocks enriched in economically valuable minerals occur in all mountain belts worldwide, yet their processes of formation are often incompletely understood. Topaz [Al2SiO4(F,OH)2] is a naturally occurring nesosilicate of great economic and industrial value, and is most commonly found in silica-rich igneous rocks. However, conspicuous 70-ft-thick bands of topaz-, sillimanite-, rutile-, and quartz-rich (TSRQ) metamorphic gneiss occur in the Evergreen region of the east-central Front Range, Colorado, immediately adjacent to "normal" amphibolite and pelitic schist horizons. Bulk-rock geochemistry and isocon analysis shows that all mobile elements (e.g. Na, K, Mg, Ca) have been leached from these TSRQ rocks when compared to adjacent F-poor lithologies, indicating that the TSRQ gneiss must have interacted at some point with halogen-rich fluids. In addition, thermobarometry conducted via conventional and phase diagram-based techniques suggests pressure-temperature conditions of equilibration of ~720 °C and ~6.0 kbar, defining isotherms consistent with metamorphism in the middle continental crust during active mountain building. In-situ U-Pb dating of monazite within TSRQ units produced concordant ages mostly between c. 1.70 Ga, recording burial and prograde metamorphism associated with the Yapavai and/or Matatzal orogeny, and c. 1.65 Ga representing the timing of later F-rich fluid metasomatism. Together, these data are interpreted as recording metasomatic alteration in the middle crust by F-rich fluids released due to crystallization of nearby plutons, such as the Boulder Creek granodiorite at c. 1.71 Ga. As such, these topaz-rich horizons are interpreted to represent in-situ transformation of an older metamorphic assemblage, and not the metamorphosed products of weathered, pre-orogenic high-F tuffs or lava flows that were subsequently buried, as suggested by some previous studies. These results have far-reaching implications for constraining the behavior of halogens in the geological environment and for defining best-practices for future exploration of F-rich metamorphic rocks and ore deposits.

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“…Such evidence includes colocation and co-orientation (cf. Caine et al, 2010) of reverse and strike-slip faults with major and minor normal faults and associated structures. However, no evidence was found to indicate reactivation of Proterozoic mylonitic structures, folds, or foliations.…”

Section: Kinematic and Paleostress Analysesmentioning

confidence: 99%

“…This suggests that early, bulk hydrothermal alteration in the incipient fault zones was important in localizing progressive strain by argillic weakening (cf. Caine et al, 2010;Backeberg et al, 2016). Fault zone architecture likely evolved from zones of distributed fracturing to composite deformation zones with well-developed younger fault cores surrounded by older damage and alteration zones.…”

Section: Fault Zone Mineralogy and Elemental Geochemistrymentioning

confidence: 99%

A comprehensive survey of faults, breccias, and fractures in and flanking the eastern Española Basin, Rio Grande rift, New Mexico

et al. 2017

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A comprehensive survey of geologic structures formed in the Earth's brittle regime in the eastern Española Basin and flank of the Rio Grande rift, New Mexico, reveals a complex and protracted record of multiple tectonic events. Data and analyses from this representative rift flank-basin pair include measurements from 53 individual fault zones and 22 other brittle structures, such as breccia zones, joints, and veins, investigated at a total of just over 100 sites. Structures were examined and compared in poorly lithified Tertiary sedi ments, as well as in Paleozoic sedimentary and Proterozoic crystalline rocks. Data and analyses include geologic maps; field observations and measurements; orientation, kinematic, and paleostress analyses; statistical examination of fault trace lengths derived from aeromagnetic data; mineralogy and chemistry of host and fault rocks; and investigation of fault versus bolideimpact hypotheses for the origin of enigmatic breccias found in the Proterozoic basement rocks. Fault kinematic and paleostress analyses suggest a record of transitional, and perhaps partitioned, strains from the Laramide orogeny through Rio Grande rifting. Normal faults within Tertiary basin-fill sediments are consistent with more typical WNW-ESE Rio Grande rift extension, perhaps de coupled from bedrock structures due to strength contrasts favoring the formation of new faults in the relatively weak sediments. Analyses of the fault-length data indicate power-law length distributions similar to those reported from many geologic settings globally. Mineralogy and chemistry in Proterozoic fault-related rocks reveal geochemical changes tied to hydro thermal alteration and nearly isochemical transformation of feldspars to clay minerals. In sediments, faulted minerals are characterized by mechanical entrainment with minor secondary chemical changes. Enigmatic breccias in rift-flanking Protero zoic rocks are autoclastic and isochemical with respect to their protoliths and exist near shatter cones believed to be related to a previously reported pre-Pennsylvanian impact event. A weak iridium anomaly is associated with the breccias as well as adjacent protoliths, thus an impact shock wave cannot be ruled out for their origin. Major fault zones along the eastern rift-flank mountain front are discontinuous and unlikely to impede regional groundwater flow into Española Basin aquifers. The breccia bodies are not large enough to constitute aquifers, and no fault-or breccia-related geochemical anomalies were identified as potential contamination sources for ground or surface waters. The results of this work provide a broad picture of structural diversity and tectonic evolution along the eastern flank of the central Rio Grande rift and the adjacent Española Basin representative of the rift as a whole and many rifts worldwide.

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To reactivate or not to reactivate—Nature and varied behavior of structural inheritance in the Proterozoic basement of the eastern Colorado Mineral Belt over 1.7 billion years of earth history

Cited by 11 publications

References 0 publications

Discovery of Major Basement‐Cored Uplifts in the Northern Galiuro Mountains, Southeastern Arizona: Implications for Regional Laramide Deformation Style and Structural Evolution

Discovery of Major Basement‐Cored Uplifts in the Northern Galiuro Mountains, Southeastern Arizona: Implications for Regional Laramide Deformation Style and Structural Evolution

Formation of Topaz-Enriched Gneiss in the East-Central Colorado Front Range via Crystallization of Mesoproterozoic Halogen-Rich Granitic Magmas

A comprehensive survey of faults, breccias, and fractures in and flanking the eastern Española Basin, Rio Grande rift, New Mexico

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