Primary and secondary flow structures in ash-flow tuffs of the Gribbles Run paleovalley, central Colorado

Chapin, Charles E.; Lowell, Gary R.

doi:10.1130/spe180-p137

Cited by 97 publications

(93 citation statements)

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“…The best control on the structural evolution of the area is provided by the voluminous ash-flow tuffs because these widespread sheets buried much preexisting topography. The tops of the voluminous welded tuff sheets and the compaction foliations within them can be used as paleohorizontal indicators, with appropriate precautions (for example, recognition of primary tilting of compaction foliations induced by post-welding flow; Chapin and Lowell, 1979).…”

Section: Volcanic Settingmentioning

confidence: 99%

Tectonic evolution of the Crater Flat basin, Yucca Mountain region, Nevada

Fridrich¹

1998

Open-File Report

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Yucca Mountain is an arcuate, multiple-fault-block ridge on the rim of Crater Rat in southern Nevada. The ridge and alluvial flat are structurally linked and together constitute the Crater Flat structural basin. This late Cenozoic basin is located on the south flank of the southwest Nevada volcanic field, which in turn lies along the northeast margin of the Walker Lane belt, a northwest-trending zone of irregular topography and structure between the Sierra Nevada and the northern Basin and Range province. The Crater Flat basin is filled dominantly by the major ash-flow tuff sheets erupted from the central caldera complex of the volcanic field, at the north boundary of the basin. Relations in the volcanic rocks, including tilting, faulting, unitthickness changes, and vertical-axis rotations, provide a detailed record of the tectonic history of Crater Flat and adjacent structural domains.Strata within Crater Flat basin are tilted dominantly eastward to southeastward along a closely spaced system of mostly west-to northwest-dipping normal faults. This tilted-domino structural style resembles that of many areas of extreme extension and detachment faulting. However, in Crater Flat, as in much of the volcanic field, this style is developed at moderate to low percentages of extension, such that detachment faulting appears unlikely. Crater Flat formed by a combination of east-west to southeast-northwest extension and northwest-directed dextral deformation, the latter of which is indicated by oblique slickenlines on most intrabasin normal faults and paleomagnetic evidence of oroflexural bending along a northwest-trending axis through the basin. The spatial variation in the percentage of extension and in the degree of vertical-axis rotation within the Crater Flat domain resembles that of a triangular pull-apart basin. A major strike-slip fault(s) may be associated with this basin but, if so, it is somehow concealed. The caldera complex at the north boundary of Crater Flat influenced the structures of this basin by locally modifying the regional stress regime and by doming the rocks peripheral to the calderas; however, the structures of Crater Flat basin are products of regional tectonism, not of caldera collapse.The new field evidence gathered in this study thus does not support previous suggestions that Crater Flat formed through the action of some single concealed master structure, such as a regional detachment fault, a caldera ring-fracture zone, or a major strike-slip fault. This is not to say that any of those three features are necessarily absent. Rather, the major conclusion at this point is that Crater Flat basin is a hybrid feature; its geometry reflects the combination of structural influences that are specific to its setting on the flank of a large caldera complex, at the boundary between the Walker Lane belt and the northern Basin-and-Range province, and at the periphery of a major domain -to the west -of extreme extension associated with detachment faulting.In the Crater Flat region, belts of active e...

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Section: Volcanic Settingmentioning

confidence: 99%

Tectonic evolution of the Crater Flat basin, Yucca Mountain region, Nevada

Fridrich¹

1998

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“…Ragan and Sheridan (1972) found that the rotated lithic clasts and rotated segments of broken fiamme might be the results of post emplacement loading. Wolff and Wright (1981) further proposed that lineation of high-grade ignimbrites are diagnostic of post-depositional "re-flowing" in contrast to the idea of Chapin and Lowell (1979) and Reedman at al. (1987) that consider these features as formed during initial deposition.…”

Section: Ignimbritic Textures: a Reviewmentioning

confidence: 91%

“…In the case of ignimbrites these features are associated with prolate, elongated fiamme and vesicles (Schmincke and Swanson, 1967;Chapin and Lowell, 1979;Wolff and Wright, 1981;Summer and Branney, 2002;Pioli and Rosi, 2005;Andrews and Branney, 2011;Brow and Bell, 2013). When the coalescence of "soft" pyroclasts reaches very high grades and the rheomorphism develops deeply in the ignimbrite the original clast features are totally obliterated and the deposit appears as a flow-banded lava-like (Andrews and Branney, 2011) that complicate the discrimination with a lava flow.…”

Section: Ignimbritic Textures: a Reviewmentioning

confidence: 99%

Paleoproterozoic felsic volcanism of the Tapajós Mineral Province, Southern Amazon Craton, Brazil

Roverato

Giordano

Echeverri-Misas

et al. 2016

Journal of Volcanology and Geothermal Research

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Amazonian rocks record one amongst the most complete and best-preserved Paleoproterozoic magmatic episodes on Earth. The present contribution documents the extremely well preserved paleoproterozoic architecture of a series of felsic rocks found in the Tapajós Mineral Province (TMP), located in the western part of Pará state, southern Amazon Craton, north of Brazil. These rocks are the first to be investigated to comprehend, based on their textural evidences, their emplacement mechanisms. Textural characterization allowed to identify three main facies with, as following reported, 1) chaotic ("Breccia") group, 2) eutaxitic ("Eutax") group and 3) parataxitic ("Paratax") group vitrophyric texture. Given the superb preservation of our samples, the investigated rocks are grouped, according to their grade of welding, into a wide variety of lithofacies from very low-grade to high-grade and rheomorphic ignimbrites. In the "paratax group" strong similarities with banding in lava flows are observed. Based on the presented data we discuss the effusive or explosive origin of the observed flow mechanisms.

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“…Since the Cardones ignimbrite was emplaced into deep valleys (van Zalinge et al 2016b), lateral flow may also reflect downslope movement of the ignimbrite, with related laminar shear (e.g. Chapin and Lowell 1979). This explains the similarity in form to metamorphic textures, including Θ-type and ϕ-type mantled porpyroclasts (Fig.…”

Section: Compaction-related Secondary Fragmentationmentioning

confidence: 99%

Causes of fragmented crystals in ignimbrites: a case study of the Cardones ignimbrite, Northern Chile

2018

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Broken crystals have been documented in many large-volume caldera-forming ignimbrites and can help to understand the role of crystal fragmentation in both eruption and compaction processes, the latter generally overlooked in the literature. This study investigates the origin of fragmented crystals in the > 1260 km 3 , crystal-rich Cardones ignimbrites located in the Central Andes. Observations of fragmented crystals in non-welded pumice clasts indicate that primary fragmentation includes extensive crystal breakage and an associated ca. 5 vol% expansion of individual crystals while preserving their original shapes. These observations are consistent with the hypothesis that crystals fragment in a brittle response to rapid decompression associated with the eruption. Additionally, we observe that the extent of crystal fragmentation increases with increasing stratigraphic depth in the ignimbrite, recording secondary crystal fragmentation during welding and compaction. Secondary crystal fragmentation aids welding and compaction in two ways. First, enhanced crystal fragmentation at crystal-crystal contacts accommodates compaction along the principal axis of stress. Second, rotation and displacement of individual crystal fragments enhances lateral flow in the direction(s) of least principal stress. This process increases crystal aspect ratios and forms textures that resemble mantled porphyroclasts in shear zones, indicating lateral flow adds to processes of compaction and welding alongside bubble collapse. In the Cardones ignimbrite, secondary fragmentation commences at depths of 175-250 m (lithostatic pressures 4-6 MPa), and is modulated by both the overlying crystal load and the time spent above the glass transition temperature. Under these conditions, the existence of force-chains can produce stresses at crystal-crystal contacts of a few times the lithostatic pressure. We suggest that documenting crystal textures, in addition to conventional welding parameters, can provide useful information about welding processes in thick crystal-rich ignimbrites.

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Primary and secondary flow structures in ash-flow tuffs of the Gribbles Run paleovalley, central Colorado

Cited by 97 publications

References 0 publications

Tectonic evolution of the Crater Flat basin, Yucca Mountain region, Nevada

Tectonic evolution of the Crater Flat basin, Yucca Mountain region, Nevada

Paleoproterozoic felsic volcanism of the Tapajós Mineral Province, Southern Amazon Craton, Brazil

Causes of fragmented crystals in ignimbrites: a case study of the Cardones ignimbrite, Northern Chile

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