Structural Investigations of the Italian Trap Allochthon, Redington Pass, Pima County, Arizona
AuthorBenson, Gregory Scott
Italian Trap Allochthon
Pima County Arizona
Santa Catalina-Rincon Metamorphic Core Complex
Rock deformation -- Arizona -- Redington Pass
Geology, Structural -- Arizona -- Redington Pass
Faults (Geology) -- Arizona -- Redington Pass
Committee ChairDavis, George H.
MetadataShow full item record
PublisherThe University of Arizona.
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AbstractItalian Trap Allochthon is a rare upper-plate exposure of Paleozoic metasedimentary and Precambrian to Tertiary crystalline tectonites in the Santa Catalina-Rincon metamorphic core complex. Elsewhere in the complex, metasedimentary tectonite is usually restricted to an autochthononous position. The internal structures of the allochthon consist of numerous low-angle faults, tear faults, and overturned asymmetric and upright folds. Close association of the low-angle faults and asymmetric folds, and vergence of the folds, indicates that these folds were formed during westward transport along the low-angle faults. The structures of the allochthon are truncated and rotated to the northeast by a listric (?) normal fault. The probable shape of the fault surface, together with the northeastward rotation of the internal structures, suggests translation of the allochthon from the northeast to the southwest. The fact that metasedimentary tectonites are found in upper- plate position indicates that the listric (?) normal faulting post-dates the metamorphism of the Paleozoic and Mesozoic strata. Metamorphism in turn was part of the development of the Santa Catalina-Rincon metamorphic core complex. It is inferred that the Italian Trap Allochthon was emplaced in the final stages of profound regional extension which prevailed during the mid-Tertiary in southern Arizona.
Degree ProgramGraduate College
Degree GrantorUniversity of Arizona
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Cenozoic stratigraphy and paleo-hydrology of the Redington-San Manuel area, San Pedro Valley, ArizonaAgenbroad, Larry D. (The University of Arizona., 1967)Post-Miocene fluvial and lacustrine units coristitute the valley fill of the San Pedro Valley, near Redington, Arizona. These sediments are relatively flat lying units deposited on older, deformed sediments, fault blocks of Tertiary volcanics, and erosion surfaces on Precambrian crystalline rocks. The sedimentary sequence is composed of silts, inudstone, sands, gravels, limestone, gypsum, diatomite, and pyroclastic units. Previous investigations have designated these lithologies one unit, the Gila Conglomerate. A recent study in the Mammoth area (Heindi, 1963) subdivided the Gila Conglomerate into the Quiburis formation, Sacaton formation and Pleistocene to Recent alluvial deposits. In the present study, this nomenclature was utilized, with a proposed subdivision of the Quiburis formation. Detailed mapping of the lithologic units indicate a lateral facies change within the Quiburis formation0 The conglomeritic member of the Quiburis formation interfingers with a central, fine-grained member, and the names Tres Alasnos, and Redington are proposed for these units. The age of the Quiburis formation is based on its stratigraphic position, and vertebrate fossils. The Qulbuns ovenlies tilted sediments containing Miocene fauna, and its upper portions contain fauna which have been assigned a middle to late Pliocene Age. The Sacaton formation was deposited on an erosion surface in the Quiburis in late Pliobene to early Pleistocene time; it was then entrenched and local, middle to late Pleistocene lacustnine units were deposited in the drainage pattern. Fresh water mollusks, horse and mammoth remains are present in the lacusbnine units. The Pleistocene lacustrine units were truncated by late Pleistocene terraces, and degradation proceeded to approximately 80 feet below the present floodplain. Aggradation occurred, to a level above the present floodplain, as attested by prehistoric hearths buried in river sediments, above the present stream gradient. Since 1880 the San Pedro River has begun another period of downcutting. The sedimentary deposits control the movement of ground water in the valley. Two hydrologic systems are present; a shallow water table system in the floodplain and river channel area, and an artesian system at 630- 1,200 feet below the valley floor in the northern portion of the study area. It is believed that deformed, pre- Miocene sedinentary units provide the source of recharge to the artesian system. Detailed mapping of the sedimentary units reveals a meandering central trough of the ancestoral San Pedro River. The contact between the Redington and Tres Alamos members of the Quiburis formation indicate the meander pattern, and its control by bedrock outcrop. Structural activity continued through Pliocene time, and is represented by north trending normal faults. Minor slump structures and small reverse faults are present in the Redington member of the Quiburis formation. A site survey, carried out during the field mapping, resulted in the location of nineteen archaeological sites. The sites range from preceramic Desert Culture to Salado and probably to later cultures such as the Apache. Older sites are peripheral to the valley axis, with more recent sites concentrated along the river. It appears that geologic-hydrologic factors controlling site location are: water sources; agricultural or gathering areas; quarry, or source material sites; and vantage points.