Tectonics of the Wolf Creek Fault Zone, southern Illinois: A consequence of Late Paleozoic transpression and transtension at the southeastern end of the Ste. Genevieve Fault System

Wolf Creek Fault Zone;Ste. Genevieve Fault System;transpression;transtension;normal faulting;strike-slip faulting;pull-apart basin;fault splay;tectonics;structural geology;Midcontinent;Illinois geology;Gorham Quadrangle;Altenburg Quadrangle;Pomona Quadrangle;Wolf Lake Quadrangle;Cobden Quadrangle;Alto Pass;Mississippian;Pennsylvanian;Degonia Sandstone

Seid, Mary ; Marshak ; Stephen

关键词: Wolf Creek Fault Zone;    Ste. Genevieve Fault System;    transpression;    transtension;    normal faulting;    strike-slip faulting;    pull-apart basin;    fault splay;    tectonics;    structural geology;    Midcontinent;    Illinois geology;    Gorham Quadrangle;    Altenburg Quadrangle;    Pomona Quadrangle;    Wolf Lake Quadrangle;    Cobden Quadrangle;    Alto Pass;    Mississippian;    Pennsylvanian;    Degonia Sandstone;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/45477/Mary_Seid.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

The Ste. Genevieve Fault System (SGFS) is a 118-mile-long (190 km-long) belt of WNW-trending faults that extends from southwestern-most Illinois, across the Mississippi River, and into southeastern Missouri, in the central (Midwest) United States.East of the Mississippi River, in an area that lies in Jackson and Union Counties, Illinois, the SGFS is about three miles (5 km) wide, and is delineated by the Ste. Genevieve Fault on the SW, and the Pomona Fault on the NE.The region between these two faults is cut by several NNW- to NNE-trending normal faults that together comprise a zone here named the Wolf Creek Fault Zone (WCFZ).While normal faulting, indicative of local crustal stretching, dominates, the region also contains subtle structures indicative of local crustal shortening.Shortening structures, which include local anticlines, and a monocline formed over a buried thrust fault, have the same trend as the normal faults.New geologic mapping and shallow drilling in an 18 mile2 (45 km2) region that includes the WCFZ indicate that normal faulting in the zone produced several tilted fault blocks of Mississippian strata; beds in these blocks now have dips between 15° and 21°.This tilting occurred prior to deposition of the sub-horizontal beds of the Pennsylvanian-age Caseyville Formation, so the contact between Mississippian and Pennsylvanian strata in the WCFZ is an angular unconformity.Existence of this angular unconformity indicates that formation of the WCFZ took place in Late Mississippian/Early Pennsylvanian time (i.e., during the Late Paleozoic).In detail, the WCFZ can be divided into three distinct structural domains—in the Western Domain, normal faults trend NNW; in the Central Domain, pre-Caseyville strata are horizontal and unfaulted; and in the Eastern Domain, normal faults trend NNE.The Western and Eastern Domains each contain two subdomains, one of east-dipping faults and one of west-dipping faults.Each pair of subdomains is separated by an anticlinal axis. Construction of a new conceptual cross section supports the hypothesis that the WCFZ is not a set of paleo-slump blocks, as has been suggested previously, but rather formed due to tectonic stress at a stepover near the southeastern end of the SGFS.To explain the existence of both shortening and extensional structures, the stress state changed over time.First, transpression associated with left-lateral strike-slip on the SGFS produced shortening structures.Later, transtension associated with right-lateral strike-slip produced an extensional pull-apart zone.Similar episodes of deformation have been found in other continental-interior fault-and-fold zones (e.g., the Cottage Grove Fault System and the Sandwich Fault) in the Illinois Basin.The timing of activity in the WCFZ implies that it, and related zones, record a period of Alleghanian/Ouachita continental-interior fault reactivation and propagation, and thus are Midcontinent manifestations of the Ancestral Rockies event.