COCORP Seismic-reflection Profiling Research Articles

Velocity models for the highly extended crust of Death Valley, California

We employ nonlinear optimization to obtain shallow velocity structure from COCORP seismic reflection profiles in the highly extended Death Valley region, California. We also use group‐velocity analysis of regional earthquake surface waves that have traversed in and near the extended domain. When compared with regional models for surrounding provinces, our results show no evidence for significant uplift of the middle crust or removal of the upper crust. We do not find fundamental upper‐crustal variations between regions proposed to have widely varying extensional histories. These observations constrain previously proposed extensional mechanisms toward less than extreme amounts of extension.

Exploring the Basement Structure of the Continental Interior: Reprocessing and Analysis of COCORP and Industrial Seismic Reflection Profiles and a Plan for Project CRATON: ABSTRACT

Exploring the Basement Structure of the Continental Interior: Reprocessing and Analysis of COCORP and Industrial Seismic Reflection Profiles and a Plan for Project CRATON: ABSTRACT

The Cordilleran Foreland Thrust Belt in Northwestern Montana and Northern Idaho From COCORP and Industry Seismic Reflection Data (1)

COCORP and petroleum industry seismic reflection profiles in northwestern Montana reveal the structure of the Cordilleran foreland thrust belt. The Front Ranges consist of thick thrust sheets containing Precambrian Belt Supergroup and Paleozoic miogeoclinal shelf rocks above a thin remnant of Paleozoic rocks and gently westward-dipping North American basement. Interpretation of the seismic data and results from a recent petroleum exploration well suggest that 15-22 km of Precambrian Belt Supergroup sedimentary rocks are present in several thrust plates beneath the eastern Purcell anticlinorium. Previous hypotheses of a large mass of Paleozoic miogeoclinal sedimentary rocks or slices of crystalline basement located beneath the eastern Purcell anticlinorium do not appear to be supported by the data. The easternmost occurrence of allochthonous basement is interpreted to be in the western part of the anticlinorium near the Montana-Idaho border. Comparison of the Cordilleran foreland thrust belt in northwestern Montana and southern Canada suggests that a change in the deep structure of the Purcell anticlinorium occurs along strike. The anticlinorium in southern Canada has been interpreted as a hanging-wall anticline that was thrust over the western edge of thick Proterozoic North American basement, whereas in northwestern Montana the anticlinorium appears to consist of a complex series of thrust sheets above highly attenuated North American basement.

The deep crustal structure of the Mojave Desert, California, from Cocorp seismic reflection data

COCORP seismic reflection profiling in the western and northern Mojave Desert of southern California has revealed the presence of numerous major low‐angle reflecting horizons within the crust. These complex, though laterally continuous, horizons are interpreted to represent major southwesterly dipping crustal fault zones, and as such they place important constraints on the tectonic evolution of the region. The upper‐most horizon is interpreted to be the Rand thrust, which, where exposed, places Precambrian and Late Cretaceous crystalline rocks over possibly younger Pelona‐Rand‐Orocopia Schist. This reflecting horizon extends for 25 km southwest of the Rand Mountains where it appears to be truncated at a depth of about 7.4 km by another horizon, which may be a later low‐angle normal fault. The other reflecting horizons are not traceable to the surface, and so greater ambiguity remains in their interpretation. The most prominent of these horizons occurs at midcrustal depths (15±6 km), exhibits a “ramp and flat” geometry, and extends over the northern area of the Mojave survey into the Basin and Range Province. A lower horizon, at depths of 20–30 km in the northern part of the survey area, is antiformal and appears to terminate above a flat and relatively continuous Moho‐depth horizon. The crustmantle transition appears to be represented by a continuous series of reflections which occur at about 10 s (33 km) in the north of the survey and at about 8–9 s (26–29 km) in the south. These reflections are offset in the vicinity of the town of Mojave. The deep intracrustal fault zones inferred from the COCORP survey may represent (1) the deep crustal continuation of the system of Mesozoic thrusts which crops out in southern Nevada and southeastern California, (2) Late Cretaceous to Early Cenozoic, northeast‐vergent thrusts related to the uplift of the Pelona‐Orocopia‐Rand Schist, or (3) low‐angle normal faults related to Early Miocene, northeast‐southwest directed crustal extension. The COCORP survey also traversed the major strike‐slip faults that bound the Mojave block. The San Andreas fault zone appears to truncate reflectors at depths of 6, 8 and 20 km within the Mojave basement, suggesting that it is a major vertical feature which extends to at least 20 km depth. Conversely, the Garlock fault does not offset an underlying reflecting horizon which occurs at 9 km depth and therefore appears to be a relatively shallow crustal feature.

The Moho in the northern Basin and Range province, Nevada, along the COCORP 40°N seismic-reflection transect

COCORP seismic-reflection profiles across Nevada at about 40°N image a prominent, essentially continuous band of reflectors at a two-way traveltime of 9 to 11 s. The approximate correspondence of this reflection time with estimates of the two-way traveltime to the Moho in this area provided by seismic-refraction data suggests that the prominent reflections are from the Moho. The relief on these reflectors (the “reflection Moho”) beneath Nevada, across a latitudinal transect of

Some results of COCORP seismic reflection profiling in the Grenville-age Adirondack Mountains, New York State

COCORP deep seismic reflection profiling in the Adirondack Mountains of northern New York State has revealed a prominent zone of layered reflectors in the lower crust of the east-central Adirondacks. The strong, layered reflectors (here termed the Tahawus complex) occur between 18 and 26 km depth, beneath the sparsely reflective, granulite-grade, surface terrane, which has been uplifted from depths greater than 20 km. The Tahawus complex apparently represents layered rocks of some type in the lower crust of the Adirondacks. Possibilities include gneissic layering, cumulate igneous layering, a layered sill complex, and underthrust sedimentary strata, The Tahawus complex may be spatially coincident with a previously detected, high-conductivity zone in the lower crust, suggesting that either unusual mineralogies or interstitial electrolytes are present in the Tahawus complex. In contrast to layered reflections discovered in the lower crust of the east-central Adirondacks and southeast of the Adirondacks, cross-cutting and discontinuous reflections are recorded from the upper crust on all the COCORP Adirondack lines, including lines in both the Adirondack Highlands and Lowlands. Available three-dimensional control suggests that reflections in the upper crust of the central Adirondacks are parallel to, and hence may be related to, the folded gneisses mapped at the surface. Shallow events are also observed on a COCORP profile close to the epicenter of the 7 October 1983 magnitude 5.2 earthquake in the central Adirondacks, but their relation to the earthquake is uncertain.

The Snake Range Décollement interpreted as a major extensional shear zone

Geological and geophysical constraints suggest that the Snake Range décollement of east‐central Nevada is a major Tertiary low‐angle normal fault zone. This interpretation is consistent with all existing data, and alleviates problems that result if large displacement across the décollement is excluded [Miller et al., 1983]. Based on published surface geology and COCORP seismic reflection profiling, we have constructed cross sections that suggest approximately 60 km of normal displacement on the décollement. Advantages of this interpretation over models that exclude large displacement are that it provides for overburden consistent with kyanite‐grade metamorphism of footwall rocks, predicts reasonable crustal thicknesses before and after extension without invoking unexposed mantle‐derived Tertiary intrusions at depth, and explains contrasting metamorphism and structural styles of hanging wall and footwall without requiring an extreme geothermal gradient during regional metamorphism and extensional strain. The present domal shape of the décollement is interpreted to result at least partly from reverse drag above an underlying, younger detachment related to much of the extension in ranges to the west of the Snake Range.

COCORP seismic profiles near Coalinga, California: Subsurface structure of the western Great Valley

COCORP seismic reflection profiles collected in 1977 on the west side of the San Joaquin Valley near Coalinga in southern California provide information on the Cenozoic and Mesozoic structures in the subsurface of the western Great Valley. The data show evidence of significant normal faulting during the Cretaceous, when this part of California was the site of a forearc basin. Neogene compression, probably associated with transform motion on the nearby San Andreas fault system, may be reactivating these pre-existing faults in a reverse sense and causing the active folding of the southern Coast Ranges. The recent Coalinga earthquake sequence that began on May 2, 1983, appears to correspond to movement on the high-angle reverse fault within the basement that is inferred from the COCORP lines.

Flexure of Anadarko Basin: ABSTRACT

The Anadarko basin in Oklahoma has long been a major oil and gas producing region and contains the deepest wells drilled in North America. The region has had a long sedimentary-tectonic history reaching back to the Proterozoic and was the site of an early Paleozoic basin. The present shape of the Anadarko basin, however, was developed in late Paleozoic times as a result of the uplift of the Wichita Mountains. COCORP seismic reflection profiles show at least 8 to 9 km (5 to 5.6 mi) of overthrusting northward, and the Anadarko basin was developed as a result of flexural bending of the lithosphere due to this shortening. Downwarping of the basin can be observed to extend for over 300 km (185 mi) northward, indicating a high flexural rigidity (Te > 40 km [25 mi]). However, nearer the Wichita front, the basin steepens rapidly as the post-Mississippian sediments thicken to over 20,000 ft (6,100 m). The shape of the bending is such that it cannot be explained by the use of a constant rigidity elastic plate model. We have modeled the post-Mississippian development of the Anadarko basin as the result of flexure of an elastic-plastic plate due to vertical and horizontal loading caused by the Wichita Mountains. Implications of these results for the development of the Anadarko basin and the mechanical properties of continental lithosphere will be discussed. End_of_Article - Last_Page 552------------

Cocorp seismic reflection profiling in the Ouachita Mountains of western Arkansas: Geometry and geologic interpretation

COCORP seismic reflection profiling in the Ouachita Mountains of western Arkansas indicates that (1) Carboniferous foreland basin deposits within the Arkoma Basin thicken dramatically toward the south, reaching an aggregate thickness in excess of 12 km (4.5 s two‐way travel time) beneath the southern edge of the Frontal Thrust Zone, (2) evidence for northward directed low‐angle thrusting within this clastic sequence is prominent, with a probable decollement surface lying at or near the contact with underlying Early Paleozoic shelf carbonates, (3) beneath the Benton Uplift a sequence of discontinuous events defines a broad antiform cresting at approximately 7 km (2.8 s); this structure appears to mimic the anticlinorial shape of the Benton Uplift indicated by the surface outcrop pattern, (4) beneath the Southern Ouachitas, south dipping stratified events are observed to depths in excess of 14 km (5.0 s), (5) deeper in the section a prominent, gently north dipping reflection occurs at approximately 22 km depth (7.6 s) beneath the northern Coastal Plain/Southern Ouachitas.Extrapolation of data along strike in the Ouachita belt, and consideration of large‐scale structure observed in other collisional orogenic belts, suggest that the reflection events observed beneath the Benton Uplift represent Early Paleozoic shelf carbonates correlative with those that floor the Arkoma Basin to the north. This interpretation requires that the Early Paleozoic deep‐water sediments exposed in the core of the Ouachitas be allochthonous, and also implies significant basement uplift beneath the core zone. To the south, the prominent package of layered reflections occurring beneath the Southern Ouachitas and northern Coastal Plain indicates that a significant portion of the crust in that region is composed of imbricate sedimentary and/or metasedimentary strata. At relatively ‘shallow’ levels these strata are correlative with the Carboniferous flysch cropping out in the Southern Ouachitas, and at somewhat deeper levels, they are correlative with the Early to Middle Paleozoic deep‐water sediments exposed on the Benton Uplift.

Comments and Replies on ‘Thin-skinned tectonics in the crystalline southern Appalachians; COCORP seismic-reflection profiling of the Blue Ridge and Piedmont’ and ‘Sequential development of the Appalachian orogen above a master decollement—A hypothesis’

Comments and Replies on ‘Thin-skinned tectonics in the crystalline southern Appalachians; COCORP seismic-reflection profiling of the Blue Ridge and Piedmont’ and ‘Sequential development of the Appalachian orogen above a master decollement—A hypothesis’

Comments and Replies on ‘Thin-skinned tectonics in the crystalline southern Appalachians; COCORP seismic-reflection profiling of the Blue Ridge and Piedmont’ and ‘Sequential development of the Appalachian orogen above a master decollement—A hypothesis’

Comments and Replies on ‘Thin-skinned tectonics in the crystalline southern Appalachians; COCORP seismic-reflection profiling of the Blue Ridge and Piedmont’ and ‘Sequential development of the Appalachian orogen above a master decollement—A hypothesis’

Comment and Reply on ‘Thin-skinned tectonics in the crystalline southern Appalachians; COCORP seismic-reflection profiling of the Blue Ridge and Piedmont’

Comment and Reply on ‘Thin-skinned tectonics in the crystalline southern Appalachians; COCORP seismic-reflection profiling of the Blue Ridge and Piedmont’

Comment and Reply on ‘Thin-skinned tectonics in the crystalline southern Appalachians; COCORP seismic-reflection profiling of the Blue Ridge and Piedmont’

Research Article| September 01, 1980 Comment and Reply on ‘Thin-skinned tectonics in the crystalline southern Appalachians; COCORP seismic-reflection profiling of the Blue Ridge and Piedmont’: COMMENT Robert H. Moench Robert H. Moench 1Mail Stop 930, U.S. Geological Survey, 25046 Federal Center, Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar Author and Article Information Robert H. Moench 1Mail Stop 930, U.S. Geological Survey, 25046 Federal Center, Denver, Colorado 80225 Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1980) 8 (9): 402. https://doi.org/10.1130/0091-7613(1980)8<402:CAROTT>2.0.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Robert H. Moench; Comment and Reply on ‘Thin-skinned tectonics in the crystalline southern Appalachians; COCORP seismic-reflection profiling of the Blue Ridge and Piedmont’: COMMENT. Geology 1980;; 8 (9): 402. doi: https://doi.org/10.1130/0091-7613(1980)8<402:CAROTT>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract No Abstract Available. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Comments and Replies on ‘Thin-skinned tectonics in the crystalline southern Appalachians; COCORP seismic-reflection profiling of the Blue Ridge and Piedmont’ and ‘Sequential development of the Appalachian orogen above a master decollement—A hypothesis’

Comments and Replies on ‘Thin-skinned tectonics in the crystalline southern Appalachians; COCORP seismic-reflection profiling of the Blue Ridge and Piedmont’ and ‘Sequential development of the Appalachian orogen above a master decollement—A hypothesis’

Comments and Replies on ‘Thin-skinned tectonics in the crystalline southern Appalachians; COCORP seismic-reflection profiling of the Blue Ridge and Piedmont’ and ‘Sequential development of the Appalachian orogen above a master decollement—A hypothesis’

Comments and Replies on ‘Thin-skinned tectonics in the crystalline southern Appalachians; COCORP seismic-reflection profiling of the Blue Ridge and Piedmont’ and ‘Sequential development of the Appalachian orogen above a master decollement—A hypothesis’

Comments and Replies on ‘Thin-skinned tectonics in the crystalline southern Appalachians; COCORP seismic-reflection profiling of the Blue Ridge and Piedmont’ and ‘Sequential development of the Appalachian orogen above a master decollement—A hypothesis’

Comments and Replies on ‘Thin-skinned tectonics in the crystalline southern Appalachians; COCORP seismic-reflection profiling of the Blue Ridge and Piedmont’ and ‘Sequential development of the Appalachian orogen above a master decollement—A hypothesis’

Thin-skinned tectonics in the crystalline southern Appalachians; COCORP seismic-reflection profiling of the Blue Ridge and Piedmont

Research Article| December 01, 1979 Thin-skinned tectonics in the crystalline southern Appalachians; COCORP seismic-reflection profiling of the Blue Ridge and Piedmont Frederick A. Cook; Frederick A. Cook 1Department of Geological Sciences, Cornell University, Ithaca, New York 14853 Search for other works by this author on: GSW Google Scholar Dennis S. Albaugh; Dennis S. Albaugh 1Department of Geological Sciences, Cornell University, Ithaca, New York 14853 Search for other works by this author on: GSW Google Scholar Larry D. Brown; Larry D. Brown 1Department of Geological Sciences, Cornell University, Ithaca, New York 14853 Search for other works by this author on: GSW Google Scholar Sidney Kaufman; Sidney Kaufman 1Department of Geological Sciences, Cornell University, Ithaca, New York 14853 Search for other works by this author on: GSW Google Scholar Jack E. Oliver; Jack E. Oliver 1Department of Geological Sciences, Cornell University, Ithaca, New York 14853 Search for other works by this author on: GSW Google Scholar Robert D. Hatcher, Jr. Robert D. Hatcher, Jr. 2Department of Geology, Florida State University, Tallahassee, Florida 32306 Search for other works by this author on: GSW Google Scholar Geology (1979) 7 (12): 563–567. https://doi.org/10.1130/0091-7613(1979)7<563:TTITCS>2.0.CO;2 Article history first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Frederick A. Cook, Dennis S. Albaugh, Larry D. Brown, Sidney Kaufman, Jack E. Oliver, Robert D. Hatcher; Thin-skinned tectonics in the crystalline southern Appalachians; COCORP seismic-reflection profiling of the Blue Ridge and Piedmont. Geology 1979;; 7 (12): 563–567. doi: https://doi.org/10.1130/0091-7613(1979)7<563:TTITCS>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract COCORP seismic-reflection profiling in Georgia, North Carolina, and Tennessee and related geological data indicate that the crystalline Precambrian and Paleozoic rocks of the Blue Ridge, Inner Piedmont, Charlotte belt, and Carolina slate belt constitute an allochthonous sheet, generally 6 to 15 km thick, which overlies relatively flat-lying autochthonous lower Paleozoic sedimentary rocks, 1 to 5 km thick, of the proto-Atlantic continental margin. Thus, the crystalline rocks of the southern Appalachians appear to have been thrust at least 260 km to the west, and they overlie sedimentary rocks that cover an extensive area of the central and southern Appalachians. The hydrocarbon potential of these sedimentary rocks is unknown and untested. The data show that the Brevard fault is the surface expression of an eastward-dipping splay off the main sole thrust, and they show, or imply, that other major faults of this region have similar origins. The data support the view that large-scale, thin crystalline thrust sheets may be significant features of orogenic zones. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.