The Santa Fe Group is a succession of Neogene sandstone, siltstone, conglomerate, and intercalated volcanics that fills the basins of the central Rio Grande rift. Data from twelve deep wells and recently released seismic profiles in the Albuquerque rift basin document a dramatic basinward thickening of the Santa Fe Group across the major basinal faults. Abbreviated thicknesses of less than 1,220 m (4,000 ft) occur on the structurally higher, outer benches, but the section thickens to more than 4,270 m (14,000 ft) in the basin center, on the downthrown sides of the basin’s seismically defined master normal faults.
Triassic evaporites strongly influenced the structural development of the Haltenbanken area of offshore Norway during Late Jurassic and Early Cretaceous time by mechanically decoupling Triassic and younger strata from older strata and basement. Many folds in the Haltenbanken area are forced folds above basement-involved normal faults. Seismic data show that they are asymmetric flexures affecting Triassic, Jurassic, and Lower Cretaceous strata above the evaporites. They commonly are cut by, or die out along strike into, basement-involved normal faults. Extensional forced folds formed, at least in part, because Triassic evaporites behaved in a ductile manner, decoupling overlying strata from underlying faulted strata and basement. Many normal faults in the Haltenbanken rea are basement-detached faults that flatten within the Triassic evaporites. Seismic data show that rollover anticlines and secondary normal faults affect Triassic, Jurassic, and Lower Cretaceous strata within the hanging walls of these basement-detached normal faults. Strata beneath the Triassic evaporites are unaffected by this deformation.
The Albuquerque Basin, located in the central portion of the Rio Grande rift, is filled by 7,350 m of Tertiary clastic sediments deposited on a "basement" of Mesozoic and Paleozoic sedimentary rocks and Precambrian crystalline rocks. The basin has been a center of Cenozoic volcanic activity over the last 37 m.y.
The Oakhurst roof pendant, near Oakhurst, California, consists of three pre-Cretaceous clastic metasedimentary rock units, surrounded and intruded by rocks of the Sierra Nevada batholith. T-..ro zones of probable sheared granitic and ultramafic rocks trend northwesterly and are approximately aligned with the Foothills fault system farther north. The dominant mesoscopic feature of the pendant is a northwesterly.striking foliation which forms a downward converging fan. Earlier-formed hornblende lineations have been transposed into this foliation plane, as shown by Schmidt-net projections. Rocks comprising the three units show three textural stages: (1) Early amph~~oles and diopside overgrown by later static amphibole pophyroblasts, Hornblende lineations in one of these units show a great-circle Schmidt-net distribut ion. (2) A superimposed, well-developed, cataclastic ~-plane (the mesoscopic foliation). (3) Late, static growth of poikiloblastic micas and diopside, straight well-crystallized micas, near polygonal quartz and feldspar, epidote and biotite after amphibole
The Albuquerque basin, located in the central portion of the Rio Grande rift, is filled by 7350 m (24,000 ft) of Tertiary clastic sediments deposited on a of Mesozoic and Paleozoic sedimentary rocks and Precambrian crystalline rocks. The basin has been a center of Cenozoic volcanic activity over the last 37 Ma. The geophysical signature of the Rio Grande rift is grossly similar to the Basin and Range province, being characterized by thin crust, anomalously low upper mantle seismic velocity, and velocity inversion in the upper crust. Additionally, there are high levels of shallow seismicity, abnormally high heat flow, regionally low Bouguer gravity values, and anomalously high electrical conductivities at shallow to mid-crustal depths. Detailed examination of regional seismic reflection data, supplemented by well control and field work, has demonstrated that the Albuquerque basin is asymmetric and structurally complex, consisting of two subbasins downdropped along low-angle to listric, normal faults of opposing structural polarity, some of which flatten at depths of about 10 km (6 mi). The northern subbasin has been downdropped along a major west-dipping, listric normal fault system, whereas the southern subbasin is bordered by a system of major, east-dipping, low-angle normal faults. The two subbasins are separated by a complex, mid-basin transverse structural zone that accommodates the differential extension and polarity change between the basins. End_Page 205------------------------ Palinspastic restorations show that the amount of extension in the Albuquerque basin ranges from 17% in the north basin to at least 28-30% in the south basin. Seismic and outcrop evidence suggest that preexisting structures in the Precambrian basement rocks, in part, may have controlled the geometry of Tertiary structures in this region.
Research Article| October 01, 1977 Structural-metamorphic chronology in a roof pendant near Oakhurst, California: Implications for the tectonics of the western Sierra Nevada L. R. RUSSELL; L. R. RUSSELL 1Department of Geosciences, Texas Tech University, Lubbock, Texas 79409 Search for other works by this author on: GSW Google Scholar S. E. CEBULL S. E. CEBULL 1Department of Geosciences, Texas Tech University, Lubbock, Texas 79409 Search for other works by this author on: GSW Google Scholar GSA Bulletin (1977) 88 (10): 1530–1534. https://doi.org/10.1130/0016-7606(1977)88<1530:SCIARP>2.0.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation L. R. RUSSELL, S. E. CEBULL; Structural-metamorphic chronology in a roof pendant near Oakhurst, California: Implications for the tectonics of the western Sierra Nevada. GSA Bulletin 1977;; 88 (10): 1530–1534. doi: https://doi.org/10.1130/0016-7606(1977)88<1530:SCIARP>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 SocietyGSA Bulletin Search Advanced Search Abstract Foliation, broken bedding, and two “shear zones” in pre-Cretaceous clastic metasedimentary rocks in a roof pendant west of Oakhurst, California, are on trend with the western Sierra Nevada metamorphic belt to the northwest. In the pendant, foliations define a westward-verging, upward-diverging fan, and lineations have orientations that plot along a great circle, or a small circle of large diameter, with a maximum at the intersection of the circle and the synoptic foliation. Rock microtextures are characterized by porphyroblast clasts, especially of hornblende, in a matrix of aligned cataclastic fragments and some superimposed static mineral growth.Three major events are interpreted. The first, M1, is characterized by probable synkinematic metamorphism of the epidote-amphibolite facies. The second, here correlated with the classical Nevadan orogeny, involved the cataclastic development of the prominent, penetrative, northwest-striking foliation surface, S1, and the incomplete transposition of M1 hornblende lineations (a kinematic axis: N50°E, 64°NE). During this event, bodies of ultramafic and granodioritic rocks were emplaced and deformed along the “shear zones.” Finally, contact metamorphism, M2, chiefly of the albite-epidote-hornfels facies, resulted from the intrusion of batholithic rocks between approximately 98 and 136 m.y. ago.Regional implications include the following: (1) the shear zones may be southerly remnants of the Foothills fault system, probably the Melones fault zone; (2) M1 could represent a moderately deep expression of the Sonoma or Antler orogenies; and (3) the kinematics of S1 favor an interpretation of primarily vertical displacement for the Nevadan deformation and, hence, lend possible support to most subduction models. 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.
INTRODUCTION The Melones fault zone is the easternmosi major element of the Foothills Fault system (Clark, 1960, 1964) of the Western Sierra Nevada metamorphic belt, California. In the southern part of the belt, it commonly separates. Mesozoic rocks on the west from Paleozoic rocks on the east, but to the north, the fault is bounded on both sides largely by Paleozoic rocks. Accordingly, E. M. Moores considers the northern segment to be significantly older than that farther south (Schweickert and Cowan, 1975). Sense of displacement along the zone is uncertain, as is the role of the fault in the tectonic evolution of the belt. For example, the zone has been interpreted as being both of possible dip-slip origin (Knopf, 1929; Russell and Cebull, 1914) and strike-slip origin (Chandra, 1953; Clark, 1960; Baird 1962). Probably, movement was complex and includes both components of displacement (Cebull, 1972), which may be related either to a single oblique-slip motion or to changes of sense with time. Recently, the Melones fault has been interpreted in terms of regional plate-tectobics models. Schweickert and Cowan (1974, 1975) depict the Melones, with some of the other Foothills faults, as sutures between collided arcs. At one place along the Melones fault zone, along the north fork of the Yuba River west of Downieville (Fig. 1), Schweickert (1976) reports lawsonite blueschist and cites such rocks as supporting the proposal that the zone is one of suturing “between diverse terranes juxtaposed by subduction” (p. 409). According to Schweickert and Cowan (1975), the rock succession along the North Yuba River, from Downieville westward for about 30 km, is a melange. If this is correct, the Melones fault zone there represents only the easternmost portion of the melange succession (see Figure 1 of Schweickert and Cowan, (1975)
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