Research Article| March 01, 1979 Progressive deformation and orogenic uplift at the southern extremity of the Andes IAN W. D. DALZIEL; IAN W. D. DALZIEL 1Lamont-Doherty Geological Observatory of Columbia University, Palisades, New York 10964 Search for other works by this author on: GSW Google Scholar KEITH F. PALMER KEITH F. PALMER 1Lamont-Doherty Geological Observatory of Columbia University, Palisades, New York 10964 Search for other works by this author on: GSW Google Scholar GSA Bulletin (1979) 90 (3): 259–280. https://doi.org/10.1130/0016-7606(1979)90<259:PDAOUA>2.0.CO;2 Article history first online: 01 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 IAN W. D. DALZIEL, KEITH F. PALMER; Progressive deformation and orogenic uplift at the southern extremity of the Andes. GSA Bulletin 1979;; 90 (3): 259–280. doi: https://doi.org/10.1130/0016-7606(1979)90<259:PDAOUA>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 The Middle to Upper Jurassic and Lower Cretaceous silicic volcanic and sedimentary rocks of Isla de los Estados, Argentina, at the southern extremity of the Andean Cordillera, have been interpreted to lie on the rear (continental) side of an Early Cretaceous marginal basin. The basin floor was uplifted, together with the magmatic arc on its Pacific side, in mid-Cretaceous time. Uplift was accompanied by inhomogeneous deformation of the rocks of the magmatic arc, of the basin floor, and particularly of those on the continental side of the basin.Detailed structural analysis shows that the rocks of Isla de los Estados are disposed in a major asymmetric, noncylindrical syncline. The island, nearly 1,000 m high, lies in the core of this fold. A strong slaty cleavage developed prior to the large-scale folding. Both bedding and early slaty cleavage were reoriented by this folding. A new foliation axial planar to the large syncline is present only on the inverted limb in the more strongly compressed eastern area. Late, flat-lying cleavages are also most strongly developed in the east, but in the lower limb of the fold.The structures are all interpreted to be the result of progressive deformation of the rocks during a single period of regional compression. The sequence of strains correlates closely with that deduced from theoretical and experimental studies of buckling. The early cleavage is thought to have developed during initial shortening of the layering of the rocks. Subsequent buckling of the thick multilayer of competent silicic volcanics produced the syncline. The late, flat-lying cleavages are considered to have resulted from gravitationally induced vertical shortening produced by the greatly increased overburden of the tectonically thickened rock pile.The dominant northward vergence of the structures undoubtedly reflects the uplift of the Pacific margin of the continent, but the initial layer-parallel shortening indicates the operation of a stress system with maximum compressive principal stress subhorizontal and at right angles to the Pacific margin. The crustal thickening resulting from the horizontal shortening and the buckling seems to have played a major role in the mid-Cretaceous orogenic uplift of the southernmost part of the Andean Cordillera. 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.
Research Article| January 01, 2004 An orphaned basement block: The Arequipa-Antofalla Basement of the central Andean margin of South America Staci L. Loewy; Staci L. Loewy 1Department of Geological Sciences, The University of Texas at Austin, Austin, Texas 78712, USA Search for other works by this author on: GSW Google Scholar James N. Connelly; James N. Connelly 1Department of Geological Sciences, The University of Texas at Austin, Austin, Texas 78712, USA Search for other works by this author on: GSW Google Scholar Ian W.D. Dalziel Ian W.D. Dalziel 2Department of Geological Sciences, The University of Texas at Austin, Austin, Texas 78712, USA and Institute for Geophysics, The University of Texas at Austin, 4412 Spicewood Springs Road, Building 600, Austin, Texas 78759, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Staci L. Loewy 1Department of Geological Sciences, The University of Texas at Austin, Austin, Texas 78712, USA James N. Connelly 1Department of Geological Sciences, The University of Texas at Austin, Austin, Texas 78712, USA Ian W.D. Dalziel 2Department of Geological Sciences, The University of Texas at Austin, Austin, Texas 78712, USA and Institute for Geophysics, The University of Texas at Austin, 4412 Spicewood Springs Road, Building 600, Austin, Texas 78759, USA Publisher: Geological Society of America Received: 01 Aug 2002 Revision Received: 27 Jun 2003 Accepted: 06 Jul 2003 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (2004) 116 (1-2): 171–187. https://doi.org/10.1130/B25226.1 Article history Received: 01 Aug 2002 Revision Received: 27 Jun 2003 Accepted: 06 Jul 2003 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Staci L. Loewy, James N. Connelly, Ian W.D. Dalziel; An orphaned basement block: The Arequipa-Antofalla Basement of the central Andean margin of South America. GSA Bulletin 2004;; 116 (1-2): 171–187. doi: https://doi.org/10.1130/B25226.1 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 The Arequipa-Antofalla Basement, a Proterozoic crustal block exposed along the central Andean margin, provides a key to interpreting the pre-Andean history of South America. New U/Pb geochronology and whole-rock Pb and Nd isotope geochemistry from the Arequipa-Antofalla Basement refine the tectonic history and delineate three distinct crustal domains that decrease in age from north to south. The northern domain of southern Peru and western Bolivia contains juvenile Paleoproterozoic 2.02–1.79 Ga intrusions that were metamorphosed at 1.82–1.79 Ga. The Mesoproterozoic central domain in northernmost Chile contains a significant Mesoproterozoic juvenile component that incorporates Paleoproterozoic crust from the northern domain. Rock units from both the northern and central domains were metamorphosed between 1.20 and 0.94 Ga, with coeval magmatism occurring only in the central domain. The southern domain in northern Chile and northwestern Argentina comprises Ordovician rocks, derived from a mix of juvenile material and older crust. Similar Ordovician magmatism (476–440 Ma) also occurred in the northern and central domains followed by metamorphism at ca. 440 Ma.Based on this refined geologic and tec tonic characterization of the Arequipa- Antofalla Basement and comparison with that of Amazonia, we conclude that: (1) the isolated exposures of the Arequipa-Antofalla Basement comprise a single basement block with multiple domains, (2) the Arequipa-Antofalla Basement was not derived from Amazonia, and (3) the Arequipa-Antofalla Basement accreted onto Amazonia during the 1.0 Ga Sunsás Orogeny. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
We constrain azimuthal anisotropy in the West Antarctic upper mantle using shear wave splitting parameters obtained from teleseismic SKS, SKKS and PKS phases recorded at 37 broad-band seismometres deployed by the POLENET/ANET project. We use an eigenvalue technique to linearize the rotated and shifted shear wave horizontal particle motions and determine the fast direction and delay time for each arrival. High-quality measurements are stacked to determine the best fitting splitting parameters for each station. Overall, fast anisotropic directions are oriented at large angles to the direction of Antarctic absolute plate motion in both hotspot and no-net-rotation frameworks, showing that the anisotropy does not result from shear due to plate motion over the mantle. Further, the West Antarctic directions are substantially different from those of East Antarctica, indicating that anisotropy across the continent reflects multiple mantle regimes. We suggest that the observed anisotropy along the central Transantarctic Mountains (TAM) and adjacent West Antarctic Rift System (WARS), one of the largest zones of extended continental crust on Earth, results from asthenospheric mantle strain associated with the final pulse of western WARS extension in the late Miocene. Strong and consistent anisotropy throughout the WARS indicate fast axes subparallel to the inferred extension direction, a result unlike reports from the East African rift system and rifts within the Basin and Range, which show much greater variation. We contend that ductile shearing rather than magmatic intrusion may have been the controlling mechanism for accumulation and retention of such coherent, widespread anisotropic fabric. Splitting beneath the Marie Byrd Land Dome (MBL) is weaker than that observed elsewhere within the WARS, but shows a consistent fast direction, possibly representative of anisotropy that has been 'frozen-in' to remnant thicker lithosphere. Fast directions observed inland from the Amundsen Sea appear to be radial to the dome and may indicate radial horizontal mantle flow associated with an MBL plume head and low upper mantle velocities in this region, or alternatively to lithospheric features associated with the complex Cenozoic tectonics at the far-eastern end of the WARS.
The Llano Orogenic Belt along the present southern margin of Laurentia, regarded as continuation of the Grenvillian Orogen along the eastern Laurentian margin and exposed in basement uplifts in central and western Texas, records an ∼300‐m.yr. history of orogenesis culminating in arc‐continent and continent‐continent collision between ∼1150 and 1120 Ma and continuing until ∼980 Ma. The shape of the orogen and kinematics of the contractional deformation along the belt, together with the high‐P metamorphic conditions attained, indicate that a previously unidentified craton served as an indentor. It is paleomagnetically acceptable for the Kalahari Craton of southern Africa to have been opposed to this margin and within ∼1500 km of present‐day central Texas at ∼1100 Ma. Moreover, the Kalahari Craton is the correct size, and the structural and metamorphic evolution of the 1200–950 Ma Namaqua‐Natal Orogenic Belt that wraps around its present southern margin is compatible with that craton having been the indentor. The ocean basin that closed between the Laurentia and Kalahari Cratons would have been comparable to the present Pacific, with island arc/terrane accretion occurring during the Mesoproterozoic along opposing active convergent margins. The coeval 1.1 Ga Keeweenawan and Umkondo magmatic provinces of Laurentia and Kalahari, respectively, are associated with rifts at a high angle to the Llano and Namaqua Orogens. The rifts are interpreted as the result of collision‐generated extensional stresses within the two cratons. The voluminous mafic igneous rocks in both provinces, however, may reflect contemporaneous plume activity. Our reconstruction for 1.1 Ga provides a testable model for the Llano Orogenic Belt of Texas and the Namaqua Orogenic Belt of southwestern Africa as opposite sides of a Himalayan‐type collisional orogen, with the Natal Belt of southeastern Africa and the originally continuous Maudheim Belt of East Antarctica as a related Indonesian‐type ocean‐continent convergence zone. This reconstruction leads to a refinement of the paleogeography of Rodinia, with the Kalahari Craton in a position isolated from both the East Antarctic and Rio de la Plata Cratons by oceanic lithosphere. It also provides the first model for the assembly of that hypothetical early Neoproterozoic supercontinent. At least four separate cratonic entities appear to have collided along three discrete segments of the apparently anastomosing global network of "Grenvillian" orogens: the type‐Grenville Belt of eastern North America and counterparts in South America, the Llano‐Namaqua Belt, and the Eastern Ghats‐Albany/Fraser Belt of India‐East Antarctica and Australia. Over the remarkably short interval of ∼200 m.yr., this first‐order composite collisional event resulted in the amalgamation of most of Earth's continental lithosphere and defined the close of the Mesoproterozoic Era.
North America was sutured to Gondwana in the terminal Alleghanian event of Appalachian orogenesis, thus completing the late Paleozoic assembly of Pangea. The suggestion that the Pacific margins of East Antarctica-Australia and Laurentia may have been juxtaposed during the Neoproterozoic prompts reevaluation of the widely held assumptions that the ancestral Appalachian margin rifted from northwestern Africa during the earliest Paleozoic opening of Iapetus, and remained juxtaposed to that margin, even though widely separated from it at times, until the assembly of Pangea. The lower Paleozoic carbonate platform of northwestern Argentina has been known for a long time to contain Olenellid trilobites of the Pacific or Columbian realm. Although normally regarded as some kind of far-travelled terrane that originated along the Appalachian margin of Laurentia, it has recently been interpreted as a fragment detached from the Ouachita embayment of Laurentia following Taconic-Famatinian collision with Gondwana during the Ordovician. The Oaxaca terrane of Mexico, on the other hand, contains a Tremadocian trilobite fauna of Argentine-Bolivian affinities, and appears to have been detached from Gondwana following the same collision. The Wilson cycle'' of Iapetus ocean basin opening and closing along the Appalachian and Andean orogens may have involved more than one such continentalmore » collision during clockwise drift of Laurentia around South America following late Neoproterozoic to earliest Cambrian separation. Together with the collisions of baltic and smaller terranes with Laurentia, this could explain the protracted Paleozoic orogenic history of both the Appalachian and proto-Andean orogens.« less
Metamorphic and sedimentary rocks of the South Orkney and South Shetland island groups and the northern tip of the Antarctic Peninsula appear to represent the products of subduction-related accretion and of sedimentation respectively in a forearc environment along the Pacific margin of Antarctica. Some of the rocks are imprecisely dated, but stratigraphic, paleontologic, and radiometric data indicate that the higher temperature part of the subduction complex was formed and all sedimentary strata deposited prior to the initiation of Gondwanaland break up. The remainder of the subduction complex, comprising comparatively high P/T assemblages, may be of late Mesozoic or even Cenozoic age.
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This atlas displays a series of reconstructions from 1 00 Ma to Present. The data displayed include coastlines and sutures (from coasts25.1995) and sediment isopachs (from isopachs.1 995). In the summer of 1994, Mobil Exploration and Producing Technical Center of Dallas, TX, gave the PLATES Project a global digital set of sediment isopachs. The data are now in PLATES format and have been assigned plate identification numbers but have not yet been assigned ages. Figure 1 (0 Ma) shows how the data have been assigned to plates. Figures 2 through 12 present reconstructions from 100 Ma to Present. The isopachs were colored according to thickness (in kilometers). For more information, contact plates@ig.utexas.edu.
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