Abstract Paleomagnetic results from Permian clastic and igneous rocks of the Carapacha Basin of the Gondwáides orogenic zone of central Argentina are mainly consistent with results reported previously from the same zone further east, e.g., in the Sierra de la Ventana. Three lithologic entities were analysed: the lower member and upper member of the Carapacha Formation, and an andesite intrusive into the upper member. The directions of their characteristic remanences are similar, differ significantly from the present field direction, and are post-folding. The in situ magnetization directions are moreover consistent with directions expected for late Permian poles of the APWP for South America. The in situ pole for the lower Carapacha Formation is 70°S, 049°E, A95=11° (San Roberto pole); the pole for the upper Carapacha, combined with similar directions from the intrusive, is 64°S, 005°E, A95=5° (Río Curacó pole). These magnetizations imply that the Carapacha Formation, with a minimum age of early Late Permian (about 260 Ma.), was deformed before the end of the Permian. Structural evidence, as well as paleomagnetic, IRM, and AMS experimental results, support the interpretations. The paleogeographic implications of these results are interpreted as a significant counterclockwise movement of Gondwana between the early and the late Permian.
Research Article| January 01, 1987 Caribbean Geological Conference, Barbados William D. MacDonald William D. MacDonald 1Department of Geological Sciences, State University of New York, Binghamton, New York 13901 Search for other works by this author on: GSW Google Scholar Author and Article Information William D. MacDonald 1Department of Geological Sciences, State University of New York, Binghamton, New York 13901 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1987) 15 (1): 89. https://doi.org/10.1130/0091-7613(1987)15<89:CGCB>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 Email Permissions Search Site Citation William D. MacDonald; Caribbean Geological Conference, Barbados. Geology 1987;; 15 (1): 89. doi: https://doi.org/10.1130/0091-7613(1987)15<89:CGCB>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.
Perennial ice from caves on and to the east of the Canadian Great Divide yield δ 18 O and δD values, which are unusually high measurements when compared with the average precipitation for the region. Furthermore, these ice data fall below and along lines of lower slope than the Global Meteoric Water Line. To explain the observed relationships, we propose the following process. A vapour‐ice isotopic fractionation mechanism operates on warm‐season vapour when it precipitates as hoar ice on entering the caves. The subsequent fall of hoar to the cave floor through mechanical overloading, along with ice derived from ground‐water seepage (with a mean annual isotopic composition), results in massive ice formation of a mixed composition. This mixed composition is what is observed in the characteristic relationships found here. Such findings suggest that a warm versus cold climate interpretation for ancient cave ice may be the opposite of that found in the more familiar polar and glacial ice cores.
The interesting analysis of Jurdy [1979] reveals a relationship between development of back arc basins and changes in relative motion of the Pacific plate and the Eurasia plate.I wish to comment on that aspect of Jurdy's analysis which deals with the motion of the Nazca plate in relation to South America in the circuit FAR(NAZ) -PAC -ANT W -ANT E -IND-AFR-SAM Jurdy notes that relative motion between East and West Antarctica is a major uncertainty in this circuit.However, another uncertainty affecting the NAZ/SAM relative motions in particular is the late Tertiary motion of the Nazca plate in relation to the Pacific.
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