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Age Determinations from Andean Peru: A Reconnaissance Survey

1974; Geological Society of America; Volume: 85; Issue: 7 Linguagem: Inglês

10.1130/0016-7606(1974)85 2.0.co;2

1943-2674

John W. Stewart, Jack F. Evernden, N. J. Snelling,

Archaeology and ancient environmental studies

Research Article| July 01, 1974 Age Determinations from Andean Peru: A Reconnaissance Survey J. W. STEWART; J. W. STEWART 1"Promisa" Mineraçāo e Prospecçoes Minerais S.A., P.O. Box 56002, Rio de Janeiro, Brazil Search for other works by this author on: GSW Google Scholar J. F. EVERNDEN; J. F. EVERNDEN 2U.S. Arms Control and Disarmament Agency, Washington, D.C. Search for other works by this author on: GSW Google Scholar N. J. SNELLING N. J. SNELLING 3Institute of Geological Sciences, 64–78 Gray's Inn Road, London WC1X 8NG, England Search for other works by this author on: GSW Google Scholar GSA Bulletin (1974) 85 (7): 1107–1116. https://doi.org/10.1130/0016-7606(1974)85 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 J. W. STEWART, J. F. EVERNDEN, N. J. SNELLING; Age Determinations from Andean Peru: A Reconnaissance Survey. GSA Bulletin 1974;; 85 (7): 1107–1116. doi: https://doi.org/10.1130/0016-7606(1974)85 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 More than 60 new K-Ar age determinations for mica, hornblende, and potassium feldspar together with a few Rb-Sr determinations on mica and potassium feldspar are presented.Micas from two gneiss samples within the Arequipa batholith intrusive belt have yielded ages of ∼660 m.y. Five samples of granitic rocks, widely scattered in the Coastal and Eastern Cordilleras, have given ages ranging from 447 to 251 m.y. In the Eastern Cordillera, stratigraphic control is sufficient in one case to confirm intrusion in Late Ordovician or Early Silurian times and, in another case, Late Permian time.Triassic and Early Jurassic apparent ages are known from the Coastal, Western, and Eastern Cordilleras; the parent rocks are both igneous and metamorphic. The metamorphic rocks are probably Paleozoic or older, and the apparent ages must be the result of Mesozoic or later disturbances. It is tentatively suggested that intrusion of granitic rocks occurred in Late Triassic or Early Jurassic times.The Coastal batholith yields a spectrum of apparent ages from ∼100 to 10 m.y. Fewer ages are available from the Arequipa batholith, and they show a more limited range – from 80 to 50 m.y. The Cordillera Blanca batholith gives very young apparent ages of from 12 to 3 m.y.Mineral ages from across the Coastal batholith get progressively younger from southwest to northeast. However, because virtually all the Andean ages have been-determined by the K-Ar method, they do not necessarily indicate a northeastward migration of intrusive foci. Very limited Rb-Sr data indicate initial 87Sr/86Sr ratios in the range 0.704 to 0.706 for the granitic rocks of the Coastal batholith. 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.