A Mesozoic alkaline province in eastern Bolivia

Research Article| November 01, 1979 A Mesozoic alkaline province in eastern Bolivia D.P.F. Darbyshire; D.P.F. Darbyshire 1Geochemistry and Petrology Division, Institute of Geological Sciences London WC1X 8NG, England Search for other works by this author on: GSW Google Scholar C.J.N. Fletcher C.J.N. Fletcher 2Overseas Division, Institute of Geological Sciences Keyworth, Nottingham NG12 5GQ, England Search for other works by this author on: GSW Google Scholar Geology (1979) 7 (11): 545–548. https://doi.org/10.1130/0091-7613(1979)7<545:AMAPIE>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 D.P.F. Darbyshire, C.J.N. Fletcher; A Mesozoic alkaline province in eastern Bolivia. Geology 1979;; 7 (11): 545–548. doi: https://doi.org/10.1130/0091-7613(1979)7<545:AMAPIE>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 Seven circular igneous intrusions of the Velasco alkaline province define a northeast-southwest lineament north of San Ignacio de Velasco in the headwaters of the Rio Paragua. Nepheline-bearing and quartz-bearing syenites make up ring complexes that are contained within a homogeneous and structureless biotite granite that is also part of the alkaline province. All intrude Precambrian gneisses. Rb-Sr whole-rock isochron ages (140 ± 6 m.y., 143 ± 4 m.y.) and K-Ar mineral ages (134 to 142 m.y.) indicate that the alkaline province was emplaced in Late Jurassic or very early Cretaceous time. K-Ar ages of 1,336 and 1,323 m.y obtained from the gneisses date the last period of metamorphism and deformation in the area. Similar alkaline provinces occur in Namibia, Angola, Brazil, and Uruguay, and this period of alkali magmatism may be related to the initial rifting of the Africa–South America plate and the formation of the proto-Atlantic. 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.