Middle Paleozoic magmatism and orogenesis in the Brooks Range, Alaska

Research Article| July 01, 1980 Middle Paleozoic magmatism and orogenesis in the Brooks Range, Alaska J. T. Dillon; J. T. Dillon 1Alaska Division of Geological and Geophysical Surveys, P.O. Box 80007, College, Alaska 99708 Search for other works by this author on: GSW Google Scholar G. H. Pessel; G. H. Pessel 1Alaska Division of Geological and Geophysical Surveys, P.O. Box 80007, College, Alaska 99708 Search for other works by this author on: GSW Google Scholar J. H. Chen; J. H. Chen 2Department of Geological Sciences, University of California, Santa Barbara, California 93106 Search for other works by this author on: GSW Google Scholar N. C. Veach N. C. Veach 3Alaska Division of Geological and Geophysical Surveys, P.O. Box 80007, College, Alaska 99708 Search for other works by this author on: GSW Google Scholar Geology (1980) 8 (7): 338–343. https://doi.org/10.1130/0091-7613(1980)8<338:MPMAOI>2.0.CO;2 Article history first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation J. T. Dillon, G. H. Pessel, J. H. Chen, N. C. Veach; Middle Paleozoic magmatism and orogenesis in the Brooks Range, Alaska. Geology 1980;; 8 (7): 338–343. doi: https://doi.org/10.1130/0091-7613(1980)8<338:MPMAOI>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 Felsic metaigneous rocks from the southern Brooks Range formerly thought to be of Cretaceous age have yielded Devonian and late Proterozoic U-Pb and Pb-Pb zircon ages. Eight slightly discordant U-Pb ages on euhedral zircons from south-central Brooks Range plutons and metavolcanic rocks define a chord that intersects concordia at 365 ±15 m.y. and 6 ± 120 m.y. Assuming episodic lead loss, the upper intercept is interpreted as the time of magmatic crystallization and the lower intercept as the time of cessation of lead loss due to metamorphism. The Middle Devonian crystallization date is supported by a Rb-Sr whole-rock isochron of 373 ± 25 m.y. Six zircon separates from the Ernie Lake and Sixtymile plutons of the south-central Brooks Range gave various late Proterozoic U-Pb and Pb-Pb ages. Because some of the zircons from these two plutons have rounded cores inherited from zircons in either the source rocks or the country rocks of the plutons, we are uncertain if the two plutons first crystallized during Proterozoic or Paleozoic time.From these data and other geologic criteria we hypothesize that (1) many Brooks Range plutons and some volcanic rocks were formed during middle Paleozoic time; (2) younger K-Ar mineral dates from these metaigneous rocks reflect a Mesozoic metamorphic event; (3) middle Paleozoic magmatic rocks together with adjacent coeval marine carbonate and clastic rocks and syngenetic ore deposits constituted an ensialic island arc or submerged continental margin magmatic belt; and (4) amphibolite-facies rocks around the plutons include early Paleozoic and late Proterozoic(?) crystalline basement to the middle Paleozoic magmatic belt. 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.