Proterozoic crustal history of the western United States as determined by neodymium isotopic mapping

Abstract

Research Article| November 01, 1987 Proterozoic crustal history of the western United States as determined by neodymium isotopic mapping VICTORIA C. BENNETT; VICTORIA C. BENNETT 1Department Earth and Space Sciences, University of California, Los Angeles, California 90024 Search for other works by this author on: GSW Google Scholar DONALD J. DEPAOLO DONALD J. DEPAOLO 1Department Earth and Space Sciences, University of California, Los Angeles, California 90024 Search for other works by this author on: GSW Google Scholar Author and Article Information VICTORIA C. BENNETT 1Department Earth and Space Sciences, University of California, Los Angeles, California 90024 DONALD J. DEPAOLO 1Department Earth and Space Sciences, University of California, Los Angeles, California 90024 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1987) 99 (5): 674–685. https://doi.org/10.1130/0016-7606(1987)99<674:PCHOTW>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 VICTORIA C. BENNETT, DONALD J. DEPAOLO; Proterozoic crustal history of the western United States as determined by neodymium isotopic mapping. GSA Bulletin 1987;; 99 (5): 674–685. doi: https://doi.org/10.1130/0016-7606(1987)99<674:PCHOTW>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 Initial Nd isotopic ratios of crystalline rocks from an area of ∼ 1.5 × 106 km2 of the western United States have been determined in order to map Precambrian age province boundaries and thus document the growth and modification of the North American continent in the Proterozoic. The use of three representative rock suites of different ages— Mesozoic and Tertiary peraluminous granitic rocks, middle Proterozoic (ca. 1.4 Ga) "an-orogenic" granitic rocks, and lower Proterozoic (ca. 1.7 Ga) igneous and metamorphic rocks—allows the ages of the provinces to be distinguished on the basis of different Nd isotopic evolution paths rather than solely on the basis of model ages. Three age provinces have been delineated, each generally northeast-southwest trending, having decreasing crystallization ages and increasing initial εNd values with increasing distance southeastward from the Archean craton. Province 1 is composed of crustal rocks of central Utah and northeastern Nevada, which are characterized by average values of εNd(1.7 Ga) ≈ 0 and TDM ≈ 2.0–2.3 Ga. Province 2 covers Colorado, southern Utah, and northwestern Arizona and has εNd(1.7 Ga) ≈ +3 and TDM ≈ 1.8–2.0 Ga. Province 3, which comprises the basement rocks of New Mexico and southern Arizona, has εNd(1.7 Ga) ≈ +5 and TDM ≈ 1.7–1.8 Ga. An additional region of province 1-type isotopic characteristics, herein named "Mojavia," is found in eastern California and western Nevada. Crust formation in each province involved a large component of mantle-derived material plus a moderate amount (∼20%) of pre-existing crust. As the new crust was built outward from the Archean nucleus, however, contributions of Archean material to the newly forming crust were more effectively screened, so that the most distal province (3) is derived almost entirely from Proterozoic mantle.The province boundaries are subparallel to the crystallization age trends determined by other workers. An exception to this is the Mojavia region of province 1, which crosscuts and truncates the other provinces in the region of the lower Colorado River. This region appears to be displaced relative to other areas of the North American basement that have similar isotopic characteristics. This suggests the presence of a previously unrecognized large-scale, left-lateral, north-south–trending basement offset of Proterozoic age in the vicinity of the California-Arizona border. 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.