Enriched Grenvillian lithospheric mantle as a consequence of long-lived subduction beneath Laurentia

Abstract

subduction beneath Laurentia Enriched Grenvillian lithospheric mantle as a consequence of long-lived Email alerting services articles cite this article to receive free e-mail alerts when new www.gsapubs.org/cgi/alerts click Subscribe to subscribe to Geology www.gsapubs.org/subscriptions/ click Permission request to contact GSA http://www.geosociety.org/pubs/copyrt.htm#gsa click official positions of the Society. citizenship, gender, religion, or political viewpoint. Opinions presented in this publication do not reflect presentation of diverse opinions and positions by scientists worldwide, regardless of their race, includes a reference to the article's full citation. GSA provides this and other forums for the the abstracts only of their articles on their own or their organization's Web site providing the posting to further education and science. This file may not be posted to any Web site, but authors may post works and to make unlimited copies of items in GSA's journals for noncommercial use in classrooms requests to GSA, to use a single figure, a single table, and/or a brief paragraph of text in subsequent their employment. Individual scientists are hereby granted permission, without fees or further

Shawinigan arc magmatism in the Adirondack Lowlands as a consequence of closure of the Trans-Adirondack backarc basin

“…Despite this, the plutons have typical igneous wholerock chemistry and radiogenic isotope values. In order to account for the anomalous δ 18 O values, Peck et al (2004) suggested that hydrothermally altered basalts and/or oceanic sediments were subducted or underthrust be neath the Frontenac terrane during closure of an ocean basin between the Frontenac terrane and the Adirondack Highlands at or prior to 1.2 Ga. Our work supports this contention, and Chiarenzelli et al (2010) identifi ed potential fragments of the underplated basalt and enriched upper mantle shown schematically in Figure 9 of Peck et al (2004).…”

Evidence for an enriched asthenospheric source for coronitic metagabbros in the Adirondack Highlands

“…Large-ion lithophile and high field strength elements concentrations in CMGs normalized to primitive mantle (Fig. 13;Sun and McDonough, 1989) show a positive Cs anomaly and a very slight negative Nb and Ti anomaly (small, and variable calcalkaline component), but otherwise contain few distinguishable anomalies, notably lacking the pronounced subduction-related signatures seen in older arc-derived plutonic rocks of the Adirondacks (Chiarenzelli et al, 2010a;McLelland and Chiarenzelli, 1990).…”

“…Also shown in Figure 13 is the incompatible element trend of CMGs compared to trends of pre-Shawinigan mafic and ultramafic rocks found in the Adirondack Lowlands (Chiarenzelli et al, 2010a). Notice the relative lack of Pb, Nb, P, and Ti anomalies in CMGs.…”

“…1090-1045 Ma). The Lowlands consist primarily of supracrustal gneisses with igneous intrusions of arc affinity (Carl and deLorraine, 1997;Chiarenzelli et al, 2010aChiarenzelli et al, , 2010bMcLelland et al, 1996;among others). Conversely, the Adirondack Highlands are primarily underlain by metaigneous rocks, including widespread granitic and charnockitic gneisses of the AMCG suite, which are much less abundant in the Lowlands.…”

“…1045 Ma (Selleck et al, 2005). Chiarenzelli et al (2010a) used trace-element chemistry and Nd systematics of early mafic and ultramafic rocks in the Lowlands to demonstrate that Laurentia was underlain by a highly enriched lithospheric mantle due to long-lived subduction and metasomatism of the mantle prior to Shawinigan orogenesis. The Shawinigan orogeny was recently interpreted as the result of the collapse of a backarc basin (Chiaren zelli et al, 2010b;McLelland et al 2010b).…”