Paper No. 28-9
Presentation Time: 9:00 AM-5:30 PM
SAMARIUM-NEODYMIUM DATES OF IGNEOUS GARNETS IN NEW ENGLAND SHOW TEMPORAL CORRELATION WITH HIGH-TEMPERATURE AND ULTRA-HIGH TEMPERATURE METAMORPHISM DURING THE ACADIAN OROGENY
High and ultra-high temperature metamorphism has been documented along the north-south trending Central Maine Terrane in New England, USA (e.g. Chamberlain & Rumble 1988; Ague et al. 2013; Sullivan 2014). The sources of heat for this metamorphism could be related to numerous nearby igneous bodies. The purpose of this study is to test that hypothesis by comparing the age of these igneous rocks to the age of geographically associated metamorphic rocks. Existing garnet geochronology of the metamorphic rocks ranges from 400 Ma in central NH, to 364 Ma in north-central MA, to 340 Ma in northeastern CT (Ostwald et al. 2014; Sullivan 2014). Here, we report new Samarium-Neodymium geochronology performed on igneous garnet from the Coys Hill Poryphyritic Granite Gneiss, a narrow north-south trending body in Massachusetts and the Cardigan pluton of the Kinsman Granodiorite in the New Hampshire Plutonic Suite (NHPS). These yielded ages of 341.3 ± 1.6 Ma; and 398.6 ± 1.1 Ma and 395.4 ±1.1 Ma, respectively, quite consistent with the geographically related metamorphic ages. The northern dates from the Kinsman samples in New Hampshire converge very well with the zircon ages (Sullivan 2014; Dorais et al., 2009; Lyons & Livingston, 1977; Barreiro & Aleinikoff, 1985) that are thought to represent the crystallization or emplacement of the syntectonic members of the NHPS. The younger ages from southern igneous and metamorphic rocks suggests a prolonged Neo-Acadian period of sustained heat in central Massachusetts and Connecticut following the main pulse of Acadian magmatism. U-Pb zircon ages from the Coys Hill Granite give 396 ± 2 Ma (Robinson et al., 1998); and thus are consistent with the hypothesis that 340 Ma represents a cooling age. The data presented in this study bring new insights about the temporal relationship between igneous rocks and Acadian and Neo-Acadian metamorphism in New England, but further study is still needed in order to understand the possible mechanisms for the high heat flow.