Southeastern Section - 64th Annual Meeting (19–20 March 2015)

Paper No. 3
Presentation Time: 8:00 AM-12:00 PM


YELVERTON, James W.1, NORTON, Rebecca A.1, STOWELL, Harold H.1, HORKLEY, L. Kenneth S.1, HOUT, Crystal2, BOLLEN, Elizabeth M.3, TOOTLE, Robert2, JACKSON Jr., William T.1, SCHWARTZ, Joshua J.4 and KLEPEIS, Keith5, (1)Geological Sciences, University of Alabama, Tuscaloosa, AL 35487, (2)Geological Sciences, University of Alabama, Box 870338, Tuscaloosa, AL 35487, (3)Geology, University of Alabama, Tuscaloosa, AL 35487, (4)Department of Geological Sciences, California State University Northridge, 18111 Nordhoff Street, Northridge, CA 91330, (5)Dept of Geology, The University of Vermont, Burlington, VT 05405,

The Western Fiordland Orthogneiss (WFO) along the western margin of South Island, New Zealand provides excellent exposures of the mid- to lower-crust of a magmatic arc formed along the Gondwana margin. Previous metamorphic studies have focused on the northern and southern plutons of the WFO. Here we present two new garnet Sm-Nd ages for granulite gneiss in Misty Pluton, central WFO.

The Misty Pluton is characterized by 2-pyroxene granulite gneiss with cross-cutting trondhjemitic veins. Garnet growth is restricted to peritectic selvages bordering the veins and porphyroblasts within a garnet reaction zone (GRZ).

Zircon 206Pb/238U SHRIMP ages range from 120–114 Ma (Sadorski et al., 2013) indicating that emplacement of the Misty Pluton and Malaspina Pluton to the south occurred over a short period of time with most ages clustering between 117 and 115 Ma. A previously published garnet Sm-Nd age of 109.2±2.0 Ma obtained from the southern Misty Pluton and 7 garnet Sm-Nd ages ranging from 110-116 Ma in the Malaspina Pluton suggests that garnet granulite metamorphism occurred soon after emplacement in both plutons.

New ages from Gold Arm of Charles Sound indicate similar timing as those determined by previous studies. Sm-Nd ages of 115.4±2.7 Ma for cores and 110.1±3.0 Ma for rims were collected from a ca. 1 cm porphyroblastic garnet from the GRZ (14NZ37). Single crystal garnet core and rim ages suggest a duration of garnet growth of ca. 5 m.y., considerably longer than previously determined garnet growth durations in the WFO. A second sample from Emelius Arm of Charles Sound (14NZ48b) yielded a garnet Sm-Nd age of 126.8±3.3 Ma. Sadorski et al., 2013 obtained a zircon 206Pb/238U age of 116.8 Ma from nearby in Emelius Arm. Therefore, the garnet is anomalously old and inclusion contamination is suspected. Apatite inclusions are common in the Misty Pluton and are a probable source of error. Revised leaching procedures are being developed for garnet in the Misty Pluton in order to completely remove apatite inclusions.