SHRIMP U-Pb zircon dating of the South Mountain Batholith, Nova Scotia: timing and duration of crystallization and evidence for inheritance

Abstract

The South Mountain Batholith (SMB) is the largest (7300 km2) granitoid body in the Appalachian Orogen. It is a composite peraluminous intrusion with early stage biotite-granodiorite to biotite-monzogranite and later leucomonzogranite to leucogranite plutons. The latter are associated with subeconomic to economic polymetallic mineral deposits, including the past-producing (1985-1992) East Kemptville Sn-Cu-Zn-Ag(-In) deposit. Sensitive High-Resolution Ion Microprobe (SHRIMP) analyses of zircon were used to constrain the timing of emplacement for phases across the SMB and to investigate potential sources of contamination to the magma. Zircon from four granodiorite to monzogranite samples and one from a more evolved leucogranite were analyzed to complement our previous SHRIMP U-Pb zircon dating of the more evolved phases (ca. 377-370 Ma). The granodiorite samples yielded ages between 384.9 ± 4.4 Ma and 375.9 ± 4.5 Ma whereas the leucogranite yielded an age of 377.7 ± 5.2 Ma (2? errors). A late monzogranitic phase on the edge of the SMB also yielded an age of 367.7 ± 4.0 Ma. Collectively, the data sets indicate an apparent span of ca. 11 to 23 Ma for emplacement and assembly of the SMB, but with most ages between ca. 378 to 370 Ma. The abundance of xenocrystic zircon cores varies throughout the complex; from common in less evolved granodiorite samples to rare in the more evolved leucogranite samples. The relative age population density pattern for the inherited cores is very similar to the detrital zircon signature for the upper stratigraphy of the Meguma Supergroup that hosts the SMB.