The age and origin of the South Mountain Batholith (Nova Scotia, Canada) as constrained by zircon U–Pb geochronology, geochemistry, and O–Hf isotopes
2022/03/08 by Luke Bickerton, Daniel J. Kontak, J. Brendan Murphy +7 · 4 citations
Earth and Planetary Sciences · Computer Science · #Geological and Geochemical Analysis #Geochemistry and Geologic Mapping #earthquake and tectonic studies
paper · pdf · doi:10.1139/cjes-2021-0097
Abstract
The South Mountain Batholith (SMB; Nova Scotia, Canada) is the largest composite batholith exposed in the Appalachians and lies entirely within the most outboard Meguma terrane. In situ and CA–TIMS U–Pb dating and in situ isotopes (Lu–Hf, O) and geochemistry for zircon from all phases of the SMB constrain its source as well as its evolution. CA–ID–TIMS for zircon yields emplacement (autocryst) ages, indicating a transition from granodiorite (378.7 ± 1.2 to 375.4 ± 0.8 Ma) to leucogranite (375.4 to 371.8 ± 0.8 Ma) over several million years. Furthermore, in situ SHRIMP, LA–MC–ICP–MS, and SIMS analyses of distinct zircon domains reveal: (1) abundant ancient xenocrysts (∼420 Ma to 2.2 Ga); (2) antecryst ages ca. 3–15 million years older than SMB emplacement; (3) autocryst δ 18 O values between +7.3‰ and +9.1‰ (V-SMOW); (4) similar isotopes, REE signatures, and derived fO 2 values among antecrysts and autocrysts; and (5) ε Hf values from the 371.8 ± 0.8 Ma Davis Lake Pluton (DLP) autocrysts that are higher (+1.74 to +4.38) than the rest of the SMB (−2.99 to +1.68). Collectively, these data suggest a protracted magmatic evolution for the SMB with melt generation and assembly from ∼390 to 370 Ma via melting of a metasomatized mantle source followed by contamination, first from the structurally underlying Avalonian terrane and later by metasedimentary wall rocks of the Meguma terrane. The most southwesterly part of the SMB (i.e., DLP) represents a petrogenetically distinct magmatic phase that underwent less overall contamination than the rest of the SMB.
Citations
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- Late Devonian lamprophyric dykes in the Meguma Zone of Nova Scotia
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Cited by
- Devonian plutons in the eastern Meguma terrane, Nova Scotia, Canada: zircon U–Pb, Lu–Hf, and O isotopic compositions, age, and petrogenetic implications
- New constraints on the timing and nature of metamorphism in the eastern Meguma terrane, Nova Scotia, Canada
- Conjugate shear model for emplacement of mid-crustal plutons during dextral transpression, southern Nova Scotia, Canada: tectonic and petrological consequences
- Investigating low dispersion isotope dissolution Lu-Hf garnet dates via in situ Lu-Hf geochronology, Kanchenjunga Himal
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