Late Paleozoic collision, delamination, short-lived magmatism, and rapid denudation in the Meguma Terrane (Nova Scotia, Canada): constraints from 40Ar/39Ar isotopic data

1995/05/01 by J. D. Keppie, J. Duncan Keppie, R. D. Dallmeyer · 88 citations
Earth and Planetary Sciences · #Carboniferous #Continental crust #Craton #Crust #Geochemistry #Geological and Geochemical Analysis #Geology #Geomorphology #High-pressure geophysics and materials #Magmatism #Paleontology #Paleozoic #Petrology #Tectonics #Terrane #Zircon #earthquake and tectonic studies

paper · doi:10.1139/e95-054

published in Canadian Journal of Earth Sciences 32(5), 644-659 (NRC Research Press)

openalex publication_date 1995/05/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/25

Abstract

The Meguma Terrane consists of 8–15 km of early Paleozoic stratified rocks, deposited on a continental basement, that were deformed and metamorphosed during the late Paleozoic as a result of lithospheric plate collision. The oldest cleavage (previously published, whole-rock, 40 Ar/ 39 Ar plateau ages of 415–395 Ma) dates the onset of crustal thickening, which was followed by voluminous, but short-lived, Late Devonian granitic and minor mafic magmatism (380–370 Ma). This magmatism may have been the product of delamination of the lower lithosphere and upwelling of asthenosphere, which effected melting above the new Moho and resulted in intrusion at depths of 5–12 km. 40 Ar/ 39 Ar plateau ages of hornblende, muscovite, and biotite indicate that, at the present erosion level, most of the Meguma Terrane cooled through ~300 °C by 368–360 Ma, slightly earlier than for the southwestern Meguma Terrane (ca. 345 Ma). The present erosion level was exhumed by the latest Devonian–Early Carboniferous (Visean): the age of the oldest unconformably overlying rocks. Subsequent burial beneath ~6 km of Carboniferous sediments would not have been sufficient to completely rejuvenate older intracrystalline mica systems and result in the observed 40 Ar/ 39 Ar mica plateau ages between ca. 350 and 260 Ma. Such rejuvenation may have resulted from migration of hot fluids along shear zones derived from the lower crust and mantle, and from granitoid magma intruded at ca. 316 Ma. The recurrence of deformation, magmatism and denudation in the middle Carboniferous suggests that further delamination may have occurred. The temperature of these fluids decreased from 400–500 °C during the Carboniferous to 300–400 °C during the Early Permian.

Citations

• Closure temperature in cooling geochronological and petrological systems
• Deep seismic reflection data from the Bay of Fundy and Gulf of Maine: tectonic implications for the northern Appalachians
• U–Pb dating of monazite and its application to geological problems

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
• Alleghanian reactivation of the Acadian fold belt, Meguma Zone, southwest Nova Scotia
• Interaction among upper crustal, lower crustal, and mantle materials in the Port Mouton pluton, Meguma Lithotectonic Zone, southwest Nova Scotia
• Saddle reef auriferous veins in a conical fold termination (Oldham anticline, Meguma terrane, Nova Scotia, Canada): reconciliation of structural and age data
• The age and origin of the South Mountain Batholith (Nova Scotia, Canada) as constrained by zircon U–Pb geochronology, geochemistry, and O–Hf isotopes
• Detrital and metamorphic 40Ar/39Ar ages from muscovite and whole-rock samples, Meguma Supergroup, southern Nova Scotia
• New constraints on the timing and nature of metamorphism in the eastern Meguma terrane, Nova Scotia, Canada
• 40Ar/39Ar age of shear zones in the southwest Meguma Zone between Yarmouth and Meteghan, Nova Scotia
• Meguma terrane orocline: U–Pb age and paleomagnetism of the Silurian Mavillette gabbro, Nova Scotia, Canada
• Conjugate shear model for emplacement of mid-crustal plutons during dextral transpression, southern Nova Scotia, Canada: tectonic and petrological consequences
• U‐Pb Geochronology of Devonian Granites in the Meguma Terrane of Nova Scotia, Canada: Evidence for Hotspot Melting of a Neoproterozoic Source
• Orogenesis and Basin Development: U‐Pb Detrital Zircon Age Constraints on Evolution of the Late Paleozoic St. Marys Basin, Central Mainland Nova Scotia
• Derivation of the Early Carboniferous Wedgeport pluton by crystal fractionation of a mafic parental magma: a rare case of an A-type granite within the Meguma terrane (Nova Scotia, Canada)
• Geochemistry, geochronology and petrogenesis of Maya Block granitoids and dykes from the Chicxulub Impact Crater, Gulf of México: Implications for the assembly of Pangea

Related

• New constraints on the timing and nature of metamorphism in the eastern Meguma terrane, Nova Scotia, Canada
• U‐Pb Geochronology of Devonian Granites in the Meguma Terrane of Nova Scotia, Canada: Evidence for Hotspot Melting of a Neoproterozoic Source
• Orogenesis and Basin Development: U‐Pb Detrital Zircon Age Constraints on Evolution of the Late Paleozoic St. Marys Basin, Central Mainland Nova Scotia
• Interaction among upper crustal, lower crustal, and mantle materials in the Port Mouton pluton, Meguma Lithotectonic Zone, southwest Nova Scotia
• 440 Ma igneous activity in the Meguma Terrane, Nova Scotia, Canada; part of the Appalachian overstep sequence?