An autochthonous Avalonian basement source for the latest Ordovician Brenton Pluton in the Meguma terrane of Nova Scotia: U–Pb–Hf isotopic constraints and paleogeographic implications

The Ediacaran–Ordovician Meguma Supergroup was thrust over Avalonia basement prior to the intrusion of post-Acadian, ca. 370 Ma, S-type granitic batholiths. This has led to two main hypotheses regarding the original location of the Meguma terrane, a continental rise prism bordering either NW Africa...

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Bibliographic Details
Published in:International journal of earth sciences : Geologische Rundschau 2018-04, Vol.107 (3), p.955-969
Main Authors: Duncan Keppie, J., Gregory Shellnutt, J., Dostal, Jaroslav, Fraser Keppie, D.
Format: Article
Language:English
Subjects:
Batholiths
Cambrian
Continental rise
Data
Earth and Environmental Science
Earth Sciences
Geochemistry
Geological time
Geology
Geophysics/Geodesy
Intrusion
Isotopes
Lead
Magma
Mineral Resources
Ordovician
Original Paper
Palaeomagnetism
Paleomagnetism
Plutons
Radiometric dating
Sedimentology
Structural Geology
Tropical environments
Zircon
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Summary:The Ediacaran–Ordovician Meguma Supergroup was thrust over Avalonia basement prior to the intrusion of post-Acadian, ca. 370 Ma, S-type granitic batholiths. This has led to two main hypotheses regarding the original location of the Meguma terrane, a continental rise prism bordering either NW Africa or Avalonia. On the other hand, the pre-Acadian, ca. 440 Ma Brenton pluton has yielded the following U/Pb LA-ICP-MS zircon data: (1) 448 ± 3 Ma population peak inferred to be the intrusive age and (2) ca. 550 and 700 Ma inherited ages common to both Avalonia and NW Africa. In contrast, Hf isotopic analyses of zircon yielded model ages ranging from 814 to 1127 Ma with most between 940 and 1040 Ma: such ages are typical of Avalonia and not NW Africa. The ages of the inherited zircons found within the Brenton pluton suggest that it was probably derived by partial melting of sub-Meguma, mid-crustal Avalonian rocks, upon which the Meguma Supergroup was deposited. Although Avalonia is commonly included in the peri-Gondwanan terranes off NW Africa or Amazonia, paleomagnetic data, faunal provinciality, and Hf data suggest that, during the Ediacaran-Early Cambrian, it was an island chain lying near the tropics (ca. 20–30 °S) and was possibly a continuation of the Bolshezemel volcanic arc accreted to northern Baltica during the Ediacaran Timanide orogenesis. This is consistent with the similar derital zircon population in the Ediacaran–Cambrian Meguma Supergroup and the Dividal Group in northeastern Baltica.
ISSN:1437-3254
1437-3262
DOI:10.1007/s00531-017-1495-4