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
Por:
Duncan Keppie, J., Shellnutt, J. Gregory, Dostal, Jaroslav, Keppie, D. Fraser
Publicada:
1 abr 2018
Categoría:
Earth and planetary sciences (miscellaneous)
Resumen:
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 A degrees 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.
Filiaciones:
Duncan Keppie, J.:
Univ Nacl Autonoma Mexico, Inst Geol, Dept Geol Reg, Mexico City 04510, DF, Mexico
Shellnutt, J. Gregory:
Natl Taiwan Normal Univ, Dept Earth Sci, 88 Tingzhou Rd Sect, Taipei 11677, Taiwan
Dostal, Jaroslav:
St Marys Univ, Dept Geol, Halifax, NS B3H 3C3, Canada
Keppie, D. Fraser:
Govt Nova Scotia, Dept Energy, Halifax, NS B3J 3J9, Canada
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