Journal
INTERNATIONAL JOURNAL OF EARTH SCIENCES
Volume 107, Issue 2, Pages 409-429Publisher
SPRINGER
DOI: 10.1007/s00531-017-1500-y
Keywords
Paleoarchean sialic crust; Peri-Gondwanan terranes; Provenance; Pb-Hf isotopes; Ediacaran; Iberian Massif
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Funding
- Faculty of Science and Technology of the University of Stavanger
- BP (British Petroleum)
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The Mora Formation (Narcea Group) is one of the oldest Precambrian supracrustal successions in northern Spain. Here, we use U-Pb and in situ Hf isotope analysis on detrital zircon to determine its age and provenance. The youngest U-Pb dates constrain the maximum depositional age of the Mora Formation at 565 +/- 11 Ma. Results indicate: (1) a dominant Ediacaran zircon population (33%; 565-633 Ma, Cadomian) within a spectrum of Neoproterozoic ages (40%; 636-996 Ma); and (2) smaller Mesoproterozoic (5%; 1004-1240 Ma), Palaeoproterozoic (11%; 1890-2476 Ma) and Archean (11%; 2519-3550 Ma) populations. Results here do not point to one specific cratonic source area; instead, detritus may have been derived from the West African craton and Amazonia, or even the concealed Iberian basement. The lack of 1.3-1.8 Ga grains suggests exclusion of the Sahara Craton as a major source, but this is not certain. This mixed composition favours a complex source history with reworking of detritus across terrane/craton boundaries. Hafnium isotope compositions indicate a range of crustal and juvenile sources, with initial epsilon(Hf) values between -15.8 and 11.1, and Hf model ages from 0.8 to 3.7 Ga. For Neoproterozoic zircons (80%), juvenile components (epsilon(Hf(i)) similar to+10) may be related to Rodinia fragmentation and the onset of an active margin setting leading to the Cadomian orogeny. Palaeoproterozoic to Paleoarchean grains (20%) all have negative epsilon(Hf) values and Meso- to Eoarchean Hf model ages. This indicates an early (Archean) sialic crustal component for northwestern Gondwana.
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