Petrological, geochemical and geochronological evidence for a Neoproterozoic ocean basin recorded in the Marlborough terrane of the northern New England Fold Belt

Citation
Mc. Bruce et al., Petrological, geochemical and geochronological evidence for a Neoproterozoic ocean basin recorded in the Marlborough terrane of the northern New England Fold Belt, AUST J EART, 47(6), 2000, pp. 1053-1064
Citations number
52
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Earth Sciences
Journal title
AUSTRALIAN JOURNAL OF EARTH SCIENCES
ISSN journal
0812-0099 → ACNP
Volume
47
Issue
6
Year of publication
2000
Pages
1053 - 1064
Database
ISI
SICI code
0812-0099(200012)47:6<1053:PGAGEF>2.0.ZU;2-8
Abstract
Petrological, geochemical and radiogenic isotopic data on ophiolitic-type r ocks from the Marlborough terrane, the largest (similar to 700 km(2)) ultra mafic-mafic rock association in eastern Australia, argue strongly for a sea -floor spreading centre origin. Chromium spinel from partially serpentinise d mantle harzburgite record average Cr/(Cr + Al) = 0.4 with associated mafi c rocks displaying depleted MORB-like trace-element characteristics. A Sm/N d isochron defined by whole-rock mafic samples yields a crystallisation age of 562 +/- 22 Ma (2 sigma). These rocks are thus amongst the oldest rocks so far identified in the New England Fold Belt and suggest the presence of a late Neoproterozoic ocean basin to the east of the Tasman Line. The next oldest ultramafic rock association dated from the New England Fold Belt is ca 530 Ma and is interpreted as backarc in origin. These data suggest that the New England Fold Belt may have developed on oceanic crust, following an oceanward migration of the subduction zone at ca 540 Ma as recorded by def ormation and metamorphism in the Anakie Inlier. Fragments of late Neoproter ozoic oceanic lithosphere were accreted during progressive cratonisation of the east Australian margin.