The Glyde Sub-basin: A volcaniclastic-bearing pull-apart basin coeval with the McArthur River base-metal deposit, Northern Territory
Titel:
The Glyde Sub-basin: A volcaniclastic-bearing pull-apart basin coeval with the McArthur River base-metal deposit, Northern Territory
Auteur:
Davidson, G. J. Dashlooty, S. A.
Verschenen in:
Australian journal of earth sciences
Paginering:
Jaargang 40 (1993) nr. 6 pagina's 527-543
Jaar:
1993-12
Inhoud:
Sedimentological, geochemical and tectonic studies have been carried out on the Glyde Sub-basin, a fault-bounded depocentre adjacent to the margin of the Batten Trough, 80 km south of the HYC Pb-Zn-Ag ore deposit, in the mid-Proterozoic McArthur Basin. Although it is unmineralized, the basin is, in some aspects, morphologically similar to the HYC Sub-basin and provides an insight into processes which occurred coevally along strike from a giant shale-hosted base-metal deposit. The geometry of the sub-basin supports an origin in a releasing bend of the Emu Fault during oblique right-lateral extension of the Emu Fault Zone, resulting in the deposition of a very thick sequence of below wave-base Barney Creek Formation carbonaceous siltstone. Prior to sub-basin development the area was covered by hypersaline carbonate tidal flats of the Coxco Dolomite Member of the Teena Dolomite. Internal syn-sedimentary normal faulting fractured the sub-basin into seven major blocks, establishing a basic geometry of northern and southern depressions, into which the W-Fold and HYC Pyritic Shale Members were successively deposited, separated by a non-depositional horst. During the subsequent deposition of undivided Barney Creek Formation the horst was submerged and greater water circulation was established. The horst continued to be an east-west barrier to clastic and volcaniclastic gravity flows, evidenced by the confinement to the northern depocentre of prograding easterly-derived carbonate-dominated turbidites. Rhyolitic volcanism in the Glyde Sub-basin commenced in the W-Fold Shale Member, and became common in the overlying Barney Creek Formation. The measurable volcanic component increases from 4.4 to 17.5% of the total sediment package southwards over 18 km, implying a southern rhyolitic source within 6-30 km. A geochemical comparison of these relatively unaltered tuffs with those intercalated in the HYC ore sequence identified a comagmatic relationship on the basis of immobile element contents, supporting a common volcanic source. This conclusion was only possible after a preliminary study found Ti, Zr, Y and Nb to be relatively immobile in the severely potassium-altered tuff of the HYC hydrothermal ore environment. Low-grade (as distinct from high temperature hydrothermal) potassium-alteration of felsic tuff throughout the McArthur Basin may have resulted from diagenetic interaction with very evolved lacustrine saline brines, whereas brines in the diagenetic environment of the Glyde Sub-basin, in which unaltered or sodically-altered tuff predominates, were comparatively less evolved.
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