Mid-Devonian ultrabasic sill near White Cliffs, New South Wales
Titel:
Mid-Devonian ultrabasic sill near White Cliffs, New South Wales
Auteur:
Bottril, R.S. Neef, G.
Verschenen in:
Australian journal of earth sciences
Paginering:
Jaargang 45 (1998) nr. 1 pagina's 93-96
Jaar:
1998-02
Inhoud:
An ultrabasic sill, about 900 m in strike length and up to 20 m thick, crops out near Spring Hill, about 39 km west-southwest of White Cliffs In western New South Wales. It occurs near the base of a thick, unfossiliferous, gently dipping sandstone sequence, probably Emsian-Eifelian (latest Early Devonian to earliest Middle Devonian) in age. The sill shows layering parallel to the enclosing strata, indicating that it probably intruded while the strata were horizontal or subhorizontal, before they were folded by the mid-Devonian (Tabberabberan) Orogeny. The dominant lithology of the sill is a greenish grey, fine-grained, massive to vesicular, micaceous rock originally containing abundant olivine and phlogopite phenocrysts and other mafic minerals, now mostly highly altered. The sill is layered, with some medium- to coarse-grained bands, and carbonate-rich pods. The rocks have variable andradite (after melilite?), diopside and dolomite contents; perovskite, sphene, calcite, apatite and spinels are also present, and alteration products include opal, smectitic clays and serpentine. The rock type is most likely to be an alnoite (an ultrabasic lamprophyre with kimberlitic affinities) and may be a potential diamond host.
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