ABSTRACT

Sandstones from the New England Orogen are mainly quartz-poor, lithic to feldspathic types derived from a volcanic arc terrane. The variation in detritus from Lower Devonian to Permian in the Tamworth Belt records a change in the nature of volcanism. The detritus becomes more felsic upwards from andesitic in the Devonian to dacitic and rhyolitic in the Upper Carboniferous and Lower Permian. Detrital quartz content is always quartz-poor but increases upwards from <1% to about 15%. Detrital pyroxene is common low in the sequence, but in younger rocks hornblende is more common. Documentation of vertical changes in sandstone composition within the Tamworth Belt allows correlation with the virtually unfossiliferous sandstones in the Tablelands Complex to the east of the Tamworth Belt. T e Woolomin association is correlated with the early to middle Devonian portion of the Tamworth Belt, the Sandon association with the late Devonian portion, and the Coifs Harbour association with the late Carboniferous to early Permian portion. Most sandstones from the New England Orogen were thus derived from an undissected volcanic arc provenance which evolved from mafic to more felsic in composition through time. The volcanic source existed for a period of more than 100 million years. Comparison with detrital sandstone compositions from known ancient and modern tectonic settings suggests that the sandstones were possibly deposited in a backarc basin, but this has not been established unequivocally, and a forearc setting is not precluded.