Interpretation of magnetic and gravity data in EBAGOOLA 1:250 000 sheet area, north Queensland

Abstract

Gravity and magnetic anomalies have been used to study the basement geology of the Ebagoola 1:250 000 sheet area, in Cape York, north Queensland. This sheet area is important for two reasons. It is probably the best exposure of a distinct Proterozoic metamorphic area outcropping in the Coen and Yambo Inliers, and differs in age, rocks and history from Proterozoic crust to the south and west that crop out in the Georgetown and Mount Isa areas. It provides a well exposed section of the reworking of the margin of the Proterozoic crust by heating, faulting and intrusion during the Siluro-Devonian. The amount of reworking increases towards the interpreted edge of the Proterozoic crust at the Palmerville Fault Zone on the east side of the Ebagoola sheet. Away from the edge of the Proterozoic crust, in the western part of Ebagoola sheet and further to the west, the metamorphic rocks are not exposed but they are thought to be of greenschist facies, and not affected by the Siluro-Devonian event. From 110 to 60 km west of the edge of the Proterozoic crust there is a strip of metamorphic rocks that is largely greenschist-facies with a simple structure, but the margins of the strip have been heated to lower-upper amphibolite grade, strongly strike-slip faulted, and intruded by granitoids to approximately the present erosional level. From 60 to 15 km from the edge, the metamorphics are uniformly at upper amphibolite grade, strongly faulted, and intruded by granitoids to levels generally above the present erosional level. Between 15 and 0 km from the edge the rocks are not exposed, but the lower magnetization is consistent with a separate episode of metamorphism. This Proterozoic margin may be a model for unexposed craton margins elsewhere with a similar magnetic pattern, such as to the south between the New England and Thomson Orogens, and the East Thomson and West Thomson Orogens.