Large-Scale Lenticles in the Lower Crust Under an Intra-Continental Basin in Eastern Australia

  1. Robert F. Mereu,
  2. Stephan Mueller and
  3. David M. Fountain
  1. D. M. Finlayson,
  2. J. H. Leven and
  3. K. D. Wake-Dyster

Published Online: 9 APR 2013

DOI: 10.1029/GM051p0003

Properties and Processes of Earth's Lower Crust

Properties and Processes of Earth's Lower Crust

How to Cite

Finlayson, D. M., Leven, J. H. and Wake-Dyster, K. D. (1989) Large-Scale Lenticles in the Lower Crust Under an Intra-Continental Basin in Eastern Australia, in Properties and Processes of Earth's Lower Crust (eds R. F. Mereu, S. Mueller and D. M. Fountain), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM051p0003

Author Information

  1. Bureau of Mineral Resources, Geology & Geophysics, Canberra, Australia

Publication History

  1. Published Online: 9 APR 2013
  2. Published Print: 1 JAN 1989

ISBN Information

Print ISBN: 9780875904566

Online ISBN: 9781118666388

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Keywords:

  • Earth—Crust—Congresses;
  • Geophysics—Congresses

Summary

Under the central Eromanga Basin region in eastern Australia seismic reflection events at two-way time greater than 7 seconds outline large-scale lenticles or pod-shaped zones in the lower crust which are possible indicators of processes at such depths. the three-dimensional shape of these lenticles has been approximately outlined along a network of deep reflection traverses [UEQU]cross the Barcoo Trough. the lenticles are a feature of the lower crust under areas of significant Devonian deposition and deformation, and appear to be attenuated, altered or absent from the lower crust under adjacent basement highs. the basement highs appear to have different deep structural features and velocities compared with the intervening basins, pointing to a different evolutionary history.

The velocity in the lenticles is greater than in the overlying upper crustal rocks of the Thomson Fold Belt. This, together with the persistence of lower crustal sub-horizontal reflections within the lenticles, suggests some form of dense high-velocity fraction from the upper mantle has been added to the lower crust early in the history of the Devonian basins. A discontinuity observed in the reflection data at mid-crustal depths between the lower crust and the overlying deformed Thomson Fold Belt suggests that the processes in the lower crust are younger than those in the upper crustal basement. Reflections at 13–14 seconds two-way time, interpreted as being at the Moho based on coincident refraction data, appear to cut dipping lower crustal reflectors near the basin margins, suggesting that the Moho has re-equilibrated after lower crustal features were formed.