The onshore record of passive margin evolution

The onshore region of passive margins has been relatively neglected because there is no unambiguous record of the denudation chronology and processes. However, apatite fission track data are sensitive to temperatures <150 degrees C, appropriate to the cooling interval relevant during denudation of passive margin topography. In order to understand the meaning of the measured fission-track age, it is crucial to consider the track-length distribution as this is where most information concerning the thermal history is available. Over the last 10 years or so, apatite fission-track analysis studies have been undertaken from a variety of passive margins and we consider data from southern Africa, Brazil, Yemen, western India and southeast Australia. These data suites are consistent with greater amounts of section removed on what is now the low elevation coastal plain, with less material lost from the hinterland. In general there is little evidence remaining of the break-up process because of protracted denudation during the subsequent evolution of the margin. Each passive margin shows different morphologies and amounts of denudation reflecting both local geomorphic and geodynamic conditions. In addition, regional structures (e.g. shear zones) show evidence of reactivation long after break-up, but still related to large-scale plate processes.