Mid Sweden University

Despite many years of study, the processes involved in the post-breakup development of passive margins remain poorly understood. Integration of apatite fission track analysis (AFTA) and stratigraphic landscape analysis (SLA) at a number of margins has provided new insights into the development of elevated passive continental margins (EPCMs). In particular, by integrating evidence from the preserved rock record and landscape with information on the deposition and erosional removal of rock units which are no longer present (“missing section”) these studies have highlighted the importance of episodic positive and negative vertical km-scale crustal movements. Based on these studies we present seven propositions regarding the formation of EPCMs and the nature of the controlling processes, viz:

1: EPCMs are not the inevitable consequence of rifting and breakup

2: Elevated topography at present-day EPCMs developed long after breakup

3: Similar EPCM landscapes at different margins suggest similar controlling processes

4: EPCMs have undergone episodic km-scale burial and exhumation rather than slow monotonic denudation, both before rifting and after breakup

5: Post-breakup km-scale exhumation at continental margins is not restricted to presently elevated onshore regions

6: Post-breakup km-scale burial and exhumation have affected presently low lying margins as well as EPCMs

7: Exhumation events show a broad level of synchroneity over continents and across oceans and correlate with plate boundary events and changes in plate motions.

These propositions imply that positive and negative vertical motions at passive margins are controlled by plate-scale processes. Another key conclusion is that present-day elevation alone provides no clue to the earlier history of a margin.

Many of the key aspects of these propositions are absent from current geodynamic models of passive margin development. Understanding the processes that control vertical movements at passive continental margins requires development of realistic geodynamic models that honour these propositions.