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Crustal Architecture Variability on Passive Margins

Abstract

Models of the crustal architecture of passive margins have changed radically over the last 10 years. Recent studies have highlighted the range of crustal types and geometries, largely based on examples from the North and South Atlantic. These models have then been applied to other margins. But, this has further revealed the complexity and variability of margin architecture and evolution, and highlighted that few margins can be fit into any one model. This has major consequences for assessments of petroleum prospectivity in New Ventures exploration.

To investigate how varied margins are, and why, we have built a portfolio of interpreted composite, deep seismic sections as geotransects. These have been compared with 2D profiles of public domain gravity and magnetics, plate kinematic models, well data and other geological information, in order to define the crustal architecture, geodynamic evolution and implications for petroleum prospectivity through basin modelling. The interpretations of crustal architecture are then extended along strike using an analogues database of different crustal types defined based on their gravity and magnetic signatures. Geotransects have been extended onshore, where possible, in order to facilitate research on the links between the passive margin and its hinterland evolution (source-to-sink).

In our modelling we have classified the crustal architecture in two ways: by observation / product (crustal type, crustal thickness); and by the process responsible (viz., using a variant of the classification of Manatschal et al.).

To facilitate this workflow, we have generated a global coverage of structural elements to define a baseline structural framework. In addition, we have used existing published results and gravity and magnetic data to define a global baseline database of crustal type geometries. These baseline databases act as “straw men” which we can use to pose hypotheses and identify areas for which we need a geotransect to evaluate specific questions. These baseline datasets also provide a context within which we can place the more detailed geotransects and the results of other research in the Basin Structure Group at the University of Leeds.