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The role of heritage in the architecture of the Andaman rift: oblique and diachronous reactivation of the basement structures

Le 6 sep 2019 par MAURIN Thomas

Author: MAURIN Thomas

Co-authors: SIRGUE Laurent, ZUCKMEYER Eric

 

The Andaman sea basin is part of various pull-apart basins all formed in a strike slip environment within a back arc setting. This strike slip tectonic regime results from a strain-partitioning process due to the oblique subduction of the Indian plate below the Sunda plate. The Andaman oceanic spreading started 5Ma ago. Considering the Early Miocene age of the rifted-apart volcanic provinces (Alcock and Sewell rises), the rifting period have been considered started in Lower to Middle Miocene in the Andaman area.

The interpretation of 2D and 3D seismic data located at various locations along the Northern margin of the Andaman basin, and calibrated by well data, revealed a 3 phased rifting history rather than a single Mio-Pliocene episode (Figure 1). The stratigraphic sequence is composed of a volcanic basement, including volcanoclastic deposits, overlain unconformably by Oligo-Miocene carbonates (locally platforms and reefs) intruded by some volcanic dykes. A Miocene to present siliciclastic sequence indicates the onset of the Irrawady Delta. This last sequence is itself intruded by volcanic sills and dykes indicative of a persistent volcanic activity.

The volcanic basement is actually mainly framed by EW normal faults associated with NS transfer zones. This structural framework controls the volcanoclastic deposits. The architecture of that initial rift is significantly different from the Mio-Pliocene one which is framed by NE-SW normal faults and NS strike slip faults: the first one is typical of an orthogonal rift system with NS extension whereas the second is

Figure 1: Seismic line showing the 3 distinct tectonic phases observed on the northern margin of the Andaman basin. Profile is located on figure 2.

 

 

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