Rotation of horizontal stresses in the Australian North West continental shelf due to the collision of the Indo‐Australian and Eurasian Plates

Abstract

There is a 40° rotation of regional maximum horizontal stress (σhmax) orientation between the western end of the Australian North West Continental Shelf (Carnarvon Basin) and its eastern end (Bonaparte Basin). A total of 625 borehole breakouts covering a cumulative length of 7.7 km in 42 wells in the Carnarvon Basin indicates a σhmax orientation of 090°–100°N. A total of 616 borehole breakouts over 6.8 km in 46 wells in the Bonaparte Basin indicates a σhmax orientation of 055°N–060°N. Together with extant data from the World Stress Map, these results indicate that regional σhmax orientation is 050°–060°N from New Guinea westward through the Bonaparte Basin to the Canning Basin (central North West Shelf). Between the Canning Basin and the Carnarvon Basin, σhmax rotates to 090°–100°N. The parallelism of σhmax orientation in the Bonaparte Basin to the Australia/Banda Arc collisional zone indicates that this collision is not generating significant net push. Rather, the 050°–060°N σhmax orientation of much of the northern Australian margin is probably controlled by the more mature New Guinea orogen to which it is approximately orthogonal. The observed rotation of σhmax can be explained solely by the focusing of the forces balancing ridge push along collisional segments of the northeastern boundary of the Indo‐Australian Plate (such as the New Guinea orogen). Although not required to account for the observed stress rotation, a slab pull force from oceanic Indo‐Australian Plate being subducted beneath the Sunda Arc cannot be dismissed.