TRANSTENSIONAL DEFORMATION OF THE LOWER CONTINENTAL CRUST, ARUNTA BLOCK, CENTRAL AUSTRALIA

We present results from a field study of lower continental crust exposed in the Arunta inlier of central Australia, which we interpret to have formed during transtension. The Mt. Hay block is a ~10 km thick, lower continental crustal section. These mafic to intermediate, granulite-grade tectonites were penetratively deformed during the Yambah event (ca 1.78 Ma), which occurred on the southern margin of the North Australian craton. Mt. Hay granulites have steeply dipping foliation and strong, steeply dipping stretching lineation. Fabrics are lineation-dominated (L>S) in km-scale lower-strain lenses, consistent with kinematic modeling. In contrast, fabrics are foliation-dominated in a km-thick high-strain zone. High strain zones are interpreted to surround the low strain lenses. The fabrics restore to a subhorizontal orientation when post-Yambah tilting is removed. Further, the lineation is not perpendicular to the margin of the North Australian craton, indicating oblique motion. Consistent, south-side-up shear sense exists in both the high- and low-strain domains, which is not consistent with kinematic modeling. The latter observation is interpreted to result from strain partitioning at depth in the crust.