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Structural expression of oblique seafloor spreading in the Macquarie Island ophiolite, Southern Ocean

¹ Division of Earth and Ocean Sciences, Nicholas School of the Environment and Earth Sciences, Duke University, Durham, North Carolina 27708, USA

The Macquarie Island ophiolite is an uplifted block of oceanic crust formed at the Australia-Pacific spreading center between 12 and 9 Ma. The sense of motion and geological processes across this plate boundary reflect an evolution from orthogonal spreading through progressively more oblique spreading to the present-day transpressional regime. The crust that makes up the island was formed during an interval of oblique spreading along east-trending spreading segments punctuated by a series of northwest-trending discontinuities. The discontinuities are accommodation zones marked by oblique-slip dextral-normal faults, localized dikes and lava flows, and extensive hydrothermal alteration, indicating that these zones were active near the spreading axis. These features provide a window into the internal structure of oceanic crust generated by oblique spreading.

Key Words: seafloor spreading • oblique-slip faults • discontinuities • transfer zones • hydrothermal circulation

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