The Pacific, Antarctic, and Macquarie lithospheric plates diverge from the Macquarie Triple Junction (MTJ) in the southwestern Pacific Ocean, south of Macquarie Island. Mor-phobathymetric, magnetic, and gravity data have been used to understand the evolution of the three accretionary/transform boundaries that meet at the MTJ. Plate velocities, estimated near the MTJ and averaged over the past 3 m.y., indicate an unstable ridge-fault-fault triple junction. The long life (>6 m.y.) of this configuration can be attributed to a rapid increase in spreading asymmetry along the Southeast Indian Ridge segment as it approaches the MTJ, and to transtension along the southernmost strand of the Macquarie-Pacific transform boundary. A major change in plate motion triggered the development of the Macquarie plate at ca. 6 Ma and makes clear the recent evolution of the MTJ, including (1) shortening of the Southeast Indian Ridge segment; (2) formation of the westernmost Pacific-Antarctic Ridge, which increased its length over time; and (3) lengthening of the two transform boundaries converging in the MTJ. The clockwise change of the Pacific-Antarctic motion (ca. 12-10 Ma) led to complex geodynamic evolution of the plate boundary to the east of the triple junction, with fragmentation of the long-offset Emerald transform fault and its replacement over a short time interval (1-2 m.y.) with closely spaced, highly variable transform offsets that were joined by short ridge segments with time-varying asymmetries in the spreading rates.

Late Miocene to recent tectonic evolution of the Macquarie Triple Junction

Accettella D.;Lodolo E.;
2023-01-01

Abstract

The Pacific, Antarctic, and Macquarie lithospheric plates diverge from the Macquarie Triple Junction (MTJ) in the southwestern Pacific Ocean, south of Macquarie Island. Mor-phobathymetric, magnetic, and gravity data have been used to understand the evolution of the three accretionary/transform boundaries that meet at the MTJ. Plate velocities, estimated near the MTJ and averaged over the past 3 m.y., indicate an unstable ridge-fault-fault triple junction. The long life (>6 m.y.) of this configuration can be attributed to a rapid increase in spreading asymmetry along the Southeast Indian Ridge segment as it approaches the MTJ, and to transtension along the southernmost strand of the Macquarie-Pacific transform boundary. A major change in plate motion triggered the development of the Macquarie plate at ca. 6 Ma and makes clear the recent evolution of the MTJ, including (1) shortening of the Southeast Indian Ridge segment; (2) formation of the westernmost Pacific-Antarctic Ridge, which increased its length over time; and (3) lengthening of the two transform boundaries converging in the MTJ. The clockwise change of the Pacific-Antarctic motion (ca. 12-10 Ma) led to complex geodynamic evolution of the plate boundary to the east of the triple junction, with fragmentation of the long-offset Emerald transform fault and its replacement over a short time interval (1-2 m.y.) with closely spaced, highly variable transform offsets that were joined by short ridge segments with time-varying asymmetries in the spreading rates.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/20.500.14083/15323
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