Tectonic trigger to the first major extinction of the Phanerozoic: The early Cambrian Sinsk event.

The Cambrian explosion, one of the most consequential biological revolutions in Earth history, occurred in two phases separated by the Sinsk event, the first major extinction of the Phanerozoic. Trilobite fossil data show that Series 2 strata in the Ross Orogen, Antarctica, and Delamerian Orogen, Australia, record nearly identical and synchronous tectono-sedimentary shifts marking the Sinsk event. These resulted from an abrupt pulse of contractional supracrustal deformation on both continents during the Pararaia janeae trilobite Zone. The Sinsk event extinction was triggered by initial Ross/Delamerian supracrustal contraction along the edge of Gondwana, which caused a cascading series of geodynamic, paleoenvironmental, and biotic changes, including (i) loss of shallow marine carbonate habitats along the Gondwanan margin; (ii) tectonic transformation to extensional tectonics within the Gondwanan interior; (iii) extrusion of the Kalkarindji large igneous province; (iv) release of large volumes of volcanic gasses; and (v) rapid climatic change, including incursions of marine anoxic waters and collapse of shallow marine ecosystems.

Exhumation and tectonic history of inaccessible subglacial interior East Antarctica from thermochronology on glacial erratics.

The geology, tectonic history and landscape evolution of ice-covered East Antarctica are the least known of any continent. Lithic boulders eroded from the continental interior and deposited in glacial moraines flanking the Transantarctic Mountains provide rare constraints on the geological history of central interior East Antarctica. Crystallization ages and ice velocities indicate these glacial erratics are not sourced locally from the Transantarctic Mountains but rather originate from the continental interior, possibly as far inland as the enigmatic Gamburtsev Subglacial Mountains. We apply low-temperature thermochronology to these boulders, including multi-kinetic inverse thermal modeling, to constrain a multi-stage episodic exhumation history. Cambro-Ordovician and Jurassic rapid-cooling episodes correlate with significant exhumation events accompanying Pan-African convergence and Gondwanan supercontinent rifting, respectively. Here we show that while Cretaceous rapid cooling overlaps temporally with Transantarctic Mountains formation, a lack of discrete younger rapid-cooling pulses precludes significant Cenozoic tectonic or glacial exhumation of central interior East Antarctica.

Absence of evidence for Palaeoproterozoic eclogite-facies metamorphism in East Antarctica: no record of subduction orogenesis during Nuna development.

The cratonic elements of proto-Australia, East Antarctica, and Laurentia constitute the nucleus of the Palaeo-Mesoproterozoic supercontinent Nuna, with the eastern margin of the Mawson Continent (South Australia and East Antarctica) positioned adjacent to the western margin of Laurentia. Such reconstructions of Nuna fundamentally rely on palaeomagnetic and geological evidence. In the geological record, eclogite-facies rocks are irrefutable indicators of subduction and collisional orogenesis, yet occurrences of eclogites in the ancient Earth (> 1.5 Ga) are rare. Models for Palaeoproterozoic amalgamation between Australia, East Antarctica, and Laurentia are based in part on an interpretation that eclogite-facies metamorphism and, therefore, collisional orogenesis, occurred in the Nimrod Complex of the central Transantarctic Mountains at c. 1.7 Ga. However, new zircon petrochronological data from relict eclogite preserved in the Nimrod Complex indicate that high-pressure metamorphism did not occur in the Palaeoproterozoic, but instead occurred during early Palaeozoic Ross orogenesis along the active convergent margin of East Gondwana. Relict c. 1.7 Ga zircons from the eclogites have trace-element characteristics reflecting the original igneous precursor, thereby casting doubt on evidence for a Palaeoproterozoic convergent plate boundary along the current eastern margin of the Mawson Continent. Therefore, rather than a Palaeoproterozoic (c. 1.7 Ga) history involving subduction-related continental collision, a pattern of crustal shortening, magmatism, and high thermal gradient metamorphism connected cratons in Australia, East Antarctica, and western Laurentia at that time, leading eventually to amalgamation of Nuna at c. 1.6 Ga.