Nimrod orogeny

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The Nimrod orogeny was a plate tectonic and orogenic event that occurred between 1730 and 1720 mya on what was then the eastern edge of East Antarctica . Together with the contemporary Kimban orogeny that occurred on the eastern fringes of the South Australian Gawler and Terre Adélie cratons, they define the existence of the Mawson craton .

These orogenic processes are collectively referred to as Nimrod-Kimban orogenesis, which were related to the subduction of lithospheric plates and the closure of ocean basins . In terms of time, they coincide with the formation range of the hypothetical supercontinent Columbia , which developed from around 2000 mya.

Origin of name

The name for the Nimrod orogeny is the Nimrod Group within the Miller Range , in which rare outcrops of the East Antarctic basement come to light. The Nimrod Group forms a heterogeneous metamorphic overprinted complex, which contains rocks up to 3100 mya old .

Geodynamic processes

During the Nimrod orogeny, the hypothetical Beardmore microcontinent collided with the eastern edge of the Mawson craton. The Beardmore microcontinent formed a narrow continuous terran strip that extended along what is now the Transantarctic Mountains to the northeastern edge of East Antarctica. It is no longer preserved, but sediments occur in the Beardmore Group of the Miller Range that are 2800 mya and 1900 to 1400 mya old, and came from different continental margins along a rift valley. The Miller Range and the Shackleton Range were wedged between the East Antarctic basement and the Beardmore microcontinent, and their basement was profoundly tectonically revised and metamorphically shaped

Rocks and metamorphoses

The Nimrod orogenesis is a significant event in which high-grade deformations, metamorphoses and crust thickening occurred between 1730 and 1720 mya. It is the oldest recorded orogenic event in East Antarctica. Evidence can be found in zircons of igneous protoliths (parent rocks) of archaic gneiss . They show metamorphic overprints between 1730 and 1720 mya. Deformed granodiorite , which intruded into the gneiss and associated metasedimentary rocks , has a crystallization age around 1730 mya. An eclogite block inserted in the gneiss underwent metamorphic recrystallization around 1720 mya. Eclogites typically arise along subduction zones . The metamorphic overprinting of the gneiss and mica schist reaches regionally from upper amphibolite facies over granulite facies to eclogite facies .

Web links

  • Justin L. Payne, Martin Hand, Karin M. Barovich, Anthony Reid, and David AD Evans: Correlations and reconstruction models for the 2500-1500 Ma evolution of the Mawson Continent. In: Palaeoproterozoic Supercontinents and Global Evolution. Geological Society, London, Special Publications, 323, 319-355. doi: 10.1144 / SP323.16 , PDF
  • Georg Kleinschmidt and Werner Buggisch: Plate Tectonic Implications of the Structure of the Shackleton Range, Antartica. In: Polarforschung 63 (1): 57-62, 1993. PDF
  • John W. Goodge: Latest Neoproterozoic basin inversion of the Beardmore Group, central Transantarctic Mountains, Antarctica. In: Tectonics, Vol. 16, No. 4, Pages 682-701, August 1997. [1]

Individual evidence

  1. ^ Nick MW Roberts: The boring billion? - Lid tectonics, continental growth and environmental change associated with the Columbia supercontinent. In: Geoscience Frontiers, Volume 4, Issue 6, November 2013, Pages 681-691. doi: 10.1016 / j.gsf.2013.05.004 , alternatively
  2. ^ John W. Goodge and C. Mark Fanning: 2.5 by of punctuated Earth history as recorded in a single rock. In: Geology; November 1999; v. 27; no. 11; p. 1007-1010. PDF
  3. ^ John W. Goodge, C. Mark Fanning and Vickie C. Bennett: U – Pb evidence of ∼1.7 Ga crustal tectonism during the Nimrod Orogeny in the Transantarctic Mountains, Antarctica: implications for Proterozoic plate reconstructions. In: Precambrian Research, Volume 112, Issues 3-4, 10 December 2001, Pages 261-288. doi: 10.1016 / S0301-9268 (01) 00193-0 , alternaiv
  4. ^ JW Goodge, P. Myrow, IS Williams, and SA Bowring: Age and Provenance of the Beardmore Group, Antarctica: Constraints on Rodinia Supercontinent Breakup. In: The Journal of Geology, Volume 110, Number 4 | July 2002. doi: 10.1086 / 340629 , alternatively
  5. ^ MH Monroe: Antarctica - Before and After Gondwana. In: Gondwana Research, Volume 19, Issue 2, March 2011, Pages 335-371. doi: 10.1016 / j.gr.2010.09.003 , alternatively