Ross Orogen

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The Ross orogen was a fold and thrust orogen on what was then the eastern edge of East Antarctica . The orogenic phase extends approximately from 580 to 480 million years (abbreviated mya ) and is related to the disintegration of the supercontinent Rodinia and the formation of Gondwana , especially Eastern Gondwana . One of the largest mountain ranges arose in the late Neoproterozoic to the Phanerozoic with a length of approx. 3,500 kilometers. As a result of long-lasting erosion with erosion, flat, undeformed hull surfaces or plains were often formed on which mighty sediment packages were deposited. B. formed the Beacon Supergroup .

The igneous geochemistry , deformation patterns, and sedimentation history are believed to be the result of convergences between paleopacific oceanic and Antarctic continental lithospheric plates . Evidence in the metamorphic regions reflects continental plate subductions lasting 60 to 100 million years , characterized by accretions and thickenings of the continental crust , island arches, and seaward growth of a plate edge accretion system.

The Ross Orogen forms the basement of today's Transantarctic Mountains , which developed from 65 mya and covers large areas of the eroded Ross Orogen.

Location and extent

The approx. 3,500 kilometer long Ross Orogen formed on what was then the eastern edge of Eastern Gondwana. In today's geography of East Antarctica, it stretches from northern Victoria Land on the Ross Sea to the Pensacola Mountains in Queen Elizabeth Land on the Weddell Sea . The Edward VII Peninsula in the westernmost Marie Byrd Land is also part of this mountain range . This corresponds to the course of the Transantarctic Mountains, which, however, only emerged from 65 mya on the basement of the Ross orogen.

Geological framework

During the disintegration of Rodinia, a superplume from 750 mya caused rift breaks in the form of a triple junction (triple point) between Laurentia and the continental mass of Proto-East Antarctica and Proto-Australia on the one hand, and between Proto-East Antarctica and the Proto-Kalahari craton ( Kaapvaal -Kraton ) on the other hand. At 720 mya the East Antarctic-Australian continental plate had completely separated. The Panthalassa , also known as the Paleo-Pacific, began to open. From 600 mya, subductions of oceans or seas led to collisions of previously separated continental plates and to the formation of Gondwana.

The subduction of the oceanic crust of the Panthalassa under the eastern edge of Gondwana, beginning to the west, produced the Terra Australis ore. It extended from northern Proto-Australia via Proto-East Antarctica, Proto-South Africa to Proto-South America with a length of approx. 18,000 kilometers and a width of up to approx. 1,600 kilometers. The Australian section is called the Delamerian Orogenic, which was followed by the East Antarctic Ross Orogenes (see also → Peripheral Orogenes in East Gondwana). In Southern Africa , the formed Cape Fold Belt (ger .: Cape Fold Belt) from.

Basement

Reconstruction of the Mawson craton with its parts in South Australia and East Antarctica

The Ross Orogen is based on an archaic to Proterozoic, multiple deformed and metamorphic overprinted cratonized basement . This is open in the Miller Range and the Geologists Range in the central area of ​​the Transantarctic Mountains (for details see Tectonic Units in the Central Transantarctic Mountains ). It is assigned to the East Antarctic section of the Mawson Craton .

Tectonic situation and time frame

The geodynamic development of the Ross orogeny comprises a long-lasting sequence of several processes that extend at least over the period of 580 to 480 mya.

Tectonic situation

During the Neoproterozoic breakup of Rodinia, a predominant stretching regime developed along the paleopacific passive continental margin of the common lithospheric plate of Proto-East Antarctica with Proto-Australia. They had their cause in the transfer of tectonically conditioned tensions in the continental crust to the outer flanks of the continent. Associated with this was a passive sinking of the edge areas and the formation of sedimentary basins .

In the recent Neoproterozoic to the early Cambrian , the continental margin underwent a significant transformation into an active plate boundary as a result of the global reorganization of plate tectonics and plate boundary stresses. With the inversion of the stretching movements, a convergence of the oceanic and continental lithospheric plates began, whereby the continental marginal basins were closed due to the subducting westward ocean floor. An active continental margin developed along this subduction zone. This was characterized by the formation of carbonate platforms , clastic and molasseartigen sedimentation, extensive continental margin volcano with various (bimodal) magmas , Inselbogen collisions , Forearc-Beckensedimentationen , tectonically related crust truncations and -verdickungen, metamorphosis rock About embossments and granitic , gabbronitische and pegmatite intrusions , transpressional deformations between the basement and supracrustal rock packages as well as high-grade reactivation of the basement.

The tectonic processes in the Ross Orogen can be compared in principle with the formation of the South American Andes and the development of microplates along Sumatra and Japan .

Timeframe

Calc-alkaline magmatism suggests that subduction began between 550-530 mya. However, the geochronology of zircons made from detritic (dragged) sandstones derived from arches of the islands suggests that significant magmatism already occurred around 580 to 560 mya. Regional isotopic and geochemical variations in granitoid rocks show increasing crustal kraton components, which can best be explained by subduction-induced melts under an eastern continental margin.

In the 550-520 mya period, the northern and central segments (Northern and Southern Victoria Land) of the Ross Orogen experienced early contractions and transpressions, while the southern segment (central Transantarctic Mountains) was dominated by persistent sedimentation and volcanism.

Between 520 and 480 mya, deformations and compressions occurred in the northern segment as a result of the accretion of an island arc and forearc sedimentation from flysch and molasse-like deposits. In the southern section, igneous island arc complexes and forearc basins accreted. The central area was characterized by continued transpression in the crystalline basement and contractions in the supracrustal complexes. In the southern segment of the orogen, complex carbonate and siliciclastic deposits dominated. Plutonism and volcanism were widespread in all areas.

Tectono-stratigraphic units

The Ross Orogen is divided into several Tektono- stratigraphic units. These are assigned to the northern and southern Victoria Land and the central areas in the Transantarctic Mountains.

Tectonic units in northern Victoria Land

The most significant geological entities in northern Victoria Land are, from west to east, the Wilson Group, the Bowers Supergroup and the Robertson Bay Group.

The Wilson Group consists predominantly of quartz and feldspathic mica schists , layered paragneiss and migmatites of the lower Paleozoic. It was associated with southern areas of the Delamerian orogen. The Bowers Group is made up of Central Cambrian to Lower Ordovician marine volcanic and clastic sedimentary rocks. It is interpreted as an island arch complex. Between the Wilson Group and the Bowers Supergroup there is a zone of mica schists with embedded blocks and lenses of mafic and ultramafic rocks. They are seen as severed pieces of the earth's lower crust and mantle . Furthermore, eclogitic and coesite-containing parageneses (mineral communities) were identified. This zone represents the geosuture between these two terrans. The Robertson Bay Group is characterized by marine turbiditic clastic sedimentary rocks, formed in the Upper Cambrian to Lower Ordovician.

These terranes were deformed differently and regionally penetrated by plutons. The older granitoids form a western belt from the Upper Cambrian to the Lower Ordovician, in which a transition from S-type to I-type granite intrusions (see granite types ) took place. These intrususes, known as Granite Harbor , correlate with Plutonic rocks of the same age in the rest of the Transantarctic Mountains. I-type granitoids formed in eastern terran areas. They form the Devonian Admiralty Intrusive. The boundary between these intrusions is viewed as a convergent tectonic zone or interpreted as an accretion area of allochthonous terrans , depending on the perspective .

The rock packages in these terranos were overprinted in different metamorphic forms . In the Wilson Group, the grade of metamorphism generally ranges from moderate amphibolite facies in the east to high grade granulite facies in the west. The period given for this is 500 to 470 mya. The paragenesis in the contact zone between the Wilson Group and the Bowers Supergroup was subject to a high to ultra-high metamorphic overprint during its formation, during which an eclogite facies developed from 500 to 480 mya . After these rocks had been exhumed, they were overprinted with lower amphibolite facies. The Bowers Supergroup and the Robertson Bay Group were subject to low-grade metamorphic overprints ranging from prehnite-pumpellyite facies to green slate facies . These metamorphoses occurred between 500 and 460 mya.

Tectonic units in southern Victoria Land

In the southern Viktorialand a complex polydeformed and metamorphic overprinted volcanic-sedimentary system forms, which was covered by extensive igneous rocks . These are assigned to the Granite Harbor. It is divided into the Skelton Group and the Koettlitz Group. Pregranitic rocks from the Skelton Group and the Koettlitz Group are exposed in separate areas, but both include marbles , migmatitic mica schists and orthogneiss , amphibolites , calcareous silicate gneiss , metaarcoses and rare pelitic mica schists that are layered in different thicknesses . It is assumed that the siliciclastics and the rocks containing calcium carbonate came from a late Neoproterozoic to early Paleozoic continental margin. They generally correlate with similar supracrustal rift sequences in the rest of the Transantarctic Mountains. The ages of detritic zirconia showed deposition periods between 1,050 to 535 mya and 950 to 551 mya. Intruded plutons in the two groups result in a minimum sedimentation age of 551 to 535 mya.

The regional division of the two groups was not based on lithostratigraphic features, but on the basis of different structural and metamorphic forms. The metamorphic range extends from the upper amphibolite facies in the northern area of ​​the Dry Valleys to the green schist facies further south near the Skelton Glacier . The Koettlitz Glacier marks the border between these high and low grade zones. Presumably it covers an important geological structural boundary. The age of detritic minerals suggests that the metasedimentary rock packages come from the same areas of origin.

Tectonic units in the central Transantarctic Mountains

In the central Transantarctic Mountains, the only crystalline basement area of ​​the Ross orogen is exposed. It is limited to the neighboring Miller Range and Geologists Range. The local, highly penetrating deformed and metamorphic overprinted archaic to proterozoic Nimrod Group is characteristic. The metasedimentary and metaplutonischen Lithostratigraphien include pelitic mica, micaceous quartzites , amphibolite , banded quarzofeldspathaltige to mafic gneiss, homogeneous hornblende gneiss in different variations, kalksilikatische gneiss (see gneiss division ), granitic to gabbronitische orthogneisses, marbles , Migmatite and relics of eclogites. These occur as separate blocks within layered gneisses and can come from lower crustal areas.

The basement was subject to strong tectono-thermal influences from the Ross orogeny between 540 and 485 mya. High grade processes have been dated to around 525 mya. A compositionally diverse sequence of magmatites intruded into the Nimrod Group. They include tonalites , diorites and granodiorites with ages between 541 and 515 mya. This indicates a pronounced reactivation of the basement. The main phase of the metamorphic Ross overprinting of the basement produced upper amphibolite facies to lower granulite facies.

To the east of the Nimrod Group are the low-grade siliciclastic and calcium carbonate supracrustal units of the Beardmore and Byrd Group. The lower sedimentary sequence includes rift fracture to passive rim deposits from the Beardmore and Lower Byrd Group. They were overlaid by widespread molasse sequences from the Upper Byrd Group, representing deep erosion of the Ross orogen and erosive exhumation of the igneous and metamorphic basement. The Beardmore Group developed between 670 and 520 mya, while the Byrd Group emerged between 545 and 531 mya. The igneous rocks of the Granite Harbor series penetrated this between approx. 540 and 480 mya. The metamorphic grade is characterized by regional green slate facies to lower amphibolite facies. The metamorphosis occurred between approximately 490 and 480 mya. These ages correspond to or are slightly younger than the emplacement ages of the late granitoid intrusions in the region.

Ductile tectonic structural deformations (tectonites) in rocks and folds were ubiquitous in the Nimrod Group during the Ross orogeny. Shear zones in the Nimrod basement run at an angle to contraction structures of the outer supracrustal units, which indicates left-directed (sinistral) transpressive plate edge movements.

The erosion of the Ross orogen led, among other things, to extensive hull areas . Sections of the up to 4 kilometers thick sequence of the Beacon Supergroup were deposited on these . Their sedimentation period extends from the Devonian around 400 mya to the early Jurassic around 180 mya. The Kukri Peneplain in the Kukri Hills forms a striking formation .

literature

  • Graham Hagen-Peter: The Metamorphic and Magmatic History of the Ross Orogen in Southern Victoria Land, Antarctica. In: A dissertation submitted in partial satisfaction of the requirements for the degree Doctor of Philosophy in Geological Sciences, September 2015. ( alexandria.ucsb.edu dissertation).
  • Timothy S. Paulsen, John Encarnación, Anne M. Grunow, Edmund Stump and others: Correlation and Late-Stage Deformation of Liv Group Volcanics in the Ross-Delamerian Orogen, Antarctica, from New U-Pb Ages . In: The Journal of Geology . tape 126 , no. 3 , March 2018, ISSN  0022-1376 , p. 307-323 , doi : 10.1086 / 697036 ( nsf.gov [PDF]).
  • SD Boger, J. McL. Miller: Terminal suturing of Gondwana and the onset of the Ross – Delamerian Orogeny: the cause and effect of an Early Cambrian reconfiguration of plate motions . In: Earth and Planetary Science Letters . tape 219 , no. 1 , 2004, ISSN  0012-821X , p. 35-48 , doi : 10.1016 / S0012-821X (03) 00692-7 .
  • Georg Kleinschmidt: Geological development and tectonic structure of the Antarctic . In: Warning signal climate: the polar regions . Verlag Wissenschaftliche Auswertungen, Hamburg 2014, ISBN 978-3-9809668-6-3 ( uni-hamburg.de [PDF]).

Individual evidence

  1. ^ ZX Li, SV Bogdanova, AS Collins, B. De Waele and others: Assembly, configuration, and break-up history of Rodinia: A synthesis . In: ScienceDirect, Precambrian Research . tape 160 , no. 1 , 2008, ISSN  0301-9268 , p. 179-210 , doi : 10.1016 / j.precamres.2007.04.021 ( bdewaele.be [PDF]).
  2. ↑ Peter A. Cawood: Terra Australis Orogen: Rodinia breakup and development of the Pacific and Iapetus margins of Gondwana during the Neoproterozoic and Paleozoic . In: Earth Science Reviews . tape 69 , no. 3-4 , March 2005, ISSN  0012-8252 , pp. 249-279 , doi : 10.1016 / j.earscirev.2004.09.001 .
  3. ↑ John Foden, Marlina A. Elburg, Jon Dougherty-Page and Andrew Burtt: The timing and duration of the Delaware Merian Orogeny: Correlation with the Ross Orogen and Implications for Gondwana assembly. In: The Journal of Geology. Volume 114, 2006, pp. 189-210 ( adelaide.edu.au PDF).
  4. ^ John W. Goodge: Metamorphism in the Ross orogen and its bearing on Gondwana margin tectonics. In: Geological Society of America, Special Paper. 419, 2007 ( semanticscholar.org PDF).
  5. ^ Edmund Stump: The Ross Orogen of the Transantarctic Mountains in Light of the Laurentia-Gondwana Split. In: GSA Today. Volume 2, No. 2, February 1992 ( geosociety.org PDF).
  6. ^ Stress and Strain. In: Lumen Geology, Module 7: Crustal Deformation. ( lumenlearning.com ).
  7. ↑ Thomas Flöottmann, George M. Gibson, Georg Kleinschmidt: Structural continuity of the Ross and Delamerian orogens of Antarctica and Australia along the margin of the paleo-Pacific . In: Geology . tape 21 , no. 4 , April 1993, ISSN  0091-7613 , pp. 319-322 , doi : 10.1130 / 0091-7613 (1993) 021 <0319: SCOTRA> 2.3.CO; 2 ( geoscienceworld.org [PDF]).
  8. ↑ G. Capponi, L. Crispini, G. di Vincenzo, C. Ghezzo, M. Meccheri, R. Palmeri, S. Rocchi: Mafic Rocks of the Bowers Terrane and Along the Wilson-Bowers Terrane Boundary: Implications for a Geodynamic Model of the Ross Orogeny in Northern Victoria Land, Antarctica . In: EGS - AGU - EUG Joint Assembly . 2003, p. 5843 , bibcode : 2003EAEJA ..... 5843C .
  9. ^ Thomas O. Wright: Sedimentology of the Robertson Bay Group, northern Victoria Land, Antarctica. In: Antarctic Journal. 1980 ( amazonaws.com PDF).
  10. ↑ AP Martin, AF Cooper, RC Price, RE Turnbull, NMW Roberts: The petrology, geochronology and significance of Granite Harbor Intrusive Complex xenoliths and outcrop sampled in western McMurdo Sound, Southern Victoria Land, Antarctica . In: New Zealand Journal of Geology and Geophysics . tape 58 , no. 1 , December 8, 2014, ISSN  0028-8306 , p. 33-51 , doi : 10.1080 / 00288306.2014.982660 .
  11. ^ ML Balestrieri, G Bigazzi: First record of the Late Cretaceous denudation phase in the Admiralty Block (Transantarctic Mountains, northern Victoria Land, Antarctica) . In: Radiation Measurements . tape 34 , no. 1-6 , June 2001, ISSN  1350-4487 , pp. 445-448 , doi : 10.1016 / S1350-4487 (01) 00204-9 .
  12. ↑ RJ Wysoczanski and AH Allibone: Age, correlation, and provenance of the Neoproterozoic Skelton Group, Antarctica: Grenville Age detritus on the margin of East Antarctica. In: The Journal of Geology. Volume 112, 2004, pp. 401-416 ( jcu.edu.au PDF).
  13. ↑ Andrew Harold Allibone: Koettlitz group meta-sediments and intercalated orthogneisses from the mid Taylor Valley and Ferrar Glacier regions. In: Thesis, Master of Science, University of Otago 1988. ( otago.ac.nz Thesis).
  14. ^ GW Grindley, Ian McDougall: Age and correlation of the Nimrod Group and other precambrian rock units in the central Transantarctic Mountains, Antarctica . In: New Zealand Journal of Geology and Geophysics . tape 12 , no. 2-3 , 1969, ISSN  0028-8306 , pp. 391-411 , doi : 10.1080 / 00288306.1969.10420290 .
  15. ^ JW Goodge, P. Myrow, IS Williams, SA Bowring: Age and Provenance of the Beardmore Group, Antarctica: Constraints on Rodinia Supercontinent Breakup . In: The Journal of Geology . tape 110 , no. 4 , June 2002, ISSN  0022-1376 , p. 393-406 , doi : 10.1086 / 340629 .
  16. ↑ Edmund Stump, Brian Gootee, Franco Talarico: Tectonic Model for Development of the Byrd Glacier Discontinuity and Surrounding Regions of the Transantarctic Mountains during the Neoproterozoic - Early Paleozoic. In: Antarctica pp 181-190. ( epic.awi.de PDF).
  17. ^ VE Neall, IE Smith: The McMurdo Oasis. In: Tuatara. Volume 15, No. 3, December 1967 ( victoria.ac.nz ).