Metamorphic core complex

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Gneisses and granites of the axial zone of the Montagne Noire : a metamorphic core complex

As a metamorphic core complex ( English metamorphic core complex ) in which it is geology a section of land designated in the original deep within the earth's crust situated, high metamorphic rocks amid significantly lower or non-metamorphic rocks come to light. The emergence of these areas is based on expansion tectonics and occurs largely without magma formation .

The process by which the middle and deeper continental crust reaches the earth's surface is relatively rapid. During the stretching process, flat shearings occur , which are designed as mylonitic shear zones. Below this Abscherhorizonte are high grade metamorphic rocks from the eclogite - granulite - or amphibolite - facies , the ductile were deformed. The rocks in the hanging wall were converted (synkinematic) into green slate facial or amphibolite facial metamorphic rocks during these movement processes ; their deformation behavior was ductile-brittle to brittle .

Descriptions / Definitions

Coney (1980) defines metamorphic core complexes as follows:

“The metamorphic core complex is generally characterized as a heterogeneous basement ridge, which is composed of older metamorphic and plutonic rocks and is overprinted by a younger mylonitic or gneiss-like texture with flat lineation and foliation. The covering terran in the hanging wall is in the unmetamorphosed state and is fragmented and consequently stretched by a system of countless relatively flat faults , the younger fault branches of which run out on the older ones. There is a shear horizon and / or a steep rise in the metamorphic grade between the basement and the cover terran. Associated brecciation and other kinematic as well as structural indicators point to sliding or shearing movements. "

The Abscherhorizont is in French as décollement and in English as a detachment called.

Lister and Davis (1989) give the following definition:

“The formation of metamorphic core complexes results from the large-scale expansion of the continental crust. The middle and lower crust is literally pulled away from below the tearing and expanding upper crust. The movement horizons required for this are subject to both spatial and temporal development. The rocks, deforming when lying down, experience a gradual upward movement, which allows them to pass through different metamorphic and structural facies and consequently imposes a characteristic sequence of mesostructures and microstructures on them. "

Occurrence

The concept of the metamorphic core complex was first developed in the Cordilleras of western North America , which is home to numerous examples:

The occurrences in the northern Cordillera come from the Eocene , whereas those in the further south (e.g. in Arizona ) are more recent.

Metamorphic core complexes are not limited to North America, they also occur in Anatolia , Iran , Tibet and New Zealand . The geologically youngest metamorphic core complex is located in eastern New Guinea ( D'Entrecasteaux Islands ).

Further occurrences of metamorphic core complexes can also be found in:

Metamorphic core complexes have even been found in the oceanic region, first in the Atlantic . Since then, a further number of these structures have been discovered in the oceanic lithosphere, mostly on mid-ocean ridges with intermediate, slow and ultra-slow spreading speeds, but also in backarc basins , for example on the mid-Atlantic ridge and the south-west Indian ridge. Some of these oceanic metamorphic core complexes have been drilled and sampled. The works show that they are primarily composed of mafic and ultramafic rocks ( gabbro and peridotite , but also dolerite ) when lying down . The shearing horizon is relatively thin and consists of hydrous phyllosilicates . Oceanic metamorphic core complexes are often associated with active hydrothermal fields.

Extraterrestrial occurrences

A structure in the center of Artemis Corona on Venus was interpreted by Spencer (2001) as a metamorphic core complex. It could well be the largest metamorphic core complex in the solar system.

Web links

Individual evidence

  1. ^ PJ Coney: Cordilleran metamorphic core complex: an overview. In: MA Crittenden, PJ Coney, GH Davis: Cordilleran Metamorphic Core Complex. Geological Society of America Memoir. 153, Boulder 1980, pp. 7-34.
  2. ^ GS Lister, GA Davis: The origin of metamorphic core complexes and detachment faults formed during Tertiary continental extension in the northern Colorado River region, USA In: Journal of Structural Geology , Volume 11, 1989, pp. 65-94, doi: 10.1016 / 0191-8141 (89) 90036-9 .
  3. ^ Herfried Grassl, Franz Weber: A deep reflection seismic in the Penninic of the eastern edge of the Alps . In: Communications of the Austrian Geological Society , Volume 93, pp. 129–138, Vienna 2003; uibk.ac.at (PDF; 1.7 MB)
  4. ^ Dan-Ping Yan et al .: Mesozoic extensional structures of the Fangshan tectonic dome and their subsequent reworking during collisional accretion of the North China Block . In: Journal of the Geological Society , January 2006; findarticles.com
  5. ↑ W. Franke: The Saxonian granulites: a metamorphic core complex . In: Geologische Rundschau , Volume 82, pp. 505-515, Stuttgart 1993
  6. ↑ H. Echtler, J. Malavieille: Extensional tectonics, basement uplift and Stephano-Permian collapse basin in a late Variscan metamorphic core complex (Montagne Noire, Southern Massif Central) . In: Tectonophysics , Vol. 177, pp. 125-138, 1990
  7. ↑ Lothar Ratschbacher, Uwe Kroner, Klaus Stanek: Regional Geology of Europe: Paläotektonik the Aegean. Script for the course, TU Bergakademie Freiberg ( geo.tu-freiberg.de ( Memento of the original from December 12, 2007 in the Internet Archive ) Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and remove then this note. MS Word ) @1@ 2Template: Webachiv / IABot / www.geo.tu-freiberg.de
  8. ↑ ACCEL - Aegean Core Complexes along at Extended Lithosphere (Western Cyclades, Greece). (No longer available online.) Archived from the original on September 29, 2010 ; Retrieved July 2, 2010 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / geologie.univie.ac.at
  9. ^ Hubert Engelbrecht: On the Cenozoic tectonic deformation of the Monticiano-Roccastrada - metamorphic - core complex; Southern Tuscany, Italy. Reports of the German Mineralogical Society, p. 80, Stuttgart 1998.
  10. ↑ Bernd Lammerer: Geology of Elba .  ( Page no longer available , search in web archives )  Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. Script for the mapping exercises Elba 2008, Departments for Geo- and Environmental Sciences, Ludwig-Maximilians-Universität München@1@ 2Template: Toter Link / www.geologie.geowwissenschaften.uni-muenchen.de  
  11. ↑ Pressure - temperature - deformation - time - development and late orogenic structural formation of a metamorphic core complex using the example of the Ecambray massif in the central Cuban collision belt . Freiberg Mining Academy and Technical University
  12. ↑ Post- excursion report: Excursion to study deposits - Namibia 1999. TU Bergakademie Freiberg
  13. ↑ Jens Paquin: Trace element distributions in orogenic garnet peridotites and garnet olivine websterites as an indicator of their geochemical and metamorphic development Dissertation of the Faculty of Natural Sciences and Mathematics of the Ruprecht-Karls-Universität Heidelberg, 2001; DNB (PDF; 5.3 MB)
  14. ↑ Donna K. Blackman, Johnson R. Cann, Bob Janssen, Deborah K. Smith: Origin of extensional core complexes: Evidence from the Mid-Atlantic Ridge at Atlantis Fracture Zone . In: Journal of Geophysical Research . tape 103 , B9, 1998, pp. 21315-21333 , doi : 10.1029 / 98JB01756 .
  15. ^ BE Tucholke, J. Lin and MC Kleinrock: Megamullions and mullion structure defining oceanic metamorphic core complexes on the Mid-Atlantic Ridge. Journal of Geophysical Research 103, B5, 1998, pp. 9857-9866, doi: 10.1029 / 98JB00167
  16. ^ Fujimoto et al .: First submersible investigations of mid-ocean ridges in the Indian Ocean. In: InterRidge News , Volume 8, No. 1, 1999, pp. 22-24; interridge.org (PDF; 10.5 MB)
  17. ^ Y. Ohara, Y. Kato, S. Kasuga: Giant Megamullion in the Parece Vela Backarc Basin. In: Marine Geophysical Researches , Volume 22, No. 1, 2001, pp. 47-61, doi: 10.1023 / A: 1004818225642 .
  18. ↑ DK Smith, JR Cann, J. Escartin: Widespread active detachment faulting and core complex formation near 13 degrees N on the Mid-Atlantic Ridge. In: Nature , Volume 442, 2006, pp. 440-443, doi: 10.1038 / nature04950 .
  19. ↑ Mathilde Cannat and a .: Modes of Seafloor Generation at a Melt-Poor Ultraslow-Spreading Ridge . In: Geology . tape 34 , no. 7 , January 7, 2006, p. 605-608 , doi : 10.1130 / G22486.1 .
  20. ↑ B. Ildefonse, D. K Blackman, B. E John, Y. Ohara, D. J Miller, C. J MacLeod: Oceanic Core Complexes and Crustal Accretion at Slow-Spreading Ridges . In: Geology . tape 35 , no. 7 , January 7, 2007, pp. 623–626 , doi : 10.1130 / G23531A.1 ( iodp.org [PDF; 416 kB ]).
  21. ↑ Jon E Spencer: Possible Giant Metamorphic Core Complex at the Center of Artemis Corona, Venus . In: Geological Society of America Bulletin . tape 113 , no. 3 , January 3, 2001, p. 333-345 , doi : 10.1130 / 0016-7606 (2001) 113 <0333: PGMCCA> 2.0.CO; 2 .