Comparative petrology and metamorphic evolution of the Limpopo (South Africa) and Lapland (Fennoscandia) high-grade terrains |
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| Authors: | L L Perchuk T V Gerya D D van Reenen A V Krotov O G Safonov C A Smit M Yu Shur |
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| Institution: | (1) Department of Petrology, Moscow State University, Moscow, Russia, RU;(2) Institute of Experimental Mineralogy, Russian Academy of Sciences, Chernogolovka, Russia, RU;(3) Department of Geology, Rand Afrikaans University, Johannesburg, South Africa, ZA |
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| Abstract: | Summary ?Detailed studies of rocks from the Limpopo (South Africa) and Lapland (Kola-Fennoscandia) high-grade terrains were carried
out in order to reveal similar geological and thermodynamic conditions in their formation. Both complexes (1) are situated
between Archean greenstone belts, (2) are younger than the belts, (3) are bounded by crustal-scale shear zones, (4) have a
similar intrusive-like (harpolith) geometry, and (5) show similar reaction textures that reflect both breakdown and growth
of garnet in each high-grade terrain. Local mineral equilibria within the textures indicate their successive formation with
cooling of the granulite facies rocks. Some of the textures in the metapelites must have resulted from the following reverse
reactions: Grt + Qtz ⇌Opx + Crd and/or Grt + Sil + Qtz ⇌ Crd. Based on these data, both the decompression cooling P-T path and the near-isobaric cooling P-T path were deduced for each HGT. However the near-isobaric cooling P-T path is not a characteristic of the central zones of both complexes studied.
Similar structural framework of the high-grade terrains, similar morphologies (shapes of granulitic bodies), similar reaction
textures developed in metapelites, and similar shapes of P-T paths suggest similarity in geodynamic history of both complexes.
Zusammenfassung ?Vergleichende Petrologie und metamorphe Entwicklung der hochgradig metamorphen Terrains von Limpopo (Südafrika) und Lappland
(Fennoscandia)
Eingehende Untersuchungen an Gesteinen aus den hochgradig metamorphen Terrains von Limpopo (Südafrika) und Lappland (Kola-Fennoscania)
sollen m?gliche ?hnlichkeiten in den geologischen und thermodynamischen Bildungsbedingungen aufzeigen.
Beide Komplexe sind
Lokale Mineralgleichgewichte innerhalb der Texturen weisen auf ihre schrittweise Bildung w?hrend der Abkühlung der granulitfaziellen
Gesteine hin. Einige der Texturen in den Metapeliten gehen auf folgende reversible Reaktionen zurück: Grt + Qtz ⇌Opx + Crd und/oder Grt + Sil + Qtz ⇌ Crd. Diese Daten erm?glichten es, sowohl den P-T Pfad der Abkühlung bei Druckentlastung sowie den fast-isobaren P-T Pfad der Abkühlung für jedes HGT zu ermitteln. Der fast-isobare P-T Pfad der Abkühlung ist jedoch kein Charakteristikum der Zentralzonen beider Komplexe.
Ein ?hnlicher struktureller Rahmen der hochgradigen Terrains, ?hnliche Morphologien (Ausbildung der Granulitk?rper), ?hnliche
Reaktionstexturen in Metapeliten und ?hnliche P-T Pfade weisen auf ?hnlichkeiten der geodynamischen Entwicklungsgeschichte beider Komplexe hin.
Received March 8, 1999; revised version accepted September 17, 1999 |
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