Major and trace element geochemistry and isotope (Sr, Nd, Pb, O) systematics of an Archaean basement involved in a 2.0 Ga very high‐temperature (1000°C) metamorphic event: In Ouzzal Massif, Hoggar, Algeria

Journal of Metamorphic Geology - Tập 14 Số 6 - Trang 667-692 - 1996
J. J. Peucat1, Ramón Buxó i Capdevila1, Amar Drareni2, Pierre Choukroune3,1, C. Mark Fanning4, J. Bernard-Griffiths1, Serge Fourcade1
1Géosciences Rennes, UPR CNRS 4661, 35042 Rennes Cedex, France (email: [email protected])
2USTHB, Institut des Sciences de la Terre, Algiers, Algeria
3CEREGE- Université Aix-Marseille 3, Domaine du Petit Arbois 13545, Aix-en-Provence Cedex 4, France.
4Research School of Earth Sciences, ANU, Canberra, ACT 0200, Australia

Tóm tắt

ABSTRACTThe In Ouzzal granulitic massif is composed mainly of various meta‐igneous rocks which, in spite of Rb, U, Th, Cs and some K and Sr mobility, can be dated and generally classified according to their chemical composition as follows.Basic and ultrabasic granulites interlayered with the metasediments correspond to (1) ultrabasic cumulates from dislocated tholeiitic bodies, (2) ancient komatiitic to high‐Mg tholeiitic basalts similar to the suites found in Archaean greenstone belts and (3) calcalkaline protoliths of high‐K andesitic composition. No geochronological constraints are available apart from the depositional age of some associated sediments which is younger than 2.70 Ga detrital zircons, and the Nd model age of the andesitic granulites of c. 3.4 Ga.In spite of the high‐grade metamorphism, the acidic magmatic precursors of the charnockites can be divided in three groups. (1) The most juvenile acid orthogneisses are trondhjemitic or tonalitic in composition, being similar to the TTG suites which are classically considered to be formed by partial melting of mantle‐derived protoliths. The 3.3–3.2 Ga TDM indicates a possible age of separation from the mantle reservoir while the plutons may have been emplaced between 3.3 and 2.7 Ga (U–Pb zircon & Nd ages). (2) A group of alkaline granitic gneisses, similar in composition to rift‐related‐granites, were emplaced at 2650±10 Ma (U–Pb & Rb–Sr ages) in a thick continental crust. (3) Calcalkaline granodioritic and monzogranitic suites derived from the partial melting of continental precursors (3.5–3.3 Ga), in lower to middle levels of the continental crust. They were emplaced close to 2.5 Ga during crustal thickening.The very high‐temperature metamorphism occurred at 2002±7 Ma from the age of synfoliation intrusions and was probably related to major overthrusting. Retrogressive metamorphism is dated at 1.95 Ga from garnet‐Nd ages. In spite of the very high‐temperature conditions, partial melting during granulite facies metamorphism may be restricted to scarce cordierite‐bearing monzogranitic gneisses. The 2.0 Ga VHT metamorphism could be related to overthrusting, extensional or underplating processes.

Từ khóa


Tài liệu tham khảo

Allègre C. J., 1968, Chronologic Rb/Sr du Précambrien de l' Haaggar occidental, Comptes Rendus Sommaires de la Société Géologique de France, 8, 259

Allègre C. J., 1972, Chronologie absolue du Précambrien de l'Ahaggar occidental, Comptes Rendus de l'Académie des Sciences, Paris, 275, 2095

10.1130/0091-7613(1976)4<596:GOTLAA>2.0.CO;2

10.1016/B978-0-444-41765-7.50006-X

10.1038/307510a0

10.1111/j.1525-1314.1996.00057.x

10.1007/BF00379743

10.1111/j.1525-1314.1992.tb00069.x

10.1029/91JB01640

10.1016/0301-9268(93)90004-L

10.1086/628212

Choukroune P., 1994, Geological Society Special Publication, 67

10.1144/gsjgs.149.2.0171

10.1016/0009-2541(93)90140-E

10.1029/JB095iB13p21503

10.1130/0091-7613(1992)020<0641:CSOTAT>2.3.CO;2

Ewart A., 1982, Andesites, 25

Feininger T., 1995, A report on the derivation and proper use of the term anorthosite, The Canadian Mineralogist, 33, 913

10.1016/0012-821X(66)90015-X

10.1007/BF00371588

10.1111/j.1525-1314.1996.00055.x

10.1038/367360a0

10.1016/0301-9268(94)90103-1

Harris N. B. W., 1986, Geological Society Special Publication, 67

10.1016/S0016-7037(81)80002-6

Jensen L. S., 1982, Komatiites, 147

10.1038/348531a0

10.1002/gj.3350220607

10.1007/BF00371718

10.1016/0012-821X(76)90140-0

Ledru P., 1994, Ages du metamorphisme granulitique dans le craton de Sao Francisco (Brésil). Implications sur la nature de l'orogène transamazonien, Comptes Rendus de l'Académie des Sciences, Paris, 318, 251

Maluski H., 1990, Location of extraneous argon in granulitic‐facies minerals: a paired microprobe‐laser probe 40Ar/39Ar analysis, Chemical Geology, 80, 193

10.1130/0016-7606(1989)101<0635:TDOG>2.3.CO;2

10.1093/petrology/28.5.921

10.1016/S0166-2635(08)70224-X

10.1016/0016-7037(73)90131-2

Maurin J. C. Peucat J. J. Kessi C.&Chauvel J. J. 1995.Evolution crustale au Congo de la fin de l'Archéen au Protérozo·que terminal. In:Géodynamique du Pratérozoique p.24.

Nabelek P. I., 1986, Trace‐element modeling of the petrogenesis of granophyres and aplites in the Notch Peak granitic stock, Utah, American Journal of Science, 71, 460

10.1093/petrology/25.4.956

10.1111/j.1525-1314.1993.tb00197.x

10.1007/BF00381441

10.1007/978-94-009-2055-2_27

Santos Pinto M., 1995, Petrogenesis of the oldest part of the Sao Francisco Craton (Bahia State, Brazil): geochronology and isotopic chemistry, Terra Abstracts EUG, 8, 103

10.1016/0012-821X(75)90088-6

Streckeisen A., 1979, A chemical approximation to the modal QAPF classification of the igneous rocks, Neues Jahrbuch Mineral Abh., 136, 169

10.1144/GSL.SP.1989.042.01.19

10.1086/629302

10.1016/S0166-2635(08)70225-1

10.1007/BF00402202

Thông tin
Thông tin xuất bản

Journal of Metamorphic Geology

Tập 14 Số 6

667-692

Thông tin tác giả