Low-grade metamorphism of Cambro-Ordovician successions in the Famatina belt, Southern-Central Andes: Burial-inversion history linked to the evolution of the proto-Andean Gondwana margin
The metamorphic P-T conditions of low-grade units from the Famatina belt, Central Andes of Argentina, were estimated through petrography, X-ray diffraction, and electron microscopy. For the Middle-Upper Cambrian Negro Peinado Formation a tectono-metamorphic event associated with intense intrafoliar...
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Servicio Nacional de Geología y Minería (SERNAGEOMIN)
2011
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oai:scielo:S0718-710620110002000032011-09-28Low-grade metamorphism of Cambro-Ordovician successions in the Famatina belt, Southern-Central Andes: Burial-inversion history linked to the evolution of the proto-Andean Gondwana marginCollo,GildaDo Campo,MargaritaNieto,Fernando Western Gondwana margin Ocloyic orogeny Famatina belt Low-grade metamorphism The metamorphic P-T conditions of low-grade units from the Famatina belt, Central Andes of Argentina, were estimated through petrography, X-ray diffraction, and electron microscopy. For the Middle-Upper Cambrian Negro Peinado Formation a tectono-metamorphic event associated with intense intrafoliar folding, with estimated temperatures between 290 and 400°C (KIcis: 0.16-0.27A°29, biotite blastesis and compositional homogeneity in dioctahedral micas) and intermediate pressure conditions (white mica b parameter: 9.010Á-9.035Á), was recognized. The Achavil Formation (Middle-Upper Cambrian) presents a main metamorphic event associated with temperatures between 200 and 290°C (KIcis: 0.26-0.41A°29) and intermediate- to low-pressure conditions (white mica b parameter values: 8.972Á-9.017Á). Some illitic substitution in dioctahedral micas also indicates lower metamorphic grade than the Negro Peinado Formation. For Upper Cambrian to Middle Ordovician sequences a burial metamorphic pattern, with a progressive decrease in metamorphic grade from Volcancito Formation to Cerro Morado Group (ca. 490-465 Ma; KIcis: 0.31-0.69A°29) and absence of tendency changes linked to strati-graphic discontinuities was proposed. Mica and chlorite are the main phyllosilicates in the oldest units, while Ilt/ Sme (R3) mixed-layer is almost the only one in the youngest. White mica b parameter indicates intermediate- to low-pressure conditions for all these sequences. This burial metamorphic pattern presents a marked break as the youngest Ordovician unit (La Aguadita Formation, after ca. 452 Ma) records higher metamorphic conditions (IKcis: 0.28-0.19A°29) than units from the Ordovician arc, with estimated temperatures between 270 and 330°C and intermediate-pressure conditions. Our results indicate that basin contraction and inversion processes related to the Ordovician Ocloyic Orogeny involved at least two well-discriminated and not superposed metamorphic episodes in this region.info:eu-repo/semantics/openAccessServicio Nacional de Geología y Minería (SERNAGEOMIN)Andean geology v.38 n.2 20112011-07-01text/htmlhttp://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-71062011000200003en |
| institution |
Scielo Chile |
| collection |
Scielo Chile |
| language |
English |
| topic |
Western Gondwana margin Ocloyic orogeny Famatina belt Low-grade metamorphism |
| spellingShingle |
Western Gondwana margin Ocloyic orogeny Famatina belt Low-grade metamorphism Collo,Gilda Do Campo,Margarita Nieto,Fernando Low-grade metamorphism of Cambro-Ordovician successions in the Famatina belt, Southern-Central Andes: Burial-inversion history linked to the evolution of the proto-Andean Gondwana margin |
| description |
The metamorphic P-T conditions of low-grade units from the Famatina belt, Central Andes of Argentina, were estimated through petrography, X-ray diffraction, and electron microscopy. For the Middle-Upper Cambrian Negro Peinado Formation a tectono-metamorphic event associated with intense intrafoliar folding, with estimated temperatures between 290 and 400°C (KIcis: 0.16-0.27A°29, biotite blastesis and compositional homogeneity in dioctahedral micas) and intermediate pressure conditions (white mica b parameter: 9.010Á-9.035Á), was recognized. The Achavil Formation (Middle-Upper Cambrian) presents a main metamorphic event associated with temperatures between 200 and 290°C (KIcis: 0.26-0.41A°29) and intermediate- to low-pressure conditions (white mica b parameter values: 8.972Á-9.017Á). Some illitic substitution in dioctahedral micas also indicates lower metamorphic grade than the Negro Peinado Formation. For Upper Cambrian to Middle Ordovician sequences a burial metamorphic pattern, with a progressive decrease in metamorphic grade from Volcancito Formation to Cerro Morado Group (ca. 490-465 Ma; KIcis: 0.31-0.69A°29) and absence of tendency changes linked to strati-graphic discontinuities was proposed. Mica and chlorite are the main phyllosilicates in the oldest units, while Ilt/ Sme (R3) mixed-layer is almost the only one in the youngest. White mica b parameter indicates intermediate- to low-pressure conditions for all these sequences. This burial metamorphic pattern presents a marked break as the youngest Ordovician unit (La Aguadita Formation, after ca. 452 Ma) records higher metamorphic conditions (IKcis: 0.28-0.19A°29) than units from the Ordovician arc, with estimated temperatures between 270 and 330°C and intermediate-pressure conditions. Our results indicate that basin contraction and inversion processes related to the Ordovician Ocloyic Orogeny involved at least two well-discriminated and not superposed metamorphic episodes in this region. |
| author |
Collo,Gilda Do Campo,Margarita Nieto,Fernando |
| author_facet |
Collo,Gilda Do Campo,Margarita Nieto,Fernando |
| author_sort |
Collo,Gilda |
| title |
Low-grade metamorphism of Cambro-Ordovician successions in the Famatina belt, Southern-Central Andes: Burial-inversion history linked to the evolution of the proto-Andean Gondwana margin |
| title_short |
Low-grade metamorphism of Cambro-Ordovician successions in the Famatina belt, Southern-Central Andes: Burial-inversion history linked to the evolution of the proto-Andean Gondwana margin |
| title_full |
Low-grade metamorphism of Cambro-Ordovician successions in the Famatina belt, Southern-Central Andes: Burial-inversion history linked to the evolution of the proto-Andean Gondwana margin |
| title_fullStr |
Low-grade metamorphism of Cambro-Ordovician successions in the Famatina belt, Southern-Central Andes: Burial-inversion history linked to the evolution of the proto-Andean Gondwana margin |
| title_full_unstemmed |
Low-grade metamorphism of Cambro-Ordovician successions in the Famatina belt, Southern-Central Andes: Burial-inversion history linked to the evolution of the proto-Andean Gondwana margin |
| title_sort |
low-grade metamorphism of cambro-ordovician successions in the famatina belt, southern-central andes: burial-inversion history linked to the evolution of the proto-andean gondwana margin |
| publisher |
Servicio Nacional de Geología y Minería (SERNAGEOMIN) |
| publishDate |
2011 |
| url |
http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-71062011000200003 |
| work_keys_str_mv |
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