Magnetic petrology of the Devonian Achala Batholith, Argentina: Titanohaematite as an indicator of highly oxidized magma during crystallization and cooling

Devonian magmatism in the Eastern Sierras Pampeanas (Córdoba, Argentina) is represented by elliptical, porphyritic, batholithic, late- to post-orogenic monzogranites emplaced in a metamorphic-plutonic basement. Two groups of Devonian granitoids are distinguished: (1) metaaluminous to weakly peralumi...

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Autores principales: Geuna, S.E., Mcenroe, S.A., Robinson, P., Escosteguy, L.D.
Formato: JOUR
Materias:
Magnetic Mineralogy and Petrology
Physics and chemistry of magma bodies
Rockand mineral magnetism
South America
basement rock
batholith
cooling
crystallization
Devonian
magma chemistry
magmatism
magnetic method
magnetic susceptibility
mineralogy
petrology
titanomagnetite
Argentina
Sierras Pampeanas
Acceso en línea:http://hdl.handle.net/20.500.12110/paper_0956540X_v175_n3_p925_Geuna
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Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA) de Universidad de Buenos Aires
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spelling todo:paper_0956540X_v175_n3_p925_Geuna2023-10-03T15:52:06Z Magnetic petrology of the Devonian Achala Batholith, Argentina: Titanohaematite as an indicator of highly oxidized magma during crystallization and cooling Geuna, S.E. Mcenroe, S.A. Robinson, P. Escosteguy, L.D. Magnetic Mineralogy and Petrology Physics and chemistry of magma bodies Rockand mineral magnetism South America basement rock batholith cooling crystallization Devonian magma chemistry magmatism magnetic method magnetic susceptibility mineralogy petrology titanomagnetite Argentina Sierras Pampeanas South America Devonian magmatism in the Eastern Sierras Pampeanas (Córdoba, Argentina) is represented by elliptical, porphyritic, batholithic, late- to post-orogenic monzogranites emplaced in a metamorphic-plutonic basement. Two groups of Devonian granitoids are distinguished: (1) metaaluminous to weakly peraluminous, hornblende-biotite bearing granitoids, and (2) peraluminous, biotite-(muscovite) bearing granitoids. Groups 1 and 2 are characterized by accessory phases of sphene-magnetite with high susceptibility, and ilmenite-(monazite-uraninite) with low susceptibility, respectively. The magnetic assemblage of the Group 2 Achala Batholith, predominantly paramagnetic, is the subject of this paper Forty-three sites were sampled in the Achala monzogranite. Overall, it is weakly magnetic, with a mean magnetic susceptibility of 1.5 × 10 -4 SI. Twenty-one sites showed titanohaematite as the magnetic carrier of a stable remanence. The titanohaematite is an accessory mineral and contains exsolved disc-shaped intergrowths of ilmenite. The weak magnetism of Achala monzogranite facies contrasts with the magnetic character of other Devonian porphyritic, batholithic monzogranites in the region. The virtual absence of magnetite, together with the presence of exsolved titanohaematite and Mn-ilmenite indicate crystallization and cooling under more oxidizing conditions. Oxidizing conditions continued into the subsolidus, causing late-stage reactions of ilmenite host grains to ilmenite + rutile+ haematite, and titanohaematite to ilmenite-poorer haematite + rutile. These reactions resulted in low susceptibility values and a strong reduction of natural remanent magnetization (NRM) intensities. Thermal demagnetization, up to 620-640°C, isolated steeply dipping, dual-polarity remanence directions. The coincidence of the Achala paleomagnetic pole with the 380-360 Myr segment of the Gondwana Apparent Polar Wander Path and the U-Pb zircon age implies that the remanence was acquired soon after emplacement. © 2008 The Authors Journal compilation © 2008 RAS. JOUR info:eu-repo/semantics/openAccess http://creativecommons.org/licenses/by/2.5/ar http://hdl.handle.net/20.500.12110/paper_0956540X_v175_n3_p925_Geuna
institution Universidad de Buenos Aires
institution_str I-28
repository_str R-134
collection Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA)
topic Magnetic Mineralogy and Petrology
Physics and chemistry of magma bodies
Rockand mineral magnetism
South America
basement rock
batholith
cooling
crystallization
Devonian
magma chemistry
magmatism
magnetic method
magnetic susceptibility
mineralogy
petrology
titanomagnetite
Argentina
Sierras Pampeanas
South America
spellingShingle Magnetic Mineralogy and Petrology
Physics and chemistry of magma bodies
Rockand mineral magnetism
South America
basement rock
batholith
cooling
crystallization
Devonian
magma chemistry
magmatism
magnetic method
magnetic susceptibility
mineralogy
petrology
titanomagnetite
Argentina
Sierras Pampeanas
South America
Geuna, S.E.
Mcenroe, S.A.
Robinson, P.
Escosteguy, L.D.
Magnetic petrology of the Devonian Achala Batholith, Argentina: Titanohaematite as an indicator of highly oxidized magma during crystallization and cooling
topic_facet Magnetic Mineralogy and Petrology
Physics and chemistry of magma bodies
Rockand mineral magnetism
South America
basement rock
batholith
cooling
crystallization
Devonian
magma chemistry
magmatism
magnetic method
magnetic susceptibility
mineralogy
petrology
titanomagnetite
Argentina
Sierras Pampeanas
South America
description Devonian magmatism in the Eastern Sierras Pampeanas (Córdoba, Argentina) is represented by elliptical, porphyritic, batholithic, late- to post-orogenic monzogranites emplaced in a metamorphic-plutonic basement. Two groups of Devonian granitoids are distinguished: (1) metaaluminous to weakly peraluminous, hornblende-biotite bearing granitoids, and (2) peraluminous, biotite-(muscovite) bearing granitoids. Groups 1 and 2 are characterized by accessory phases of sphene-magnetite with high susceptibility, and ilmenite-(monazite-uraninite) with low susceptibility, respectively. The magnetic assemblage of the Group 2 Achala Batholith, predominantly paramagnetic, is the subject of this paper Forty-three sites were sampled in the Achala monzogranite. Overall, it is weakly magnetic, with a mean magnetic susceptibility of 1.5 × 10 -4 SI. Twenty-one sites showed titanohaematite as the magnetic carrier of a stable remanence. The titanohaematite is an accessory mineral and contains exsolved disc-shaped intergrowths of ilmenite. The weak magnetism of Achala monzogranite facies contrasts with the magnetic character of other Devonian porphyritic, batholithic monzogranites in the region. The virtual absence of magnetite, together with the presence of exsolved titanohaematite and Mn-ilmenite indicate crystallization and cooling under more oxidizing conditions. Oxidizing conditions continued into the subsolidus, causing late-stage reactions of ilmenite host grains to ilmenite + rutile+ haematite, and titanohaematite to ilmenite-poorer haematite + rutile. These reactions resulted in low susceptibility values and a strong reduction of natural remanent magnetization (NRM) intensities. Thermal demagnetization, up to 620-640°C, isolated steeply dipping, dual-polarity remanence directions. The coincidence of the Achala paleomagnetic pole with the 380-360 Myr segment of the Gondwana Apparent Polar Wander Path and the U-Pb zircon age implies that the remanence was acquired soon after emplacement. © 2008 The Authors Journal compilation © 2008 RAS.
format JOUR
author Geuna, S.E.
Mcenroe, S.A.
Robinson, P.
Escosteguy, L.D.
author_facet Geuna, S.E.
Mcenroe, S.A.
Robinson, P.
Escosteguy, L.D.
author_sort Geuna, S.E.
title Magnetic petrology of the Devonian Achala Batholith, Argentina: Titanohaematite as an indicator of highly oxidized magma during crystallization and cooling
title_short Magnetic petrology of the Devonian Achala Batholith, Argentina: Titanohaematite as an indicator of highly oxidized magma during crystallization and cooling
title_full Magnetic petrology of the Devonian Achala Batholith, Argentina: Titanohaematite as an indicator of highly oxidized magma during crystallization and cooling
title_fullStr Magnetic petrology of the Devonian Achala Batholith, Argentina: Titanohaematite as an indicator of highly oxidized magma during crystallization and cooling
title_full_unstemmed Magnetic petrology of the Devonian Achala Batholith, Argentina: Titanohaematite as an indicator of highly oxidized magma during crystallization and cooling
title_sort magnetic petrology of the devonian achala batholith, argentina: titanohaematite as an indicator of highly oxidized magma during crystallization and cooling
url http://hdl.handle.net/20.500.12110/paper_0956540X_v175_n3_p925_Geuna
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AT robinsonp magneticpetrologyofthedevonianachalabatholithargentinatitanohaematiteasanindicatorofhighlyoxidizedmagmaduringcrystallizationandcooling
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