Southern Central Andes Neogene magmatism over the Pampean Flat Slab: implications on crustal and slab melts contribution to magma generation in Precordillera, Western Argentina

ABSTRACT A Miocene to Pliocene (13 to 4.6 Ma) mostly pyroclastic sequence is exposed along the Iglesia Valley, to the east of the former main volcanic arc. This area is a transitional region between Cordillera Frontal and Precordillera, over the flat slab segment of the Southern Central Andes, at 29...

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Autores principales:	Poma,Stella, Ramos,Adriana, Litvak,Vanesa D., Quenardelle,Sonia, Maisonnave,Emma B., Díaz,Iris
Lenguaje:	English
Publicado:	Servicio Nacional de Geología y Minería (SERNAGEOMIN) 2017
Materias:	Miocene magmatism Geochemistry Radiometric age Arc expansion Shallow subduction
Acceso en línea:	http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-71062017000300249
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spelling	oai:scielo:S0718-710620170003002492017-10-16Southern Central Andes Neogene magmatism over the Pampean Flat Slab: implications on crustal and slab melts contribution to magma generation in Precordillera, Western ArgentinaPoma,StellaRamos,AdrianaLitvak,Vanesa D.Quenardelle,SoniaMaisonnave,Emma B.Díaz,Iris Miocene magmatism Geochemistry Radiometric age Arc expansion Shallow subduction ABSTRACT A Miocene to Pliocene (13 to 4.6 Ma) mostly pyroclastic sequence is exposed along the Iglesia Valley, to the east of the former main volcanic arc. This area is a transitional region between Cordillera Frontal and Precordillera, over the flat slab segment of the Southern Central Andes, at 29°30’ S to 30°00’ S. New radiometric ages, geochemical data, petrography and field relationships are evaluated to establish differences and similarities between Miocene arc-related sequences across the main arc and its expansion towards a back arc position, in western Precordillera. Analyzed rocks have a magmatic arc signature partially like the former main volcanic arc to the west. The Iglesia Valley rocks are LREE-enriched (La/Sm: 3.7-6.5) with respect to HREE (Sm/Yb: 2.2-6.0) and define patterns with a pronounced slope. Sm/Yb ratios generally increase with time, as pressures increase, with retention of HREE in residual mineralogy, particularly garnet at Sm/Yb>4. Volcanic activity in Cordillera Frontal and the volcanic-volcaniclastic expression in Precordillera show a continuous increase in the La/Yb ratio with decreasing age. Variations in the residual mineral phase equilibrating with magmas would be related to the progressive increase in crustal thickness due to the tectonic compressive regime resulting from shallow subduction since Middle Miocene. The data presented suggest that the arc magmatic activity during the Miocene was expanded notably to the East in relation to the location of the main arc at Valle del Cura, in Cordillera Frontal. The extensive amplitude of the volcanic arc activity is indicative of the slab gradual flattening. Particularly, the mantle-derived magmas from Lomas del Campanario Formation (Western Precordillera) are enriched by subduction related fluids but also by crustal components. It is interpreted that the cause of the geochemical differences between the back arc position rocks and the main arc lay in the heterogeneous composition of the underlying continental crust involved in both locations. Presence of volcanic rocks with adakitic geochemical affinity probably reflect astenospheric-derived melts that interacted through a heterogeneous and thickened crust toward the surface.info:eu-repo/semantics/openAccessServicio Nacional de Geología y Minería (SERNAGEOMIN)Andean geology v.44 n.3 20172017-09-01text/htmlhttp://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-71062017000300249en10.5027/andgeov44n3-a02
institution	Scielo Chile
collection	Scielo Chile
language	English
topic	Miocene magmatism Geochemistry Radiometric age Arc expansion Shallow subduction
spellingShingle	Miocene magmatism Geochemistry Radiometric age Arc expansion Shallow subduction Poma,Stella Ramos,Adriana Litvak,Vanesa D. Quenardelle,Sonia Maisonnave,Emma B. Díaz,Iris Southern Central Andes Neogene magmatism over the Pampean Flat Slab: implications on crustal and slab melts contribution to magma generation in Precordillera, Western Argentina
description	ABSTRACT A Miocene to Pliocene (13 to 4.6 Ma) mostly pyroclastic sequence is exposed along the Iglesia Valley, to the east of the former main volcanic arc. This area is a transitional region between Cordillera Frontal and Precordillera, over the flat slab segment of the Southern Central Andes, at 29°30’ S to 30°00’ S. New radiometric ages, geochemical data, petrography and field relationships are evaluated to establish differences and similarities between Miocene arc-related sequences across the main arc and its expansion towards a back arc position, in western Precordillera. Analyzed rocks have a magmatic arc signature partially like the former main volcanic arc to the west. The Iglesia Valley rocks are LREE-enriched (La/Sm: 3.7-6.5) with respect to HREE (Sm/Yb: 2.2-6.0) and define patterns with a pronounced slope. Sm/Yb ratios generally increase with time, as pressures increase, with retention of HREE in residual mineralogy, particularly garnet at Sm/Yb>4. Volcanic activity in Cordillera Frontal and the volcanic-volcaniclastic expression in Precordillera show a continuous increase in the La/Yb ratio with decreasing age. Variations in the residual mineral phase equilibrating with magmas would be related to the progressive increase in crustal thickness due to the tectonic compressive regime resulting from shallow subduction since Middle Miocene. The data presented suggest that the arc magmatic activity during the Miocene was expanded notably to the East in relation to the location of the main arc at Valle del Cura, in Cordillera Frontal. The extensive amplitude of the volcanic arc activity is indicative of the slab gradual flattening. Particularly, the mantle-derived magmas from Lomas del Campanario Formation (Western Precordillera) are enriched by subduction related fluids but also by crustal components. It is interpreted that the cause of the geochemical differences between the back arc position rocks and the main arc lay in the heterogeneous composition of the underlying continental crust involved in both locations. Presence of volcanic rocks with adakitic geochemical affinity probably reflect astenospheric-derived melts that interacted through a heterogeneous and thickened crust toward the surface.
author	Poma,Stella Ramos,Adriana Litvak,Vanesa D. Quenardelle,Sonia Maisonnave,Emma B. Díaz,Iris
author_facet	Poma,Stella Ramos,Adriana Litvak,Vanesa D. Quenardelle,Sonia Maisonnave,Emma B. Díaz,Iris
author_sort	Poma,Stella
title	Southern Central Andes Neogene magmatism over the Pampean Flat Slab: implications on crustal and slab melts contribution to magma generation in Precordillera, Western Argentina
title_short	Southern Central Andes Neogene magmatism over the Pampean Flat Slab: implications on crustal and slab melts contribution to magma generation in Precordillera, Western Argentina
title_full	Southern Central Andes Neogene magmatism over the Pampean Flat Slab: implications on crustal and slab melts contribution to magma generation in Precordillera, Western Argentina
title_fullStr	Southern Central Andes Neogene magmatism over the Pampean Flat Slab: implications on crustal and slab melts contribution to magma generation in Precordillera, Western Argentina
title_full_unstemmed	Southern Central Andes Neogene magmatism over the Pampean Flat Slab: implications on crustal and slab melts contribution to magma generation in Precordillera, Western Argentina
title_sort	southern central andes neogene magmatism over the pampean flat slab: implications on crustal and slab melts contribution to magma generation in precordillera, western argentina
publisher	Servicio Nacional de Geología y Minería (SERNAGEOMIN)
publishDate	2017
url	http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-71062017000300249
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Southern Central Andes Neogene magmatism over the Pampean Flat Slab: implications on crustal and slab melts contribution to magma generation in Precordillera, Western Argentina

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