geology and structure of the malpaso caldera and el ocote
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Geology and structure of the Malpaso caldera andEl Ocote ignimbrite Aguascalientes MexicoTo cite this article Jorge Nieto-Obregoacuten and Gerardo Aguirre-Diacuteaz 2008 IOP Conf Ser EarthEnviron Sci 3 012008
View the article online for updates and enhancements
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1
Geology and structure of the Malpaso caldera and El Ocote ignimbrite
Aguascalientes Mexico
Nieto-Obregoacuten Jorge (Facultad de Ingenieriacutea UNAM Coyoacaacuten 04510 Meacutexico DF
MEXICO nietoservidorunammx)
Aguirre-Diacuteaz Gerardo (Centro de Geociencias UNAM Campus Juriquilla 76220
Quereacutetaro Qro Meacutexico gergeocienciasunammx)
Keywords caldera ignimbrite faults graben
1 Introduction
A new caldera is reported west of the city of Aguascalientes Mexico (Figure 1) The
caldera is a volcano-tectonic depression highly fractured and faulted and was filled by
voluminous pyroclastic products related to the caldera collapse Due to these
characteristics Aguirre-Diacuteaz et al (2008) classify it as a graben caldera It is truncated by
younger normal faults of the Calvillo and Aguascalientes grabens (Nieto-Obregoacuten and
Aguirre-Diacuteaz 2007a) In this work we present a summary of the geologic and structural
observations on this caldera
2 Stratigraphy
The general stratigraphy in the caldera area consists of 1) a Mesozoic metamorphic
basement 2) a continental sedimentary sequence (red beds) that is intercalated with
pyroclastic surge deposits and non-welded ignimbrites erupted in the calderarsquos earlier stage
3) The El Ocote Ignimbrite the main product of the caldera 4) rhyolitic domes that
represent post-collapse effusive eruptions of highly viscous rhyolitic magma which in turn
are related to other ignimbrites and pyroclastic breccias produced by flank collapse of the
domes and 5) andesitic feeder dykes and associated flows that intrude and cover all the
caldera sequence (Figure 2) Normal faulting associated with Calvillo and Aguascalientes
grabens facilitated the emplacement of these dykes and lavas
Collapse Calderas Workshop IOP PublishingIOP Conf Series Earth and Environmental Science 3 (2008) 012008 doi1010881755-130731012008
ccopy 2008 IOP Publishing Ltd 1
2
Figure 1 Simplified geologic map of the Caldera of Malpaso showing the major structures
and main lithologic units
The El Ocote Ignimbrite fills the caldera depression and extends several km outwards from
the caldera The intra-caldera facies consist of a high grade reomorphic ignimbrite with
lava-like features including flow banding and folds The pyroclastic nature of this unit is
demonstrated by the presence of a eutaxitic fabric with abundant elongated fiammes and
cm-size lithics rotated within the flow foliation
Collapse Calderas Workshop IOP PublishingIOP Conf Series Earth and Environmental Science 3 (2008) 012008 doi1010881755-130731012008
2
3
Figure 2 Simplified stratigraphic column and description of main units
Devitrified glass shards and axiolites of collapsed pumices are observed under the
microscope The glass shard matrix is deformed by flow around rigid phenocrysts (Figure
3) This ignimbrite is considered as reomorphic because there is evidence of ductile
deformation of hot pyroclastic material forming folds of different styles that include gentle
open close tight isoclinal and sheath type The open folds are often formed from refolded
folds of the foliation Structural elements such as foliation axial planes fold axis and
elongation lineations suggest deposition over an irregular surface flowing in different
directions from various sources within and in the borders of the caldera (Nieto Obregoacuten
and Aguirre Diacuteaz 2007b) The reomorphic ignimbrite is mainly distributed in the central
portion of the caldera and although its thickness has not been observed complete more than
300 m are exposed in the southern border of the caldera in the Sierra El Laurel The extra
caldera facies of this unit has thinner thicknesses from 20 to 150 m observed in the Mesa
san Joseacute de Gracia and to the south of Sierra El Laurel
Collapse Calderas Workshop IOP PublishingIOP Conf Series Earth and Environmental Science 3 (2008) 012008 doi1010881755-130731012008
3
4
Figure 3 Photomicrograph of El Ocote Ignimbrite Note the deformation of the glass
shards due to intense welding around a feldspar phenocryst
3 Structure
The area is affected by two types of faults of different ages 1) volcano-tectonic faults
produced by caldera subsidence processes and 2) tectonic faults of post-caldera age that
truncate the western and eastern borders of the caldera To the east the caldera is cut by the
western fault system of the Aguascalientes Graben and to the west by the eastern fault
system of the Calvillo Graben From the calderarsquos fault data and stratigraphy we conclude
that the caldera formed by the chaotic subsidence collapse of the magma chamber roof in a
piece-meal style and thus we classify it as a piece-meal graben caldera (sensu Aguirre-
Diacuteaz et al 2007)
References
Aguirre Diacuteaz GJ Labarthe-Hernaacutendez G Tristaacuten-Gonzaacutelez M Nieto-Obregoacuten J and
Gutieacuterrez-Palomares I 2007 Graben Calderas Volcano-tectonic explosive collapse
structures of the Sierra Madre Occidental Mexico Geophysical Research Abstracts
Collapse Calderas Workshop IOP PublishingIOP Conf Series Earth and Environmental Science 3 (2008) 012008 doi1010881755-130731012008
4
5
Vol 9 04704 S-Ref-ID 1607-7962graEGU2007-A-04704 European Geosciences
Union 2007
Aguirre-Diacuteaz GJ Labarthe-Hernaacutendez G Tristaacuten-Gonzaacutelez M Nieto-Obregoacuten J
Gutieacuterrez-Palomares I 2008 Ignimbrite Flare-up and graben-calderas of the Sierra
Madre Occidental Mexico in J Martiacute and J Gottsmann eds ldquoCaldera Volcanism
Analysis Modelling and Responserdquo Developments in Volcanology 10 Elsevier
Amsterdam 492 p (143-180 pp)
Nieto-Obregoacuten Jorge and Aguirre-Diaz Gerardo 2007a Geologiacutea y Estructura de la
caldera de Malpaso Aguascalientes Mexico Geos Vol 27 no1 p 131-132
Nieto-Obregoacuten Jorge and Aguirre-Diaz Gerardo 2007b Ignimbrita El Ocote Una
ignimbrita de muy alto grado en la caldera de Malpaso Aguascalientes Meacutexico
Mexico Geos Vol 27 no1 p 130
Collapse Calderas Workshop IOP PublishingIOP Conf Series Earth and Environmental Science 3 (2008) 012008 doi1010881755-130731012008
5
1
Geology and structure of the Malpaso caldera and El Ocote ignimbrite
Aguascalientes Mexico
Nieto-Obregoacuten Jorge (Facultad de Ingenieriacutea UNAM Coyoacaacuten 04510 Meacutexico DF
MEXICO nietoservidorunammx)
Aguirre-Diacuteaz Gerardo (Centro de Geociencias UNAM Campus Juriquilla 76220
Quereacutetaro Qro Meacutexico gergeocienciasunammx)
Keywords caldera ignimbrite faults graben
1 Introduction
A new caldera is reported west of the city of Aguascalientes Mexico (Figure 1) The
caldera is a volcano-tectonic depression highly fractured and faulted and was filled by
voluminous pyroclastic products related to the caldera collapse Due to these
characteristics Aguirre-Diacuteaz et al (2008) classify it as a graben caldera It is truncated by
younger normal faults of the Calvillo and Aguascalientes grabens (Nieto-Obregoacuten and
Aguirre-Diacuteaz 2007a) In this work we present a summary of the geologic and structural
observations on this caldera
2 Stratigraphy
The general stratigraphy in the caldera area consists of 1) a Mesozoic metamorphic
basement 2) a continental sedimentary sequence (red beds) that is intercalated with
pyroclastic surge deposits and non-welded ignimbrites erupted in the calderarsquos earlier stage
3) The El Ocote Ignimbrite the main product of the caldera 4) rhyolitic domes that
represent post-collapse effusive eruptions of highly viscous rhyolitic magma which in turn
are related to other ignimbrites and pyroclastic breccias produced by flank collapse of the
domes and 5) andesitic feeder dykes and associated flows that intrude and cover all the
caldera sequence (Figure 2) Normal faulting associated with Calvillo and Aguascalientes
grabens facilitated the emplacement of these dykes and lavas
Collapse Calderas Workshop IOP PublishingIOP Conf Series Earth and Environmental Science 3 (2008) 012008 doi1010881755-130731012008
ccopy 2008 IOP Publishing Ltd 1
2
Figure 1 Simplified geologic map of the Caldera of Malpaso showing the major structures
and main lithologic units
The El Ocote Ignimbrite fills the caldera depression and extends several km outwards from
the caldera The intra-caldera facies consist of a high grade reomorphic ignimbrite with
lava-like features including flow banding and folds The pyroclastic nature of this unit is
demonstrated by the presence of a eutaxitic fabric with abundant elongated fiammes and
cm-size lithics rotated within the flow foliation
Collapse Calderas Workshop IOP PublishingIOP Conf Series Earth and Environmental Science 3 (2008) 012008 doi1010881755-130731012008
2
3
Figure 2 Simplified stratigraphic column and description of main units
Devitrified glass shards and axiolites of collapsed pumices are observed under the
microscope The glass shard matrix is deformed by flow around rigid phenocrysts (Figure
3) This ignimbrite is considered as reomorphic because there is evidence of ductile
deformation of hot pyroclastic material forming folds of different styles that include gentle
open close tight isoclinal and sheath type The open folds are often formed from refolded
folds of the foliation Structural elements such as foliation axial planes fold axis and
elongation lineations suggest deposition over an irregular surface flowing in different
directions from various sources within and in the borders of the caldera (Nieto Obregoacuten
and Aguirre Diacuteaz 2007b) The reomorphic ignimbrite is mainly distributed in the central
portion of the caldera and although its thickness has not been observed complete more than
300 m are exposed in the southern border of the caldera in the Sierra El Laurel The extra
caldera facies of this unit has thinner thicknesses from 20 to 150 m observed in the Mesa
san Joseacute de Gracia and to the south of Sierra El Laurel
Collapse Calderas Workshop IOP PublishingIOP Conf Series Earth and Environmental Science 3 (2008) 012008 doi1010881755-130731012008
3
4
Figure 3 Photomicrograph of El Ocote Ignimbrite Note the deformation of the glass
shards due to intense welding around a feldspar phenocryst
3 Structure
The area is affected by two types of faults of different ages 1) volcano-tectonic faults
produced by caldera subsidence processes and 2) tectonic faults of post-caldera age that
truncate the western and eastern borders of the caldera To the east the caldera is cut by the
western fault system of the Aguascalientes Graben and to the west by the eastern fault
system of the Calvillo Graben From the calderarsquos fault data and stratigraphy we conclude
that the caldera formed by the chaotic subsidence collapse of the magma chamber roof in a
piece-meal style and thus we classify it as a piece-meal graben caldera (sensu Aguirre-
Diacuteaz et al 2007)
References
Aguirre Diacuteaz GJ Labarthe-Hernaacutendez G Tristaacuten-Gonzaacutelez M Nieto-Obregoacuten J and
Gutieacuterrez-Palomares I 2007 Graben Calderas Volcano-tectonic explosive collapse
structures of the Sierra Madre Occidental Mexico Geophysical Research Abstracts
Collapse Calderas Workshop IOP PublishingIOP Conf Series Earth and Environmental Science 3 (2008) 012008 doi1010881755-130731012008
4
5
Vol 9 04704 S-Ref-ID 1607-7962graEGU2007-A-04704 European Geosciences
Union 2007
Aguirre-Diacuteaz GJ Labarthe-Hernaacutendez G Tristaacuten-Gonzaacutelez M Nieto-Obregoacuten J
Gutieacuterrez-Palomares I 2008 Ignimbrite Flare-up and graben-calderas of the Sierra
Madre Occidental Mexico in J Martiacute and J Gottsmann eds ldquoCaldera Volcanism
Analysis Modelling and Responserdquo Developments in Volcanology 10 Elsevier
Amsterdam 492 p (143-180 pp)
Nieto-Obregoacuten Jorge and Aguirre-Diaz Gerardo 2007a Geologiacutea y Estructura de la
caldera de Malpaso Aguascalientes Mexico Geos Vol 27 no1 p 131-132
Nieto-Obregoacuten Jorge and Aguirre-Diaz Gerardo 2007b Ignimbrita El Ocote Una
ignimbrita de muy alto grado en la caldera de Malpaso Aguascalientes Meacutexico
Mexico Geos Vol 27 no1 p 130
Collapse Calderas Workshop IOP PublishingIOP Conf Series Earth and Environmental Science 3 (2008) 012008 doi1010881755-130731012008
5
2
Figure 1 Simplified geologic map of the Caldera of Malpaso showing the major structures
and main lithologic units
The El Ocote Ignimbrite fills the caldera depression and extends several km outwards from
the caldera The intra-caldera facies consist of a high grade reomorphic ignimbrite with
lava-like features including flow banding and folds The pyroclastic nature of this unit is
demonstrated by the presence of a eutaxitic fabric with abundant elongated fiammes and
cm-size lithics rotated within the flow foliation
Collapse Calderas Workshop IOP PublishingIOP Conf Series Earth and Environmental Science 3 (2008) 012008 doi1010881755-130731012008
2
3
Figure 2 Simplified stratigraphic column and description of main units
Devitrified glass shards and axiolites of collapsed pumices are observed under the
microscope The glass shard matrix is deformed by flow around rigid phenocrysts (Figure
3) This ignimbrite is considered as reomorphic because there is evidence of ductile
deformation of hot pyroclastic material forming folds of different styles that include gentle
open close tight isoclinal and sheath type The open folds are often formed from refolded
folds of the foliation Structural elements such as foliation axial planes fold axis and
elongation lineations suggest deposition over an irregular surface flowing in different
directions from various sources within and in the borders of the caldera (Nieto Obregoacuten
and Aguirre Diacuteaz 2007b) The reomorphic ignimbrite is mainly distributed in the central
portion of the caldera and although its thickness has not been observed complete more than
300 m are exposed in the southern border of the caldera in the Sierra El Laurel The extra
caldera facies of this unit has thinner thicknesses from 20 to 150 m observed in the Mesa
san Joseacute de Gracia and to the south of Sierra El Laurel
Collapse Calderas Workshop IOP PublishingIOP Conf Series Earth and Environmental Science 3 (2008) 012008 doi1010881755-130731012008
3
4
Figure 3 Photomicrograph of El Ocote Ignimbrite Note the deformation of the glass
shards due to intense welding around a feldspar phenocryst
3 Structure
The area is affected by two types of faults of different ages 1) volcano-tectonic faults
produced by caldera subsidence processes and 2) tectonic faults of post-caldera age that
truncate the western and eastern borders of the caldera To the east the caldera is cut by the
western fault system of the Aguascalientes Graben and to the west by the eastern fault
system of the Calvillo Graben From the calderarsquos fault data and stratigraphy we conclude
that the caldera formed by the chaotic subsidence collapse of the magma chamber roof in a
piece-meal style and thus we classify it as a piece-meal graben caldera (sensu Aguirre-
Diacuteaz et al 2007)
References
Aguirre Diacuteaz GJ Labarthe-Hernaacutendez G Tristaacuten-Gonzaacutelez M Nieto-Obregoacuten J and
Gutieacuterrez-Palomares I 2007 Graben Calderas Volcano-tectonic explosive collapse
structures of the Sierra Madre Occidental Mexico Geophysical Research Abstracts
Collapse Calderas Workshop IOP PublishingIOP Conf Series Earth and Environmental Science 3 (2008) 012008 doi1010881755-130731012008
4
5
Vol 9 04704 S-Ref-ID 1607-7962graEGU2007-A-04704 European Geosciences
Union 2007
Aguirre-Diacuteaz GJ Labarthe-Hernaacutendez G Tristaacuten-Gonzaacutelez M Nieto-Obregoacuten J
Gutieacuterrez-Palomares I 2008 Ignimbrite Flare-up and graben-calderas of the Sierra
Madre Occidental Mexico in J Martiacute and J Gottsmann eds ldquoCaldera Volcanism
Analysis Modelling and Responserdquo Developments in Volcanology 10 Elsevier
Amsterdam 492 p (143-180 pp)
Nieto-Obregoacuten Jorge and Aguirre-Diaz Gerardo 2007a Geologiacutea y Estructura de la
caldera de Malpaso Aguascalientes Mexico Geos Vol 27 no1 p 131-132
Nieto-Obregoacuten Jorge and Aguirre-Diaz Gerardo 2007b Ignimbrita El Ocote Una
ignimbrita de muy alto grado en la caldera de Malpaso Aguascalientes Meacutexico
Mexico Geos Vol 27 no1 p 130
Collapse Calderas Workshop IOP PublishingIOP Conf Series Earth and Environmental Science 3 (2008) 012008 doi1010881755-130731012008
5
3
Figure 2 Simplified stratigraphic column and description of main units
Devitrified glass shards and axiolites of collapsed pumices are observed under the
microscope The glass shard matrix is deformed by flow around rigid phenocrysts (Figure
3) This ignimbrite is considered as reomorphic because there is evidence of ductile
deformation of hot pyroclastic material forming folds of different styles that include gentle
open close tight isoclinal and sheath type The open folds are often formed from refolded
folds of the foliation Structural elements such as foliation axial planes fold axis and
elongation lineations suggest deposition over an irregular surface flowing in different
directions from various sources within and in the borders of the caldera (Nieto Obregoacuten
and Aguirre Diacuteaz 2007b) The reomorphic ignimbrite is mainly distributed in the central
portion of the caldera and although its thickness has not been observed complete more than
300 m are exposed in the southern border of the caldera in the Sierra El Laurel The extra
caldera facies of this unit has thinner thicknesses from 20 to 150 m observed in the Mesa
san Joseacute de Gracia and to the south of Sierra El Laurel
Collapse Calderas Workshop IOP PublishingIOP Conf Series Earth and Environmental Science 3 (2008) 012008 doi1010881755-130731012008
3
4
Figure 3 Photomicrograph of El Ocote Ignimbrite Note the deformation of the glass
shards due to intense welding around a feldspar phenocryst
3 Structure
The area is affected by two types of faults of different ages 1) volcano-tectonic faults
produced by caldera subsidence processes and 2) tectonic faults of post-caldera age that
truncate the western and eastern borders of the caldera To the east the caldera is cut by the
western fault system of the Aguascalientes Graben and to the west by the eastern fault
system of the Calvillo Graben From the calderarsquos fault data and stratigraphy we conclude
that the caldera formed by the chaotic subsidence collapse of the magma chamber roof in a
piece-meal style and thus we classify it as a piece-meal graben caldera (sensu Aguirre-
Diacuteaz et al 2007)
References
Aguirre Diacuteaz GJ Labarthe-Hernaacutendez G Tristaacuten-Gonzaacutelez M Nieto-Obregoacuten J and
Gutieacuterrez-Palomares I 2007 Graben Calderas Volcano-tectonic explosive collapse
structures of the Sierra Madre Occidental Mexico Geophysical Research Abstracts
Collapse Calderas Workshop IOP PublishingIOP Conf Series Earth and Environmental Science 3 (2008) 012008 doi1010881755-130731012008
4
5
Vol 9 04704 S-Ref-ID 1607-7962graEGU2007-A-04704 European Geosciences
Union 2007
Aguirre-Diacuteaz GJ Labarthe-Hernaacutendez G Tristaacuten-Gonzaacutelez M Nieto-Obregoacuten J
Gutieacuterrez-Palomares I 2008 Ignimbrite Flare-up and graben-calderas of the Sierra
Madre Occidental Mexico in J Martiacute and J Gottsmann eds ldquoCaldera Volcanism
Analysis Modelling and Responserdquo Developments in Volcanology 10 Elsevier
Amsterdam 492 p (143-180 pp)
Nieto-Obregoacuten Jorge and Aguirre-Diaz Gerardo 2007a Geologiacutea y Estructura de la
caldera de Malpaso Aguascalientes Mexico Geos Vol 27 no1 p 131-132
Nieto-Obregoacuten Jorge and Aguirre-Diaz Gerardo 2007b Ignimbrita El Ocote Una
ignimbrita de muy alto grado en la caldera de Malpaso Aguascalientes Meacutexico
Mexico Geos Vol 27 no1 p 130
Collapse Calderas Workshop IOP PublishingIOP Conf Series Earth and Environmental Science 3 (2008) 012008 doi1010881755-130731012008
5
4
Figure 3 Photomicrograph of El Ocote Ignimbrite Note the deformation of the glass
shards due to intense welding around a feldspar phenocryst
3 Structure
The area is affected by two types of faults of different ages 1) volcano-tectonic faults
produced by caldera subsidence processes and 2) tectonic faults of post-caldera age that
truncate the western and eastern borders of the caldera To the east the caldera is cut by the
western fault system of the Aguascalientes Graben and to the west by the eastern fault
system of the Calvillo Graben From the calderarsquos fault data and stratigraphy we conclude
that the caldera formed by the chaotic subsidence collapse of the magma chamber roof in a
piece-meal style and thus we classify it as a piece-meal graben caldera (sensu Aguirre-
Diacuteaz et al 2007)
References
Aguirre Diacuteaz GJ Labarthe-Hernaacutendez G Tristaacuten-Gonzaacutelez M Nieto-Obregoacuten J and
Gutieacuterrez-Palomares I 2007 Graben Calderas Volcano-tectonic explosive collapse
structures of the Sierra Madre Occidental Mexico Geophysical Research Abstracts
Collapse Calderas Workshop IOP PublishingIOP Conf Series Earth and Environmental Science 3 (2008) 012008 doi1010881755-130731012008
4
5
Vol 9 04704 S-Ref-ID 1607-7962graEGU2007-A-04704 European Geosciences
Union 2007
Aguirre-Diacuteaz GJ Labarthe-Hernaacutendez G Tristaacuten-Gonzaacutelez M Nieto-Obregoacuten J
Gutieacuterrez-Palomares I 2008 Ignimbrite Flare-up and graben-calderas of the Sierra
Madre Occidental Mexico in J Martiacute and J Gottsmann eds ldquoCaldera Volcanism
Analysis Modelling and Responserdquo Developments in Volcanology 10 Elsevier
Amsterdam 492 p (143-180 pp)
Nieto-Obregoacuten Jorge and Aguirre-Diaz Gerardo 2007a Geologiacutea y Estructura de la
caldera de Malpaso Aguascalientes Mexico Geos Vol 27 no1 p 131-132
Nieto-Obregoacuten Jorge and Aguirre-Diaz Gerardo 2007b Ignimbrita El Ocote Una
ignimbrita de muy alto grado en la caldera de Malpaso Aguascalientes Meacutexico
Mexico Geos Vol 27 no1 p 130
Collapse Calderas Workshop IOP PublishingIOP Conf Series Earth and Environmental Science 3 (2008) 012008 doi1010881755-130731012008
5
5
Vol 9 04704 S-Ref-ID 1607-7962graEGU2007-A-04704 European Geosciences
Union 2007
Aguirre-Diacuteaz GJ Labarthe-Hernaacutendez G Tristaacuten-Gonzaacutelez M Nieto-Obregoacuten J
Gutieacuterrez-Palomares I 2008 Ignimbrite Flare-up and graben-calderas of the Sierra
Madre Occidental Mexico in J Martiacute and J Gottsmann eds ldquoCaldera Volcanism
Analysis Modelling and Responserdquo Developments in Volcanology 10 Elsevier
Amsterdam 492 p (143-180 pp)
Nieto-Obregoacuten Jorge and Aguirre-Diaz Gerardo 2007a Geologiacutea y Estructura de la
caldera de Malpaso Aguascalientes Mexico Geos Vol 27 no1 p 131-132
Nieto-Obregoacuten Jorge and Aguirre-Diaz Gerardo 2007b Ignimbrita El Ocote Una
ignimbrita de muy alto grado en la caldera de Malpaso Aguascalientes Meacutexico
Mexico Geos Vol 27 no1 p 130
Collapse Calderas Workshop IOP PublishingIOP Conf Series Earth and Environmental Science 3 (2008) 012008 doi1010881755-130731012008
5