Space-time patterns of Cenozoic arc volcanism in central Mexico:

From the Sierra Madre Occidental to the Mexican Volcanic Belt

Luca Ferrari* Instituto de Geología, Universidad Nacional Autónoma de México, Apdo. Postal 70-296 Ciudad Universitaria,
04510 México, Distrito Federal, México
Margarita López-Martínez Departamento de Geología, Centro de Investigación Cientifica y Enseñanza Superior de Ensenada,
Apdo. Postal 2732, C.P. 22860, Ensenada, Baja California, México
Gerardo Aguirre-Díaz Unidad de Ciencias de la Tierra, Instituto de Geología, Universidad Nacional Autónoma de México,
Gerardo Carrasco-Núñez Campus Juriquilla, Apdo. Postal 1-742, C.P. 76001 Querétaro, Querétaro, México

ABSTRACT Duplicate sampling of a specific unit occurred

A histogram of 778 isotopic ages of magmatic rocks younger than Eocene in central only in a few cases, in which we have used only
Mexico shows a multimodal distribution with peaks at about 30 Ma, 23 Ma, 10 Ma, and 5 Ma. the age obtained by the most reliable method
The sample suite displays systematic spatial variations with age that likely reflect the pro- (Ar/Ar rather than K/Ar) or published more
tracted transition from the north-northwest–trending arc of the Sierra Madre Occidental to recently. In addition, to eliminate low-quality
the east-west–trending Mexican Volcanic Belt. The reorientation of the arc is accompanied by data, entries with 2σ error in excess of 15% of the
a change in the dominant composition of the products from silicic ignimbrites and rhyolites to age were discarded, unless the error was less than
andesitic and basaltic lavas. The observed transition is related to the Miocene reorganization of 1 m.y. Based on this criteria, a subset of 784 dates
the subduction system following the cessation of subduction off Baja California and the east- was left for analysis.
ward motion of the Caribbean–Farallon–North America triple junction along the southeast- To analyze the space-time variation of the vol-
ern margin of Mexico. Our data support an early–middle Miocene age for the initiation of sub- canism, the data were plotted in a frequency histo-
horizontal subduction in southern Mexico and confirm that the locus of arc volcanism was gram (Fig. 2) and in geographic maps. The fre-
primarily controlled by the geometry of plate boundaries and the thermal structure of the sub- quency distribution of our data shows peaks with
ducting slab. high age at about 30 Ma, 23 Ma, 10 Ma, and 4 Ma
(Fig. 2), which, in agreement with other authors
INTRODUCTION of the Sierra Madre Occidental volcanism and (e.g., Kennett et al., 1977), we consider to reflect
Cenozoic subduction-related volcanism covers the inception of the Mexican Volcanic Belt. the intensity of magmatic activity in a region
a large part of western and central Mexico and where volumetric estimations are missing (see
has been referred to as two major arcs: the north- CENTRAL MEXICO also below for discussion). To analyze the spatial
northwest–trending Sierra Madre Occidental GEOCHRONOLOGIC DATABASE evolution of magmatism, several geographic
volcanic province and the roughly east-west– We have compiled isotopic ages of subduc- maps were produced using different time inter-
trending Mexican Volcanic Belt. The two vol- tion-related magmatic rocks ranging from the vals. On the basis of magmatic minima and/or
canic belts overlap between the Pacific coast and Oligocene to the present in the region between lat changes in a geographic pattern we found that the
the longitude of Mexico City (Fig. 1). The limit N16° and N24° and long W106° and W95°. Ages five periods of time shown in Figure 3 were the
in space and time between these volcanic of subduction-related volcanic rocks ranging most significant for the purpose of this paper. The
provinces has never been agreed upon, partly from 30 to 12 Ma in southern Baja California main features emerging from the present database
because there has never been a comprehensive were also included, as this part of the Peninsula are similar to those seen by Ferrari et al. (1994a)
presentation of the geographic evolution of the was within those coordinates during this time with only 60% of the present data, which con-
magmatic activity over the entire region. A view span. The database is an update of that used by firms that our dataset is sufficiently representative
of the locus of volcanism through time in central Ferrari et al. (1994a), and includes information of the Neogene volcanism of central Mexico.
Mexico is also useful to constrain models of the about location, rock type, method of dating,
kinematic evolution of the subducting slab de- material dated, and source of the reported age.
110° 100°
duced from the tomographic images of the upper All dates are calculated or recalculated using the
30°
mantle (e.g., van der Lee and Nolet, 1997). A International Union for Geoscience conventional
complete description of the geographic pattern decay constants (Steiger and Jäger, 1977). New
Si
er

of volcanism awaits a systematic geologic map- unpublished dates obtained during an ongoing
ra
M

ping, which is still to be undertaken in several project for the first geologic map of the entire
ad
re

areas of Mexico. Nevertheless, isotopic age Mexican Volcanic Belt are also used. The data- North American
Oc

plate
determinations, which have nearly doubled in the base currently contains 825 entries; ~15% of
c
id
en

past decade, can provide a first definition of the them are unpublished. These data are available
tal

Pacific plate
Neogene evolution of arc volcanism in central through the GSA data repository1.
Mexico. In this work, we use the most updated As any compilation of this type, one may be Rivera MVB
20° plate
compilation of isotopic ages for central Mexico concerned that data could be biased by over-
to analyze the variation in time and space of the sampling of a particular unit or by low-quality data.
continental volcanism in relation with the evolu- 0 500 km Cocos
tion of the subduction system and to solve the plate
1Data Repository item 9928, Compilation of ages
long-debated problem of the age of the waning of rocks in Central Mexico, is available from Docu- Figure 1. Geodynamic setting of Mexico show-
ments Secretary, GSA, P.O. Box 9140, Boulder, CO ing main Cenozoic volcanic provinces. MVB—
*E-mail: luca@servidor.unam.mx. 80301. Mexican Volcanic Belt.

Data Repository item 9928 contains additional material related to this article.

Geology; April 1999; v. 27; no. 4; p. 303–306; 4 figures. 303

 100 100 teristic features: the broad orientation of the arc
and the dominant composition of the rocks.

Number of isotopic ages

80 Figure 3 shows that the volcanic arc had almost
Figure 2. Frequency distri- the orientation of the modern Mexican Volcanic
bution (right side scale) Belt already since middle Miocene times. The
and log-normal plot (left 60
variation in the dominant composition of dated
side scale) of data per 10
1 m.y. interval. Multimodal rocks is shown in Figure 4, where a threshold was
40
distribution suggests that chosen at 63% of SiO2, corresponding to the
volcanism occurs in pulses lower limit of rhyolitic composition. The figure
(see text for discussion). 20 illustrates clearly that the dominant composition
Smoothing (bold line) was
obtained by averaging two of dated rocks changed rapidly from silicic to
adjacent values. 0 intermediate-mafic during the middle Miocene,
0 5 10 15 20 25 30 35
Age (Ma)
with a turning point at about 15 Ma.
We believe that the observed variations of
Alkaline Mafic Intermediate Silicic spatial distribution and composition of vol-
canism allow a conclusive assessment of the
temporal definition of the two arcs. Although no
EVOLVING GEOGRAPHIC PATTERNS Pasquarè et al., 1991), and a roughly east-west– volcanic lull can be observed at the continental
OF OLIGOCENE TO PRESENT trending segment in Puebla and Veracruz (López- scale of our study area, it can be seen that the
MAGMATISM IN CENTRAL MEXICO Infanzon, 1990). A last and isolated locus of transition from the Sierra Madre Occidental to
The first snapshot, between 38 and 25 Ma, was volcanism is also observed in eastern Oaxaca the Mexican Volcanic Belt occurred in early to
chosen because it encompasses the major episode (Ferrusquía-Villafranca, 1996) as a remnant of middle Miocene times, and that an arc with the
of ignimbritic volcanism in the Sierra Madre the previous configuration. characteristics of the Mexican Volcanic Belt
Occidental, the so-called ignimbrite flare-up By the late Miocene, the arc had reached a already existed by the late Miocene, as proposed
(McDowell and Clabaugh, 1979). Recent works stable orientation (Fig. 3d) with a west-north- by Ferrari et al. (1994a).
demonstrated that silicic to intermediate vol- west–east-southeast trend west of lat W102° and
canism with these ages is also widespread south a roughly east-west orientation in the remaining RELATION TO THE EVOLUTION OF
of the Mexican Volcanic Belt (e.g., in Pasquarè part. The dominant products were basaltic lavas THE SUBDUCTION SYSTEM
et al., 1991; Alba-Aldarve et al., 1996; Morán emplaced from the Pacific coast to the longitude When compared with the geographic evolu-
Zenteno et al., 1999). Rocks of these ages appear of Mexico City in the form of extensive plateaus tion of volcanism in western North America, the
distributed in an ~300-km-wide and N150°- (Ferrari et al., 1994b [and references therein]). Mexican case seems relatively simple. The data
trending arc, which extends continuously from Andesitic complexes are also present in southern indicate a progressive reorientation of the vol-
Zacatecas and San Luis Potosí to eastern Queretaro (Carrasco-Núñez et al., 1989; Perez- canic arc that can be related to the change in the
Michoacán, Guerrero, and western Oaxaca, Venzor et al., 1997) and more to the east, in thermal structure of the subducting slab and to
where it is now truncated by the present trench northern Puebla (Carrasco-Núñez et al., 1997). changes in the plate boundary geometry. North of
(Fig. 3a). The apparent exceptional width of the Since 7 Ma, the arc has remained in its orienta- lat N22°, volcanism terminated ca. 17 Ma, about
volcanic arc during this period is probably due to tion, but the volcanic front migrated toward the 5 m.y. earlier than the end of Farallon subduction
the abundant ages of ignimbrites, which can trench. This is especially evident in the western off Baja California (Lonsdale, 1991). At that
travel as much as 100 km from the source. Mexican Volcanic Belt, where the volcanic front time, the slab subducting at the trench was less
By the early Miocene (Fig. 3b), the arc had was at 180 km from the trench in the late Miocene than 5 Ma (Lonsdale, 1991). As pointed out by
rotated counterclockwise by ~30° and has and is now at only 110 km. The dominant volcanic Severinghaus and Atwater (1989), very young
approached the paleo-trench off Baja California. products are andesites. However, a widespread and hot oceanic crust in the subduction zone
Voluminous silicic ignimbrites of these age are episode of silicic volcanism is observed between 7 releases fluids before arriving in contact with the
exposed in southern Baja California (Hausback, and 3.5 Ma either in the western (Gilbert et al., mantle wedge, thus inhibiting partial melting and
1984), Nayarit-northern Jalisco (Scheubel et al., 1985; Rossotti et al., 1997) or in the central part of arc volcanism.
1988; Moore et al., 1994; Nieto-Samaniego et al., the Mexican Volcanic Belt (Aguirre-Díaz, 1997). The reorientation of the central and eastern part
1999), and Guanajuato (Cerca-Martínez, 1998). of the arc during early and middle Miocene time
Less-differentiated rocks are also present in LIMIT BETWEEN THE SIERRA MADRE appears related to the change in the geometry of
northern Michoacán in the Morelia and Zita- OCCIDENTAL AND THE MEXICAN the North America–Farallon–Caribbean plate
cuaro areas (Pasquarè et al., 1991; Capra et al., VOLCANIC BELT boundaries. Morán-Zenteno et al. (1996) demon-
1997). East of long W98°30′ and between lat In the past, no agreement has been reached strated that the eastward motion of the Chortis
18°30′ and 17°, the volcanism almost ceased but about the onset of Mexican Volcanic Belt activity, block (Caribbean plate) during the Neogene pro-
persisted in northwestern Oaxaca (Ferrusquía- which has been suggested to be Quaternary gressively modified the subducting boundary
Villafranca et al., 1988). (Demant, 1978), late Pliocene (Cantagrel and between the North America and Farallon plates,
In the middle Miocene (17–12 Ma), the arc Robin, 1979), early Pliocene (Nixon et al., 1987), forming a new trench in an inland position. On the
extended eastward and reached the coast of the or late Oligocene (Mooser, 1972). In a certain other hand, Pardo and Suarez (1995) related the
modern Gulf of Mexico (Fig. 3c). This “discon- way this may be a semantic problem. Like plate oblique orientation of the Quaternary Mexican
tinuous” arc included a north-west–trending seg- boundaries, volcanic arcs are moving objects on Volcanic Belt with respect to the trench with an
ment located on the southern margins of the Gulf the earth surface, and any spatial definition of a along-trench variation in the slab dip, observing
of California (Gastil et al., 1979; Hausback, given arc may be viewed as a snapshot in a con- that the Cocos plate has a very shallow dip
1984), an east-southeast–trending segment mainly tinuously changing scenario. beneath the central and eastern part of the vol-
represented by andesitic successions between However, the Sierra Madre Occidental and the canic arc. The initiation of subhorizontal subduc-
northern Michoacán and Mexico city area (e.g., Mexican Volcanic Belt have at least two charac- tion in central Mexico is unknown. However, the

304 GEOLOGY, April 1999

 # #
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a b

Figure 3. Geographic dis- 24

17 - 12 Ma 12 - 7 Ma
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central Mexico since 38 #

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Ma. Universe transverse 22

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106 104 102 100 98 96 e f

data presented here show an abrupt cessation of 1979), and has been recently documented that Composition of dated rocks
volcanism south of lat 18° and a landward jump of most of the silicic volcanism in Guanajuato, San 100
% of Mafic to Intermediate vs. Silicic

the volcanic front during the early Miocene Luis Potosí, and Zacatecas also occurred be- 90

(Fig. 3b); they also show a volcanic front close to tween 31 and 28 Ma (Nieto-Samaniego et al., 80
70 Silicic
the present position by the middle Miocene 1999). The second peak at ca. 23 Ma is corrobo-
60
(Fig. 3c). Based on these observations, we pro- rated by over 1000 m of silicic ignimbrite with
50
pose that the shallowing of the subducting slab this age found in southern Durango (El Salto 40
occurred during early to middle Miocene. sequence, McDowell and Keizer, 1977), north- 30
ern Jalisco (Bolaños area, Scheubel et al., 1988), Mafic to intermediate
20
IS VOLCANISM REALLY EPISODIC? and northeastern Nayarit (Ferrari, unpublished 10
Although we lack systematic volumetric esti- data), which account for about 80% of the vol- 0
0 5 10 15 20 25 30 35
mations of volcanic rocks per time interval, sev- canism in these areas. In the Mexican Volcanic Age (Ma)
eral observations indicate that most of the peaks Belt, a late Miocene mafic pulse is substantiated
Figure 4. Variation of composition of dated
of isotopic ages shown on Figure 2 reflect real by 10.5 to 9 Ma basaltic successions, over 800 m
rocks, expressed as percentage of rocks hav-
pulses of intense volcanic activity. First of all, the thick in places, which cover ≈3500 km3 in ing mafic to intermediate versus silicic com-
geographic coverage of the database (Fig. 3f) is Nayarit and Jalisco (Ferrari et al., 1997) and for position per 1 m.y. intervals. Mafic to inter-
very good, at least for the central part of the study which we estimate a volume 2 to 3 times larger mediate—basaltic to dacite, silicic—rhyolite
area. Other geologic observations can support the than the volcanic rocks emplaced from 8 to 5 Ma. (SiO2 > 63%). Note rapid change from silicic to
intermediate-mafic varieties during middle
episodicity of volcanism. A pulse at ca. 30 Ma is A volcanic pulse in the last 5 m.y. is more diffi- Miocene. Smoothing (bold line) obtained by
well known in the Sierra Madre Occidental to the cult to evaluate because the database is clearly averaging two adjacent values. Same data
north of the study area (McDowell and Clabaugh, biased by the large number of dates obtained for subset as in Figures 2 and 3.

GEOLOGY, April 1999 305

recent and active volcanoes. One argument and Queretaro: Geofísica Internacional, v. 33, Morán-Zenteno, D. J., Corona-Chavez, P., and Tolson,
favoring the existence of a pulse in the Quater- p. 107–124. G., 1996, Uplift and subduction erosion in south-
Ferrari, L., Nelson, S. A., Rosas-Elguera, J., Aguirre- western Mexico since the Oligocene: Pluton geo-
nary is that a single large stratovolcano of the Díaz, G., and Venegas-Salgado, S., 1997, Tec- barometry constraints: Earth and Planetary Sci-
Mexican Volcanic Belt has a volume of one order tonics and volcanism of the western Mexican ence Letters, v. 141, p. 51–65.
of magnitude greater than the entire Michoacán- Volcanic Belt, in Magmatism and Tectonics in Morán-Zenteno, D. J., Alba-Aldave, L., Corona-
Guanajuato volcanic field (Hasenaka and Car- Central and Northwestern Mexico—A selection Ezquivel, R., Reyes-Salas, M., Martínez-Serrano,
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michael, 1985), and that all the large strato-
sions: Instituto de Geología, Universidad Na- and tectonic significance of the Tertiary silicic
volcanoes in the Mexican Volcanic Belt are less cional Autónoma de México, p. 85–29. volcanism in northern Guerrero, México: Revista
than 1.6 Ma. We believe that the above examples Ferrusquía-Villafranca, I., 1996, Contribución al Mexicana de Ciencias Geologicas (in press).
are a strong suggestion that volcanism occurred conocimiento geológico de Chiapas—El área Nieto-Samaniego, A., Ferrari, L., Alaniz-Alvarez, S.,
in pulses over the entire central Mexico. More Ixtapa-Soyaló: Boletín 109, Instituto de Geo- Labarthe-Hernandez, G., and Rosas-Elguera, J.,
logía, Universidad Nacional Autónoma de Méx- 1999, Variation of Cenozoic extension and vol-
systematic estimates of volcanic rates and a care- ico, 130 p. canism across the southern Sierra Madre Occi-
ful comparison with the plate tectonic evolution Ferrusquía-Villafranca, I., McDowell, F., W., Martínez- dental volcanic province, Mexico: Geological So-
may lead to a better understanding of the reasons Hernandez, E., Barrios-Rivera, H., and Garcia- ciety of America Bulletin (in press).
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of continental Tertiary basins in the Oaxaca State: Harakal, J. E., 1987, K-Ar and geologic data
ACKNOWLEDGMENTS Geological Society of America Abstracts with bearing on the age and evolution of the Trans-
Work was supported by grants UNAM-PAPIIT Programs, p. A59. Mexican Volcanic Belt: Geofísica Internacional,
IN108196 and CONACYT 0152P-T to L. Ferrari. Gastil, G., Krummenacher, D., and Jensky, A. W., 1979, v. 26, p. 109–158.
D. Morán-Zenteno, S. Nelson, and S. Venegas kindly Reconnaissance geology of west-central Nayarit, Pardo, M., and Suarez, G., 1995, Shape of the subducted
provided unpublished isotopic ages. Reviews by Mexico: Summary: Geological Society of Amer- Rivera and Cocos plates in southern Mexico:
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