Hawaiites and Related Lavas in the Atenguillo Graben, Western Mexican Volcanic Belt

Hawaiites and related lavas in the Atenguillo graben, western Mexican Volcanic Belt

KEVIN RIGHTER 1 IAN SE CARMICHAEL I ^ePartment of Geology and Geophysics, University of California, Berkeley, California 94720

ABSTRACT rift-rift-rift triple junction (Chapala rift, Colima rift, and Tepic-Zacoalco rift; Fig. 1). The Colima rift and the Tepic-Zacoalco rift outline the Jalisco Hawaiite and mugearite, alkali-olivine basalt, and basaltic ande- Structural Block (Allan and others, 1991; Johnson and Harrison, 1989). site have erupted from three shield volcanoes in the Atenguillo graben, Our understanding of this complex area of contractile, extensional, and Jalisco, Mexico. The youngest shield volcano, La Laja (0.66 Ma), is strike-slip tectonics is still very poor. The presence of alkaline and peralka- the focus of this study. Basal pyroclastic surge deposits of basaltic ash, line volcanic rocks in the rifts, together with significant extensional and Iapilli, and blocks are overlain by seven to eight, 5- to 10-m-thick strike-slip faulting in the Colima and Tepic-Zacoalco rifts, respectively, hawaiite flows. Pillow lavas along a 4-km stretch on the southeast have led Luhr and others (1985), Allan and others (1991), and Wallace flank of the volcano and lake-bed sediments define a shoreline and and others (1992) to suggest that the Jalisco Block is rifting away from the lake bottom southward to the town of Atenguillo. Eruption of La Laja Mexican mainland. This rifting event may represent the latest in a series of apparently dammed the northward-flowing Atenguillo River and northward-propagating spreading-ridge jumps along the East Pacific Rise. formed a lake of as much as 100-m depth. Subsequent fluvial erosion A second hypothesis, suggested by DeMets and Stein (1990), appeals to has destroyed the lava dam, exposing the shield succession. Discharge oblique subduction of the Cocos Plate to explain passive rifting in the rates for the Atenguillo River and rainfall estimates for the Atenguillo Colima rift and sinistral slip in the Chapala-Oaxaco fault zone and the basin both suggest that this lake formed within 20 to 40 yr. Eruption eastern MVB. 3 of nearly 10 km of material within 10 to 100 yr indicates an output Alkalic basaltic volcanism occurred in the western MVB, where 3 rate of 0.1 to 1 km /yr, which is larger than any rate calculated for north-south-oriented normal faulting at the northern margin of the Jalisco volcanoes in the Mexican Volcanic Belt (MVB), but similar in magni- Block apparently influenced magma emplacement and eruption. Several tude to that of Mauna Loa and Kilauea volcanoes (Hawaii). The older shield volcanoes, Cerro Tio Cleto, Cerro La Laja Los Cerritos, and an volcanoes, El Vigia (2.7 Ma) and Tio Cleto (3.6 Ma), are composed of unnamed shield near the village of El Vigia (hereafter referred to as Tio basaltic-andesite and alkali-olivine basalt, respectively. Cleto, La Laja, and El Vigia), as well as several lava plateaus, were active The composition of these lavas is unusual for a continental-arc in the Atenguillo and the Ameca River valleys between 3.6 Ma and 0.64

setting. Total FeO, Ti02, and alkali concentrations are higher than Ma (Fig. 2). These volcanoes lie south of the andesite central volcano, those of basic calc-alkaline lavas from the western MVB. Aikaline- Volcán Ceboruco, approximately 180 km from the Middle America earth/light-rare-earth and light-rare-earth/high-field-strength ele- Trench. Their alkaline character (hawaiite, mugearite, and alkali-olivine ment ratios in these lavas are low relative to those of calc-alkaline basalt) is unusual for such a position within a continental arc. La Laja was lavas but similar to those of oceanic-island basalt values. Such compo- selected for detailed study because it is the best preserved and most access- sitional traits coupled with a high magma-output rate are characteris- ible of the shield volcanoes. tic of oceanic-island volcanoes. Both hydrous, fluid-enriched, sub-arc mantle, and oceanic-island-type mantle components are present be- GEOLOGIC SETTING neath western Mexico; contemporaneous subduction and extension of this region of the western MVB allow tapping of both sources and Regional Geology and Tectonics thus the eruption of compositionally diverse lavas. Two fault-bounded basins are within the Jalisco Block (Wallace and INTRODUCTION others, 1992). The Mascota valley, which runs north from the town of Mascota (Fig. 1), contains numerous calc-alkaline and alkaline cinder and The east-to-west-trending Mexican Volcanic Belt (MVB) is a com- lava cones that range in age from 0.5 Ma to Holocene (based on presence plex continental volcanic arc that is related to active subduction of the of an unvegetated block lava flow west of Mascota) (Lange and Carmi- Rivera and Cocos plates beneath western Mexico. Volcanic centers within chael, 1990,1991; Luhr and others, 1989). Lava types include phlogopite the arc include Volcán Ceboruco, V. Colima, V. Popocateptl, and V. Ori- lamprophyre, high-Mg basaltic andesite, absarokite, and hornblende an- zaba (Fig. 1). The western part of the MVB is structurally and tectonically desite. The Atenguillo graben (Fig. 1), located to the east and running from complicated by the presence of three tectonic lineaments that form a Los Volcanes northward to the Ameca River (Wallace and others, 1992),

Additional material for this article (seven tables) may be obtained free of charge by requesting Supplementary Data 9235 from the GSA Documents Secretary.

Geological Society of America Bulletin, v. 104, p. 1592-1607,11 figs., 5 tables, December 1992.

1592

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/104/12/1592/3381340/i0016-7606-104-12-1592.pdf by guest on 25 September 2021 HAWAIITES, ATENGUILLO GRABEN, MEXICAN VOLCANIC BELT

106» W 105° W 104» W 103» W 102» W 22» N Figure 1. Map of the western Mexican Volcanic Belt. The Jalisco Block boundaries are defined by the Tepic-Zacoalco rift, the Colima rift, and the Middle America Trench. Position of normal faults from Johnson and Harrison (1989). Outlined area is the northern Atenguillo graben, enlarged in Figure 2; 21» N graben faults are from Wallace and others (1992). Volcanic centers are Volcán San Juan (1), Sanganguey (2), Tepetiltic (3), Ceboruco (4), Tequila (5), Sierra la Prima- vera (6), Colima (7, 8), and Paricutin and Jorullo in the Michoacán-Guanajuato Vol- canic Field (MGVF). Cities are Guadalajara 20» N (G), Tepic (T), Ameca (A), Puerto Vallarta (PV), Mascota (M), Los Volcanes (LV), and Colima (C). The inset (upper right) shows the entire Mexican Volcanic Belt (triangles represent, from west to east, Volcán San Juan, Ceboruco, Colima, Paricutin, Jorullo, Popo- catépetl, Pico de Orizaba, San Andres Tuxtla, 19» N and El Chichón). Major tectonic boundaries are the Middle America Trench (MAT); the East Pacific Rise (EPR); the Rivera Fracture Zone (RFZ); and the Cocos (C), Pacific (P), Rivera (R), and North America (NA) plates 0 km 100 (after Drummond, 1981). fci j.i- =i

18» N

contains a remarkably diverse suite of Pliocene alkaline and calc-alkaline (Fig. 2 and Table 1). Four vents comprising ash- to block-sized pyroclastic lavas, including K-rich minette, leucitite, absarokite, vogesite, hornblende material, including bombs that range in size from 0.3 to 3 m, are associated andesite, basaltic andesite, and basalt (Wallace and Carmichael, 1989, with the lava flows. The groundmass of a bomb (KR-259) from one of 1992). North of these lavas (still within the Atenguillo graben) are the these vents also has an age of 2.7 Ma (Fig. 2 and Table 1). The lavas at El Pliocene-Pleistocene shield volcanoes, La Laja (0.66 Ma), Tio Cleto (3.6 Vigia contain phenocrysts of plagioclase and olivine and have a trachytic Ma), El Vigia (2.7 Ma); an andesitic shield volcano, La Cienega (2.2 Ma); texture, in which the groundmass plagioclase laths are of similar composi- and an andesitic plateau near Agua Zarca (2.9 Ma) (Fig. 2 and Table 1). tion to the microphenocrysts (Table 2). Olivine contains small inclusions Lava plateaus Mesa Llano Grande (3.4 Ma), Amajaquillo (2.5 Ma), and of spinel octahedra. There are cubic and rhombohedral oxides in the El Rosario (0.64 Ma) are in the northern part of the area, in the Ameca groundmass of most samples. River valley (Fig. 2 and Table 1). The shield volcanoes and plateaus in the Ameca and Atenguillo River valleys constitute a total of approximately 50 Tio Cleto km3 of lava flows. Although the faulting associated with the graben has not been mapped in detail, emplacement of lavas in this region is thought Tio Cleto (Cerro Tio Cleto) is older than the flanking volcanoes, La to be controlled by the predominantly north-south-oriented extensional Laja and El Vigia. This alkali-olivine basalt shield volcano is a prominent faulting (Wallace and Carmichael, 1992; Wallace and others, 1992). eroded knoll that is in the path of the Atenguillo River; its eruption once diverted the flow of the Atenguillo River to the east (Fig. 2). The lavas are El Vigia cut by a fault that runs along the Atenguillo River. The exposed alkali- olivine basalt flows have a total volume of approximately 1 km3; however, El Vigia (unnamed on maps) is a basaltic-andesite shield volcano much of Tio Cleto has been eroded. The underlying rocks in the vicinity of near the western edge of the Atenguillo graben. It overlies and is banked Tio Cleto include Cretaceous ash flow, granite and granodiorite of un- up against Cretaceous ash flows that make up most of the graben walls known age (perhaps related to the batholith complexes to the west; Kohler (Wallace and Carmichael, 1989). A series of 10 basaltic-andesite flows, and others, 1988), and lacustrine sediments. A columnar-jointed flow near exposed in the Atenguillo river canyon directly beneath the town of El the base of the volcano, and within the village of Tio Cleto, is 3.6 Ma old Vigia, indicates a minimum eruptive volume of approximately 11.5 km3. (Fig. 2 and Table 1). The Tio Cleto alkali-olivine basalts may have either A flow from the top of the shield (KR-260) yields a K-Ar age of 2.7 Ma glomeroporphyritic plagioclase or olivine phenocrysts, but typically both

Geological Society of America Bulletin, December 1992 1593

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/104/12/1592/3381340/i0016-7606-104-12-1592.pdf by guest on 25 September 2021 RIGHTER AND CARMICHAEL

104° 40' 104 30' T 1 Amajaquillo 2.5 Ma

20° 50' Figure 2. Map of the Atenguillo valley, with the entire volcanic field, from La Laja in the south to Amajaquillo in the north. Indi- vidual alkaline volcanic centers are La Laja, El Vigia, Tio Cleto, Mesa Llano Grande, and El Rosario. Calc-alkaline centers are Agua Mesa Zarca, La Cienega, and Amajaquillo. K-Ar Llano Grande dates of all centers are listed below their 3.4 Ma names; locations of dated samples are dotted. See Table 1 for K-Ar data. Town abbrevia- tions are as follows: G, Guachinango; LC, La Cienega; LG, Llano Grande; Z, Zacatongo; T, Tepuzhuacan; ADC, Amatlan de Canas. El Vigia This map was constructed using CETENAL 2.7 Ma topographic maps F13D-52, -62, and -72. 20° 40'

Agua Zarca 2.9 Ma

La Laja 0.66 Ma

0 km 5 ZD 20° 30'

occur together. Olivine phenocrysts commonly have inclusions of spinel the volcano gives a K-Ar age of 2.2 Ma (Table 1). A plateau south of El octahedra. These lavas also contain olivine, plagioclase, titano-magnetite, Vigia, near the village of Agua Zarca, consists of several andesite flows, the and augite as microphenocrysts or in the groundmass (Table 2). topmost flow giving an age of 2.9 Ma (Fig. 2 and Table 1). Mesa Llano Grande consists of five to six alkali-olivine basalt flows, and it is approxi- Rio Ameca Plateaus and Northern Atenguillo Graben mately 30 km2 and 100-200 m thick. A sample from the top flow of this plateau yields a K-Ar age of 3.4 Ma (Table 1). Near the junction of the At the northern end of the Atenguillo graben, the Atenguillo River two rivers is a broad plateau of basaltic andesite (referred to as Amaja- joins the Ameca River. Several Pliocene and Pleistocene shield volcanoes quillo after a nearby village) with a 150- to 200-m escarpment on the and lava plateaus are in this region (Fig. 2). Cerro La Cienega is a broad, north and west edge (Fig. 2); the lowest flow gives a K-Ar age of 2.5 Ma deeply eroded, andesite shield volcano. A flow from the southwest side of (Table 1). The youngest plateau in this area (named after the town of El

1594 Geological Society of America Bulletin, December 1992

TABLE 1. K-Ar DATA

40 , K Sample wt. Ar Age 12 40 (±2 a) Sample Volcano Ut. Long. Material (wt%) (E) (IO" mol/g) % Ar* (Ma)

KR-102 La Laja 20°31.55' 104=28.76' gms 1.465 4.10454 1.676 13.2 0.65 0.06 LV-167 La Laja 20°31.30' 104=29.05' gms 1.479 5.20000 1.714 7.1 0.67 0.04 KR-259 El Vigia 20°40.65' 104°34.17' gms 1.095 2.35265 5.077 26.3 2.69 0.18 KR-260 El Vigia 20°40.63' 104=34.54' gms 1.177 2.13296 5.567 34.3 2.74 0.16 KR-109 Tio Cleto 20°38.29' 104°30.23' gms 0.972 4.08461 6.072 16.9 3.55 0.21

MAS-324 Amajaquillo 20»56.22- 104=35.32' gms 1.087 7.21844 4.650 18.2 2.47 0.12 MAS-326 Rosario 20°54.87' 104=29.60' gms 1.214 6.21324 1.341 6.6 0.64 0.10 KR-122 M. Llano Grande 20°48.07' 104=32.41' gms 1.400 3.91274 8.355 32.2 3.38 0.10

LL-48 La Ciénega 20=41.49' 104°30.14' gms 1.758 3.76036 6.645 19.7 2.18 0.10 KR-110 Agua Zarca 20°37.80' 104°32.49' gms 2.375 1.65940 11.950 64.6 2.89 0.07

1 1 10 _l 40 4 40 Note: decay constants are \ + \£. = 5.81 X 10"' yr" ; A,, - 4%2 ' 10 yr~'; X = 5.543 x 10"'°yr ; K/KT(M3l= 1.167 x 10~ (Steiger and Jager, 1977); Ar* refers to radiogenic component. Samples were prepared following methods described by Allan (1986). K analyses were performed in duplicate by J. Hampel and K. Righter using flame photometry. Ar extractions were performed by T. Becker, Institute for Human Origins—Geochronology Center, using techniques of Dalrymple and Lanphere (1969). gms refers to groundmass.

TABLE 2. MODAL ANALYSES OF ROCKS FROM LA LAJA, TIO CLETO, EL VIGIA, AND VICINITY (1,500 2,000 POINTS COUNTED)

Sample OI Cpx Pl Phl Hbl Oxide Qtz Xeno. Vesiclle s Sxls gms

Volcan La Laja

BLC-1 P 0.1 33.9 66.1 Lapilli clast mp 2.8 31.0 •KR-102 P 2.5 55.7 44.3 Base flow mp 11.2 40.5 1.5 KR-161 P 2.3 98.9 1.1 Mid flow mp 7.2 21.3 60.6 7.4 •LV-167 P 2.8 93.0 7.0 Mid flow mp 23.9 62.6 3.7 KR-169 P 3.7 15.5 79.7 2Ó.3 Top flow mp 11.6 1.4 43.4 4.2 KR-142 P 0.2 0.6 0.5 70.1 29.9 Summit mp 3.4 9.4 50.4 5.6 KR-150 P 5.2 55.0 45.0 Pillow mp 10.9 38.9 KR-151 P 1.5 44.2 55.8 Pillow mp 9.1 33.6 tr KR-152 P 2.9 50.1 49.9 Pillow mp 10.8 36.4 tr

Volcan Tio Cleto

•KR-109 P 3.3 0,1 99.4 0.6 Basalt mp 8.3 3.4 78.7 5.6 KR-247 P 3.7 23.5 27.2 72.8 Basalt mp

Volcan El Vigia

•KR-259 P 2.6 10.6 4.0 85.3 Basaltic andesite mp 0.1 1.3 •KR-260 P 2.1 0.3 6.3 93.7 Basaltic andesite mp 3.9

Mesa Llano Grande

•KR-122 P 2.2 86.4 13.6 Basalt mp 5.6 22.9 55.8 tr

Volcan La Cienega

•LL-48 P 0.1 75.3 24.7 Andesite mp 15.8 58.0 1.4

Agua Zarca plateau

"KR-110 P 1.0 0.1 2.0 15.1 84.9 Andesite mp 0.7 3.1 8.2

•Sample has been dated (see Table 1 and Fig. 2); p = phenocrysts; mp = microphenocrysts; gms = groundmass. Phenocrysts—width >0.3 mm; microphenocrysts—0.3 mm > width > 0.03 mm, groundmass < 0.03 mm; after Wilcox (1954).

Rosario), lies north of the Ameca River (Fig. 2), along the highway east of el Comalito to the west and Sierra Verde to the east, are composed Tepuzhuacan. A date of 0.64 Ma was obtained on this alkali basalt (Table primarily of ignimbrite, diorite, and metabasalt. The ignimbrite that under- 1). The plateaus in the Rio Ameca valley have been tilted to the north lies the volcano is part of the same Cretaceous group that forms the along listric normal faults (Nieto-Obregon and others, 1989). basement of the entire Atenguillo, Los Volcanes, and Mascota area (Wal- lace and Carmichael, 1989). Above the Cretaceous basement are fluvial La Laja Stratigraphy sediments consisting of sandstone; rare lenticular beds of extremely fine- grained white sediments (perhaps lacustrine), and conglomerate with cob- La Laja (Cerro La Laja Los Cerritos) is in the center of the fault- bles of minette, basalt, and rhyolitic ash flow. A series of minette and bounded Atenguillo River valley and defines the southern end of this leucitite flows, contemporaneous with those described by Wallace and volcanic field (Fig. 2). The north-south-trending mountain ranges, Sierra Carmichael (1989), underlie La Laja in the south, and range in age from

Geological Society of America Bulletin, December 1992 1593

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/104/12/1592/3381340/i0016-7606-104-12-1592.pdf by guest on 25 September 2021 RIGHTER AND CARMICHAEL

2.5 to 3.3 Ma (Fig. 3). A tabular remnant of a hornblende andesite flow, Figure 3. Geologic map and stratigraphic columns for La Laja which is cut by a normal fault, is exposed just north of La Laja (Fig. 3). La (Cerro La Laja Los Cerritos). The pyroclastic unit that makes up the Laja is a symmetric shield volcano with a base that ranges from 7 to 10 km base of La Laja crops out as a ledge along the east edge of the volcano, in diameter. It has a well-defined, but eroded, summit caldera and slopes and thus the unit is not on the map even though it does exist. Contour varying from 6° on the south flank to 11° on the east flank. The base of the lines below 1,300 m in the Atenguillo River are left out for clarity; the volcano is an eastward-dipping plane with an elevation of 1,250 m in the river elevation at the north edge of the map is 900 m, and 1,150 m at east and 1,500 m in the west (Fig. 3). The flows cover approximately the south edge. Numbered dots in the map are keyed to the strati- 50 km2, with an eruptive volume of 8.8 km3. Stratigraphic columns were graphic columns below. See text for a discussion of features within constructed from data collected at seven sites around the perimeter of the each unit. Hatched line is a normal fault that cuts the andesite. LL is volcano (Fig. 3). the town of La Laja, and C is the town of Cuyutlan. Pyroclastic Deposits. The oldest volcanic unit of La Laja consists of ~80-m-thick pyroclastic deposits with clasts of ash- to block-sized material (location 2, Fig. 3). Layering is made up of massive fine to coarse ash beds, massive (as much as 5 cm) ash-supported lapilli layers, and mixed lapilli and block massive layers. Folding and folds that are truncated by overlying phenocrysts and augite in the groundmass (2% to 20%) (Table 2). Plagio- horizontal layers are interpreted to be convolute lamination caused by clase microphenocrysts define a trachytic texture in all samples and occur either gravity sliding of sloping water-saturated tephra or shear deforma- as small (<0.3-mm width) zoned laths. Groundmass quench-textured oli- tion from the overriding base surge flow. Large-scale cross bedding (1 to 2 vines are ubiquitous. m), small scour features, and U-shaped channels (4 to 5 m wide and 1 m Lacustrine Sediments. To the east and south of location 7, lacustrine deep) are characteristic features of pyroclastic surge deposits. Blocks are sediments as thick as 5 m overlie the lava flows. Similar sediments are commonly vesicular basalt (BLC-1; Table 2); less common are blocks of exposed on the south flank of the shield (at 1,400 m), along the main road Cretaceous ash flow. This sequence thins and fines (< 1-m-thick ash) to the near location 6. Outcrops of these sediments extend southward in the west, east, and south (locations 1, 3, 4, 5, 6, Fig. 3). Structures within the Atenguillo Valley toward San Pablo and Atenguillo (Fig. 4). Many of ash include finely layered cross bedding and cross stratification, massive these sediments contain a monaxon variety of sponge spicules and indicate units (0.5 to 1 m) without bedding, finely interbedded layers (1 to 3 mm), a relatively stable lacustrine environment. wave-like layers with 15 cm peak-to-peak distance, intraformational rip- up clasts in some of the larger cross beds, and turbulent boundaries be- Geologic History—La Laja tween lapilli- and ash-sized layers that resemble chute and pool structures. Material within the ash and lapilli layers consists of angular glass shards, The series of oxbow bends in the Rio Atenguillo south of La Laja, crystals of plagioclase and olivine, and rare lapilli- and ash-sized pieces of and the fluvial sediments found beneath the volcanic units of the shield, silicic ash flow. suggest that the pre-La Laja terrain consisted of a broad, meandering river Lava Flows and Pillows. Approximately 25 m of columnar-jointed valley bounded by the Cretaceous rhyolite ranges. Pliocene and Pleisto- lava is exposed near the town of La Laja (location 1). Seven to eight cene andesite and minette flows are present throughout the valley. La hawaiite flows, punctuated by 1- to 2-m rubbly, brecciated zones form the Laja's first activity was a phreatomagmatic eruption, which produced a top 80 m of the north flank of the volcano (location 3). No soil layers are series of pyroclastic surges and airfali deposits and built a small, asymmet- preserved. Thin (< 1 m), lenticular layers of ash and blocks, however, were rical tuff cone or tuff ring within the Atenguillo River valley. After a short deposited between a few of the flows. The finely layered ash is deformed hiatus, low viscosity lavas erupted to form the shield. The initial flows and depressed by blocks of vesicular lava (bedding sags). On the southeast dammed the Atenguillo River, forming a lake (paleolake La Laja; Fig. 4). flank of the volcano are two to three hawaiite flows, totaling 20 m in Subsequent lavas flowed into the lake and formed pillows. The lava flow- thickness (location 5). The flows are underlain by elongate pillow lavas, lava pillow contact records a paleo-lake level of 1,320 m (between sites 4 which form a 40-m-thick layer (Fig. 3). The pillows have corrugations and and 7), whereas later flows increased the height of the lava dam to 1,400 fault slivers on their exteriors and are similar in shape to those described by m. The lake survived long enough to deposit at least 10 m of sediment. The Moore and others (1971) and Moore (1975), from subaqueous eruptions Atenguillo River breached the lava dam and cut down through the basalt- down steep bottom slopes in Hawaii and Sicily (Mt. Etna) (see also rhyolite contact on the east flank (at the present location of the river, Fig. Basaltic Volcanism Study Project, 1981, section 5.3). The hawaiite flow 3); subsequent downcutting of the Atenguillo River has exposed the east above the ash layer (KR-102) yields a K-Ar age of 0.65 Ma (Table 1). edge of the shield. Finally, 20 m of hawaiite flows and approximately 55 m of pillow lavas are exposed on the south edge of the shield (location 6). The first flow Magma Output Rate above the pillow-lava layer (LV-167) has a K-Ar age of 0.67 Ma (Table 1). Samples KR-102 and LV-167 are identical in age, given the uncertain- The duration of activity at La Laja can be estimated by considering ties in the K-Ar determinations (see Table 1). In the west (location 7), the two lines of evidence. First, the 8 to 10 flows making up the shield of La flows are vesiculated and taper out against the Cretaceous ash-flow Laja lack soil horizons between them, and in most cases, the base of a flow basement. rests directly above the top of the previous flow. In a few cases, intervening All of the hawaiite flows contain between 1% and 5% euhedral, lenses of ash retained their original volcanic features (bedding sags) and were subhedral, and irregularly shaped olivine phenocrysts (Table 2). The pil- preserved by successive overriding hawaiite flows. Soil may form on vol- low lavas generally have fewer olivine phenocrysts and substantially more canic ash in at least 200 years, as it has at Volcán Jorullo (1759-1774), groundmass glass (45% to 55%; Table 2) than the subaerial lavas. Most of central Mexico (Luhr and Carmichael, 1985), whereas at Volcán Paricutin the flows contain groundmass olivine (3% to 24%), plagioclase microphe- (1943-1952), very little soil has developed in 50 years (Wilcox, 1954). nocrysts (40% to 63%), and glass (1% to 45%), whereas the more-evolved This is consistent with a short-duration eruptive event (perhaps less than flows collected near the summit of La Laja have augite and plagioclase 50 years).

1594 Geological Society of America Bulletin, December 1992

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/104/12/1592/3381340/i0016-7606-104-12-1592.pdf by guest on 25 September 2021 20° 37.5'

20° 35'

20° 30'

104° 35' 104° 25'

Elevation (m) Elevation (m)

Geological Society of America Bulletin, December 1992 1597

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/104/12/1592/3381340/i0016-7606-104-12-1592.pdf by guest on 25 September 2021 RIGHTER AND CARMICHAEL

104° 35' 104° 25'

Rio Atenguillo

20° 35' - Cv/

Arroyo el Platanar ' Dam

Arroyo la Canoa

Figure 4. Map of the Aten- guillo River and paleolake La Laja. The approximate location of the lava dam is indicated, as well as the location of the lake it 20P 30' - produced. Pillow lavas are present along the south edge of the shield volcano, where the dam is shown on the map (they are KM1 Lake La Laja never found on the north or (1400m contour) west edges). Lake sediment lo- La Laja shield calities, which overlie the shield volcano flows near the volcano, are shown here by solid dots. The lake deposit Atenguillo River was deflected locality to the east from its original di- rect course to the north. Town names are as follows: LL, La Laja; C, Cuyutlan; SP, San Pablo; and A, Atenguillo. 20° 25' -

5 km Rio Atenguillo

20P 20'

Second, if the lake that formed upon eruption of La Laja had a width x depth x velocity; Leopold and others, 1964; w=10m, d=lm, v = shoreline at the 1,400-m contour (Fig. 4), then it had an area of 75 km2, 1 m/s) indicates that a lake of this size could form in 40 years. A second depth of < 100 m, and therefore a maximum volume of approximately 7.5 estimate, which is based on annual precipitation rates (1 m/yr; Comision km3. One can estimate how quickly a lake of this size could form in two de Estudios del Territorio Nacional, 1981) in the Atenguillo drainage ways. Calculation of the discharge rate (Q) of the Atenguillo River (Q = basin (400 km2) and the assumption that all rainfall returns to the river

1594 Geological Society of America Bulletin, December 1992

system, indicates that such a lake could fill in 20 years. Although both of these estimates rely on climatic variables, there was an interglaciation at 0.65 Ma, as there is today (Shackleton and Opdyke, 1976), and these estimates should not change by an order of magnitude. If the lava dam were built in stages (> 100 yr), then one might expect to see lake sediments interbedded with the lava flows and pillows; this is not observed. Rather, the thick (50 m), continuous sequence of pillow lavas is consistent with a short duration event. It seems that La Laja could have formed in 10-100 yr, which, coupled with the eruptive volume of approximately 10 km3, would indicate an output rate of 0.1 to 1 km3/yr (Fig. 5). Comparison of this output rate to other eruptions in Mexico reveals its large relative magnitude. Output rates at stratovolcanoes such as Co- lima and Ceboruco are approximately 5 x 10 3 to 7 x 10 3 km3/yr, as are those at the monogenetic cinder cone Paricutin (Luhr and Carmichael, 1990; Hasenaka and Carmichael, 1985). The output rates at the rhyolite dome complex, Sierra la Primavera, are even lower (Mahood, 1980). Output rates at other central volcanoes from continental- and oceanic-arc settings, such as Arenal (Costa Rica), Fuji (Japan), and Fuego (Guate- mala) (Crisp, 1984), are of the same magnitude as the Mexican central Figure 5. Volume of eruption versus duration estimated for La volcanoes, although Kluychevskoy (Kamchatka) is somewhat higher, at a Laja. Diagonal lines are lines of constant eruption rates from 10~4 to rate of 5 x 10 2 km3/yr. The output rate at La Laja is closer in magnitude 102 km3/yr. La Laja plots as a rectangle, due to the uncertainty in to eruptions such as those occurring at Hawaii (Mauna Loa and Kilauea; calculating a duration of eruption (see text for discussion). Shown for Swanson, 1972; Crisp, 1984) and lower than those in Iceland (Laki; reference are Mexican calc-alkaline volcanic centers (triangles) Pari- Thorarinsson, 1969) (Fig. 5). This large-magnitude magma output rate cutin (P), Colima (Co), Ceboruco (Ce), Sierra la Primavera (SLP— seems unusual for the MVB; however, it should be noted that basaltic Mahood, 1980), and the entire MGVF (Hasenaka and Carmichael, shield volcanoes are present in central Mexico (Sierra Chichinautzin; Mar- 1985); island and continental arc volcanic centers (circles) Kluychev- tin del Pozzo, 1982) and other arcs such as the Cascades (Lassen Volcanic skoi (Ky), Fuji (Fj), Arenal (A), and del Fuego (Fg) (Crisp, 1984); and Area; Williams, 1932), but very little output rate information is available oceanic island basalt volcanoes (squares) Laki, Iceland (Thorarinsson, from these areas. 1969), Mauna Loa (ML), and Kilauea (Ki) (Crisp, 1984). Note the large eruption rate of La Laja relative to other calc-alkaline volcanoes MINERAL CHEMISTRY in Mexico.

Mineral compositions were determined on a wavelength dispersive ARL-SEMQ electron microprobe, with eight spectrometers. Microprobe analyses for olivine, augite, plagioclase, glass, and oxides (Tables 6 through 12) can be obtained from the GSA Data Repository1. Operating condi- for all three volcanoes. More Fo-rich olivines have higher NiO concentrations were as follows: accelerating voltage of 15 keV, sample current of 30 tions (as much as 0.24% in phenocrysts); more Fa-rich olivines have higher nA, and 10 s counting times. X-ray intensities were corrected for beam CaO concentrations (as much as 0.34% in groundmass). drift, detector dead-time losses, standard drift, peak interferences, and background. Standards used in these determinations include a wide range Plagioclase of natural (orthoclase, albite, diopside, chromite, barite, apatite) and syn- thetic (fayalite, Ti02, MgO, MnO) materials. Plagioclase microphenocrysts are ubiquitous in these volcanoes. In the La Laja summit flows, phenocrysts (AnggAbsoOr! cores to

Olivine An39Ab530r7 rims), and normally zoned microphenocrysts (An54 to

An|6) are both present. The most Or-rich plagioclase forms rims of the Olivine phenocryst cores in the La Laja shield flows have the compo- summit flow microphenocrysts (Or 12; Fig. 6). There are no plagioclase

sition Fo77, and rims are more FeO rich, Fo65_66 (Fig. 6). The olivine phenocrysts in the shield flows. The La Laja shield flow microphenocrysts

phenocrysts in La Laja summit flows are more FeO rich, with Fo62 cores are normally zoned, ranging from An57 cores to An32 rims. In all micro- and F058 rims. Olivine fragments and crystals in the ash/lapilli tuff at the phenocrysts, SrO varies from 0.35 wt% (core) to 0.12 wt% (rim). FeO base of La Laja are similar in composition to those in the flows, ranging ranges from 0.79 wt% in plagioclase cores to 0.99 wt% in the rims. BaO from F077 cores to Fo^s rims (Fig. 6). Groundmass olivine is consistently contents are relatively insignificant, at less than 0.06 wt%. more FeO-rich than the phenocryst olivine. In the shield flows, ground-

mass olivine ranges from Fo65 to FO6Q, whereas in the summit flows, Augite groundmass olivine ranges from F055 to F047 (Fig- 6). Olivine phenocrysts from El Vigia and Tio Cleto are more magnesian, ranging from Fogi cores Augite is in the groundmass in several, but not all, of the La Laja to F072 rims. Groundmass olivines define a range similar to those in La flows and appears as a phenocryst in the summit flows (KR-142). Laja (FO63 to FOGG). Minor oxides, NiO and CaO, show systematic trends Representative microprobe analyses of groundmass and phenocryst augite are plotted in Figure 6. Zoning from core to rim in the summit-flow phenocrysts is subtle in terms of MgO, FeO, and CaO, but is more 'Tables 6 through 12 may be secured free of charge by requesting Supplemen- significant in terms of Ti02 (1.14 to 1.56 wt%) and A1203 (3.45 to tary Data 9235 from the GSA Documents Secretary. 4.77 wt%).

Geological Society of America Bulletin, December 1992 1593

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/104/12/1592/3381340/i0016-7606-104-12-1592.pdf by guest on 25 September 2021 RIGHTER AND CARMICHAEL

nents of 0.363 and 0.557, respectively. There are no coexisting rhombohedral oxides in any of the La Laja samples. Spinel inclusions in olivine phenocrysts from Tio Cleto and El Vigia

contain more Cr203 and A1203 than any of the La Laja inclusions and

thus have lower Fe2Ti04 and Fe304 concentrations. Considering all three

volcanoes, it is clear that the highest Cr203 and A1203 inclusions are in the most magnesian olivines. Tio Cleto lavas contain spinel grains in the groundmass, whereas the El Vigia lavas contain both spinel and rhombohedral oxides in the groundmass.

WHOLE-ROCK COMPOSITIONS

Major-, minor-, and trace-element analyses were obtained by wet chemical analysis (Table 3), and by X-ray fluorescence (XRF) techniques An (Tables 4 and 5), using a SpecTrace 440 X-ray Spectrometer. Samples for XRF major-element analysis were prepared by mixing 0.500 g of sample and 3.500 g Li tetraborate flux, and then fusing the mixture into 2-mm- thick glass disks. Samples for trace-element analysis were prepared by mixing 3 g of powdered sample with five drops of polyvinyl alcohol (PVA) solution; this mixture was then pressed into a pellet with an outside casing of boric acid. Standards used in these analyses were a well-analyzed set of natural lavas, including several U.S. Geological Survey (USGS) standards. One additional sample, LV-167, was analyzed by neutron activation analysis for trace elements (Table 5). The La Laja shield lava contains sparse phenocrysts of olivine, ande-

sine microphenocrysts, and normative andesine (An37_39); it has a differ-

entiation index (D.I.) between 30 and 45 (Table 3) and K20 < (Na20 - 2). These characteristics indicate that this lava is hawaiite (Muir and Tilley, 1961; MacDonald, 1968; Thompson and others, 1972; LeBas and others, 1986; Nelson and Carmichael, 1984). The summit lava at La Laja contains andesine-oligoclase microphenocrysts (most sodic is An^), has a D.I. > 45, and is therefore mugearite. The lava of La Laja defines a narrow compositional range with 51.8 to 53.6 wt% Si02 and 3.8 to 5.5 wt% MgO. Figure 6. Plagioclase, augite, and olivine compositions from La Laja (circles), Tio Cleto (triangles), and El Vigia (squares). Solid sym- TABLE 3. WHOLE-ROCK WET CHEMICAL ANALYSES AND CIPW NORMS bols are phenocryst analyses; open symbols are groundmass analyses.

There are no plagioclase or augite phenocrysts in the La Laja shield LV-167 102 142 109 260 flows. Olivine is plotted along the base of the pyroxene quadrilateral. La Laja La Laja La Laja Tio Cleto El Vigia La Laja groundmass olivine is plotted outside of the quadrilateral to Si02 52.72 52.35 53.32 49.15 54.47

show clearly the compositional range in both phenocryst and Ti02 2.09 2.06 2.26 1.98 1.46 groundmass olivines. AI2O3 15.91 16.05 16.68 15.95 17.01 f=2°3 2.21 1.72 1.91 3.42 2.29 FeO 7.44 7.86 7.20 6.60 5.58 MnO 0.17 0.16 0.16 0.16 0.14 MgO 5.02 5.17 3.72 6.61 4.69 CaO 7.24 7.32 7.64 8.41 7.60

Na20* 3.84 3.93 4.23 3.59 3.84

Oxides K20» 1.77 1.73 1.88 1.15 1.38 P2°5 0.49 0.55 0.59 0.50 0.48 H O- 0.1? 0.09 0.12 0.89 0.15 Spinel octahedra are distinct grains within the groundmass of all 2 Total 99.09 98.99 99.71 98.41 99.09 flows, as well as inclusions within olivine and augite phenocrysts. Oxide

inclusions from the entire suite of La Laja lavas cover a large composi- CIPWt Norm (wt%) tional range. The cores of these inclusions are (>203, AI2O3, and MgO QZ 0.66 0.35 4.15 rich, becoming more Ti02 and FeO rich in the rims. The compositional Or 10.46 10.22 11.11 6.80 8.15 Ab 32.49 33.25 35.79 30.38 32.49 range is defined by sample 102 on the high Cr203-Al203-Mg0 end and An 20.95 21.04 20.97 24.01 25.10 the summit flow, 142, on the high Ti02, FeO end. The magnetite compo- Di 9.62 9.58 10.77 11.61 7.68 Hy 16.32 14.50 12.16 8.77 14.16 nent increases slightly from core to rim in these inclusions; NiO and CaO Ol 2.62 6.07 Mt 3.20 2.49 2.77 4.96 3.32 vary sympathetically with MgO. The groundmass oxides are ulvospinel- Ilm 3.97 3.91 4.29 3.76 2.77 titanomagnetite solid solutions, containing small amounts of Cr203 (<2.7 Ap 1.16 1.30 1.40 1.18 1.14 D.I. 43.61 43.48 47.26 37.17 44.80 wt%), A1203 (<3.2 wt%), and MgO (<3.5 wt%). The sum of the calcu-

lated Fe2Ti04 and Fe304 components cluster at approximately 0.90 for Note: analysis were I.S.E. Carmichael and J. Hampel. most of the La Laja flows. For the summit flows these spinels are more "Alkalies were analyzed by flame photometry. tciPW normative minerals were calculated as defined by Cross and others (1902). FeO rich and Q2O3, AI2O3 poor and have Fe304 and Fe2Ti04 compo-

1594 Geological Society of America Bulletin, December 1992

FeO* and Ti02 vary from 9.00 to 9.63 and 2.02 to 2.21 wt% (Fig. 7). and Roeder (1974). Since all of these lavas contain less than 5% olivine

KzO and P2O5 covary with these oxides, ranging from 1.67 to 2.02 and phenocrysts only, core olivine compositions can be taken to represent the 0.55 to 0.67 wt%, respectively. This lava plots just above the alkaline- olivine in equilibrium with the bulk liquid (whole-rock) composition.

subalkaline line of MacDonald and Katsura (1964) on an alkali vs. Si02 Such calculations yield temperatures of between 1,035 °C and 1,160 °C diagram (Fig. 7). Samples from the summit of La Laja define the high (±40 °C) for La Laja, with the highest temperatures for the least-evolved

Si02, low MgO end. The ash and lapilli samples contain slightly less FeO samples: #102 (1,145 °C), #161 (1,156 °C), #150 (1,158 °C). The lowest

and Ti02, and more Si02, than the subaerial lava, whereas the pillow and temperatures are associated with the most-evolved summit samples: #142 subaerial lavas are chemically indistinguishable. (1,035 °C). Calculated temperatures for Tio Cleto are higher (1,190 °C for Ni and Cr abundances vary from <50 to 70 ppm and <50 to 110 sample #109); from El Vigia, samples #259 and #260 yield temperatures ppm, respectively, and these ranges are defined on the upper and lower of 1,175 °C and 1,105 °C, respectively. ends by samples 142 (summit) and 102 (Fig. 8). Sr, Ba, Nb, Rb, and Y all There are no rhombohedral oxides in the La Laja lavas, which pro- exhibit a very narrow concentration range (Table 5). Rare-earth-element (REE) concentrations for LV-167 are normalized in Figure 9 against ordinary chondrite values of Nakamura (1974). The pattern in Figure 9 illustrates light-REE enrichment, relative to heavy-REE enrichment, with La/Lu = 93, Ce/Yb = 26.8, and 2REE = 142.45 ppm. The REE analysis of sample LV-167, is plotted along with REE patterns for two Colima andesites (Luhr and Carmichael, 1980), and a minette from the southern Atenguillo graben (Wallace and Carmichael, 1989) (Fig. 9). La Laja basalts are light-REE enriched relative to the andesites, but not as enriched as the minette. Three additional samples are plotted in Figure 9: two trachybasalts from the Santiago River canyon (Wopat, 1990), and an alkali-olivine basalt from a cinder cone near Volcán Sanganguey (Nelson and Carmichael, 1984). All three of these patterns are nearly identical to that of LV-167. The lava of Tio Cleto contains phenocrysts of olivine and labradorite microphenocrysts, plots within the alkaline field of MacDonald and Kat- sura (1964), and thus is alkali-olivine basalt (LeBas and others, 1986; Nelson and Carmichael, 1984). The Tio Cleto alkali-olivine basalt is more 1 1 1 1 silica poor and MgO rich and also defines a narrow compositional range • b) with 49.2 to 49.8 wt% Si02 and 5.6 to 7.5 wt% MgO (Fig. 7). Cr and Ni abundances are higher than those of La Laja, ranging from 100 to 170, and 50 to 110 ppm, respectively. All other analyzed trace elements, Rb, Sr, Y, Zr, Nb, Ba, Ce, and Nd are lower in abundance than in La Laja lavas •

(Fig. 8). - The El Vigia lava plots in the subalkaline field of MacDonald and « m Katsura (1964), contains olivine and plagioclase phenocrysts and O • IH co labradorite-andesine microphenocrysts, and is basaltic andesite. El Vigia H • basaltic andesite has a narrow compositional range which is distinct from that of La Laja or Tio Cleto lavas (Figs. 7 and 8). El Vigia lava contains

more Si02 (52.9 to 55.5 wt%) and A1203 (16.9 to 17.5) and less Ti02 Calc-alkaline (1.33 to 1.52) and FeO* (7.17 to 8.65). Cr abundances are similar to those 1 1 L 1 1 of Tio Cleto, but Ni is lower, ranging from 35 to 80 ppm. Sr is decidedly higher than the other volcanoes (750 to 1,100 ppm). Nb is much lower than the other two volcanoes (10 to 14 ppm).

Temperature and Oxygen Fugacity

The liquidus temperatures of these lavas can be estimated by utilizing the olivine-liquid thermometer developed by Roeder and Emslie (1970)

Figure 7. Major-element chemical variation diagrams for La Laja (circles), El Vigia (squares), and Tio Cleto (triangles). Small dots represent alkali basalt, hawaiite, and mugearite from cinder cones near Volcán Sanganguey (Nelson and Carmichael, 1984); calc-alkaline lavas are from the Mascota valley (Lange and Carmichael, 1990). Note the high alkali, FeO*, and Ti02 values of the Atenguillo lavas relative 48 50 52 54 to the calc-alkaline lavas. Solid line in alkalies vs. Si02 diagram is alkaline-subalkaline lava division of MacDonald and Katsura (1964). Si02 (wt%)

Geological Society of America Bulletin, December 1992 1593

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/104/12/1592/3381340/i0016-7606-104-12-1592.pdf by guest on 25 September 2021 RIGHTER AND CARMICHAEL

TABLE 4. MAJOR-ELEMENT ANALYSES (XRF) OF LAVAS FROM LA LAJA, TIO CLETO, EL VIGIA, AND ASSOCIATED VOLCANOES (wt%)

s¡o2 T¡O2 AI2O3 Fe203 FeO MnO MgO CaO Na20 K2O r2o5 LOI Total

La Laja

12" 53.3 2.15 16.7 8.79 0.15 3.7 7.38 4.05 1.85 0.67 98.74 101* 53.0 1.95 16.0 4.70 4.62 0.15 4.6 6.42 3.20 1.55 0.57 4.00 100.76 150* 52.4 2.04 15.7 2.12 7.53 0.15 5.5 7.00 3.68 1.78 0.59 0.64 99.13 151" 52.4 2.06 15.6 1.97 7.42 0.15 5.2 7.04 3.87 1.77 0.57 0.53 98.58 152* 52.4 2.05 15.6 2.38 7.45 0.15 5.4 6.91 3.72 1.75 0.61 0.86 99.28 156 52.6 2.06 16.2 9.61 0.17 5.3 7.28 4.3 1.61 0.63 0.22 99.98 161* 53.6 2.05 15.9 2.19 7.65 0.16 5.4 7.09 3.79 1.87 0.57 0.17 100.44 169* 51.8 2.13 15.8 1.93 7.89 0.17 5.0 7.26 3.80 1.77 0.62 0.56 98.73

Tio Cleto

247* 49.6 2.04 16.2 9.79 0.16 5.6 8.20 3.56 1.24 0.53 2.27 99.19 248 49.2 1.89 15.9 10.04 0.16 7.5 8.07 3.9 1.09 0.44 1.53 99.72 268* 49.8 1.97 16.4 10.05 0.18 6.6 8.50 3.50 1.12 0.47 1.89 100.48 269 49.3 1.93 16.3 10.04 0.17 6.9 8.46 3.6 1.11 0.47 2.39 100.67

El Vigia

22 55.5 1.33 17.5 7.17 0.12 4.3 7.23 4.0 1.44 0.43 0.85 99.87 112 53.3 1.52 17.3 8.34 0.14 5.1 7.91 4.9 1.21 0.42 100.14 113 52.9 1.52 16.9 8.49 0.14 5.1 7.70 3.6 1.23 0.38 0.67 98.55 114 54.6 1.38 17.4 7.95 0.21 5.1 7.42 4.2 1.35 0.44 100.02 255* 53.4 1.52 17.0 8.65 0.15 5.3 7.77 3.78 1.22 0.43 0.39 99.68 259* 53.2 1.52 17.1 8.63 0.14 5.8 7.69 3.77 1.23 0.42 99.44

El Rosario

243 53.4 1.29 16.4 7.46 0.14 6.2 8.39 3.1 1.43 0.40 98.29 MAS-326* 53.4 1.40 16.6 1.06 5.85 0.16 5.7 8.48 3.55 1.31 0.45 0.89 98.84

Amajaquillo

288 55.2 1.12 17.9 7.18 0.13 3.7 6.92 3.8 1.52 0.45 97.91 MAS-324* 56.2 1.10 17.8 1.56 4.99 0.14 3.5 6.76 4.41 1.32 0.43 0.52 98.74

Mesa Llano Grande

122* 51.9 1.86 16.0 8.86 0.14 5.9 8.96 2.99 1.30 0.34 98.23 MAS-428 52.5 2.02 16.0 9.37 0.19 4.8 7.80 3.8 1.81 0.51 98.83

Amallan de Canas

MAS-434* 51.9 1.73 16.9 8.84 0.15 5.1 8.78 4.32 1.44 0.46 99.65

La Cienega

48* 57.4 1.13 16.5 6.83 0.14 3.9 6.00 3.96 2.01 0.47 0.46 98.83 222 59.9 0.79 18.2 5.60 0.07 2.8 6.03 3.4 1.47 0.21 99.39

Agua Zarca plateau

110* 59.8 0.99 16.1 5.11 0.08 3.8 6.02 5.06 2.70 0.45 0.59 100.65 111 57.9 0.68 16.6 4.67 0.08 4.6 5.95 4.2 2.06 0.23 97.07

Note: FeO determined volumetrically for La Laja samples; total iron as FeO for other samples. Uncertainty in the XRF major-element analyses are as follows, based on 19 replicate analyses of LV-167: Si02(0.6%), Ti02(1.4%), AUO-, (0.9%), FeO (1.9%), MnO (2.6«), MgO (4.5%), CaO (2.7%), Na20 (14.7%), K20 (2.4%), P2Os (4.7%). "Alkalies by flame photometry; analysts were J. Hampel and K. Righter.

hibits the use of calibrated two-oxide oxygen barometers. Experimentally hypabyssal peridotite, which have values of ANNO = -2 to -3 (Christie determined relations between oxygen fugacity, ferric-ferrous ratio, bulk and others, 1986; Bryndzia and others, 1989). These oxidized values are composition, and temperature have been calibrated by Kress and Carmi- consistent with the compositions of the spinel included in olivine pheno-

chael (1991). Utilizing measured values of the ferric-ferrous ratio, bulk crysts, which contain a significant Fe304 component and very little Cr203 composition (Tables 3 and 4), and an arbitrary temperature of 1,200 °C, and AI2O3 relative to such spinels in MORBs. the fC>2 of seven lavas from La Laja, one from Tio Cleto, and one from El Vigia has been calculated relative to the nickel-nickel oxide buffer DISCUSSION (ANNO). Relative f02 is useful in that it is independent of temperature, because the ferric-ferrous ratio of a liquid remains nearly constant as it is Petrogenesis equilibrated at various temperatures along an oxygen buffer curve (Kress and Carmichael, 1991). The La Laja values range from ANNO = -0.4 to All of the La Laja hawaiites have low Ni, Cr, and MgO concentra- +0.4 (Fig. 10), the Tio Cleto lava has ANNO = 1.3, and the El Vigia lava tions relative to primitive lavas in the western MVB (Luhr and others, has ANNO = 1.0. The values for the El Vigia lava agree well with f02 1989), which suggests that they are derived from a more primitive parent. calculations based on coexisting cubic and rhombohedral groundmass A likely candidate for such a parent is the older alkali-olivine basalt found oxide compositions, which yield log f02 = -13.1 (ANNO = ~0.7) (Ghi- at Tio Cleto (Fig. 2), which contains up to 7.5 wt% MgO, 167 ppm Cr, orso and Carmichael, 1981). La Laja lavas are more reduced than minettes and 111 ppm Ni. Attempts to produce a La Laja shield hawaiite (#102) from the Atenguillo and Colima grabens (ANNO = +4 to +6; Carmichael, from a Tio Cleto alkali-olivine basalt (#109) solely by means of olivine 1991) and the Colima and Ceboruco andesites (ANNO = +2 to +3; Carmi- and oxide fractionation yield poor results (sum of the squares of the chael, 1991), but oxidized relative to mid-ocean-ridge basalt glass and residuals [2r2] = 5-10) by least-squares mixing models (XLFRAC,

1594 Geological Society of America Bulletin, December 1992

TABLE 5. TRACE-ELEMENT ANALYSES (XRF) OF LAVAS FROM LA LAJA, TIO CLETO, EL VIGIA, AND ASSOCIATED VOLCANOES (VALUES IN ppm)

V Cr Ni Cu Zn Rb Sr Y Zr Nb Ba La Ce

La Laja

12 257 31 101 21 727 38 294 27 712 36 79 101 263 85 41 27 96 27 737 32 255 21 900 37 83 102 251 107 68 45 101 20 723 33 273 24 756 38 83 142 232 20 96 22 742 36 304 28 702 38 77 150 256 102 55 28 104 19 789 33 273 24 776 41 86 151 268 101 57 31 106 20 803 33 280 24 798 39 83 152 267 109 67 31 107 19 789 32 275 26 769 37 86 156 262 93 58 36 104 19 711 31 263 23 638 32 71 161 254 97 54 32 96 21 769 33 275 25 778 39 78 169 269 94 50 27 108 22 698 33 279 25 727 37 70

Tio Cleto

109 248 159 106 35 90 14 736 31 188 14 598 32 71 247 253 99 52 37 88 16 684 30 178 20 542 30 63 248 234 167 111 33 90 13 720 27 160 16 507 29 62 268 243 159 93 39 86 13 577 29 165 18 474 20 56 269 240 161 90 35 86 14 584 28 161 17 458 21 54

El Vigia

22 176 81 36 22 80 19 1,072 96 191 9 637 77 94 112 189 117 54 33 90 16 771 162 181 14 516 59 76 113 205 124 44 35 88 16 775 83 186 14 510 28 62 114 191 140 65 32 86 16 823 136 195 11 676 32 76 255 197 158 77 27 90 14 743 34 179 14 524 31 57 259 204 158 72 31 89 18 738 27 181 13 500 26 55 260 181 117 54 12 89 20 867 34 194 13 570 31 65

El Rosario

243 171 174 88 42 77 18 595 28 203 17 586 24 60 MAS-326 137 136 91 49 82 18 661 27 218 20 637 18 55

Amajaquillo

288 136 72 20 26 94 14 956 24 136 5 809 23 55 MAS-324 100 18 29 93 11 889 25 135 8 924 22 50

Mesa Llano Grande

122 227 140 86 29 88 20 606 27 173 17 569 20 64 MAS-428 241 111 82 35 82 29 564 30 198 19 542 19 58

Amallan de Canas

MAS-434 200 79 44 40 79 19 606 24 192 19 631 24 60

La Ciénega

48 147 81 24 21 86 28 720 114 260 11 991 60 87 222 125 94 26 23 67 26 653 23 128 6 952 20 46

Agua Zarca plateau

110 116 109 72 33 83 29 2,094 15 237 5 1,197 51 98 111 102 156 96 39 66 30 1,258 17 157 4 899 33 56

Neutron activation analysis: LV-167 (values in ppm)

Ba Rb Sr Ni Cr Sc Zn U Th Hf La Ce Nd Sm Eu Tb Yb Lu 690 20 800 50 96 22.2 110 0.8 2.2 6.2 33.5 67 30 6.13 2.16 0.8 2.50 0.36

Hole, uncertainty in XRF trace-element analyses is as follows, based on duplicate analyses of approximately 50 samples. V (2.8%), Cr (4.3%), Ni (6.4%), Cu (8.1%), Zn (3.4%), Pb (9.4%), Rb (5.4%), Sr (0.55%), Y (4.5%), Zr (2.6%), Nb (11.3%), Ba (0.57%), La (8.6%), and Ce (3.0%).

Stormer and Nicholls, 1978), mostly due to poor CaO and AI2O3 fits. tion of an 8-10 kbar olivine-augite-plagioclase cotectic, the hawaiite (La

Fractionation of 4.2% Fo77 (#102 cores), 8% augite (#142 cores), 15.5% Laja) contains only olivine, and the basaltic andesite (El Vigia) and alkali- plagioclase (#102 microphenocryst), and 3.2% spinel (#102 inclusion) from olivine basalt (Tio Cleto) contain olivine and plagioclase phenocrysts. If a Tio Cleto lava (#109), however, yields a close match to La Laja sample fractionation of olivine, augite, and plagioclase occurred, as suggested by #102 (Sr2 = 0.1). Trace-element calculations (for V, Cr, Ni, Zr, Nb, Ba, Sr, our fractionation calculations, then complete separation of augite (and Rb, La, and Ce) are consistent with the fractionation of this phase assem- plagioclase in the case of La Laja) from the parent magma must have blage as well (using partition coefficients tabulated by Hanson [1980], Gill occurred. This cryptic clinopyroxene and plagioclase fractionation effect is [1981], and Henderson [1982] and Rayleigh fractionation [Rayleigh, not an uncommon one; it is seen in both oceanic and continental examples, 1896]). In addition, it is possible to derive La Laja mugearite (142) from such as mid-ocean-ridge tholeiite (Bryan and others, 1976; Shibata and hawaiite (102) by means of olivine fractionation alone (Sr2 <0.1). others, 1979), continental-flood basalt (Thompson, 1972), and basalt and Consideration of the Di-Oliv-Qtz projection of Sack and others andesite from the Mascota valley (Lange and Carmichael, 1990) and (1987) indicates that the La Laja mugearite, which contains augite, in Volcán Jorullo, central Mexico (Luhr and Carmichael, 1985). Evidence addition to olivine and plagioclase phenocrysts, falls along a low-pressure that such fractionation occurs at depth may be found at Maar Hoya cotectic (Fig. 11). Although the other Atenguillo lavas plot near the loca- Alverez, in the Valle de Santiago Maar Field, Guanajuato, Mexico

Geological Society of America Bulletin, December 1992 1593

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/104/12/1592/3381340/i0016-7606-104-12-1592.pdf by guest on 25 September 2021 RIGHTER AND CARMICHAEL

Figure 8. Trace-element variation diagrams for La Laja, El Vigia, and Tio Cleto (symbols for these centers as in Fig. 7). Hawaiian samples are from the BVSP suite (BVSP, 1981). The calc-alkaline lavas are from the Atenguillo graben (La Cienega and Agua Zarca; this study) and Mascota valley (Lange and Carmichael, 1990). The s subduction-related lavas in c include these calc-alkaline lavas as well o. as alkaline lavas from Wallace and Carmichael (1989), Allan and o. Carmichael (1984), and Luhr and Carmichael (1981). The small dots £ are as in Figure 7. The La Laja and Tio Cleto lavas do not exhibit the high LIL/HFSE ratios typical of subduction-related lavas and specifi- cally have lower Sr/Zr, La/Nb, and Ba/TiOj ratios than calc-alkaline lavas from the MVB.

400

Source Characteristics and Tectonic Setting

Calc-alkaline b) Calc-alkaline lavas (those that are subalkaline and lacking iron enrichment) are present throughout the MVB, forming large volcanic centers such as Volcán Colima (Luhr and Carmichael, 1980) and Volcán Cebo- ruco (Nelson, 1980), and also small, local centers within the Jalisco Block a (Lange and Carmichael, 1990; this study, Fig. 2). The major-element OH composition of lavas from La Laja, Tio Cleto, and El Vigia is distinct in 1 3 three ways from these calc-alkaline lavas. First, FeO and TÍO2 are more CO J abundant than in the calc-alkaline suites (Fig. 7). Second, these lavas are more alkaline than the calc-alkaline suites (except for El Vigia), in that they plot above the division line of MacDonald and Katsura (1964) (Fig. 7). Third, these lavas have generally lower AI2O3 content than lavas from the calc-alkaline suite. 20 30 40 50 60 A nearly universal characteristic of subduction-related lavas is their enrichment of alkali (K, Rb) and alkaline-earth (AE) elements (Ba, Sr) Nb (ppm) relative to high-field-strength (HFS) elements (Ti, Nb, Zr) and LREE (Perfit and others, 1980; Gill, 1981; Arculus and Johnson, 1981; Hickey 10000 c) S ubduction-related 1000 F- 9 La Laja D 1000 • Colima Andesite A Minette 100 r IN •c O loo -a G O J= O PQ Hawaii ^ 10 r W 10 06 4 6 8 10

MgO (wt.%) J L J I I I I L J I I I L La Ce Nd Sm Eu Tb Yb Lu

(Murphy, 1986; Righter and Carmichael, 1991) and at cinder cones Figure 9. Normalized rare-earth-element pattern for La Laja around Sanganguey Volcano (Giosa and Nelson, 1985; Verma and Nel- (LV-167 solid circles), plotted together with two Colima andesite son, 1989), both of which contain cumulate gabbroic xenoliths with plagi- (Luhr and Carmichael, 1980), a minette from the Los Volcanes area oclase, aluminous augite, olivine, and magnetite in approximately the (Wallace and Carmichael, 1989), two basalts from the Santiago Can- proportions required of the fractionation calculations presented here. In yon (Wopat, 1990), and a basalt from near Volcán Sanganguey (Nel- summary, La Laja parent magmas may have undergone high-pressure son and Carmichael, 1984) (last three shown as solid lines). REE fractionation of olivine, augite, and plagioclase, which was later followed abundances are normalized to chondritic values given by Nakamura by lower-pressure olivine and plagioclase fractionation. (1974). Analysis of LV-167 is presented in Table 5.

1594 Geological Society of America Bulletin, December 1992

the La Laja and Tio Cleto lavas are similar in composition to oceanic- • Mascota island basalts, and that slab-derived material played a minor role in the 4- genesis of these lavas. Moreover, the high Rb/Cs ratio (>60; Table 5) of co B Atenguillo La Laja sample LV-167 is inconsistent with involvement of subducted 0) 03 >> sediments (Gill 1981). The El Vigia basaltic-andesite is subalkaline and p—H 3- has trace-element ratios that overlap both those of the calc-alkaline and the ca tí oceanic lavas (Figs. 7 and 8), suggesting greater involvement of slab- ca derived material. Lavas with similarities to oceanic-island basalt (and compositionally o £ distinct from tyical calc-alkaline lavas in the western Mexican Volcanic Belt [WMVB]) have also erupted in the Rio Ameca valley (Nieto- Obregon and others, 1989; this study), near Volcán Tequila (Wopat, 1990), and north of Guadalajara (Wallace and others, 1992), covering a Luk large area in the WMVB and having a collective volume of over 100 km3. -1.0 0.0 1.0 2.0 3.0 The coexistence of calc-alkaline lavas and these mildly alkaline basalts A NNO lava implies that two distinct mantle sources gave rise to these different types. This situation has been documented at several other localities in the Figure 10. Histograms of ANNO values for hawaiite from the WMVB where alkali-olivine basalt and hawaiite have erupted in close Atenguillo graben (La Laja), and basaltic-andesite from the Mascota association with the calc-alkaline lavas of Volcán Sanganguey (Nelson and Volcanic Field (Lange and Carmichael, 1990). Note that ANNO Carmichael, 1984) and Volcán Las Navajas (Nelson and Livieres, 1986). values for the oceanic-island-type basalts are more reducing than Sr and Nd isotopic and trace-element data from these northwest MVB those for the calc-alkaline lavas. See text for discussion. volcanoes (Verma and Nelson, 1989) also support the existence of two distinct mantle sources. Reagan and Gill (1989) suggested that more reduced material from and others, 1986, Hildreth and Moorbath, 1988). One index of this en- the asthenosphere is the source of the oceanic-island-type basalt, and that

richment is the Ba/Ti02 ratio, which is plotted against MgO (Fig. 8). The oxidized mantle wedge is the source for calc-alkaline lavas, but they did Atenguillo lavas have Ba/Ti02 lower than the subduction-related lavas, not present data on oxygen fugacity to evaluate this hypothesis. The redox similar to that of the Hawaiian suite of lavas (Basaltic Volcanism Study state of the La Laja hawaiite is at the NNO buffer (Fig. 10). The hawaiite Project, 1981). La Laja and Tio Cleto lavas also have elevated Nb abun- is not primitive lava, and the discussion above indicates that it is the result dances (14-28 ppm) relative to the calc-alkaline lavas (<10 ppm). Low of extensive crystal fractionation. Fractionation of Fe2+-bearing phases Ba/Nb, Sr/Zr, Ba/La, La/Nb, and La/Zr ratios (Fig. 8) demonstrate that such as olivine and augite will tend to increase the Fe3+/Fe2+ of the liquid, so that the hawaiite parent liquid may have originally been more reduced, below the NNO buffer. These reducing values are in contrast to the more oxidized values (ANNO = +0.5 to +3.0; Fig. 10) from primitive basaltic

+Plagioclase

1 bar cotectic

Figure 11. Di-Ol-Sil projection of Sack and others (1987) showing 1 bar cotectic defined by the experi- ments of Walker and others (1979) and Grove and oth- Piotai = 2 kbar ers (1982), a schematic 2 kbar cotectic defined by Spulber and Rutherford (1983), and a 15 kbar cotectic taken from Stolper (1980). La Laja shield lavas are shown as solid circles; El Vigia lavas, as squares; and Tio Cleto lavas, as triangles. La Laja summit lavas 15kbar,dry »4 (open circles) lie along a low-pressure cotectic.

> ¿V

Olivine

Geological Society of America Bulletin, December 1992 1605

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/104/12/1592/3381340/i0016-7606-104-12-1592.pdf by guest on 25 September 2021 RIGHTER AND CARMICHAEL

andesite (Ni = 150 ppm; Cr = 280 ppm) from the Mascota valley. These Bloomer, S. H., Stern, R. J., Fisk, E., and Geschwind, C. H., 1989, Shoshonitic volcanism in the northern Mariana Arc 1: Mineralogic and major and trace element characteristics: Journal of Geophysical Research, v, 94, p. 4469-4496. two distinct redox states for the calc-alkaline and oceanic-island-type Bryan, W. B., Thompson, G., Frey, F. A., and Dickey, J. S., 1976, Inferred setting and differentiation in basalts from the Deep Sea Drilling Project: Journal of Geophysical Research, v. 81, p. 4285-4304. lavas, then, support Reagan and Gill's suggestion. Bryndzia, L. T., Wood, B. J., and Dick, H.J.B., 1989, The oxidation state of the Earth's suboceanic mantle from oxygen thermobarometry of abyssal spinel peridotites: Nature, v. 341, p. 526-527. The superposition of active rifting on subduction-zone tectonics pro- Carmichael, I.S.E., 1991, The redox state of basic and silicic magmas: A reflection of their source regions?: Contributions vides a complex setting, in both oceanic and continental environments. to Mineralogy and Petrology, v. 106, p. 129-141. Christie, D. M., Carmichael, I.S.E., and Langmuir, C. H., 1986, Oxidation state of mid-ocean ridge basalt glasses: Earth Such tectonic complexity is not confined to the Mexican Volcanic Belt and and Planetary Science Letters, v. 79, p. 397-411. Comision de Estudios del Territorio Nacional (CETENAL), 1981, Carta de Precipitación Total Anual: Mexico, Dirección is present in several arcs. Both calc-alkaline and oceanic-island-type basalt General de Geografía del Territorio Nacional, scale 1:1,000,000. erupted contemporaneously in the Cascades (Mt. St. Helens, Halliday and Crisp, J., 1984, Rates of magma emplacement and volcanic output: Journal of Volcanology and Geothermal Research, v. 20, p. 177-211. others, 1983; Mt. Adams and the Simcoe Volcanic Field, Leeman and Cross, W., Iddings, J. P., Pirsson, L. V., and Washington, H. S., 1902, A quantitative chemico-mineralogical classification and nomenclature of igneous rocks: Journal of Geology, v. 10, p. 555-690. others, 1990), in Costa Rica (Turrialba Volcano, Reagan and Gill, 1989), Dalrymple, G. B., and Lanphere, M. A., 1969, Potassium-argon dating: San Francisco, California, W.H. Freeman and Co., in the vicinity of Fiji (Gill and Whelan, 1989a, 1989b), in the Volcano and 250 p. DeMets, C., and Stein, S., 1990, Present day kinematics of the Rivera Plate and implications for tectonics in southwestern Mariana Arcs (Bloomer and others, 1989, and Lin and others, 1989), and Mexico: Journal of Geophysical Research, v. 95, p. 21931-21948. Drummond, K. J., compiler, 1981, Plate tectonic map of the circum-Pacific region: Northeast quadrant: Tulsa, Oklahoma, in the south-central Andes (Munoz and Stern, 1989). Many of these American Association of Petroleum Geology, scale 1:10,000,000. localities are associated with evolving tectonic conditions (contractile to Ghiorso, M. S., and Carmichael, I.S.E., 1981, A Fortran IV computer program for evaluating temperatures and oxygen fugacities from the compositions of coexisting iron-titanium oxides: Computers in Geosciences, v. 7, p. 123-129. extensional). Gill, J. B., 1981, Orogenic andesites and plate tectonics: Berlin, Germany, Springer-Verlag, 390 p. Gill, J., and Whelan, P., 1989a, Early rifting of an oceanic island arc (Fiji) produced shoshonitic to tholeiitic basalts: Calc-alkaline and oceanic-island-type lavas plot near the 8-10 kbar Journal of Geophysical Research, v. 94, p. 4561-4578. Gill, J., and Whelan, P., 1989b, Post-subduction oceanic island alkali basalts in Fiji: Journal of Geophysical Research, cotectic (Fig. 11), suggesting that these magmas resided at similar depths in v. 94, p. 4579-4588. the crust before eruption (30-40 km). Their spatial and temporal associa- Giosa, T. A., and Nelson, S. A., 1985, Gabbroic xenoliths in alkaline lavas in the region of Sanganguey volcano, Nayarit, Mexico: Geological Society of America Abstracts with Programs, v, 17, p. 593. tion is an indication of the heterogeneity in the sub-arc mantle, consisting Grove, T. L., Gerlach, D. C., and Sando, T. W., 1982, Origin of calc-alkaline series lavas at Medicine Lake Volcano by fractionation, assimilation and mixing: Contributions to Mineralogy and Petrology, v. 80, p. 160-182. of an H20- and incompatible element-rich mantle wedge in the volcanic Halliday, A. N„ Failick, A. E., Dickin, A. P., McKenzie, A. B., Stephens, W. E., and Hildreth, W., 1983, The isotopic and front (Luhr and others, 1989), as well as an oceanic-island mantle compo- chemical evolution of Mt. St. Helens: Earth and Planetary Science Letters, v. 63, p. 241-256. Hanson, G. N., 1980, Rare earth elements in petrogenetic studies of igneous systems: Annual Reviews of Earth and nent (Verma and Nelson, 1989; Nelson and Carmichael, 1984; this study). Planetary Science, v. 8, p. 371-406. Hasenaka, T., and Carmichael, I.S.E., 1985, The cinder cones of Michoacán-Guanajuato, central Mexico: Their age, The oceanic-island mantle component may be tapped in western Mexico volume and distribution and magma discharge rate: Journal of Volcanology and Geothermal Research, v. 25, due to the unusual plate dynamics associated with the migration of the p. 105-124. Hasenaka, T., and Carmichael, I.S.E., 1987, The cinder cones of Michoacán-Guanajuato, central Mexico: Petrology and East Pacific Rise (EPR) onto the Mexican mainland. The EPR may be chemistry: Journal of Petrology, v. 28, p. 241-269. Henderson, P., 1982, Inorganic geochemistry: London, England, Pergamon Press, 353 p. actively propagating northward into Mexico, following a series of Miocene Hickey, R. L., and Frey, F. A., 1986, Geochemical characteristics of boninite series volcanics: Implications for their source: to Pliocene propagations of the northern East Pacific Rise (Luhr and Geochimica et Cosmochimica Acta, v. 46, p. 2099-2115. Hildreth, W., and Moorbath, S., 1988, Crustal contributions to arc magmatism in the Andes of central Chile: Contribu- others, 1985). Alternatively, thermal resorption of, and the break tions to Mineralogy and Petrology, v. 98, p. 455-489. Johnson, C. A., and Harrison, C.G.A., 1989, Tectonics and volcanism in central Mexico: A Landsat thematic mapper (Rivera-Cocos boundary) in, the young Rivera slab (Nixon, 1982; DeMets perspective: Remote Sensing of the Environment, v. 28, p. 273-286. and Stein, 1990), may cause changes in the pattern of asthenospheric Kóhler, H„ Schaaf, P., Müller-Sohnius, D., Emmerman, R., Negendank, J.F.W., and Tobschall, H. J., 1988, Geochrono- logical and geochemical investigations on plutonic rocks from the complex of Puerto Vallarta, Sierra Madre del upwelling, resulting in the passive relocation of the EPR. Whether this Sur: Geofísica Internacional, v. 27, p. 519-542.

Kress, V. C., and Carmichael, I.S.E., 1991, The compressibility of silicate liquids containing Fe203 and the effect of process is passive or active, western Mexico is undergoing extension as a composition, temperature, oxygen fugacity and pressure on their redox states: Contributions to Mineralogy and result. Petrology, v. 108, p. 82-92. Lange, R. A., and Carmichael, I.S.E., 1990, Hydrous basaltic andesites associated with minette and related lavas in western Mexico: Journal of Petrology, v. 31, p. 1225-1259. Lange, R. A., and Carmichael, I.S.E., 1991, A potassic volcanic front in western Mexico: The lamprophyric and related ACKNOWLEDGMENTS lavas of San Sebastian: Geological Society of America Bulletin, v. 103, p. 928-940. LeBas, M. J., LeMaitre, R. W., Streckeisen, A., and Zanettin, B., 1986, A chemical classificaiton of volcanic rocks based on the total alkali-silica diagram: Journal of Petrology, v. 27, p. 745-750. This research is supported under the auspices of National Science Leeman, W. P., Smith, D. R., Hildreth, W., Palacz, Z., and Rogers, N„ 1990, Compositional diversity of late Cenozoic basalts in a transect across the southern Washington Cascades: Implications for subduction zone magmatism: Foundation Grant EAR-90-17135 to Carmichael. We gratefully acknowl- Journal of Geophysical Research, v. 95, p. 19561-19582. Leopold, L. B., Wolman, M. G., and Miller, J. P., 1964, Fluvial processes in geomorphology: San Francisco, California, edge the field assistance of R. Anderson, J. Buffington, G. Moore, G. Pool, W.H. Freeman and Co., 522 p. Lin, P.-N., Stern, R. J., and Bloomer, S. H., 1989, Shoshonitic volcanism in the northern Mariana Arc 2: Large ion K. Schneider, P. Wallace, and M. Welch and the logistical assistance of lithophile and rare earth element abundances: Evidence for the source of incompatible element enrichment in H. Houck. J. Donovan provided assistance with electron microprobe intraoceanic arcs: Journal of Geophysical Research, v. 94, p. 4497-4514. Luhr, J. F., and Carmichael, I.S.E., 1980, The Colima Volcanic Complex, Mexico: I. Post-caldera andesites from Volcán analysis, and J. Hampel, with flame photometry and XRF analysis. Colima: Contributions to Mineralogy and Petrology, v. 71, p. 343-372. Luhr, J. F., and Carmichael, I.S.E., 1981, The Colima Volcanic Complex, Mexico: II. Late-Quaternary cinder cones: T. Teague prepared thin sections and microprobe samples. K-Ar analyses Contributions to Mineralogy and Petrology, v. 76, p. 127-147. were performed by T. Becker of the Institute for Human Origins, Berkeley. Luhr, J. F., and Carmichael, I.S.E., 1985, Jorullo Volcano, Michoacán, Mexico (1759-1774): The earliest stages of fractionation in calc-alkaline magmas: Contributions to Mineralogy and Petrology, v. 90, p. 142-161. Notes of and discussions with T. Johnson, R. Lange, and especially Luhr, J. F., and Carmichael, I.S.E., 1990, Penological monitoring of cyclical eruptive activity at Volcán Colima, Mexico: P. Wallace were indispensable. The reviews of E. James, J. Pallister, and Journal of Volcanology and Geothermal Research, v. 42, p. 235-260. Luhr, J. F., Nelson, S. A., Allan, J. F., and Carmichael, I.S.E., 1985, Active rifting in southwestern Mexico: Manifestations M. Reagan greatly improved the manuscript. of an incipient eastward spreading ridge jump: Geology, v. 13, p. 54-57. Luhr, J. F., Allan, J. F., Carmichael, I.S.E., Nelson, S. A., and Hasenaka, T., 1989, Primitive calc-alkaline and alkaline rock types from the western Mexican Volcanic Belt: Journal of Geophysical Research, v. 94, p. 4515-4530. MacDonald, G. A., 1968, Composition and origin of Hawaiian lavas: Geological Society of America Memoir 116, REFERENCES CITED p. 477-522. MacDonald, G. A., and Katsura, T., 1964, Chemical compositions of Hawaiian lavas: Journal of Petrology, v. 5, Allan, J. F., 1986, Geology of the northern Colima and Zacoalco grabens, southwest Mexico: Late Cenozoic rifting in the p. 82-133. Mexican Volcanic Belt: Geological Society of America Bulletin, v. 97, p. 473-485. Mahood, G. A., 1980, Geological evolution of a Pleistocene rhyolitic center—Sierra la Primavera, Jalisco, Mexico: Allan, J. F., and Carmichael, I.S.E., 1984, Lamprophyric lavas in the Colima graben, SW Mexico: Contributions to Journal of Volcanology and Geothermal Research, v. 8, p. 199-230. Mineralogy and Petrology, v. 88, p. 203-216. Martin del Pozzo, A. L., 1982, Monogenetic vulcanism in the Sierra Chichinautzin, Mexico: Bulletin of Volcanology, v. 45, Allan, J. F„ Nelson, S. A., Luhr, J. F„ Carmichael, I.S.E., Wopat, M., and Wallace, P. J., 1991, Pliocene-Recent rifting in p. 9-24. SW Mexico and associated volcanism: An exotic terrane in the making, in Dauphin, J. P., and Simoneit, B.R.T., Moore, J. G., 1975, Mechanism of formation of pillow lava: American Scientist, v. 63, p. 269-277. eds., The Gulf and peninsular province of the Californias: American Association of Petroleum Geology Memoir, Moore, J. G., Cristofolini, R., and Guidice, A. L., 1971, Development of pillows on the submarine extension of Recent v. 47, p. 425-445. lava flows, Mt. Etna, Sicily: U.S. Geological Survey Professional Paper 750-C, p. 89-97. Arculus, R. J., and Johnson, R. W., 1981, Island-arc magma sources: A geochemical assessment of the roles of slab- Muir, I. D., and Tilley, C. E., 1961, Mugearites and their place in alkali igneous rock series: Journal of Geology, v. 69, derived components and crustal contamination: Geochemical Journal, v. 15, p. 109-133. p. 186-201. Basaltic Volcanism Study Project (BVSP), 1981, Basaltic volcanism on the terrestrial planets: New York, Pergamon Press, Munoz, J. B., and Stern, C. R., 1989, Alkaline magmatism within the segment 38°-39°S of the Plio-Quaternary Volcanic 1,286 p. Belt of the southern South American continental margin: Journal of Geophysical Research, v. 94, p. 4545-4560.

1594 Geological Society of America Bulletin, December 1992

Murphy, G. P., 1986, The chronology, pyroclastic stratigraphy and petrology of the Valle de Santiago Maar Field, central Steiger, R. H., and Jager, E., 1977, Subcommission on geochronology: Convention on the use of decay constants in geo- Mexico [M.S. thesis]: Berkeley, California, University of California, 42 p. and cosmo-chronology: Earth and Planetary Science Letters, v. 36, p. 359-362. Nakamura, N., 1974, Determination of REE, Ba, Fe, Mg, Na, and K in carbonaceous and ordinary chondrites: Geochim- Stolper, E., 1980, A phase diagram for mid-ocean ridge basalts: Preliminary results and implications for pedogenesis: ica et Cosmochimica Acta, v. 38, p. 757-773. Contributions to Mineralogy and Petrology, v. 74, p. 13-24. Nelson, S. A., 1980, Geology and petrology of Volcán Ceboruco, Nayarit, Mexico: Geological Society of America Stormer, J. C., and Nicholls, J., 1978, XLFRAC: A program for the interactive testing of magmatic differentiation models: Bulletin, part 2, v. 9!, p. 2290-2431. Computers and Geosciences, v. 4, p. 143-159. Nelson, S. A., and Carmichael, I.S.E., 1984, Pleistocene to recent alkalic volcanism in the region of Sanganguey Volcano, Swanson, D. A., 1972, Magma supply rate of Kilauea Volcano 1952-1971: Science, v. 175, p. 169-170. Nayarit, Mexico: Contributions to Mineralogy and Petrology, v. 85, p. 321-335. Thompson, R. N., 1972, The 1 atm melting patterns of some basaltic volcanic series: American Journal of Science, v. 272, Nelson, S. A., and Livieres, R. A., 1986, Contemporaneous calc-alkaline and alkaline volcanism in the region of p. 901-932. Sanganguey Volcano, Nayarit, Mexico: Geological Society of America Bulletin, v. 97, p. 798-808. Thompson, R. N., Esson, J., and Dunham, A. C., 1972, Chemical variation in lavas of the Isle of Skye: Journal of Nieto-Obregon, J., Urrutia-Fucugauchi, J., Cabral-Cano, E., and Guzman-de la Campa, A., 1989, Evidence of a listric Petrology, v. 13, p. 219-253. component in the Ameca River Fault: Implications of motion on the Jalisco Block, Mexico: Geological Society of Thorarinsson, S., 1969, The Lakagigar eruption of 1783: Bulletin of Volcanology, v. 33, p. 910-928. America Abstracts with Programs, p. A92. Verma, S. P., and Nelson, S. A., 1989, Isotopic and trace element constraints on the origin and evolution of alkaline and Nixon, G. T., 1982, The relationship between Quaternary volcanism in central Mexico and the seismicity and structure of calc-alkaline magmas in the northwestern Mexican Volcanic Belt: Journal of Geophysical Research, v. 94, subducted oceanic lithosphere: Geological Society of America Bulletin, v. 93, p. 514- 523. p. 4531-4544. Perfit, M. R., Gust, D. A., Bence, A. E., Arculus, R. J., and Taylor, S. R., 1980, Chemical characteristics of island-arc Walker, D., Shibata, T., and DeLong, S. E., 1979, Abyssal tholeiites from the Oceanographer Fracture Zone, II. Phase basalts: Implications for mantle sources: Chemical Geology, v. 30, p. 227-256. equilibria and mixing: Contributions to Mineralogy and Petrology, v. 70, p. 111-125. Rayleigh, J.W.S., 1896, Theoretical considerations respecting the separation of gases by diffusion and similar processes: Wallace, P., and Carmichael, I.S.E., 1989, Minette lavas and associated leucitites from the western front of the Mexican Philosophical Magazine, v. 42, p. 77-107. Volcanic Belt: Petrology, chemistry and origin: Contributions to Mineralogy and Petrology, v. 103, p. 470-492. Reagan, M. K., and Gill, J. B., 1989, Coexisting calc-alkaline and high-niobium basalts from Turrialba Volcano, Costa Wallace, P., and Carmichael, I.S.E., 1992, Alkaline and calc-alkaline lavas near Los Volcanes, Jalisco, Mexico: Geochem- Rica: Implications for residual titaoites in arc magma sources: Journal of Geophysical Research, v. 94, ical diversity and its significance in volcanic arcs: Contributions to Mineralogy and Petrology (in press). p. 4619^633. Wallace, P., Carmichael, I.S.E., Righter, K., and Becker, T., 1992, Volcanism and tectonism in western Mexico: A contrast Righter, K., and Carmichael, I.S.E., 1991, Fe^/Fe2* ratios in megacrysts and host alkali basalts from the Valle de of style and substance: Geology, v. 20, no. 7, p. 625-628. Santiago Maar Field, central Mexico: Eos, v. 68, p. 360. Wilcox, R. E., 1954, Petrology of Paricutin Volcano, Mexico: United States Geological Survey Bulletin, v. 965C, Roeder, P. L., 1974, Activity of iron and olivine solubility in basaltic liquids: Earth and Planetary Science Letters, v, 23, p. 281-353. p, 397-410. Williams, H., 1932, Geology of the Lassen Volcanic National Park: University of California Publications in the Geological Roeder, P. L., and Emslie, R. F., 1970, Olivine-liquid equilibrium: Contributions to Mineralogy and Petrology, v. 29, Sciences, v. 21, p. 195-385. p. 275-289. Wopat, M., 1990, Quaternary alkaline volcanism and tectonics in the Mexican Volcanic Belt near Tequila, Jalisco, Sack, R. O., Walker, D., and Carmichael, I.S.E., 1987, Experimental petrology of alkalic lavas: Constraints on cotectics of southwest Mexico [Ph.D. thesis]: Berkeley, California, University of California, 280 p. multiple saturation in natural basic liquids: Contributions to Mineralogy and Petrology, v. 96, p. 1-23. Shackleton, N, J., and Opdyke, N. D., 1976, Oxygen-isotope and paleomagnetic stratigraphy of Pacific Core V28-239 late Pliocene to latest Pleistocene, in Cline, R. M., and Hays, J. D., eds., Investigation of late Quaternary paleoceanog- raphy and paleodimatology: Geological Society of America Memoir 145, p. 449-464. Shibata, T., DeLong, S. E., and Walker, D., 1979, Abyssal tholeiites from the Oceanographer Fracture Zone: Contribu- tions to Mineralogy and Petrology, v. 70, p. 89-102. MANUSCRIPT RECEIVED BY THE SOCIETY JULY 19,1991 Spulber, S. D., and Rutherford, M. J., 1983, The origin of rhyolite and plagiogranite in oceanic crust: An experimental REVISED MANUSCRIPT RECEIVED MAY 20,1992 study: Journal of Petrology, v. 24, p. 1-25. MANUSCRIPT ACCEPTED MAY 22,1992

Printed in U.S.A.

Geological Society of America Bulletin, December 1992 1593

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/104/12/1592/3381340/i0016-7606-104-12-1592.pdf by guest on 25 September 2021