JOHN S. STUCKLESS Department of Geology. Stanford University, Stanford, California 94305 MICHAEL F. SHERIDAN Department of Geology, Arizona State University, Tempe. Arizona 85281 Tertiary Volcanic Stratigraphy in the Goldfield and , Arizona

ABSTRACT Superstition Mountains of central Arizona (Fig. Recent work provides the basis for establish- 1). These rocks are associated with the Supersti- ing a stratigraphic column for units within the tion cauldron complex (Sheridan and others, Superstition cauldron of central Arizona. Two 1970). All rock units here described lie within new formations are defined. The Geronimo the 375-sq-km area of the caldera interior. Head Formation is a Miocene rhyolite tuff con- The petrography and stratigraphy of the cald- taining rhyolite, quartz latite, and basalt lava era deposits are more complex than those re- flows. The Superstition Tuff is a Miocene quartz ported for several ranges within a 200-km latite welded tuff composed of three members. northeast-southwest strip through this region The Siphon Draw Member, Dogie Spring (Sell, 1968). Parts of the Superstition sequence Member, and Canyon Lake Member were em- are similar to columns from distant ranges sug- placed in order of decreasing age. The Dogie gesting that some outflow rocks from this cen- Spring Member intertongues with the Ge- ter are of regional significance. Nearby outflow ronimo Head Formation. Numerous radiomet- rocks are either removed by erosion or buried ric and fission track dates support the field by basin-fill deposits. Thin outflow units similar determination of the stratigraphic sequence. to the Superstition Tuff and Geronimo Head Formation have been found in the McDowell INTRODUCTION Mountains 25 km to the west of the area re- A thick sequence of ash flows, lavas, and vol- ported (Kokalis, 1971) as well as in the Malpais canic breccias is exposed in the Goldfield and Hills of the San Tan Mountains 45 km to the

GOLDFIELD MOUNTAINS

DOGIE SPRING Geronimo Head Formation DU] Superstition Tuff Canyon Lake Member SUPERSTITIO Dogie Spring Member EU OUNTAINS Siphon Draw Member ETTTj

Figure 1. Distribution of units, Superstition Cauldron, Arizona.

Geological Society of America Bulletin, v. 82, p. 3235-3240, 2 figs., November 1971

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southwest (Blucher and Kinnison, unpub. re- for exposures at its type section (sees. 7 and 8, port). T. 1 N, R. 9 E) in Siphon Draw (Fig. 1). It is In the Superstition Mountains the sequence approximately 670 m thick and conformably is dominated by welded quartz latite tuffs which onlaps a series of unnamed dacite domes, lavas, were formerly correlated with the Apache Leap and autoclastic breccias. The Siphon Draw dis- Tuff (Peterson, 1968; Sheridan and Stuckless, plays complex cooling at the type section where 1969). The Apache Leap Tuff that occurs in the nine distinct partings are separated by thin da- Superior region about 40 km to the east is cite breccias or airfall lenses. Rocks overlying thought to be a distinct outflow unit that may or the Siphon Draw Member are not preserved at may not be related to this volcanic center. As- the type section, which is within the resurgent sociated with the welded tuff is a thick section dome of the Superstition cauldron. At other of nonwelded rhyolite tuffs and breccias. places within the Superstition Wilderness Area it is unconformably overlain by a series of non- SUPERSTITION TUFF welded rhyolite ashflows and epiclastitic Quartz latite ash-flow tuffs are here named breccias of the Geronimo Head Formation. the Superstition Tuff for their extensive expo- Fission track dates on zircons from the top sures in the Superstition Wilderness Area. The and bottom of the Siphon Draw Member are type section is the composite of the type sec- 24.5 ± 0.5 m.y. and 24.2 -j- 0.9 m.y., respec- tions of its three members. This formation is tively. A K-Ar date on a sample of this unit also present 25 km to the west in the McDowell from Black Mesa (Table 2), yielded an age of Mountains and may extend 45 km southwest 22.6 + 1.0 m.y. (Damon, 1969). It may be into the San Tan Mountains. Within the Super- distinguished from other members by its mode stition area the Superstition Tuff displays all of quartz > , plagioclase > sanidine with acces- degrees of compaction, but typically is densely sory sphene, zircon, apatite, and magnetite. welded and devitrified. The color darkens with The second member of the Superstition Tuff welding ranging from pinkish to pale red. is here named the Dogie Spring Member. This The formation is divided into three members welded quartz latite tuff is a simple cooling unit which are distinguished from one another and in its type section of Dogie Spring (Fig. 1) and from the Apache Leap Tuff and Geronimo has been dated by K-Ar ratios in biotite at 18.4 Head Formation by relative phenocryst per- ± 0.6 m.y. (Table 3). centages (Table 1) and radiometric ages (Ta- The tuff attains a maximum thickness of 180 bles 2 and 3). The Apache Leap Tuff has been m in the vicinity of Dogie Spring, although the dated by K/Ar ratios in biotite at 20 m.y. base is not exposed in the type section. The (Creasey and Kistler, 1962, p. DI) and 19.9 member is underlain and overlain by non- + 0.9 m.y. (Damon and Bikerman, 1964, p. welded ash of the Geronimo Head Formation. 72). The Dogie Spring Member is distinguished The lowermost member of the Superstition from the Apache Leap Tuff and other members Tuff is here named the Siphon Draw Member of the Superstition Tuff by a mode of quartz >

TABLE 1. MODAL DATA OF RELATIVE PHENOCRYST PERCENTAGES FOR THE APACHE LEAP TUFF, THE SUPERSTITION TUFF, AND THE GERONIMO HEAD FORMATION

Unit Phenocrysts Quartz Sanidine Plagioclase Biotite Hornblende Accessories

1 39 11 3 71 9 2 3 2 42 47 11 34 5 1 3 3 29 44 21 26 5 tr 3 4 30 36 13 40 9 tr 4 5 10 35 27 25 6 tr 3 6 20 36 25 21 7 2 8

1. Apache Leap Tuff, average from Peterson (1961) 2. Siphon Draw Member, average of 10 samples 3. Dogie Spring Member, average of 4 samples 4. Canyon Lake Member, average of 6 samples 5. Geronimo Head Formation, average of 9 ash-flow samples 6. Geronimo Head Formation, average of 4 lahar samples

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Sample Zircon Sphene Apatite number Unit (age in m.y.) (age in m.y.) (age in m.y.)

AP 244 Quartz-poor dacite 28.7' Apache Leap Tuff 29.6 fA 2,0 ±0, 28.9 28.8

AP 236 Siphon Draw Member 24.9 25.4 24.3 25.2 24.1 24.5 ±0.4 26.0 25.4 26.0 23.9 24.3 24.1 25.4 ± 0.6 25^0 23.8 25.2 27.2 25.9 26.3 AP 232 Siphon Draw Member 24.7 26.6 24.8 ±2.3 24.8 25.0 24'2 24 2 ±05 21'6 22.6 ' ±U'3 20.5 23.6 24.0 25.3 24.1 23.0 23.4 ±0.9 24.3 22.7 21.8 23.0 25.3 22.2 AP 27A Rhyolite dike 16.8 Geronimo Head Fm. 18.5 13.5 16.4 16-° ± L3 14.6 16.0 AP 200 Quartz latite lava 17.1 11.2 Geronimo Head Fm. 15.5 17.0 17.5 16.5 16.3 16.1 ±0.8 16.3 14.4 20.1 15.8 13.5 j 17.5 16.1 ± 1.1 16.5 16.0 14.8 16.5 15.8 17.8 16.2. AP 234 Canyon Lake Member 15.4 15.7 15.6 14.7 14.2 14.9 ±0.8 15.8 15.8 16.3 13.6 15.5 15.4 ±0.8 13.5 14.3 17.7 15.5J

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TABLE 3. K-AR DATA AND AGES FOR THE SUPERSTITION VOLCANIC SEQUENCE

Ar4°Rad 10 Ar40/K40 40 Sample K2O X IQ- Ar Rad number Unit Type % moles/g X IQ-3 Age in m.y.

8074* Siphon biotite 8.94 2.53 17.6 Draw 3.16 34.2 Member 3.02 52.4 2.99 1.34 22.6 ± 1.0 8073* Quartz biotite 8.93 2.91 21.2 latite 2.78 dome 2.82 1.26 21.3 ±0.8 8062* Basanite whole 1.85 0.490 1.05 11.4 17.8 ±3.1 rock AP-205f Dogie biotite 8.76 2.388 1.079 56.0 18.4 ±0.6 Spring Member AP-215f Geronimo sanidine 8.50 2.050 0.9563 79.8 16.3 ±0.5 Head ash flow t Apache biotite 19.9 ±0.9 Leap Tuff

"From Damon, P. E. (1969, p. 49). Averages are weighted. t Silberman, M. L. (1970, written commun.). * From Damon, P. E., and Bikerman, M. (1964, p. 72).

plagioclase, and plagioclase is nearly equal to Draw Member of the Superstition Tuff and is sanidine (Table 1). Accessory minerals include conformably overlain by a glassy quartz latite sphene, zircon, apatite, and magnetite. lava. The uppermost member of the Superstition The rhyolite ash flows vary from partially Tuff is here named the Canyon Lake Member welded to nonwelded and are generally zeolit- after its type section at Canyon Lake, 1.0 km ized. Lithic inclusions of dacite and basalt are northwest of Tortilla Flat (Fig. 1). The tuff is abundant. In outcrop both the tuff and epiclas- preserved within a graben and the base is not tic breccias are white to pale yellow. Although visible. Approximately 180 m of tuff is exposed the ash flows and lahars have different total in the type section. Here it is overlain by a phenocryst percentages, the relative abun- series of rhyolite gravels and locally by an alkali dances are nearly identical indicating that the olivine basalt. Elsewhere the tuff is underlain by lahars are derived directly from the ash flows rhyolite ash flows and epiclastic breccias of the (Table 1). Geronimo Head Formation. The Canyon Lake The base of the Geronimo Head Formation Member is a simple cooling unit and is distin- is younger than the 24-m.y.-old Siphon Draw guished by modes of plagioclase is nearly equal Member. Ash flows at the base of the to quartz and quartz is > sanidine (Table 1). Geronimo Head Formation are unconformably Fission-track dating of zircons from this mem- overlain by an extruded quartz latite lava that ber yields an age of 14.9 + 0.8 m.y. (Table 2). has been dated by K/Ar ratios in biotite at 21.3 + 0.8 m.y. (Damon, 1969). A quartz latite GERONIMO HEAD FORMATION dome that intrudes this unit at Apache Gap is A thick sequence of rhyolite ash flows and dated at 20.1 ± 1.2 m.y. (Damon, 1969). The epiclastic breccias of the Superstition Wilder- uppermost ash flow of the formation has been ness Area and Goldfield Mountains is here dated by K/Ar ratios in sanidine at 16.3 + 0.5 named the Geronimo Head Formation after its m.y. (Table 3) making it older than the Canyon type section at Geronimo Head (Fig. 1), where Lake Member of the Superstition Tuff. the formation attains a thickness of 430 m. The unit is somewhat thicker in the Goldfield Mountains where it is interbedded with rhyo- RADIOMETRIC DATES lite lavas and intruded by numerous rhyolite The Tertiary volcanics have been dated by dikes. It unconformably overlies the Siphon use of fission tracks and K-Ar ratios. These data

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are reported in Tables 2 and 3, respectively. the Siphon Draw Member (Table 2) with K-Ar The procedure used in the fission track dating ages (Table 3) shows that only three of the is essentially the same as described by Naeser dates overlap at the 1

thickness evidence to indicate that the fresh black glassy in meters quartz latite and rhyolite domes formed after Figure 2. Stratigraphic column for units within the 16.1 m.y. Most of the rhyolite intrusives appear Superstition cauldron. 1. Precambrian basement, 2. Ar- to cut the Geronimo Head Formation and the kosic conglomerate (White Tail equivalent), 3. Older younger domes, and one dike north of Dogie dacite domes, 4. Siphon Draw Member, Superstition Tuff, 5. Quartz latite lava, Goldfield Mountains, 6. Spring (Fig. 1) near sample AP 219 cuts the Quartz latite dome, Apache Gap, 7. Geronimo Head For- lava which is dated at 16.1 m.y. mation, 8. Dogie Spring Member, Superstition Tuff, 9. The Dogie Spring Member is also interbed- Basanite lava, Black Mesa, 10. Rhyolite and quartz latite ded with the Geronimo Head Formation and lavas, domes, and dikes, 11. Canyon Lake Member, Superstition Tuff, 12. Younger Rhyolite gravels. Units has been dated at 18.4 +_ 0.6 m.y. (Table 3). with vertical line pattern are basalts and basanites (thick- Although this age overlaps with the age of the ness exaggerated). Apache Leap Tuff, it has been named as a sepa-

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rate unit on the basis of its modal data (Table ACKNOWLEDGMENTS 1). The writers are deeply indebted to C. W. The youngest member of the Superstition Naeser for his assistance in fission-track dating Tuff is the Canyon Lake Member. Fission track techniques and to M. L. Silberman for his K/Ar ages on this unit are 14.9 ± 0.8 m.y. for zircon age determinations. We are grateful to Paul and 15.4 + 0.8 m.y. for sphene. These ages are Damon who made the initial K-Ar dates on in good agreement with the field relations which rocks from this sequence. We also wish to thank suggest that this tuff is younger than the R. W. Kopf, P. W. Lipman, and T. L. Pewe for Geronimo Head Formation and most of the reviewing the manuscript and making several silicic domes and lavas. Because the basalt of helpful suggestions. Canyon Lake overlies this unit it must be younger than 15 m.y. The youngest unit ex- REFERENCES CITED posed in the area is a flat-lying rhyolitic con- glomerate which overlies the Canyon Lake Creasey, S. C., and Kistler, R. W., 1962, Age of Member. some copper bearing porphyries and other igne- ous rocks in Southeastern Arizona, in Geologi- cal Survey Research 1962: U.S. Geo). Survey HISTORY Prof. Paper 450-D, p. D1-D5. Damon, P. E., 1969, Correlation and chronology of Tertiary volcanism started with the extrusion ore deposits and volcanic rocks: U.S. Atomic of a thin alkali olivine basalt over a terrain of Energy Comm., Ann. Prog. Rept. no. COO-689- moderate to low relief. This was followed by 120, p. 90. the intrusion and extrusion of dacite domes (29 Damon, P. E., and Bikerman, M., 1964, Potassium- m.y.). The early dacites were quartz-poor and argon dating of post Laramide plutonic and vol- were followed by more voluminous "normal" canic rocks within the Basin and Range province dacites. The last phases of dacite volcanism of Southeastern Arizona and adjacent areas: were accompanied by the eruption of the Arizona Geol. Soc. Digest, v. 8, p. 63-78. Siphon Draw Member of the Superstition Tuff Kokalis, P. G., 1971, Terraces of the Lower Salt River Valley, Arizona [M.S. thesis]: Flagstaff, (24.4 m.y.) contemporaneous with caldera col- Arizona State Univ. lapse. Naeser, C. W., and McKee, E. H., 1970, Fission- The first ash flows of the Geronimo Head track and K-Ar ages of Tertiary ash-flow tuffs, Formation erupted either during the last phases north central Nevada: Geol Soc. America Bull., of collapse or shortly thereafter. These ash v. 81, p. 3375-3384. flows were accompanied by an alkali olivine Petersen, D. W., 1968, Zoned ash-flow sheet in the basalt and were closely followed by the extru- region around Superior, Arizona: Ariz. Geol. sion and intrusion of quartz lathe domes and Soc. Southern Arizona Guidebook III, p. 215- lavas (20 m.y. and 21 m.y.). Resurgence of the 222. quartz latite magma updomed the central core Sell, J. D., 1968, Correlations of some post-Lara- mide Tertiary units, Globe (Gila County) to of the Superstition caldera. Gila Bend (Maricopa County), Arizona: Ariz. A similar volcanic cycle started with the erup- Geol. Soc. Southern Arizona Guidebook III, p. tion of the Dogie Spring Member of the Super- 69-74. stition Tuff (18.4 m.y.). This was followed by Sheridan, M. F., and Stuckless,J. S., 1969, Volcanics a basanite lava (18 m.y.), more rhyolite ash related to the Black Mesa caldera, central flows of the Geronimo Head Formation (16.3 Arizona [abs.]: Geol. Soc. America, Abs. with m.y.), and more quartz latite lavas and domes Programs for 1969, Pt. 3 (Cordilleran Sec.) p. (16.1 m.y.). 60-61. Volcanism came to a close between 10 and Sheridan, J. F., Stuckless, J. S., and Fodor, R. V., 1970, A Tertiary silicic cauldron complex at the 15 m.y. ago. The Canyon Lake Member of the northern margin of the Basin and Range prov- Superstition Tuff (15 m.y.) appears to be the ince, central Arizona, U.S.A.: Bull. Volcanol., last ash flow and was closely followed by the v. 34, no. 3, p. 649-662. extrusion of a thin alkali olivine basalt. The final volcanic event appears to have been the em- MANUSCRIPT RECEIVED BY THE SOCIETY MARCH 22, 1971 placement of small rhyolite dikes and domes REVISED MANUSCRIPT RECEIVED JUNE 10, 1971 PRESENT ADDRESS (STUCKLESS): NORTHERN ILLINOIS around the outer margin of the Superstition UNIVERSITY, DEPARTMENT OF GEOLOGY, DE KALB, caldera. ILLINOIS 60115.

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