Mesozoic Stratigraphy of the Patagonia Mountains and Adjoining Areas, Santa Cruz County, Arizona GEOLOGICAL SURVEY PROFESSIONAL PAPER 658-E Mesozoic Stratigraphy of the Patagonia Mountains and Adjoining Areas, Santa Cruz County, Arizona By FRANK S. SIMONS MESOZOIC STRATIGRAPHY IN SOUTHEASTERN ARIZONA GEOLOGICAL SURVEY PROFESSIONAL PAPER 658-E Descriptive stratigraphy of Triassic, Jurassic, and Cretaceous rocks that are mainly rhyolites but that include some sedimentary rocks and intermediate volcanic rocks UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1972 UNITED STATES DEPARTMENT OF THE INTERIOR ROGERS G. B. MORTON, Secretary GEOLOGICAL SURVEY W. A. Radlinski, Acting Director For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 - Price 40 cents (paper cover) Stock Number 2401-1205 CONTENTS Page Page Abstract El Cretaceous rocks . E13 Introduction 1 Bisbee Formation . .. 13 Triassic and Jurassic rocks... ... ... ... 2 Fossils and age. _....... 16 Canelo Hills Volcanics. ... ... 2 Volcanic rocks of lower Alum Gulch 16 Triassic or Jurassic rocks ._- . 3 Volcanic rocks of Dove Canyon.. 17 Volcanic rocks in the southern Patagonia Trachyandesite of Meadow Valley 18 Mountains ... __ __ . .... 3 Tuff and shale.... ... ..... 18 UX Ranch block . 3 Thin lava flows 19 Duquesne block.........._ ..... .. ...... 3 Thick lava flows 20 Corral Canyon block..... _ . .. 6 Chemical composition 20 Volcaniclastic sequence . .._ . 6 Alteration of trachyandesitic lavas. ... 20 Volcanic sequence.. .._. 7 Age .. - - 21 American Mine block. .._ 8 Cretaceous or Tertiary rocks ... ......... 21 Thunder Mine block _ 9 Volcanic rocks of the Humboldt Chemical composition... ....... ....... 9 mine-Trench Camp area ... ... 21 Age and correlation.. 10 Volcanic rocks of Red Mountain 22 Volcanic and sedimentary rocks References cited.. -.. _ 23 in the Flux mine area..___....._..._ . 12 ILLUSTRATIONS Page FIGURE 1. Index map of part of southeastern Arizona . - ... E2 2. Generalized geologic map and sections of part of the Patagonia Mountains and Canelo Hills.. .... 4 3. Sketch of a partial section of volcanic and sedimentary rocks of the UX Ranch block north of the Kansas mine ... _.__ . -_ __ - -- - - -. - - --- - -- 6 4. Sketch of a partial section of sedimentary and epiclastic volcanic rocks in the lower part of the Bisbee Formation west of the UX Ranch. -__. .._. .. 14 5. Sketch of a geologic section of volcanic and sedimentary rocks of the trachyandesite of Meadow Valley along a gully northeast of the Little Outfit Ranch._ . ..._ 19 TABLES Page TABLE 1. Comparison of chemical analyses, norms, and semiquantitative spectrographic analyses of Mesozoic volcanic rocks, Patagonia Mountains, with those of associated igneous and Nockolds' average rocks._- Ell 2. Average chemical analyses of rhyelites and granites, Patagonia Mountains 12 3. Comparison of chemical analyses, norms, and semiquantitative spectrographic analyses of trachyandesite and rhyodacite of Meadow Valley with those of Nockolds' average rocks 21 III MESOZOIG STRATIGRAPHY IN SOUTHEASTERN ARIZONA MESOZOIG STRATIGRAPHY OF THE PATAGONIA MOUNTAINS AND ADJOINING AREAS, SANTA GRUZ COUNTY, ARIZONA By FRANK S. SIMONS ABSTRACT older volcanic rocks. The volcanic-sedimentary sequence south­ The Patagonia Mountains and Canelo Hills in the Lochiel west of the Canelo Hills is mainly epiclastic volcanic con­ and Nogales 15-minute quadrangles of southeastern Arizona glomerate of andesitic composition with some more-silicic consist in large part of volcanic and sedimentary rocks of tuff and tuffaceous sandstone; some of these rocks resemble Mesozoic age. These rocks are in fault contact with Pre- those underlying the trachyandesite farther north. cambrian plutonic igneous rocks and overlie or are faulted The youngest rocks, of Late Cretaceous or early Tertiary against Paleozoic sedimentary rocks ranging in age from age, are coarse silicic tuff, tuff breccia, and lava west of Cambrian to Permian. They have been intruded by granodi- Trench Camp, where they are at least 800 feet thick, and orite of early Tertiary age and are overlain by sedimentary massive silicic volcanic rocks of uncertain origin on Red and volcanic rocks of middle Tertiary to Holocene age. At Mountain, where the thickness is perhaps 1,500 feet. These least 75 percent of the Mesozoic stratigraphic column is vol­ canic, mostly silicic volcanics; the remainder is sedimentary rocks lie unconformably on rocks of Late Cretaceous and with some interbedded volcanic rocks. The entire section is of Triassic or Jurassic age. not exposed in any one area, and correlations between areas and structural blocks are uncertain. The aggregate total INTRODUCTION thickness is unknown but is at least 10,000 feet and probably is 14,000 to 15,000 feet. The Patagonia Mountains, a north-northwesterly Silicic volcanic rocks of probable Triassic or Jurassic age trending range lying east of Nogales and south of make up several structural blocks in the southern half of Patagonia in southeastern Arizona (fig. 1), consist the Patagonia Mountains. Correlation between blocks is in large part of Mesozoic volcanic and sedimentary uncertain, but the thickness of the volcanic sequence is esti­ mated to be at least 6,000 to 7,000 feet and probably is con­ rocks. This report describes these rocks, together siderably more. Rocks are mostly rhyolitic lava, welded tuff, with some of similar age in nearby parts of the and tuff interlayered with minor sandstone, conglomerate, Canelo Hills to the east and in the intervening area and less-silicic volcanic rocks. Most of the Canelo Hills con­ at the head of the San Rafael Valley. Figure 2 is a sist of rhyolitic lava and welded tuff very similar to those in the Patagonia Mountains; the lava is at least 1,000 feet generalized geologic map showing the distribution thick, and the overlying welded tuff is at least 6,000 feet thick. of these rocks, which range in age from Triassic Cretaceous rocks consist of several thousand feet of dom- to Late Cretaceous or early Tertiary. Plutonic igne­ inantly fine grained sedimentary rocks assigned to the Bisbee ous rocks of Mesozoic age are also widely represented Formation of Early Cretaceous age in the central Patagonia in the same region but are noted only briefly herein. Mountains; several thousand feet of dominantly trachy- andesitic lava in the northern Patagonia Mountains, upper The layered rocks comprise six cartographic units San Rafael Valley, and Canelo Hills; and at least 2,000 'feet of known or strongly inferred Mesozoic age and two of heterogeneous volcanic and sedimentary rocks on the units of uncertain but probable Late Cretaceous southwest flank of the Canelo Hills. The Bisbee Formation or early Tertiary age. Some pairs of units may be comprises mostly brown siltstone and mudstone with numer­ stratigraphic equivalents but either do not crop ous thin limestone beds and some sandstone, conglomerate, and tuffaceous rocks; it rests disconformably on Triassic or out in the same area or are separated by major Jurassic silicic volcanic rocks. The trachyandesite is perhaps faults and therefore are described separately. Only 3,000 feet thick in the Patagonia Mountains, where it lies partial sections are available for all but one unit, unconformably either on Triassic or Jurassic volcanic rocks and correlations are uncertain. The aggregate total or on about 1,500 feet of rhyolitic to latitic lava and tuff, thickness is unknown; in the Patagonia Mountains which in turn rest unconformably on the older volcanics. this thickness is at least 10,000 feet and probably In the Canelo Hills, where the trachyandesite is much thin­ ner, it is underlain conformably by 1,000 feet or more of is as much as 14,000 or 15,000 feet, and in the tuff, shale, and conglomerate, which are faulted against Canelo Hills it may be 10,000 feet or more. Volcanic El E2 MESOZOIC STRATIGRAPHY IN SOUTHEASTERN ARIZONA rocks of silicic to intermediate composition make A3-A9) ; hence, they will not be discussed here in up 75 percent or more of the Mesozoic stratigraphic detail. The formation is divided into three informal column; the remainder is sedimentary rocks and members: a lower, volcaniclastic and volcanic mem­ some interlayered volcanic beds. ber as much as 2,000 feet thick; a middle, rhyolite Fieldwork was done over a period of about 7 member at least 1,000 feet thick; and an upper, months during 1960-63 as part of the geologic map­ rhyolitic welded tuff member at least 6,000 feet ping of the Lochiel and Nogales 15-minute quad­ thick. It is assigned a Late Triassic and Early rangles. Office work included microscopic study of Jurassic age on the basis of field relations with about 275 thin sections and X-ray diffractometer paleontologically dated rocks of Permian age and analysis of 30 altered rocks. Chemical analyses were of Early Cretaceous age, and on the basis of radio- made by rapid rock analysis methods (Shapiro and metric ages of 173±7 m.y. (million years) deter­ Brannock, 1962) on 14 volcanic rocks and two gran­ mined by the potassium-argon method on biotite ites. Various sections of the report have been from the welded tuff member and 144±4 m.y. deter­ strengthened by discussions with my colleagues mined by the same method on biotite from the lower John R. Cooper, Harald Drewes, Philip T. Hayes, member. The lower member was correlated by Hayes and Robert B. Raup, all of whom were working (1970a, p. A8-A9) with the Gardner Canyon For­ concurrently in adjacent or nearby areas; none, mation of the Santa Rita Mountains (Drewes, 1968, however, should be held responsible for any con­ p. C7), for which a radiometric age of 190±20 m.y. clusions reached herein. (Triassic) was obtained by the lead-alpha method on zircon from a dacite. In the area under consid­ TRIASSIC AND JURASSIC ROCKS eration, the Canelo Hills Volcanics are in fault CANELO HILLS VOLCANICS contact with the trachyandesite of Meadow Valley The Canelo Hills Volcanics (fig.