Download GEOLOGY WALK 2013 - Cascabel Conservation Association

GEOLOGY WALK 2013 Cascabel Conservation Association The rhyolites and dacites (darker) of the Galiuro Volcanics within Hot Springs Canyon TRIP LEADERS Mick Meader, Retired staff member, Department of Geosciences, University of Arizona Chris Eastoe, Head of the Laboratory of Isotope Geochemistry, University of Arizona James Callegary, Groundwater Hydrologist/Geophysicist, U.S. Geological Survey, Tucson Hot Springs Canyon Geology Walk November 16, 2013 Led by Norm “Mick” Meader1, Chris Eastoe2 and James Callegary3 Introduction Our discussion and walk today will emphasize the younger geology (from the present back to 30 m.y. or so) of Hot Springs Canyon and Wash. The features and rocks we will examine include the Upper Miocene Quiburis Formation (~5‐7 million years [m.y.] old); the San Manuel Formation (~19‐21 m.y. old); the Teran Wash Fault, which downfaults the San Manuel Formation against the Gailuro Volcanics; and the Galiuro Volcanics (24‐29 m.y. old). We will also briefly discuss the Cretaceous Willow Canyon Formation (~120 m.y. old), exposed somewhat farther up the canyon, and the Laramide Orogeny (50‐90 m.y. ago), which intensely deformed the Willow Canyon Formation. The Basin and Range Province Hot Springs Canyon lies in the southern Basin and Range Province, which began taking its present form about 15 m.y. ago. This province extends from northern Mexico to southeastern Oregon and southern Idaho. It is characterized by horsts and grabens (upthrown and downthrown blocks forming mountains and basins), although we now understand that these basins are usually bounded on one side by a single curved fault. This faulting originally produced many “closed” basins that eventually filled with sediment and which were integrated into a regional drainage network beginning about 5 m.y. ago. The Quiburis Formation The geological unit in which our walk begins is the Upper Miocene (~5‐7 m.y. old) Quiburis Formation, which was deposited in a closed basin having no outlet. The lowest point in this basin, where lakebeds are preserved, was somewhat north of Mammoth. Hot Springs Canyon is located at the very southern end of this basin, and the sediments here were deposited at the lower ends of alluvial fans (on a “braidplain”) that entered the valley from the mountains to the east and west. About 14 miles south of Hot Springs Canyon, a bedrock high called the Narrows separates the Quiburis basin from the St. David basin, in which the reddish, mostly clay sediments surrounding Benson were deposited. Beginning in the Pliocene Epoch about 5 m.y. ago, a through‐flowing regional drainage network formed that linked these closed basins with 1
Mick received his M.S. in geology in 1977 from the University of Arizona and served as a staff member in the Department of Geosciences for 23 years before retiring in 2010. 2
Chris received his Ph.D. from the University of Tasmania in 1979 and came to the University of Arizona in 1982 to fill a tenure‐track position in economic geology. He now heads the Laboratory of Isotope Geochemistry in the Department of Geosciences. 3
James received his Ph.D. from the University of Arizona in 2005 and currently works with the U.S. Geological Survey in Tucson as a groundwater hydrologist and geophysicist. 1 drainages to the west. This resulted in the downcutting of Quiburis sediments and their progressive removal from the basin. This erosion produced Hot Springs Canyon and the present topography that surrounds us within the valley. San Manuel Formation As we hike upstream toward the “Yellow Cliffs,” we will next encounter the San Manuel Formation, which was deposited in an environment similar to that of the Quiburis Formation. It contains many granitic conglomerate clasts that were eroded from the Precambrian (1667 m.y. old) Johnny Lyon Granodiorite to the south‐southeast in the area of the Narrows. The formation was deposited 19‐21 m.y. ago and represents northward flow down a paleo‐San Pedro Valley. The Teran Wash Fault The Teran Wash Fault is one of the primary structures that we will see today, and it drops the San Manuel Formation down against the Galiuro Volcanics. The fault follows the western face of the “Yellow Cliffs,” crossing Teran Wash several miles to the south. This fault dips ~35° to the west and offsets the San Manuel Formation approximately 1‐2 kilometers. The date of movement on the fault is somewhat younger (~20‐25 m.y.) than the formation of the Catalina‐
Rincon metamorphic core complex, which is described below. It is unusual for normal faults to dip at such a low angle; 60° is much more common. It is possible that the fault was rotated to shallower dips by motion on later underlying faults. The Formation of the Santa Catalina‐Rincon Metamorphic Core Complex The San Manuel Formation was deposited following the eruption of the Galiuro Volcanics (the “Yellow Cliffs”) near the end of a period of extreme crustal extension, or spreading, that created the Rincon and Santa Catalina Mountains 25‐30 m.y. ago. These are called “metamorphic core complexes” because they contain intensely deformed metamorphic and igneous rocks from deeper (>10 km) in the crust. These “core complexes” formed at nearly the same time as the great eruptions of volcanic rocks that make up the Galiuro Mountains, and they are surrounded by a subhorizontal, or “detachment,” fault that connected with a “breakaway” fault along the western face of the Galiuro Mountains. This period of great crustal spreading was initiated by the subduction of the East Pacific Rise (EPR) beneath the western edge of North America. The East Pacific Rise is the oceanic spreading center that generated the crust of the Pacific Ocean, and as Arizona overroad the EPR, the crust began to extend. Galiuro Volcanics The Galiuro Volcanics, which make up the Galiuro Mountains and the Yellow Cliffs, erupted 24‐
29 m.y. ago. They are composed predominantly of rhyolitic and dacitic ash flows (the volcanic equivalent of granite) that resulted from the melting of the continental crust, and they were ejected from a caldera in gigantic explosions that dwarfed the eruption of Mt. St. Helens. They 2 are part of an enormous belt of volcanic rocks that extends far south into Mexico and which today makes up the Sierra Madre Occidental. The caldera from which they erupted is inferred to have been in the vicinity of the Santa Teresa Mountains northeast of the Galiuro Mountains. The granite that makes up the Santa Teresa Mountains has the same age and chemistry as the Galiuro Volcanics. Soza Mesa Fault Farther up the canyon is the Soza Mesa fault, which juxtaposes the Galiuro Volcanics above the Cretaceous Willow Canyon Formation. It dips ~10° to the west and has accommodated 2‐4 kilometers of movement. Dickinson and others suggest that this fault may be the eastward extension of the core‐complex detachment fault that underlies the San Pedro Valley and which surfaces on the east side of the Rincon Mountains. The fault must be somewhat younger, however, than the 24‐29 m.y. old Galiuro Volcanics, which it offsets. The Willow Canyon Formation and the Laramide Orogeny Upstream from the Soza Mesa fault are exposures of the Cretaceous (~120 m.y. old) Willow Canyon Formation, which was deposited in a rift basin that was linked to the southeast with the Gulf of Mexico. The sediments of the Willow Canyon Formation were deposited by rivers flowing southeastward toward the Gulf down the axis of the rift. Upstream from these sediments to the north‐northwest near the basin’s edge were alluvial fans and braidplains similar to those represented in the Quiburis and San Manuel formations. These sediments were intensely deformed during the Laramide Orogeny, or mountain‐building episode, that occurred between 50 and 90 m.y. ago. It was during this orogeny that the Rocky Mountains of Colorado and Wyoming were formed as well. This mountain‐building episode was associated with an increased westward rate of movement of North America over the Pacific plate, which produced great compressional stresses in the crust. Volcanism also initially accompanied this compression in this area, producing the Mule Shoe Volcanics yet farther up the canyon. Diorite Intrusion Just upstream from the wash in which the Soza Mesa fault is exposed is a dark, somewhat angular “boulder.” This is actually a bedrock remnant, not a loose rock, and it is an igneous intrusion within the Willow Canyon Formation. It contains somewhat more silica than a basalt and is equivalent to an andesite, a volcanic rock found within the Mule Shoe Volcanics farther upstream. The contact between the Willow Canyon Formation and the intrusion is exposed on the northwest side of the stream bed as well as upstream on the southeast side. This intrusion is undated but presumed to be of the same age as the Muleshoe Volcanics, which are between 74 and 77 million years old. 3 Geologic Map of Hot Springs Canyon. Lines with black rectangles are low‐angle normal faults. Lines with triangles are the Hot Springs thrust fault. (From Waldrip, 2008)
4 ROCK UNITS AND STRUCTURES Typical exposure of the 5‐7 million year old Quiburis Formation on the northwest side of Hot Springs Wash. This is the most extensive unit in the lower San Pedro Valley. The Quiburis Formation overlying the 19‐21 m.y. old San Manuel Formation. 5 Outcrop of the San Manuel Formation on the southeast side of Hot Springs Wash. Note the tafoni weathering (the circular holes in the rock). Growth of crystals of various types of salt within the rock frequently cause this type of weathering in arid environments. Close up of bedding within the San Manuel Formation. In Hot Springs Wash the majority of the larger clasts within the formation are 1.67 billion‐year‐old Johnny Lyon Granodiorite, which makes up the Johnny Lyon Hills to the south and the bedrock Narrows of the San Pedro River. The formation is named for exposures near San Manuel.
6 The Teran Wash fault on the northwest side of Hot Springs Wash near the mouth of Hot Springs Canyon. Total displacement on the fault is approximately 1.4 kilometers. The Galiuro Volcanics within Hot Springs Canyon. These are predominantly rhyolite, which is the volcanic equivalent of granite, and are between 25 and 29 million years old. The caldera or crater from which they erupted is inferred to have been in the vicinity of the Santa Teresa Mountains northeast of Aravaipa Canyon. 7 The Soza Mesa fault exposed in a wash on the northwest side of Hot Springs Canyon. This fault dips ~10º to the southwest and is referred to as a detachment fault because of its low angle. The fault is only slightly younger than the Galiuro Volcanics, or between 20 and 25 million years old. Diorite intrusion within the Willow Canyon Formation just upstream from the exposure of the Soza Mesa fault. Although not dated, this intrusion is presumably of the same age as the Mule Shoe Volcanics farther up Hot Springs Canyon, which erupted between 74 and 77 million years ago.
8 9 10 Basin and Range Province of the Western United States (U.S. Geological Survey radar imagery) showing the location of Hot Springs Wash. 11 Formation of the Basin and Range Province. Prior to 30 m.y. ago, an oceanic spreading center, the East Pacific Rise, lay west of North America. Then beginning 30 m.y. ago, westward‐moving North America began to override the spreading center, which began pulling western North America apart, progressively forming the Basin and Range Province and the San Andreas fault. (From Atwater, 1970) Geologists initially visualized the formation of the Basin and Range with planar normal faults bounding both sides of each range. Later, seismic imagery revealed that essentially all faults are curved, and most valleys and ranges are asymmetrical. 12 Deposition of the Quiburis Formation occurred in a closed basin prior to 5 m.y. ago. The area of Hot Springs Canyon (Saguaro‐Juniper) was at the far southern end of this basin and received coarser sediment. 13 Models for Quiburis Formation deposition. The top two diagrams characterize Quiburis depo‐
sition in the area of Hot Springs Canyon. The bottom model characterizes Quiburis deposition in the area of Mammoth. 14 15 Relationship of volcanism to the angle of the subducting slab. The Laramide Orogeny (50‐90 m.y. ago) occurred in the middle setting above as the rate of subduction accelerated and the dip of the slab decreased. The Galiuro Volcanics erupted in the bottom scenario beginning around 30 m.y. ago as the rate of subduction slowed and the dip of the slab increased. Volcanism shifted back westward to Arizona from New Mexico when this occurred. (From Kring, 2002) 16 The explosive formation of rhyolite ash flows and tuffs, which represent most of the volcanics in the Galiuro Mountains. (From Kring, 2002) Outline of the caldera or crater (large dots) in the Santa Teresa Mountains from which the Galiuro Volcanics presumably erupted. The Galiuro Mountains are to the left, the Santa Teresa Mountains to the right. (From Hauck, 1985) 17 Relationship of the Galiuro Mountains to the Santa Catalina/Rincon Mountains and the Pinaleno Mountains. Initially, the Catalinas and the Pinalenos rose as the Galiuros sank, preserving the thick sequence of volcanic rocks in the Galiuro Mountains between them. Red = granite of various ages, blue = Paleozoic sedimentary rocks, green = Mid‐Tertiary volcanic rocks. The hachured areas are rocks sheared by faulting. (From Davis, 1987; reprinted 1990) 18 19 20 21 Deposition of the 120 m.y. old Willow Canyon Formation in Hot Springs Canyon (location of Saguaro‐
Juniper lands) occurred just within the rift basin that stretched into Arizona from the ancestral Gulf of Mexico. 22 References Atwater, Tanya, 1970, Implications of plate tectonics for the Cenozoic tectonic evolution of western North America, Bulletin of the Geological Society of America, v. 81, p. 3513‐3536. Bilodeau, W. L., 1986, The Mesozoic Mogollon highlands, Arizona: An early Cretaceous rift shoulder, Journal of Geology, v. 94, p. 724‐735. Davis, G. H., 1987, Saguaro National Monument, Arizona: Outstanding display of the structural characteristics of metamorphic core complexes, in Hill, M. L., ed., Cordilleran Section of the Geological Society of America: Geological Society of America Centennial Field Guide, v. 1, p. 35‐40. Dickinson, W. R., 1991, Tectonic setting of faulted Tertiary strata associated with the Catalina core complex, in southern Arizona, Geological Survey Special Paper 264, 106 pp, Geological Society of America, Boulder, Colo. Dickinson, W. R., and M. A. Klute (editors), 1987, Mesozoic Rocks of Southern Arizona and Adjacent Areas: Arizona Geological Society Digest, v. 18, 394 pp. Goodlin, T. C., 1985, Stratigraphic and structural relations of the area south of Hot Springs Canyon, Galiuro Mountains, Arizona, M.S. thesis, University of Arizona, Tucson, 101 pp. Goodlin and Mark, 1987, Tectonic implications of stratigraphy and structure of Cretaceous rocks and overlying mid‐Tertiary cover in Hot Springs Canyon, Galiuro Mountains, southeastern Arizona, in Dickinson, W. R., and M. A. Klute, eds., Mesozoic Rocks of Southern Arizona and Adjacent Areas: Arizona Geological Society Digest, v. 18, p. 177‐188. Hauck, W.R., 1985, Correlation and geochemical zonation of the mid‐Tertiary volcanic and intrusive rocks in the Santa Teresa and northern Galiuro Mountains, Arizona, M.S. Thesis, University of Arizona, Tucson, 140 pp. Kring, D. A., 2002, Desert Heat – Volcanic Fire, The Geologic History of the Tucson Mountains and Southern Arizona: Arizona Geological Society Digest 21, 103 pp. Ladd, T. W., 1975, Stratigraphy and petrology of the Quiburis Formation near Mammoth, Pinal County, Arizona, M.S. thesis, University of Arizona, Tucson, 103 pp. Mark, R. A., 1985, Structural and sedimentary geology of the area north of Hot Springs Canyon, southern Galiuro Mountains, Cochise County, Arizona, M.S. thesis, University of Arizona, Tucson, 96 pp. Spencer, J. E., and Reynolds, S. J., 1986, Some aspects of middle Tertiary tectonics of Arizona and southeastern California, in Beatty, B., and Wilkinson, P.A.K., eds., Frontiers in Geology and Ore Deposits in Arizona and the Southwest: Arizona Geological Society Digest, v. 16, p. 102‐107. Waldrip, R. W., 2008, Late Cretaceous thin‐skinned shortening in southern Arizona, M.S. thesis, University of Arizona, Tucson, 34 pp. 23