AND MINERAL DEPOSITS of the GRANITE WASH MOUNTAINS, WEST-CENTRAL ARIZONA by Stephen 1
Total Page：16
File Type：pdf, Size：1020Kb
GEOLOGIC MAP, GEOLOGIC EVOLUTION; AND MINERAL DEPOSITS OF THE GRANITE WASH MOUNTAINS, WEST-CENTRAL ARIZONA by Stephen 1. Reynolds! , Jon E. Spencer! , Stephen E. Laubach2 3 4 Dickson Cunningham , and Stephen M. Richard Arizona Geological Survey Open-File Report 89-04 August 1989 Updated September,1993 (5 pages added) Arizona Geological Survey 416 W. Congress, Suite #100, Tucson, Arizona 85701 Produced in cooperation with the U.S. Geological Survey as part ofthe Cooperative Geologic Mapping (COGEOMAP) Program 1- Arizona Geological Survey, 845 N. Park Ave., # 100, Tucson, AZ 85719 2 - Bureau ofEconomic Geology, The University ofTexas, Box X, University Station, Austin, TX 78713 3 - Dept of Geosciences, Univ. ofArizona, Tucson, AZ 85721 i presently at Dept. of Geological Sciences, The University ofTexas, Austin, TX 78713 4 - Dept. of Geological Sciences, Univ. of California, Santa Barbara, CA 93106 This report is preliminary and has not been edited or reviewed for conformity with Arizona Geological Survey standards INTRODUCTION and others, 1987, in press), and some parts of The Granite Wash Mountains are located this report derive from these earlier publica in west-central Arizona and are contiguous tions. Previous geologic studies in the range with the Harcuvar Mountains to the northeast consist mostly of regional reconnaissance and the Little Harquahala Mountains to the (Bancroft, 1911; Wilson, 1960; Kam, 1964; south. They are part of the Maria [old and Wilson and others, 1969; Rehrig and thrust belt, a belt of large folds and major Reynolds, 1980) and two theses covering thrust faults that trends east-west through limited areas (Ciancanelli, 1965; Marshak, west-central Arizona and southeastern 1979). California (Reynolds and others, 1986). In the Granite Wash Mountains, late Mesozoic REGIONAL GEOLOGIC SETTING deformation related to the Maria belt affected The oldest rocks in the region are a diverse suite of rock units, including Proterozoic gneiss, schist, amphibolite, and Proterozoic crystalline rocks, Paleozoic car dioritic to granitic rocks. These are deposi bonate and quartzose clastic rocks, and tionally overlain by a 1-km- thick sequence of Mesozoic sedimentary, volcanic, plutonic, and Paleozoic carbonate and clastic rocks. Indi hypabyssal rocks. This deformation was vidual Paleozoic formations maintain their mostly deep seated and produced an assort distinctive characteristics, even where ment of folds, cleavages, and both ductile and metamorphosed and greatly attenuated (Stone brittle shear zones. Several discrete episodes et aI., 1983), and are therefore extremely of deformation occurred, resulting in refolded useful for unraveling complex structure. folds, folded and refolded thrust faults, and complex repetition, attenuation, and trunca Mesozoic sedimentary and volcanic rocks tion of stratigraphic sequences. Greenschist in the region can be subdivided into the facies metamorphism accompanied deforma following four units (in ascending strati tion and was most intense along the major graphic order): thrusts. Deformation and metamorphism were followed by emplacement of two Late (1) Buckskin Formation (Reynolds and Cretaceous intrusions and numerous dikes. Spencer, 1989), a sequence of variably cal careous siliciclastic rocks and phyllite, with The geology of the Granite Wash Moun local conglomeratic, feldspathic, and tains was mapped between 1982 and 1988 as evaporitic intervals. This unit rests deposi part of the U.S. Geological Survey - Arizona tionally on Permian Kaibab Formation and Geological Survey Cooperative Geologic largely correlates with Triassic Moenkopi Mappitig (COGEOMAP) Program, whose goal Formation of the Colorado Plateau (Reynolds is to map the geology of the Phoenix 1° X 2° and others, 1987); quadrangle. The entire mountain range was mapped at a scale of 1:24,000 (Reynolds and (2) Jurassic or Late Triassic Vampire Spencer), with additional, generally more Formation (Reynolds and Spencer, 1989), detailed mapping in the central (Laubach and consisting of impure quartzose sandstone and Reynolds), northern (Cunningham), and quartzite, with conglomerate at the base and northwestern (Richard) parts of the range. In locally higher in the section. Because of a addition to the mapping, we performed major episode of Late Triassic or Early detailed structural and petrographic analysis Jurassic uplift, the basal conglomerate at key localities. unconformably overlies a variety of older rock units, including Buckskin Formation, This report accompanies a 1:24,000-scale Paleozoic rocks, and Proterozoic crystalline black-and-white map and presents the results rocks (Reynolds and others, 1989). The for of the mapping and describes major findings mation probably correlates with the Jurassic about stratigraphy, structure, and metamor Glen Canyon Group of the Colorado Plateau phism. Some aspects of the research have (Reynolds and others, 1987); been presented elsewhere (Reynolds and others, 1983, 1986b, 1987, 1988, 1989; (3) Jurassic intermediate to silicic Cunningham, 1986; Laubach, 1986; Laubach volcanic and volcaniclastic rocks dated at about 160 Ma (Reynolds and others, 1987). upright folds and major ductile and brittle This unit largely consists of feldspar- and thrust faults. The folds are associated with quartz-phyric ash-flow tuffs, hypabyssal extreme attenuation of Paleozoic and intrusions, volcaniclastic rocks, and their Mesozoic sections and widely involve the un schistose, metamorphosed equivalents. The derlying Proterozoic crystalline basement. volcanic sequence is locally accompanied by The larger thrust zones include tectonic slices contemporaneous(?) granitoid plutons (Tosdal of Jurassic or Proterozoic crystalline rocks and others, in press); and and commonly juxtapose thrust plates with contrasting Mesozoic sequences and histories. (4) McCoy Mountains Formation, a The thrust and folds have been locally over sequence of dominantly clastic rocks of printed by northeast-vergent shearing and a Jurassic age (Harding and Coney, 1985), late, southwest-dipping cleavage (Richard, Cretaceous (Stone and others, 1987) age, or 1988). both (Tosdal and others, in press). In several ranges, the McCoy Mountains Formation is 5 Late Cretaceous and early Tertiary to 7 km thick and has been subdivided into granitoid plutons and dikes intruded after the following six members (from bottom to thrusting and were accompanied by deforma top): (a) basal sandstone member one; (b) tion and amphibolite-facies metamorphism in basal sandstone member two; (c) mudstone the Harcuvar and Harquahala Mountains member; (d) conglomerate member; (e) (Rehrig and Reynolds, 1980; DeWitt and sandstone member; and (f) siltstone member others, 1988) but not in the Granite Wash (Harding and Coney, 1985). These thick se Mountains. A major episode of Late quences define a west-northwest-trending Cretaceous to early Tertiary regional uplift outcrop belt, termed the McCoy basin followed plutonism and metamorphism, as (Harding and Coney, 1985; Reynolds and indicated by widespread 70 to 45 Ma K- Ar others, 1986), which includes the Granite cooling ages on a variety of rock types, by Wash, Little Harquahala, Plomosa, and Dome the relatively deep-level character of exposed Rock Mountains of Arizona and the McCoy, Late Cretaceous and early Tertiary granitoids, Palen, and Coxcomb Mountains of and by the absence of Upper Cretaceous and southeastern California. Some· sections of lower· Tertiary supracrustal:rocks(Reynolds McCoy Mountains Formation are thinner (less and others, 1986b, 1988). than 2 km) and cannot be unambiguously correlated with these six members (Harding Middle Tertiary history of the region and Coney, 1985). To differentiate the two included widespread volcanism, dike different sequences of McCoy Mountains emplacement, and sedimentation that was Formation, we have used the term Apache commonly synchronous with normal faulting, Wash facies for the thinner sequence (after fault-block rotation, and tens of kilometers of Harding and Coney, 1985) and basin facies transport on gently dipping, ductile shear for the thicker sequence (Reynolds and zones and detachment faults (Reynolds and others, 1986). Spencer, 1985; Spencer and Reynolds, 1989, in press). The Harcuvar Mountains, adjacent Subsequent to deposition of the McCoy to the Granite Wash Mountains, are a Mountains Formation, late Mesozoic tec metamorphic core complex that was tectoni tonism affected the region. Deformation and cally denuded during middle Tertiary detach metamorphism were apparently concentrated ment faulting (Rehrig and Reynolds, 1980). in the east-west-trending Maria fold and Late Tertiary and Quaternary events in the thrust belt, which extends from the Palen and region included: (1) minor Basin and Range Coxcomb Mountains of southeastern Califor normal faulting that blocked out some present nia to the Harquahala and Eagle Tail Moun basins, (2) movement on northwest-trending tains of west-central Arizona (Reynolds and strike-slip, reverse, and normal faults within others, 1986b, 1988; Hoisch and others, 1988). the ranges, (3) eruption of basaltic lavas, (4) The thrust belt is characterized by generally deposition of nonmarine clastic rocks and the southeast-, south-, and southwest-vergent Pliocene Bouse Formation, and (5) integration structures, including large recumbent to of previously internal drainage systems with 2 accompanying sediment deposition in alluvial the range. These thrusts subdivide the range fans and along stream channels. into four