K-Ar and F-T Ages for Syntectonic Mid-Tertiary Volcanosedimentary Sequences Associated with the Catalina Core Complex and San Pedro Trough in Southern Arizona W.R
Total Page:16
File Type:pdf, Size:1020Kb
K-Ar and F-T ages for syntectonic mid-Tertiary volcanosedimentary sequences associated with the Catalina core complex and San Pedro trough in southern Arizona W.R. Dickinson and M. Shafiqullah Isochron/West, Bulletin of Isotopic Geochronology, v. 52, pp. 15-27 Downloaded from: https://geoinfo.nmt.edu/publications/periodicals/isochronwest/home.cfml?Issue=52 Isochron/West was published at irregular intervals from 1971 to 1996. The journal was patterned after the journal Radiocarbon and covered isotopic age-dating (except carbon-14) on rocks and minerals from the Western Hemisphere. Initially, the geographic scope of papers was restricted to the western half of the United States, but was later expanded. The journal was sponsored and staffed by the New Mexico Bureau of Mines (now Geology) & Mineral Resources and the Nevada Bureau of Mines & Geology. All back-issue papers are available for free: https://geoinfo.nmt.edu/publications/periodicals/isochronwest This page is intentionally left blank to maintain order of facing pages. 15 K-Ar AND F-T AGES FOR SYNTECTONIC MID-TERTIARY VOLCANOSEDIMENTARY SEQUENCES ASSOCIATED WITH THE CATALINA CORE COMPLEX AND SAN PEDRO TROUGH IN SOUTHERN ARIZONA WILLIAM R. DICKINSON Department of Geological Sciences, University of Arizona, Tucson, AZ 85721 MUHAMMAD SHAFIQULLAH Geologic features that define the Catalina core complex complex" of Keith and others, 1980; "Catalina-Rincon and San Pedro trough near Tucson in southeastern Arizona metamorphic core complex" of Bykerk-Kauffman and were produced by Tertiary extensional tectonism that Janecke, 1987). The term "San Pedro trough" is adapted accompanied crustal thinning (Davis and Hardy, 1981; here from oral usage developed by J. D. Lowell (personal Davis, 1983; Spencer, 1984). Stratigraphic and structural communication, 1984) during his classic study of the tilted relations of syntectonic sedimentary and associated vol San Manuel and Kalamazoo porphyry copper orebodies canic sequences of mid-Tertiary age help constrain the in (Lowell, 1968). ferred timing and geometry of extensional deformation The San Pedro trough is an elongate structural depres (Dickinson, 1984; Dickinson and Shafiqullah, 1986). This sion flanked on the southwest by the Catalina core com paper presents unpublished K-Ar and fission-track age plex, with mid-Tertiary mylonitic fabric along its southwest determinations that control the chronostratigraphy of key flank, and associated uplands lying farther north (fig. 1); to mid-Tertiary successions, and sets the new data in the con the northeast, the faulted front of the relatively unde- text of previously available information. formed Galiuro Mountains block is the breakaway zone for We infer that mid-Tertiary strata within the area have the detachment fault system that bounds the core com been affected principally by extensional deformation. Con plex. Tilted homoclines of mid-Tertiary strata are exten sequently, local or gentle folding that can be interpreted as sively exposed along the San Pedro trough, where they lie evidence of crustal shortening (Keith and Wilt, 1985) is unconformably beneath erosional remnants of younger ascribed instead to accommodation of kinematics asso Cenozoic basin fill, and are also locally exposed within ciated with crustal thinning by extensional fault systems eroded uplands of varied character to the southwest. having irregular geometric configurations (Naruk and others, 1987). STRATIGRAPHtC NOMENCLATURE The stratigraphic framework of mid-Tertiary horizons ANALYTICAL INFORMATION within the San Pedro trough, and flanking the Catalina core complex, has been obscured by proliferation of local forma- Analytical procedures discussed by Damon and others tional names, some unpublished but widely cited, and by (1 983) were used in this study (constants: X/j = 4.963 x inadvertent miscorrelations. The legend of figure 1 indi 10-10 yr-1, \e = 0.581 x IC^® yr"\ X = 5.544 x IQ-i® cates the lithostratigraphic terminology preferred here. yr~i ♦oK/K = 1.167 x 10"* atom/atom). Fission-track age A consistent set of Oligocene-Miocene formations, in determinations were done using methods described by cluding local members and fades, can be mapped through Naeser (1976) at the fission-track laboratory of the U.S. out the San Pedro trough and the uplands north of the Geological Survey in Denver and at the Uruversity of Catalina core complex: mid-Oligocene Mineta Formation, Arizona. Error estimates were made at 2 standard devia upper Oligocene Galiuro Volcanics, Oligocene-Miocene tions by combining Poisson errors of fossil, induced, and Cloudburst Formation, and lower Miocene San Manuel For neutron dosimetry counts. mation. Chronostratigraphic correlations and facies rela tionships remain unclear in detail between these units and acknowledgments various subunits of the Oligocene-Miocene Pantano Forma tion in the Tucson Basin and Cienega Gap south of the Wfi thank R. S. Balcer, J. J. Dickinson, J. B. Hansen, Catalina core complex. Overlying gently deformed J Lazerus R B. Scarborough, J. E. Spencer, J. L. Walsh, Miocene-Pliocene sequences are designated variously in and W w' Weibel for help in collecting samples, and R. R. different modern drainage basins; their stratigraphy is Butcher A. Fleming, and D. J. Lynch for participation in discussed here only as necessary to clarify the structural K-Ar analytical work. P. E. Damon advised us in various and stratigraphic relationships of the underlying mid- staaes of the study and C. W. Naeser helped us with Tertiary units. fission-track methodology. Field and laboratory work was suDDorted by National Science Foundation Grant EAR DATA PRESENTATION 80-18231 and by the Laboratory of Geotectonics in the Department of Geosciences at the University of Arizona. Our new analytical results are given in the following sec tions. Previously published K-Ar ages relevant for discus DISCUSSION sion of the new data are compiled in tables 1 -3 Locations of our samples and those of table 2 are plotted on figure 1 MORPHOSTRUCTURAL TERMINOLOGY Figure 2 displays the array of ages for mid-Tertiary volcanic rocks demonstrating a late Oligocene puise of intermediate The term "Catalina core complex" is adopted here (after volcanism. Figure 3 shows the distribution of key mid- Rehrig and Reynolds, 1980) to designate the Cordilleran Tertiary stratigraphic sections correlated in figure 4 which core complex denoted also by several other more cumber also indicates the past stratigraphic usages of previous some names ("Santa Catalina-Rincon-Tortolita crystalline authors. [ISOCHRON/WEST, no. 52, March 1989] 16 □ post-mid-Miocene basin fill mid-Tertiary sedimentary rocks Tsm, San Manuel Formation main highways Tss, Soza Canyon facies Tsk. Kelsey Canyon facies Tsp, Paige Canyon facies rivers & streams Tcs. sedimentary member of - dome Cloudburst Formation ARIZONA Tpa. Pantano Formation normal contacts Tmi, Mineta Formation mid-Tertiary volcanic rocks fault contacts Ttv. volcanics of Tucson Mts. Tcv. volcanic member of River Hayden Cloudburst Formation detachment fault, dotted where concealed Tgv, Galiuro Volcanics mkJ-Tertiary mylonitic fabric ATgw-^ \ y mylonitic lineation mkJ-Tertiary granitic rocks along flank of (Catalina and Tortolita Catalina Core Complex Plutons) Aravaip^ II pre-Upper Eocene bedrock " (varied) ^Mammoth Falcon Valley a—rDesert San Manuel 32*30'N Catajipa Piuton Tortolita Piuton Safford Tucson Basin I C-Valley— Hills K-Ar localities 2« this paper 32» OO'N Table 2 figure 1 Geologic map of CataHna core complex and San Pedro trough showing areal distribution of tilted homoclines of dated mid- Tertiary volcanosedimentary successions in relation to older bedrock exposures and Lunanr hnsin fill (after Dickinson, 1987,1988). Local (T9"77)"and^o°oTunS Banks (1980), Budden (1975), Davis (1980), Drewes (ISOCHRON/WEST, no. 52, March 1989] 17 PUBLISHED K-Ar AGES TABLE 1. Published K-Ar ages for mId-Tertlary volcanic fields TABLE 2. Published K-Ar ages for mid-Tertiary volcanic rocks of Tucson and Galluro Mountains near Catallna core complex and San Pedro trough (continued) See fig. 1 for general locations, (w) whole rock, (b) biotite, (s) Age (Ma) sanidine, (p) plagioclase, (f) feldspar. All ages cited in recalculated form reported by Reynolds and others (1986) using most accurate currently known decay constants (numbers from their listing in E. quartz latlte lava of The (h) 25.1 ±0.4 Banks and brackets). Each data set (A, B, C, D) given in apparent stratigraphic Huerfano butte west of (b) 23.5±0.4 others, 1979 order from oldest to youngest. Suizo Mountains [#694 & #617] Age(Ma) F. quartz latlte lava near Chief (b) 26.7 ±0.5 Banks and A. Galluro Volcanics of Galluro Mountains (Creasey and Krieger, Butte north of Tortollta others, 1979 1978; coordinate sanidine K-Ar ages for several samples are Mountains [#765] consistently 1 -3 Ma younger): G. ollvlne-bearing basalt lava (w) 21.0±0.5 Banks and ash-flow tuff of lower part[#8491 (b) 28.9 ±0.8 at base of San Manuel others, 1979 rhyolite dike in lower part [#81 7] (b) 28.1 ±0.8 Formation In Three Buttes Holy Joe (ash-flow tuff) Member [ave. of area [#535] #785 & #786] (b) 27.3 ±0.8 H. basaltic lava near base of (w) 28.3 ±0.6 Shaflqullah and Tuff of Bear Springs Canyon [#661] (b) 24.4 ±0.7 type Cloudburst Formation others, 1978 Aravalpa (ash-flow tuff) Member[#752] (b) 26.4 ±1.0 In Cloudburst Wash near Hells Half Acre Tuff Member[#703] (b) 25.3 ±0.7 Mammoth [#826] 8. Safford Peak area of northern Tucson Mountains (BIkerman I. rhyolite dike Intruding Pre- (b) 22.8 ±0.7 Marvin and Cambrian basement In Dobson, 1979 and Damon, 1966): Putnam Wash west of Rlllito andeslte (Ignlmbrlte?)[#946] (b) 39.4±1.3 mouth of Aravalpa Creek 25.2 ±1.4 Safford Peak bedded tuff[#697] (b) [#597 = #576] Contzen Pass vltrophyre (Ignlmbrlte?)[#760] (w) 26.6 ±1.2 Safford Peak andeslte (Ignlmbrlte?)[#832] (b) 28.5±1.9 J. rhyodaclte tuff near top of (b) 17.5 ± 1.0 Berry and Safford Peak daclte neck [#690] (b) 25.1 ±0.9 tuffaceous sandstone Inter others, 1976 val In San Manuel Formation C.