K-Ar and fission-track ages (dates) of volcanic intrusive, altered, and metamorphic rocks in the Mohave Mountains area, west- central Arizona J.K. Nakata, M.A. Pernokas, K.A. Howard, J.E. Nielson, and J.R. Shannon Isochron/West, Bulletin of Isotopic Geochronology, v. 57, pp. 21-32 Downloaded from: https://geoinfo.nmt.edu/publications/periodicals/isochronwest/home.cfml?Issue=57 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. 21 K-Ar AND FISSION-TRACK AGES (DATES) OF VOLCANIC INTRUSIVE, ALTERED, AND METAMORPHIC ROCKS IN THE MOHAVE MOUNTAINS AREA, WEST-CENTRAL ARIZONA J. K. NAKATA M. A. PERNOKAS U,S. Geological Survey, Menio Park, CA 94025 K. A. HOWARD J. E. NIELSON U.S. Geological Survey, Denver, CO 80225 J. R. SHANNON Current address: Crown Resource Corp., Republic, WA 99166 114^30' The Mohave Mountains and adjacent ranges of west-central Arizona (fig. 1) occupy a key area for unraveling the evolution of Tertiary tectonics in the SSS3S333SSS8S3SS$S!sOUTLINE OF FIGURE 2. «®S35S8S538S3S3S?3SSSS« Colorado River extensional corridor. The IA Powell Peak area lies in the east part of the north- BUCK MOUNTAINS trending, 100-km-wide corridor, and Tumarion flanks a belt of metamorphic core com Peak plexes that define the center of the cor ridor (Davis and others, 1980; Howard and John, 1987). Field studies in the Mohave Mountains area indicate a record of extension-related Tertiary intrusion, volcanism, sedimentation, detachment MOHAVE MOUNTAINS faulting, tectonic fragmentation, and tilting (Howard and others, 1982a, in Grossman press; Pike and Hansen, 1 982; Nakata, 1 982; Light and others, 1 983; Nielson, ARIZONA 1986; Nielson and Glazner, 1986; Howard and John, 1987; Nielson and Havasu City Lake Beratan, in press). The dating was carried Havasu out partly to support an appraisal of mineral-resource potential (Light and others, 1983). Preliminary K-Ar dates reported earlier (Light and others, 1 983; CALIFORNIA Nielson, 1986; Glazner and others, AUBREY 1 986) are here fully documented, and in HILLS some cases have been corrected. Correc BiaWlLLAMS tions follows discovery by Nakata of a MOUNTAINS spike calibration error. In this paper we report 57 conventional O I NEVADA K-Ar and 7 fission-track ages (dates) on \ 52 rock samples located in figure 2. We ARIZONA term those with mixed cooling histories \ WHIPPLE dates, following Armstrong (1966), to MOUNTAINS emphasize that they do not necessarily correspond to emplacement ages. Dated 10km rocks include 13 volcanic, 14 dike, 6 granitoid, and 9 gneissic rocks and 6 rocks that experienced alteration related FIGURE 1. Location map of the Mohave Mountains area, AZ. to mineralizing processes. Materials dated by K-Ar were: biotite, sanidine, plagioclase, muscovite, sericite, hornblende, and whole The ages on volcanic rocks (figs. 3a, 4)in most cases are rocks. Zircon was dated by fission tracks. Figure 3 divides consistent with or close to the crystallization age inferred the dated rocks into four sample groups and presents from regional geologic relations, although dates on some histograms of the ages, identified by the material dated. hornblende and sanidine separates seem too young. These ages help to calibrate the time of Tertiary deposi Tertiary and Mesozoic dikes and stocks (fig. 3b) yielded tion and deformation, constrain the timing of different biotite ages that in many cases are geologically consistent styles of Tertiary magmatism, and provide age information as emplacement ages but, whole-rock, plagioclase, and helpful for interpreting Tertiary uplift, Mesozoic alteration hornblende dates are nearly all variant. Secondary and intrusion, and cooling of Proterozoic rocks. We inter muscovite from altered gneiss yielded dates that can be pret ages of events from these dates within the framework interpreted as near the age of alteration, but finer grained of our working model established by field studies from I0W-K2O sericite and zircon yielded younger dates. Dates 1979 to 1987. determined from biotite and zircon (fission-track) on [ISOCHRON/WEST, no. 57,July 1991] 22 114022*30- 114015*00" 114007*30- KILOMETERS Amphibolrte POWELL PEAK BUCK Augen FAULT 46 1^3 Basalt 14.6 MOUNTAINS Granite 597]. I ; (WRK-Ar) IB. K-Ar) Tonalite 863 (B. K-Ar). 73.8 ; 14 Andesite porphyry (Z.FT) 19.8 (WaK-Ar) 47 • 22J-* ' 13 Volcanic breccia O'orite » Tuff 18.0 (San. K-Ar) 48.0 (B. K-Af) 72 5 0 Obrite 32.0 (B. K-Ar) (H. K-Ar) 27 "/» Toff 17.6 Dacite 20.8 '- '(San, K-Ar) Aug0n^«\.^9 Granite 18.1^ (B. K-Ar) Gneiss \ (B, K-Ar). 16.6(Z. FT) 41 Gneiss 49.2 Rhyolite 15.1 -c* " ^ :. (B.K-Ar) (P. K-Ar)V .^ (Z- ^• 24 Dadte 19.8 (B. K-Ar) 19 ArKfesite 78.1 r,: * V*- •* **A10 19.1 (B, K-Ar). (Wa K-Ar) . ^ .• .;(B. K-Ar). 16.3 ;\'8\ Latite><TXi7.2(H.K 19 ■ I 16 Diorite 2^6 K-Ar) - .w (B. K-Af) Altered rockX Andesite r: . / (H. K-Ar). 26.9(H. K-Ar) •102 (WM. K-Af\ ^2.9 (WR. K-Ar) 18 ArKfeshe 42.7 •/ 1 crossman\block • (P. K-Ar) /- • V.17 Diorite 21.7 Leucogneiss (H. K-Ar) 28 VOuanz diorrte 7 Tuff 116 (B.K-Ar) 22 MicrodiorHe 21.5 (B.K-Ar) • Augen gneiss 52 29.2 (H. K-Ar) (P. K-Ar) 45 13.8 (B. K-Ar) 21 Microdiorite 42.0 Amphibolite / . > < A187 (B. K-Ar) (WR.K-Ar) 40 Ill (H.K-Ar)S: 25# ^31 Rhyolite 62.3 33 Altered gneiss 54.9 23# Dadte 19.2 ^ (B.K-Ar) (Ser. K-Ar) Dadte 18.4 34 Altered gneiss 65.0 ;^-.a(WaK-Af). (B.K-Af) 37 Altered gneiss (Ser. K-Ar). 78.0(Z. FT)^ 11.3(WR-A, K-Ar) 92.0 (WM.K-Ar) 35 Altered gneiss 91.4 (WM. K-Ar) 1 Basalt 11.1 ■» 36 Altered gneiss 89.7 A V , (V/M. K-Ar) EXPLANATION Lake Quaternary deposits Havasu City rr<~!r3 < > - * !1 deposits Perlhe < i.'' 7 ^ - ^ ^ 2 Tuff 12.7 V • (San. K-Ar) Pre-Teniary rocks (Cretaceous and Proterozoic) Contact BILL WILLAMS MOUNTAINS Lo/r-angle fault- Hachures on upper plate 48 Gneiss 130 AUBREY HILLS ^ (B. K-Ar). 81.7 (Z. FT) Sample Flock^YP^ Mineral dated kxation^ j Age tMe) Method # 39 Microdiorite 24 DACITE 20.8 (B. K-AR) 26 Dacite 19. 332 (H. K-Ar) / (B. K-Ar) Z- Sinriplifiod QooloGic index men of fha im u >a which was collected from the WhioDle Mountaine showing sample localities and dates except for sample number 26, not portrayed for graphic simplicltv The minnrai ot the map area. The northwest-southeast trending Mohave Mountains dike swarm Is sanldlne, Ser = serlclte, WR = whole rock, WM J°white B = blotlte, H = hornblende, P = plagloclase, San = mica, Z = zircon. and zircon (fission-track) (Armstrong 1966; Turner and If cooling Is relatively slow and excess radiogenic products Forbes 1976; Harrison and others 1979; and Hurford are not incorporated by the minerals, those species with 1986). This order varies depending upon the extraction ower bloclung temperatures will give younger ages than technique used to determine the blocking temperature (Harrison and Fitzgerald 1986; Gaber and others 1988). those with higher blocking temperatures. A common order Other factors that complicate interpretation of the numerical of progressively decreasing closure or annealing tempera age include rate of cooling, mineral structure, and availability tures is; hornblende (K-Ar), muscovite (K-Ar), biotite (K-Ar) of excess radiogenic argon from external sources. [ISOCHRON/WEST. no. 57, July 19911 23 WR SAM 10 8 8 8 A. VOLCANIC ROCKS B N P H H SAM H WR WR WR WR 8 JH 1 1 1 1 1 i i i i ! I I I I I i 300 500 700 900 1100 1300 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95100 200 400 600 800 1000 1200 10 B. DIKES AND STOCKS N 5 m —r—r n n Fi T—I—r —!—I—i—I—I—I—I—I—I—I—I / 300 500 700 900 1100 1300 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95100 200 400 600 800 1000 1200 10 0. ALTERED GNEISS N 5 Isr] faTI (T1 "I I i I I i I I I I I 1 I I I 1 i I I iN/ l I I ; I I i ! I I j I 0 5 10 15 20 25 30 35 40 45 50 55 60 6570 75 80 8590 95l002OO^00400®00gOO^°°3QQ900Q0'Q'9°2O02°° 10 D. PROTEROZOIC ROCKS N HL n—r I I 1 n—r 1—r ^ . n . n , , , F! 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 ^°°200^°%0^°°600^°°800^°°1 OoV°1200^°° AGE (Ma) FIGURE 3. Histograms of dates, divided into four groups of samples. Abbreviations: (K-Ar) WR = whole rock, H = homblende, P plagioclase, San = sanidine, B = biotite, M = muscovite, Ser = sericite; (fission-track) Z = zircon.