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An Alkali-Basalt Through Trachyte Suite, Mesa'chivato Mount Taylor Volcanic Field, New Mexico

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An Alkali-Basalt Through Trachyte Suite, Mesa'chivato Mount Taylor Volcanic Field, New Mexico An alkali-basalt through trachyte suite, Mesa'Chivato Mount Taylor volcanic field, New Mexico L. S. CRUMPLER Department of Planetary Sciences, University of Arizona, Tucson, Arizona 85721 Geological Society of America Bulletin, Part II, v. 91,.p. 1293-1331, 8 figs., 5 tables, May 198.0.Doc. no. MOO501 ite) and trachyte compositions. This ABSTRACT' progression, together with minor-element A complete alkali basalt through trachyt and isotopic data,. suggests that the .. volcanic suite has been documented from suite evolved by fractional crystalliza- the central part of the Mount Taylor 301- tion of basaltic magmas. canic field, New Mexico (the southeast Volcanologic diversity of the field is margin of the Cdlorado Plateau) showing illustrated by the variety of land forms, mineralogic, chemical , and field relations including numerous maars, pit craters, similar to alkalic volcanism of both silicic flow-domes, and distinct north- continental and oceanic settings through- easterly oriented fissures. Northeast- out the world. Thus, the Mount Taylor southwest oriented faults with as much as field is fundamentally distinct from the 30-m displacements were active concurrently -. ._ .'I a predominaqfly calc-alkalic to low-Ti with the volcanism, and,.-speral faults y%, I 'L / k: alkali basaltfc volcanism of the Basin are superposed on fYssure lines, suggesting and Range Provice as a whole. that the volcanism was a consequence of Eruptions of the rocks began in deep fracturing of the margin of the f Pliocene-Pleistocene time with alkali Colorado Plateau by late Cenozoic Basin basalt (basanatoid) and cont iniied through and Range faulting. intermediate (hawai'ite, mugearite, benmor- 1293 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/91/5_Part_II/1293/3429676/i0016-7606-91-5-1293.pdf by guest on 02 October 2021 ;rtY*'.--- (i? :k -_, . .:, .:, ..!.'I' (>,'r ' $' . \.~ .. .A*' '* _,.I.. $7 1 just beyond the western margin of the Kio INTRODUCTION Grande RiEt , as defined. by Cordeli (1978), Volcanism in the Pliocene-Pleistocene makes it the only k'&wn example of a Mount Taylor volcanic field (Mesa Chivato) classic rift volcanic suite associated of New Mexico included :he eruption of with the Rio Crande Rift. two distinct petrologic suites, the first GEOLOGIC SETTJN~ of which is uncommon in the North American General mainland and includes an alkali basalt- hawaiite-mugearite benmorite- trachyte The Mount Taylor field is dominated by I volcanic suite with sodic affinities, akin the Mount Taylor composite volcano (Hunt, to Hawaiian alkalic volcanism. The 1938; Lipman and others, 1979; Crumpler, second suite consists of a diverse series 1978) and lies on the southwest edge of of porphyritic alkali basalts and domi- the Colorado Plateau, 100 km west of. I nantly aphyric hawaii tes, unconforrnably Albuquerque. and the Rio Grande Val iey overlying the lavas of the preceding of central New Mexico. The' style of alkalic suite. Petrographic, chemical, volcanism is similar to that of other and isotopic data, together with detailed Colorado plateau-marginal volcanic fields mapping (1:24,000) of the interior of (Hunt, 1956; Best and Brinhall, 1974; the field (Crumpler, 1976, 1977) indicate Thornbury, 1965), such as the 3an Fran- that both suites are characterized by . cisco and Springerville-W:~ite Piountains relatively simple trends in which basaltic Fields, Arizona, in that Khere is complex lavas preceded more silicic flows. Thus, clustering of smaller basaltic and silPbic volcanism in the Mount Taylor field is vents associated with a single large significant by virtue of its compositional composite volcano of dominantly andcsi tic range and uniqueness in the record of to dacitic composition. Detailed mapping d - late Cenoioic volcanism in the western covered part of Mesa'Chivato, which United States. Furthermor.e, its location extends 50 km northcast from Piount Taylor Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/91/5_Part_II/1293/3429676/i0016-7606-91-5-1293.pdf by guest on 02 October 2021 1 (Fig. 1) .at an .average elevation of with 10- to 20-m vertjcal displacements. 2,700 m, some j00 to 400 m above the A few cinder cones. appear to be super- adjoining Rio Puerco,and its tributaries.- imposed on faults several kilometres long, t The mapped part (Fig. 2)' includes about and some cone5 show resulting minor ., ', * 100 cinder-and-spatter cones, trachyte vertical offsets, as do the underlying. flow-domes, maar-s, and pit craters, most basalt flows. Referring to the sequence of which lie on distinct north-northeast- - of fault scarp degradation of Xallace oriented fissures. In'many cases, indl- (1977, Fig. 3), most of the scarps have I1 0 vidual craters and flow-domes are elonga- been reduced to "wash-controlled" slopes, ted in a north-northeast sense. the last stage in the degradation series. Considering such evidence as the age of . Late Cenozoic Tectonics the flows ('about 3 m.y.), the resistance The Mount Taylor field lies on the of the basaltic flows, and the present I Jemez lineament (Jones, 1952; Mayo, 1958) ,. gentle slopes of what were formerly steep and although the field is elongate in a flow margins, the faulting probably trend approximately parallel to the trend dates cToser to the time of volcanic -.. .. of tne lineament (N50°E), individual activity in the field than to the present. fissures trend N30°E. Northeasterly Thus, the fault scarps indicate that there fissures occur in adjacent fields along has been moderate, seismicity in this area, the lineament as well, including the at least through Pleistocene time. Th,is Bandera field in the southwest' (Laughlin may likewise be true of some faulting in * and others, 1972) and the pre-Valles Q the adjoining Rio Puerco fault'belt . Caldera'basalts of the Cerros del Rio (Slack a-nd Campbell, 1976). which forms .- field'to the northeast (Aubele, 1978, 1979) the transition zone between the Colorado Several of the more prominenf fissures Plateau and the Rio Grande rift. The in the Mount Taylor-field are cut by ubiquitous northeast trends are also parallel north-northeast-oriented faults manifest in the numerous dikes and volcanic Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/91/5_Part_II/1293/3429676/i0016-7606-91-5-1293.pdf by guest on 02 October 2021 1296 Figure 1. Location of- the Mount Taylor volcanic field with respect to other late Cenozoic extrusive volcanic rokcs and the Rio Grand’e rift, i) New Mexico. Map ’modified from Woodward and others (1975). Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/91/5_Part_II/1293/3429676/i0016-7606-91-5-1293.pdf by guest on 02 October 2021 1297 EXPLANATION - h m >R - 12m Fi'gure 2. Simplified geologic map UNCONFORMlTy . I-- of the northern interior of the Mount r Taylor volcanic Meld. Mapping based on the,El Dado.Mesa and Laguna Seca m 7% minuKe -topogfaphic quadrangles. Circled sample location numbers refer to analysis numbers of Table 3. Contact lines within units represent separable flow margins, or separate vent centers , 'mBENMORITE c and their slopes. "Porphyritic alkali MAAR RIM MUGEARITE __ - EJECTA .. -.. _.-- basalt" locally includes megacryst- bearing alkali basalt, and "late hawaiite" locally includes silicic alkali basalt. Figure 2 is continued on-the following f raves. m] TRACHYTE IF]MESAVEROE GROUP srRllC'TUR4L 'CRATER ,i. FAULT Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/91/5_Part_II/1293/3429676/i0016-7606-91-5-1293.pdf by guest on 02 October 2021 1298 U03O' 109m' Figure 2. (Continued) Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/91/5_Part_II/1293/3429676/i0016-7606-91-5-1293.pdf by guest on 02 October 2021 1299 ..I ..I ... ... ... ..I ..4 01I !.: Figure 2. (Continued) I Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/91/5_Part_II/1293/3429676/i0016-7606-91-5-1293.pdf by guest on 02 October 2021 30 necks of the Rio Pu,erco VaLley (Johnson, folding is not restricted in its effects 1907), and they suggest a history of to the crust, butcmost influence (or be tensile stress along ‘the Colorado Plateau- influenced by) the upper mantle as well. Rio Grande rift juncture through The fact remains that there is a clear Quaternary time. relationship between the sag and the dis- tribution of volcanic centers in the Mount Relation to Colorado Plateau Tectonics Taylor field. The,Mount Taylor volcano, Hunt ‘(1938) first recognized the fact a complex center of andesitic and alkalic that the Mount Taylor field lavas uncon- lavas, lies on the deepest point of the formably overlie the Late Cretaceous to Acoma sag; the field to the north, includ- early Tertiary (Laramide) structural de- ing the entire assemblage of vents for pression known as the Acoma sag (Kelley, the alkalic suite reported here, lies 1955) and suggested that the sag and the along itas north-northeast structural volcanism ?re somehow related (Fig. 3). trough-like extension. Because the Acoma sag predates the It is probable that the relationship I volcanism by as much as 70 m.y., it may does reflect fundamental chemical or reflect a fundamental influence of uplifts thermal displacements of unknown ‘origin and basins#*which typify the tectonics of during Laramide time of the upper mantle. the Colorado Plateau, on the underlying Why such an event should manifest itself mantle, or alternately an influence of as surface volcanism 70 m.y. later is mantle dynamics on vertical crustal move- enigmatic. A number of scenarios can be ments. Colorado Plateau uplifts and conjured up explaining the significance ’basins (Woodward, 1973) evoke compressional of such tectonic sags with respect to tectonism, crustal folding, and lateral an alkalic suite in a continental terrain, displacements caused by regional stresses but such models arc futile until the on the Colorado.
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