Research about San Francisco volcanic field

USGS2016

Database compilation for the geologic map of the San Francisco volcanic field, north-central Arizona

The main component of this publication is a geologic map database prepared using geographic information system (GIS) applications. The geodatabase of geologic points, lines, and polygons was produced as a compilation from five adjoining map sections originally published as printed maps in 1987 (see references in metadata). Four of the sections (U.S. Geological Survey Miscellaneous Field Studies Maps MF–1957, MF–1958, MF–1959, MF–1960) were created by scanning and geo-referencing stable base map material consisting of mylar positives. The final section (MF–1956) was compiled by hand tracing an enlargement of the available printed paper base map onto mylar using a #00 rapidograph pen, the mylar positive was then digitally scanned and geo-referenced. This method was chosen because the original basemap materials (mylar positives) for the MF–1956 section were unavailable at the time of this publication. Due to the condition of the available MF–1956 map section used as the base (which had previously been folded) the accuracy within the boundary of the MF–1956 section is presumed to be degraded in certain areas. The locations of the degraded areas and the degree of degradation within these areas is unclear. Final compilation of the database was completed using the ArcScan toolset, and the Editor toolset in ESRI ArcMap 10.1. Polygon topology was created from the lines and labels were added to the resultant geological polygons, lines, and points. Joseph A. Bard and David W. Ramsey updated and corrected the geodatabase, created the metadata and web presence, and provided the GIS-expertise to bring the geodatabase and metadata to completion. Included are links to files to view or print the original map sheets and the accompanying pamphlets. The orignial geologic maps were prepared under the Geothermal Research Program of the U.S. Geological Survey as a basis for interpreting the history of magmatic activity in the volcanic field. The San Francisco field, which is largely Pleistocene in age, is in northern Arizona, just north of the broad transition zone between the Colorado Plateau and the Basin and Range province. It is one of several dominantly basaltic volcanic fields of the late Cenozoic age situated near the margin of the Colorado Plateau. The volcanic field contains rocks ranging in composition from basalt to rhyolite—the products of eruption through Precambrian basement rocks and approximately a kilometer of overlying, nearly horizontal, Paleozoic and Mesozoic sedimentary rocks. About 500 km 3 of erupted rocks cover about 5,000 km 2 of predominantly Permian and locally preserved Triassic sedimentary rocks that form the erosionally stripped surface of the Colorado Plateau in Northern Arizona.

Arizona↗

USGS1987

Geologic map of the east part of the San Francisco Volcanic Field, north-central Arizona

The geologic map of the east part of the San Francisco volcanic field (called the East map area) is one of five adjoining geologic maps (fig. 1) prepared under the Geothermal Research Program of the U.S. Geological Survey as a basis for interpreting the history of magmatic activity in the volcanic field. This map is a revision of an earlier one (Moore and Wolfe, 1976). Detail of pyroclastic and alluvial deposits has been reduced for clarity on this uncolored version, and eolian deposits, represented by numerous active dunes of basaltic ash, have been completely omitted. Small cinder cones developed over rootless vents on the basalt flow (Qbb) of = vent 2019 have also been omitted. In addition, a few changes have been made in correlations of flows and vents. The stratigraphic classification has been modified because magnetic-polarity determinations and new K-Ar ages indicate that the physiographically defined Tappan and Woodhouse age groups (Moore and others, 1976) overlap significantly in age, and the rocks of those age groups are now assigned to the Brunhes or Matuyama Polarity Chronozones (Mankinen and Dalrymple, 1979). The San Francisco field, which is largely Pliocene and Pleistocene in age, is in northern Arizona, just north of the broad transition zone between the Colorado Plateau and the Basin and Range province. It is one of several dominantly basaltic volcanic fields of late Cenozoic age situated near the southern margin of the Colorado Plateau. The East map area encompasses approximately 1,220 km 2 . The volcanic field contains rocks ranging in composition from basalt to rhyolite--the products of eruption through Precambrian basement rocks and approximately a kilometer of overlying, nearly horizontal, Paleozoic and Mesozoic sedimentary rocks. About 500 km 3 of erupted rocks cover about 5,000 km 2 of predominantly Permian and locally preserved Triassic sedimentary rocks that form the erosionally stripped surface of the Colorado Plateau in northern Arizona. In the East map area, basalt, basaltic andesite and locally associated small dacite domes, and, in a few cases, andesite were extruded from numerous individual vents, each of which presumably erupted briefly and then became inactive. Such short-lived vents, represented mainly by cinder cones or tuff rings, are widely distributed over the map area, and their flows cover much of its surface. However, repeated eruption of andesite, dacite, and rhyolite domes and flows formed the O'Leary Peak eruptive center in the northwest part of the map area, and flows of andesite (Qa 1 and Qa 2 ) from the San Francisco Mountain stratovolcano entered the East map area from the west. A northeastward progression of volcanism during the past 15 m.y., from central Arizona into the San Francisco volcanic field, is shown by the compilation of Luedke and Smith (1978). Although complicated in detail, a general northeastward to eastward progression of volcanic activity is also apparent within the San Francisco volcanic field. Thus, much of the eruptive activity of the East map area occurred late in the development of the San Francisco field, and the East map area includes the youngest volcanic rocks of the field. These youngest rocks were formed during the Sunset Crater eruption, which occurred within the past 1,000 years (Smiley, 1958). A northeast-trending, faulted monocline occurs near Doney Mountain in the north-central part of the East map area, and a broad north- to northwest-trending anticline occurs at the east edge of the map area. Nearby volcanic rocks are not folded or faulted by either structure. Northwest-trending normal faults of small throw occur in the southern and northwestern parts of the map area. The faults in the northwestern part transect basalt flows of Matuyama and Brunhes ages (Tmb, Qmb, and Qbb). The volcanic rocks are not faulted elsewhere in the East map area. However, local northwestward elongation and alignment of vent deposits, as shown for example by the fissure deposits of the Sunset Crater eruption (Qbsbf), indicate the presence of a northwest-trending fracture system that apparently localized some of the eruptive feeders.

Arizona↗

USGS1979

Major and trace element data with partition coefficients for lava flows from the San Francisco volcanic field

Major and trace element data from San Francisco Mountain (a stratovolcano), as well as major element data from representative flows of the surrounding volcanic field (figure 1), are presented in this report. Also included are conventional and normalized partition coefficients for trace elements in each of the coexisting mineral phases and mesostasis from San Francisco Mountain lavas. The San Francisco Mountain lavas are from the upper portion of the southeast slope of Humphreys Peak which is composed of three petrographically distinct types: (1) a lower series of hornblende pyroxene andesites, (2) a middle group of hypersthene dacites, and (3) an upper series of olivine andesites. The sequence of volcanic flows was measured and analyzed for the major elements and fifteen trace elements Sc, V, Cr, Cq Ni, Cu, Zn, Ga, Sr, Y, Zr, Ba, La, Ce, and Yb) in each of the coexisting mineral phases, groundmass and bulk rock. The constituent mineral phases (not all are present in every sample) are plagioclase, hypersthene, augite, hornblende, olivine, magnetite, and ilmenite/hematite.

Arizona↗