Gravity and magnetic anomalies associated with Tertiary volcanism and a Proterozoic crustal boundary, Hopi Buttes volcanic field, Navajo Nation (Arizona)

Conference · Wed Jan 01 04:00:00 EST 1992 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:6135904

Donovan-Ealy, P F ^[1]; Hendricks, J D ^[2]

---

1. Northern Arizona Univ., Flagstaff, AZ (United States). Geology Dept.
2. Geological Survey, Flagstaff, AZ (United States)

The Hopi Buttes volcanic field is located in the Navajo Nation of northeastern Arizona, near the southern margin of the Colorado Plateau. Explosive phreatomagmatic eruptions from late Miocene to mid-Pliocene time produced more than 300 maar-diatremes and deposited limburgite tuffs and tuff breccia and monchiquite dikes, necks and flows within a roughly circular 2,500 km[sup 2] area. The volcanic and volcaniclastic rocks make up the middle member of the Bidahochi Formation, whose lower and upper members are lacustrine and fluvial, respectively. The Bidahochi Formation overlies gently dipping Mesozoic sedimentary rocks exposed in the southwestern portion of the volcanic field. Two significant gravity and magnetic anomalies appear within the Hopi Buttes volcanic field that are unlike the signatures of other Tertiary volcanic fields on the Colorado Plateau. A circular 20 mGal negative gravity anomaly is centered over exposed sedimentary rocks in the southwestern portion of the field. The anomaly may be due to the large volume of low density pyroclastic rocks in the volcanic field and/or extensive brecciation of the underlying strata from the violent maar eruptions. The second significant anomaly is the northeast-trending Holbrook lineament, a 5 km-wide gravity and magnetic lineament that crosses the southeastern part of the volcanic field. The lineament reflects substantial gravity and magnetic decreases of 1.67 mGals/km and 100 gammas/km respectively, to the southeast. Preliminary two-dimensional gravity and magnetic modeling suggests the lineament represents a major Proterozoic crustal boundary and may correlate with one of several Proterozoic faults exposed in the transition zone of central Arizona. Gravity modeling shows a 3--5 km step'' in the Moho near the crustal boundary. The decrease in depth of the Moho to the northwest indicates either movement along the fault or magmatic upwelling beneath the volcanic field.

• OSTI ID: 6135904
• Report Number(s): CONF-921058--
• Conference Information: Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 24:7
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
ARIZONA
CENOZOIC ERA
COLORADO PLATEAU
CONTINENTAL CRUST
DEVELOPED COUNTRIES
DIKES
EARTH CRUST
GEOLOGIC AGES
GEOLOGIC FORMATIONS
GEOLOGIC MODELS
GEOLOGIC STRUCTURES
GEOLOGY
GEOPHYSICAL SURVEYS
GRAVITY SURVEYS
LINEAMENTS
LITHOLOGY
MAGNETIC SURVEYS
MOUNTAINS
NORTH AMERICA
PETROLOGY
PRECAMBRIAN ERA
ROCKS
SEDIMENTARY ROCKS
SURVEYS
TERTIARY PERIOD
USA
VOLCANIC REGIONS
VOLCANISM