Regional Gravity Survey of the Hurricane Fault Area and Iron Springs District, Utah

Abstract

During 1963 and early 1964 a regional gravity survey consisting of 660 stations was made along the Hurricane fault area and in the Iron Springs district, Utah, over an area of about 1900 square miles. The complete Bouguer gravity anomaly map (2-mgal contour interval) shows gravity values ranging from about –156 mgal at low elevations near Washington in the south to about –212 mgal at intermediate elevations near Cedar City in the north. The gravity patterns confirm that: (1) the Basin and Range type Hurricane and Washington faults both intersected the north-eastward trending Virgin-Kanarra fold of Laramide age) and (2) the Virgin anticline and the Kanarra fold constituted a single continuous fold prior to transection and dislocation by the Hurricane fault. The gravity anomalies in the Cedar Valley and Escalante Desert areas indicate several other major Basin and Range faults or fault zones that bound grabens and horsts, including the Cedar Valley, Avon, and Lund grabens and the Table Butte horst. An extensive gravity high over the Iron Springs district indicates that the quartz monzonite porphyry forming the three aligned outcropping intrusions (The Three Peaks, Granite Mountain, and Iron Mountain) and the Stoddard Mountain intrusion is probably continuous at relatively shallow depth throughout the district and extends west-southwest from the Stoddard Mountain area. Another gravity high of approximately the same magnitude corresponds with the Antelope Range and may be caused either by an extension at depth of the same quartz monzonite porphyry mass or by a structural block that may exist throughout the Iron Springs district.