RESEARCH· ·1970·

B82
GEOPHYSICS
J
I
37·~~------~~----L-~J-----~--------------L-~--------J_----~~-i-----L-------L--~--~--~
B 0 10 20 30 40 Ml LES B '
EXPLANATION
~ --,soo---
Magnetic contours
Hachures indicate closed area of lower magnetic
intenBit11; dashed where incomplete. Interval
JOOgammas
Flight lines
FIGURE 2.-Reconnaissanee aeromagnetic map of the Trinidad quadrangle (Zietz and Kirby, 1968). Values are .total
magnetic intensity relative to an ar:bitrary datum. Main magnetic field of the ~earth, supplied by the U.S. Coast and
Geodetic Survey and based on E'poch 1955, has been removed. Aeromagnetic survey flown between 7,000- and 16,000-
foot barometric elevation. A-A' (near top of map) and B-B' (at botJtom of map), location of models shown on
figures 3 and 4.
ment mass of high density and magnetic susceptibility
along the arch. ·
Near the east end of B-B', the magnetic profile
shows a 350-gamma positive anomaly over the volcanic
flows of the Raton l\1esas (fig. 4). However, the model
studies and configuration of the observed Inagnetic
anomaly suggest that the source is an intrabasement
body of intermediate composition and perhaps is a
source of the basaltic flow rocks. The plug shown on
the geologic map near l\1orley may be an apophysis of
the body thought to cause the anomaly (fig. 1). The
20-gamma positive anomaly superimposed on the 350-
gamma anomaly correlates with the surface volcanic
exposures. Inasmuch as the volcanic. flow rocks are
olivine basalts, which generally are highly Inagnetic,
we examined the possibility that the 350-gamma magnetic
anomaly was caused by the surface volcanics of
finite thickness. The calculated anomaly, which was a
typical plate configuration, did not fit the observed
anomaly. In addition, the flow thickness of about 2,000
feet that is required to produce the a1nplitude of the
observed profile is considerably greater than known
thicknesses of flows in the area.
Regional northeasterly trends in the gravity and
magnetic data may represent faults or shear zones in
the crystalline basement. One trend extends from La