Geology Reference
In-Depth Information
300 km
Co
GREAT
PLAINS
SPANISH
PEAKS
COLORADO
PLATEA U
NAVAJO
TWO
BUTTES
DULCE
ESPANOLA
BASIN
NM
Rio Grande Rift
A Z
MEXICO
Fig. 4.13 Location of the Navajo volcanic complex and Dulce dyke (Colorado plateau), Spanish
Peaks and Espanola basin in RioGrande Rift and Two Buttes (Colorado) (after Gibson et al. 1993)
4.5.5 Dulce Dike
There are dike swarms at Dulce (Fig. 4.13 ) in the Jicarilla Apache Indian Reser-
vation (37
°
N, 107
°
W) about 102 km west of the present day rift axis. The dikes
trend NNE
SSW parallel to Early Miocene phase of extension of the Rio Grande
rift in intrusive sediments of Cretaceous and Tertiary age.
The dike swarms outcrop in an area about 50 km long and 30 km wide and
include, minette, vogesite and spessartite. The K/Ar techniques yield an age of
27
-
24 Ma. The K 2 O content of the two minettes of Dulce dike swarm from
Montezuma Creek varies between 2.21 and 3.00 (wt%) and has an age of
24.3
-
25.0 Ma.
-
4.5.6 Spanish Peaks
The Spanish Peaks (Fig. 4.13 ) is located in the westernmost part of the Great Plains
(37
W), 80 km east of the present day rift axis (Gibbson et al. 1991;
Gibson et al. 1993). This locality is famous for radial dike swarms. The ages of
apatite and zircon for the two dikes, as determined by the Fission Track method,
range between 27.5 and 20 Ma (Smith 1984, cited by Gibson et al. 1993). The
radial dikes have variable chemistry, and they can be described as trachyandesite,
minette, kersantite, trachyte, rhyolite and K-rich ma
°
30
N, 105
°
c dikes. The dikes vary in
width between 0.3 and 30 m and may extend up to 23 km.
 
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