Friday, April 19, 2013

Crude Map of Some Porphyry Dikes in Water Canyon

A couple days ago, we were looking at some rhyolite porphyry dike exposures, mostly on the north ridge of Water Canyon, an area MOH and I hike every now and then.
Google Earth image of the area (north to the right).
Crude map of the dikes.
On this second Google Earth image, I've added the approximate extent of the rhyolite porphyry dikes in bright turquoise. Contacts should be considered approximate. The south end near the canyon appears to be complicated by a fault as shown in dark blue, and that slope, although mostly of porphyry, appears to contain either beds or blocks of quartzite, possibly caught up within a couple merging or anastomosing dikes.

Across the canyon farther to the south (left edge of the image), a thin bed of quartzite is shown in blue running along one edge of a dike. I'm not really sure that the bed correlates directly with what looks like another thin quartzite bed directly across the canyon from it to the north (right). Also along that southern edge, a single turquoise line marks the east extent of another dike area. I'm not really sure what is going on between that line and the blue quartzite line, but those rocks look more like sediments or quartzite than dike rock in Google Earth.

What might not be clear from the image is that at least one, and maybe two or more, intermediate to mafic dikes of unknown age cut across the switchbacked road east of the rhyolite porphyry dikes of presumed Tertiary age.
What appear to be pieces of intermediate to mafic dike rock, with associated greenish outcrop in the road just behind my hand.
The intermediate or mafic dikes or sills look slightly reddish brown on enlarged images.
Google Earth image with approximate trace of one intermediate or mafic dike added in bright green.
Google Earth image showing approximate areas of rhyolite porphyry dikes hachured in bright turquoise. 
In the last image, sans intermediate or mafic dikes, I've added hachures to make it more clear where the rhyolite porphyry occurs. Again, the areas just north and south of the canyon are rough approximations of reality, and all contacts as drawn represent my best estimation, having been followed in part in the field and filled in using Google Earth.

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