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Fuchs, W.A., 1980

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Bibliographic Reference

Fuchs, W.A., 1980, Tertiary tectonic history of the Castle Mountain-Caribou fault system in the Talkeetna Mountains, Alaska: University of Utah, Salt Lake City, Ph.D. dissertation, 162 p., illust. (some color), maps.


Mapping on a scale of 1:24,000 of 264 km2 along 39 km of the Castle Mountain-Caribou fault system has revealed four Tertiary tectonic events. (1) Faulting with an oblique net slip (right-lateral, north side) initiated uplift on the Castle Mountain-Caribou fault in the late Paleocene. At that time the Castle Mountain splay fault was either nonexistent or inactive. (2) In Eocene time, uplift occurred along both the Castle Mountain splay and Caribou faults when the block between the two faults was raised as a rotational fault block with a pivot at the splay. The uplift of the splay block, which resulted in north-northwesterly tilting, was probably in response to thermal expansion caused by intense magmatic activity. Paleomagnetic data indicate that the tilting occurred (immediately?) prior to the injection of high-level intrusives of quartz latite domes. Northward thrust faulting near the splay and intrusion of albite granite porphyry in the fault zone immediately west of the splay may have occurred at the time of uplift of the splay block. (3) A period of extension was accompanied by intrusion within the splay block of diabase dikes and dike swarms trending 116 degrees. (4) In a late tectonic phase, reactivation of the Caribou fault alternated with strike-slip motion north-trending cross faults, producing a 'meat-slicer' effect. Motion was then transferred from the Caribou fault to a parallel subsidiary fault just to the the south, the Boulder Creek fault, which may still be active. Overall post-Eocene vertical motion across the Castle Mountain-Caribou fault system has been estimated by other workers to be 3 to 3.5 km (north side up). This author estimates post-Paleocene strike slip (right-lateral) on the Caribou fault to be 14.5 km. Total post-Paleocene strike-slip on the Castle Mountain fault may be somewhat larger by addition of the partitioned component on the Castle Mountain splay fault, giving a total post-Paleocene strike-slip of perhaps 20 km. Post-Eocene strike-slip (right-lateral) on the Castle Mountain splay fault has been determined to be 5 km based on an offset volcanic dome.

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