Tectonic blocks at Horse Mountain, N. California: A unique occurrence of mafic blueschists in serpentinite along the South Fork fault adjacent to the Klamath Mountains
- Mount Holyoke Coll., Hadley, MA (United States). Geology Dept.
- Humboldt State Univ., Arcata, CA (United States). Geology Dept.
- IT Corp., Albuquerque, NM (United States)
High-pressure metamorphic blocks within serpentine occur between the South Mtn Schist, Jsfm, (Pickett Peak terrane) of the Franciscan Complex and rocks of the Western Jurassic belt of the Klamaths in the Willow Creek Quadrangle. These rounded to ellipsoidal tectonic blocks range from 1--50 meters and have foliated chlorite [+-] actinolite rinds which presumably resulted from interaction between the mafic blocks and host serpentinite. Metamorphic assemblages within the blocks include lawsonite + glaucophane + chlorite + pumpellyite + albite and subsets of the above with omphacite [+-] quartz [+-] phengite [+-] epidote [+-] aragonite. Relic igneous augite is common, sometimes with omphacite or glaucophane overgrowths. Veins of pumpellyite or fibrous to granular omphacite are rare and epidote + albite [+-] calcite veins are common. Whole-rock chemistry, initial [sup 87]Sr/[sup 86]Sr, and relic augite compositions indicate perhaps both island arc and ocean floor basalt protoliths. Whole rock [delta][sup 18]O range from 4.7--10.2 permil indicating both low- and high-temperature alteration of the protolith in a seafloor setting. These blocks are chemically, mineralogically, and texturally similar to tectonic blocks in the Central Franciscan belt and to metabasites in the Pickett Peak terrane to the south where the Coast Range fault places Jsfm against the Coast Range Ophiolite (CRO), yet omphacite-bearing tectonic blocks in serpentinite have not been reported anywhere else along the South Fork fault adjacent to the Klamath Mountains. These unique blocks are associated with a particularly wide zone of ultramafic rocks, at least some of which appear to have upper-plate Josephine Ophiolite affinity. However, the tectonic block-bearing serpentinite is intercalated by imbricate thrusting with Jsfm suggesting an affinity to the CRO.
- OSTI ID:
- 5290282
- Report Number(s):
- CONF-9305259--
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Journal Name: Geological Society of America, Abstracts with Programs; (United States) Vol. 25:5; ISSN GAAPBC; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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