Trinity Complex plagiogranites, Klamath Mtns. , California: Late Precambrian to Early Paleozoic tectonism and magmatism
Conference
·
· Geological Society of America, Abstracts with Programs; (United States)
OSTI ID:5019996
- Univ. of Nebraska, Lincoln, NE (United States). Dept. of Geology
Three ages of plagiogranites (PG) are reported from the Trinity Complex: late Proterozoic to earliest Cambrian (570 Ma), Ordovician (469--475 Ma), and Silurian (412 Ma). Minor Ordovician PG intrudes 570 Ma cumulate gabbros and is only moderately deformed. Silurian PG is related to voluminous gabbroic magmatism (Waling et al. 1981) and is relatively undeformed. However, 570 Ma PG in the Gregg Ranch area from Gazelle Mtn. to Lovers Leap is intensely deformed and is either part of the Trinity ophiolite sequence or blocks of Trinity ophiolite within melange of the Gregg Ranch Complex. The 570 Ma PG of Gregg Ranch consists of light gray, medium-grained fresh PG, interleaved with darker finer-grained PG that contains abundant sulfides (pyrite, chalcopyrite). Both types are cataclastic: after ductile stretching, quartz (Q) and plagioclase (PL) grains were broken and rotated. Though surrounded by fine fragmental Q and PL matrix, some larger pieces fit back together. Thus, the PG experienced deformation under P-T conditions across the ductile to brittle transition. A change in fabric and joint orientations from NW to NE across the area suggests the rocks were subsequently folded at least once. The 570 Ma Trinity ophiolite was intensely deformed prior to intrusion of minor PG in the Ordovician. Silurian magmatism postdates all major deformation and records no later orogenic events in the Trinity Complex other than warping and uplift.
- OSTI ID:
- 5019996
- Report Number(s):
- CONF-9305259--
- Conference Information:
- Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 25:5
- Country of Publication:
- United States
- Language:
- English
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