Detailed structure and stratigraphy of the eastern Marble Mountain terrane, Klamath Mountains, CA
- Stanford Univ., CA (United States). Dept. of Geology
Amphibolite-grade rocks in the eastern Marble Mountains (MM), N. California, consist of several fault-bounded, SSE-dipping lithotectonic units. Each unit is ca. 2 km thick and is characterized by differences in rock type, metamorphism, and structural style. The lowermost unit composed of well-foliated and lineated epidote amphibolite grading upward into clinopyroxene-bearing amphibolite with a consistent NE-SW lineation. Structurally overlying these rocks are andalusite- and staurolite-bearing, epidote-amphibolite facies rocks (Wright Lake assemblage (WLa)) that have variable foliation and lineation orientations. The WLa consists of meta-supracrustal rocks with well-preserved relict textures, and massive, meta-ultramafic rock. Supracrustal rocks include polymict conglomerate and breccia, fine- to medium-grained clastic rocks, alkalic pillow basalt, chert, and carbonate. Conglomerate clasts include partially recrystallized granitoids and quartzite. Previous studies have interpreted the WLa to represent a fragment of oceanic crust, but coeval coarse-grained sedimentation and alkalic volcanism, small volume of mafic volcanics, conglomerate composition, and lack of oceanic plutonic and hypabyssal rocks suggest deposition in an arc-related rift or transtensional basin. Previous studies have also described the terrane as melange, but recognition of local pseudostratigraphy allows mapping of multiply folded, isoclinal, nappe-like structures. Small-scale nappes are generally 100+ m thick and are imbricated with massive meta-ultramafic rocks along gently to steeply east-dipping shear zones. Shear zones are characterized by metamorphosed ultramafic fault rocks that suggest a range of brittle to ductile behavior. Regionally distributed, Ar/Ar hornblende ages of 149.9[+-]0.4, 150.3[+-]0.6, 152.1[+-]4.7, 152.5[+-]2.5 Ma and Ar/Ar biotite ages of 148.8[+-]2.6 and 149.9[+-]0.4 Ma indicate the MM terrane cooled rapidly through ca. 500--300 C in the Late Jurassic.
- OSTI ID:
- 5129483
- Report Number(s):
- CONF-9305259-; CODEN: GAAPBC
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Vol. 25:5; Conference: 89. annual meeting of the Cordilleran Section and the 46th annual meeting of the Rocky Mountain Section of the Geological Society of America (GSA), Reno, NV (United States), 19-21 May 1993; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
AMPHIBOLITES
ISOTOPE DATING
PETROLOGY
STRATIGRAPHY
CALIFORNIA
GEOLOGIC FORMATIONS
ARGON ISOTOPES
GEOLOGIC FAULTS
GEOLOGIC HISTORY
GEOLOGIC STRUCTURES
GEOLOGY
METAMORPHISM
PETROGENESIS
AGE ESTIMATION
DEVELOPED COUNTRIES
GEOLOGIC FRACTURES
ISOTOPES
METAMORPHIC ROCKS
NORTH AMERICA
ROCKS
USA
580000* - Geosciences