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GEOREF RECORD

Tilting, burial, and uplift of the Guadalupe igneous complex, Sierra Nevada, California

Peter J. Haeussler and Scott R. Paterson
Tilting, burial, and uplift of the Guadalupe igneous complex, Sierra Nevada, California
Geological Society of America Bulletin (October 1993) 105 (10): 1310-1320

Abstract

It is often incorrectly assumed that plutons have a relatively uneventful structural history after emplacement. The 151 Ma Guadalupe Igneous Complex (GIC) in the Foothills Terrane, California, was involved in three post-emplacement events: (1) approximately 30 degrees of southwest-side-up tilting during ductile regional faulting and contraction, (2) burial of the pluton from approximately 4 to 12 km during crustal thickening of the wall rocks, and (3) uplift with only minor tilting in the Late Cretaceous. Tilting of the pluton is indicated by (1) southwest to northeast gradational changes from layered gabbros and diorites to granites and granophyres; (2) northeastward dips of layering in gabbro, internal contacts, and bedding of overlying coeval(?) volcanic rocks; (3) northeastward decrease in wall-rock metamorphic grade; and (4) paleomagnetic data from 14 localities across the pluton. We argue that tilting occurred between 146-135 Ma during southwest-northeast-directed regional contraction. This contraction is indicated by widespread folds and cleavages and by reverse motion on the Bear Mountains fault zone (BMFZ), a large northeast-dipping shear zone that bounds the GIC on its southwest side. Burial of the GIC, which overlapped in time but outlasted tilting, is suggested by (1) post-emplacement contractional faulting, folding, and cleavage development; (2) analyses of strains associated with widespread cleavage that indicate vertical thickening of approximately 100%; and (3) microstructural and mineral assemblage data that indicate shallow emplacement of the GIC, in contrast to mineral assemblage and limited geobarometric data from adjacent 120-110 Ma plutons that indicate moderate emplacement levels. Late Cretaceous uplift is indicated by 95-75 Ma sedimentary rocks that unconformably overlie the 120-110 Ma plutons. This geologic history is interesting for several reasons. First, although the GIC participated in extensive post-emplacement deformation, it lacks internal structural evidence of these events, except locally along the Bear Mountains fault zone. Second, the agreement between paleomagnetic and structural evidence for tilting suggests that no large latitudinal displacement of the GIC is required. Third, the paleomagnetic data also help to define the geometry of the magma chamber now represented by the GIC. Lack of streaking of paleomagnetic site-mean directions demonstrates that the pluton acted as a single unit after cooling through the blocking temperature (450-560 degrees C) of low-titanium titanomagnetite; however, variations in the dip of internal layering and contacts, from 70 degrees at the base to 30 degrees near the top of the pluton, indicate that not all of these features were horizontal and planar when they formed. We propose that this variation in dip of layering is most consistent with sidewall crystallization of magma resulting in drape of layering along the walls of the intrusion. Therefore, internal layering within this pluton does not record paleohorizontal.


ISSN: 0016-7606
EISSN: 1943-2674
Coden: BUGMAF
Serial Title: Geological Society of America Bulletin
Serial Volume: 105
Serial Issue: 10
Title: Tilting, burial, and uplift of the Guadalupe igneous complex, Sierra Nevada, California
Affiliation: University of California at Santa Cruz, Earth Sciences Board and Institute of Tectonics, Santa Cruz, CA, United States
Pages: 1310-1320
Published: 199310
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 41
Accession Number: 1993-038117
Categories: Structural geology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 5 tables, geol. sketch map
N37°19'60" - N37°40'00", W120°30'00" - W119°19'60"
Secondary Affiliation: University of Southern California, Department of Geological Sciences, Los Angeles, CA, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 1993
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