Abstract
Peraluminous and metaluminous plutonic rocks of the Peninsular Ranges batholith near Borrego Springs in southern California were mylonitized in the large shear zone known as the eastern Peninsular Ranges mylonite zone (EPRMZ). Accompanying mylonitization in this portion of the EPRMZ was metamorphism at intermediate-low-pressure amphibolite-facies conditions. Deformation in the zone overlapped in time with Cretaceous intrusion of the batholith. In the San Ysidro Mountain — Pinyon Ridge area, four north-south trending zones of differing intensity of deformation have been defined; from east to west the degree and style of deformation gradually change from undeformed or weakly deformed rocks to strongly mylonitized rocks.
Electron microprobe analysis shows that recrystallized hornblende, biotite, and plagioclase are variable in composition, probably reflecting a range of metamorphic conditions accompanying deformation. Comparison of mineral compositions with those from mafic schists of Vermont suggests conditions ranged from andalusite-staurolite through sillimanite-muscovite grades as defined for pelitic rocks. Stability of muscovite+quartz in mylonite assemblages and lack of remelting of granitic rocks indicate that temperature did not exceed about 650° C during mylonitization and lithostatic pressure did not exceed about 5 kbar. Over time, any given rock volume experienced a range of temperature, lithostatic pressure, and perhaps fluid pressure and differential stress.
Mineral reactions in the zone involved hydration, requiring introduction of water. The possibility of large-scale migration of K and Fe is suggested by whole-rock chemical data. Brittle and ductile deformation features are closely associated in one part of the EPRMZ. The combined evidence suggests the presence of a pore fluid with fluid pressure close to lithostatic pressure. Short periods of low fluid pressure and possible high differential stress cannot be ruled out.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Albee AL, Ray L (1970) Correction factors for electron probe microanalysis of silicates, oxides, carbonates, phosphates, and sulfates. Anal Chem 42:1408–1414
Anderson JR (1977) The polymetamorphic sequence in the Paleozoic rocks of northern Vermont: a new approach using metamorphic veins as petrologic and structural markers. Unpubl PhD thesis, California Inst Technology
Anderson JR (1980) A study of mylonitic rocks from major fault zones (report). US Geol Surv Open-file Report 80-1154
Anderson JR (1982) A study of mylonitic rocks from major fault zones (summary of report). US Geol Surv Open-file Report 82-65:399–400
Bence AE, Albee AL (1968) Empirical correction factors for the electron mircroanalysis of silicates and oxides. J Geol 76:382–403
Bohlen SR, Essene EJ, Hoffman KS (1980) An update on feldspar and oxide thermometry in the Adirondack Mountains, New York. Geol Soc Am Bull, Part I 91:110–113
Brown PE, Essene EJ, Kelly WC (1978) Sphalerite geobarometry in the Balmat-Edwards district, New York. Am Mineral 63:250–257
Champion DE, Albee AL, Chodos AA (1975) Reproducibility and operator bias in a computer-controlled system for quantitative electron microprobe analysis. Microbeam Anal Soc Proc Annu Conf:55A–55F
Chodos AA, Albee AL, Gancarz AJ, Laird J (1973) Optimization of computer-controlled quantitative analysis of minerals. Microbeam Anal Soc Proc Annu Conf:45A–-45C
Christie JM, Ord A (1980) Flow stress from microstructures of mylonites: example and current assessment. J Geophys Res 85:6253–6262
Davis ME (1981) Petrology, structure, and geochemistry of a portion of the Carthage-Colton mylonite zone, South Edwards quadrangle, NW Adirondacks. Unpubl MA thesis, SUNY-Binghamton
Davis ME, Anderson JR (1983) Metamorphism accompanying mylonitization of hornblende-quartz syenite, Carthage-Colton mylonite zone, NW Adirondacks. Geol Soc Am Abstr with Program 15:141
Evans BW (1965) Application of a reaction-rate method to the breakdown of muscovite plus quartz. Am J Sci 263:647–667
Fraser DM (1931) Geology of the San Jacinto quadrangle south of San Gorgonio Pass. Calif Div Mines Geol Bull 27:494–540
Holdaway MJ (1971) Stability of andalusite and the aluminum silcate phase diagram. Am J Sci 271:97–131
Laird J (1977) Phase equilibria in mafic schist and the polymetamorphic history of Vermont. Unpubl PhD thesis, California Inst Technology
Laird J, Albee AL (1981a) High pressure metamorphism in mafic schist from northern Vermont. Am J Sci 281:97–126
Laird J, Albee AL (1981b) Pressure, temperature, and time indicators in mafic schist: their application to reconstructing the polymetamorphic history of Vermont. Am J Sci 281:127–175
Larsen ES (1948) Batholith and associated rocks of Corona, Elsinore, and San Luis Rey quadrangles, southern California. Geol Soc Am Mem 29
Shapiro L (1967) Rapid analysis of rocks and minerals by a single solution method. US Geol Surv Prof Paper 575B:B187–191
Shapiro L, Brannock WW (1962) Rapid analysis of silicate, carbonate and phosphate rocks. US Geol Surv Bull 1144 A
Sharp RV (1966) Ancient mylonite zone and fault displacements in the Peninsular Ranges of southern California. Geol Soc Am Spec Paper 101:333
Sharp RV (1967) San Jacinto fault zone in the Peninsular Ranges of southern California. Geol Soc Am Bull 78:705–730
Sharp RV (1979) Some characteristics of the eastern Peninsular Ranges mylonite zone. US Geol Surv Open-file Report 79-1239:258–267
Sibson RH (1980) Transient discontinuities in ductile shear zones. J Struct Geol 2:165–171
Stoddard EF (1980) Metamorphic conditions at the northern end of the northwest Adirondack Lowlands. Geol Soc Am Bull, Part I 91:100–102
Theodore TG (1970) Petrogenesis of mylonites of high metamorphic grade in the Peninsular Ranges of southern California. Geol Soc Am Bull 81:435–450
Tuttle OF, Bowen NL (1958) Origin of granite in light of experimental studies in the system NaAlSi3O8-KAlSi3O8-SiO2 H2O. Geol Soc Am Mem 74
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Anderson, J.R. Petrology of a portion of the Eastern Peninsular Ranges mylonite zone, Southern California. Contr. Mineral. and Petrol. 84, 253–271 (1983). https://doi.org/10.1007/BF00371290
Received:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF00371290