Geochronological constraints on the tectonic history of the Peninsular Ranges bathlolith of Alta and Baja California: tectonic implications for western Mexico

Ortega-Rivera, Amabel (2003) Geochronological constraints on the tectonic history of the Peninsular Ranges bathlolith of Alta and Baja California: tectonic implications for western Mexico. Special Paper - Geological Society of America, vol.374, pp.297-335, 2003

Authors	Ortega-Rivera, Amabel
Year	2003
Title	Geochronological constraints on the tectonic history of the Peninsular Ranges bathlolith of Alta and Baja California: tectonic implications for western Mexico
Source	Special Paper - Geological Society of America, vol.374, pp.297-335, 2003
Book editors	Johnson, Scott E; Paterson, Scott R; Fletcher, John M; Girty, Gary H; Kimbrough, David L; Martin-Barajas, Arturo
ISBN	813723744
ISSN	0072-1077
GeoRef	2004-026602
Keywords	absolute age; Ar/Ar; Baja California; batholiths; chemical composition; Cretaceous; dates; deformation; East Pacific; faults; fission tracks; geochemistry; granites; Gulf of California; I-type granites; igneous rocks; intrusions; K/Ar; Mesozoic; metamorphic rocks; Mexico; mineral composition; nesosilicates; nomenclature; North America; North Pacific; Northeast Pacific; orthosilicates; Pacific Ocean; paleogeography; paleomagnetism; Peninsular Ranges; Peninsular Ranges Batholith; petrology; plate tectonics; plutonic rocks; Rb/Sr; reconstruction; relative age; rifting; sedimentary rocks; Sierra Madre Occidental; Sierra San Pedro Martir Pluton; silicates; stratigraphy; tectonics; U/Pb; Upper Cretaceous; volcanic rocks; zircon; zircon group

Abstract

A compilation of existing age data and new age determinations (U/Pb zircon, (super 40) Ar/ (super 39) Ar step-heating, K/Ar, Rb/Sr, and apatite fission-track dates) for the Peninsular Ranges batholith of Alta and Baja California provides geochronological constraints on the tectonic history of the Peninsular Ranges batholith and tectonic implications for western Mexico. The plutons of the Peninsular Ranges batholith of Alta and Baja California between the 28 degrees N and 34 degrees N parallels were emplaced from west to east between ca. 140 to 80 Ma (U/Pb zircon dates) and display (super 40) Ar/ (super 39) Ar hornblende and biotite plateau dates that range from 118 to 83 Ma and 116 to 80 Ma, respectively, and biotite K/Ar dates as young as 65 Ma. Rapid cooling is indicated by the small differences in U/Pb zircon and cogenetic (super 40) Ar/ (super 39) Ar dates. Mineral pairs having mainly concordant dates yield (super 40) Ar/ (super 39) Ar cooling ages that also systematically decrease from southwest to northeast. Also, monotonic eastward youngling of ages across various plutons was found as was previously reported for the Sierra San Pedro Martir pluton. This systematic regional and local eastward younging may be explained by the systematic tilting of pluton-sized crustal blocks containing individual plutons. The northeastward decrease in ages across the Peninsular Ranges batholith and across some of its plutons is therefore attributed to regional eastward migration of granitic intrusion foci combined with rapid differential exhumation histories and superimposed east-side-up tilting of crustal-sized blocks containing some of the plutons and beautifully exemplifies the short time lapse between batholith intrusion and unroofing. Additionally, apatite fission-track dates from samples collected across the Peninsular Ranges, from Ensenada to San Felipe, Baja California, establish that there is also an eastward younging of ages from 104 Ma to 51 Ma from west to east and also across plutons. The fission-track dates indicate that from west to east, present exposures of much of the western Peninsular Ranges batholith have been within <<3 km of the Earth's surface (assuming a normal geothermal gradient) since Early Cretaceous time, and that by early Tertiary time, much of the eastern Peninsular Ranges had cooled to temperatures of <110 degrees C, indicating rapid exhumation histories and superimposed east-side-up tilting shown by younger ages at higher elevations within plutons. The batholith was sufficiently uplifted during the Late Cretaceous such that 10-15 km of material was eroded off the eastern part of the batholith by early Paleocene time. Furthermore, a regional compilation of the available age data for western Mexico provides geochronological constraints for the testing of controversial paleomagnetic and geological models for the tectonic evolution of the Mesozoic Peninsular Ranges of Alta and Baja California. The controversy involves different perceptions of the geologic development of western Mexico and southernmost California as derived from paleomagnetic studies and regional geology. Whereas the geological data and plate tectonic reconstructions seem to indicate a northward motion between 300 and 500 km with respect to the rest of North America since the Cretaceous, paleomagnetic data suggest much greater movement involving at least 2500 km of northward translation for the Baja peninsula during the same period.

291 samples from this reference

Results Map Plot Download

Sample	Rock name	Major	Trace	Isotope
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First 200 shown; open the results for all.

Sample	Rock name	Major	Trace	Isotope
101
102
103
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107
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110
110
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109
139
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Sample	Rock name	Major	Trace	Isotope
101
102
103
104
105
106
107
108
110
110
110
111
112
109
139
139
139
140
113
113
114
114
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Sample	Rock name	Major	Trace	Isotope
101
102
103
104
105
106
107
108
110
110
110
111
112
109
139
139
139
140
113
113
114
114
114
115
115
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72
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