HR: 14:00h
AN: V23C-01    [Abstracts]
TI: Structural Indicators for the Emplacement of Cretaceous Plutonic Complexes from the Southern Peninsular Ranges Batholith, Mexico
AU: * Delgado-Argote, L
EM: ldelgado@cicese.mx
AF: CICESE, KM 107 Carretera Tijuana-Ensenada, Ensanada, BC 22860, Mexico
AU: Pena-Alonso, T
EM: alepena@cicese.mx
AF: CICESE, KM 107 Carretera Tijuana-Ensenada, Ensanada, BC 22860, Mexico
AU: Weber, B
EM: bweber@cicese.mx
AF: CICESE, KM 107 Carretera Tijuana-Ensenada, Ensanada, BC 22860, Mexico
AU: Molina, R
EM: rmolina@geociencias.unam.mx
AF: UNAM, Juriquilla, Queretaro, Queretaro, QRO 00000, Mexico
AU: Boehnel, H
EM: hboehnel@geociencias.unam.mx
AF: UNAM, Juriquilla, Queretaro, Queretaro, QRO 00000, Mexico
AU: Valencia, V
EM: victorv@geo.arizona.edu
AF: University of Arizona, 1040 east fourth street, Tucson, AZ 85721-0077, United States
AB: According with the premise that all plutons are nearly circular in plan view in almost any environment, we interpret pluton-related structures (PRS) from LandsatTM images in Baja California, between latitudes 28 and 29N. In this region the NW regional trending of the Peninsular Ranges Batholith changes to be E-W. The presence and shape of the plutons is inferred from the fracture distribution, which parallels compositional zoning, or can be related to the basic stress anisotropy. It is common that nested or concentric discrete bodies form plutonic complexes. It is proposed from a PRS curve-density map that the ridges are zones of higher rates of magma accumulation and their axis can be correlated with magma flow direction. The largest, named Main Ridge, is 30 km long, trending E-W. Because magma moves laterally at shallow depths, we interpret broad areas where lateral movements of magma promote the development of second-order ridges that occupy cortical discontinuities. Three Cretaceous plutonic complexes (U-Pb ages of zircons), showing different structures, lithology and associations with the enclosing rocks were selected for their comparative analyses. From west to east: Punta Prieta (PP; 128.1 +/- 2.1Ma), Nuevo Rosarito (NR; 108 +/- 2.2 Ma) and two from La Rinconada (LR; 113 +/- 2.2 Ma and 102.4 +/- 1.5 Ma). PP is located in the Pacific coast; NR and LR are in the western and southwestern edge of the Main Ridge, respectively. Excepting in PP, vertical fractures (longitudinal) tend to be parallel to the ridges. In PP, the sense of flow is inferred from the 290° trending of vertical fractures, dikes and magmatic foliation, together with conspicuous shearing planes trending 283/73 and 292/78 developed in the plutonic and enclosing rocks, respectively. In NR vertical fractures, magmatic foliation, permeation structures and foliation of the enclosing rock (metabreccia of 139.5 +/- 2 Ma) show a remarkable NNW orientation, parallel to a second order ridge; in the two plutons of LR vertical fractures, magmatic foliation and dikes trend 300° and more than 80 percent of the horizontal fractures average 294/21. For more than 50 km, the complexes located in the crest and western edges of the Main Ridge show a tectonic foliation trending 311/78. This foliation is almost absent in the northern edge of the Main Ridge. It is proposed that the distribution of the plutonic complexes is the result of almost E-W cortical discontinuities.
DE: 3642 Intrusive structures and rocks
SC: Volcanology, Geochemistry, and Petrology [V]
MN: 2007 Joint Assembly