Paper No. 6
Presentation Time: 9:00 AM-6:00 PM
LEAD, STRONTIUM, AND NEODYMIUM ISOTOPE CONSTRAINTS ON THE ORIGIN OF THE GUERRERO COMPOSITE TERRANE, WEST-CENTRAL MEXICO
POTRA, Adriana1, HICKEY-VARGAS, Rosemary2, MACFARLANE, Andrew W.1 and SALTERS, Vincent J.3, (1)Earth and Environment, Florida International University, 11200 SW 8th Street, University Park, PC 344, Miami, FL 33199, (2)Earth and Environment, Florida International University, 11200 SW 8th street, University Park, PC 344, Miami, FL 33199, (3)Earth, Ocean and Atmospheric Science, Florida State University and National High Magnetic Field Laboratory, B302 NHMFL FSU, 1800 E. Paul Dirac Dr, Tallahassee, FL 32310-3706, apotr001@fiu.edu
New Pb, Sr, and Nd isotope data of crustal rocks from the southern part of Guerrero terrane are presented to provide a clearer picture of their origin. Basement rocks from the Triassic Arteaga and Triassic-Jurassic Tejupilco Complexes define two Pb isotope trends. Tejupilco suite rocks have lower present-day
208Pb/
204Pb (38.694 – 39.098) and
207Pb/
204Pb (15.643 – 15.650) values than rocks from the Arteaga Complex (38.906 – 39.216 and 15.623 – 15.693). Sr and Nd isotope ratios from both suites plot in the enriched quadrant (
87Sr/
86Sr
(i) = 0.694276 – 0.711284 and
143Nd/
144Nd
(i) = 0.511964 – 0.512509), implying evolved sources. The Cretaceous sedimentary rocks define two clusters: the Huetamo Sequence with less evolved isotopic signatures (
208Pb/
204Pb = 38.369 – 38.610;
207Pb/
204Pb = 15.563 – 15.641;
87Sr/
86Sr = 0.705301 – 0.707575;
143Nd/
144Nd = 0.512565 – 0.512810) and the Zihuatanejo Sequence (
208Pb/
204Pb = 38.510 – 38.892;
207Pb/
204Pb = 15.580 – 15.643;
87Sr/
86Sr = 0.708848 – 0.709362;
143Nd/
144Nd = 0.512753). Cenozoic plutonic rocks from La Verde have more radiogenic Pb (
208Pb/
204Pb = 38.574 – 38.983;
207Pb/
204Pb = 15.565 – 15.654) than samples from Inguaran (
208Pb/
204Pb = 38.754;
207Pb/
204Pb = 15.621), La Esmeralda (
208Pb/
204Pb = 38.473;
207Pb/
204Pb = 15.539), and El Malacate (
208Pb/
204Pb = 38.663;
207Pb/
204Pb = 15.620), and their Sr and Nd isotope ratios (
87Sr/
86Sr
(i) = 0.705175 and
143Nd/
144Nd
(i)= 0.512608) are correlated and plot within the enriched mantle field.
Present-day Pb isotope ratios of SW Mexican basement from the Mesozoic Guerrero and Paleozoic Mixteca terranes are similar to those of N Peruvian Mesozoic Olmos and Paleozoic Maranon Complexes, but are more radiogenic than Grenville-age basement from E Mexico (Oaxaca, Juarez, and Maya terranes) and N Colombia (Santa Marta massif). These results and the similar age of these basement rocks reveal a different evolution. Radiogenic isotope analyses suggest the involvement of two end-members in the generation of Huetamo Sequence rocks: the radiogenic basement represented by Arteaga Complex and oceanic basalts. Pb isotope values of igneous rocks from Inguaran, La Esmeralda, and El Malacate indicate derivation from Huetamo Sequence rocks and those from La Verde imply assimilation of materials from Arteaga Complex.
