Geological Society of America

T106 Multidisciplinary Studies of Convergent Plate Boundaries (Posters): In Honor of Jason Saleeby, 2012 MGPV Distinguished Geologic Career Awardee

Monday, 5 November 2012
9:00 AM - 6:00 PM
Hall B

LEAD, STRONTIUM, AND NEODYMIUM ISOTOPE CONSTRAINTS ON THE ORIGIN OF THE GUERRERO COMPOSITE TERRANE, WEST-CENTRAL MEXICO

Paper number: T106-6
Program: Technical Sessions
Time: 9:00 AM – 6:00 PM

Authors

Adriana Potra Presenting Author
Florida International University, Miami, FL
Rosemary Hickey-Vargas
Florida International University, Miami, FL
Andrew W. Macfarlane
Florida International University, Miami, FL
Vincent J. Salters
Florida State University and National High Magnetic Field Laboratory, Tallahassee, FL

Abstract

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.