The post-tectonic Etla pluton intrudes the ∼1 Ga granulitie Oaxacan Complex that cooled through 450°C by ∼945 Ma. The Etla pluton consists of massive, coarse, porphyritic granodiorite-monzogranite (plagioclase, K-feldspar, quartz, biotite ± hornblende) with fine-grained felsic rocks along the margin. Geochemistry indicates that it is a peraluminous. I-type, medium-K, cale-alkaline, volcanic-arc granite-trondjemite with relatively low contents of high-field-strength elements and flat REE patterns. U-Pb zircon isotopic analyses fall on a chord with intercepts at 180 ± 50 Ma and 920 ± 25 Ma: the latter is similar to the 207Pb/206Pb age of 917 ± 6 Ma of the least discordant (1%) analysis and is inferred to date the time of intrusion. This plulon is synchronous with similar igneous activity in Avalonia (eastern Appalachians) and in Tocantins Province of central Brazil, which may form parts of a peri-Amazonian magmatic arc. 40Ar/39Ar laser step-heating analyses of biotite and K-feldspar yielded plateau ages of207 ±5 Ma and 221 ± 3 Ma, respectively, that may be related to Phanerozoic reheating.
|Number of pages||15|
|Journal||International Geology Review|
|Publication status||Published - Jul 2003|