Sr, Nd and Pb isotopic and geochemical constraints for the origin of magmas in Popocatépetl volcano (central Mexico) and their relationship with the adjacent volcanic fields

Abstract

We present new geochemical data (major- and trace-elements, as well as Sr and Nd isotopic compositions) of volcanic rocks erupted from Popocatépetl volcano during the volcanic event from December 2000 to January 2001. These data along with an exhaustive compilation of geochemical and Sr, Nd, and Pb isotope data reported for Popocatépetl rocks and nearby volcanic areas are used to examine the origin and geochemical evolution of the magmas in the central Mexican volcanic belt (CMVB). During this period of volcanic eruptions Popocatépetl produced ash columns as high as 7 km. Pyroclastic flows and lahars were observed after the completion of the activity. Samples of banded pumice and a bomb fragment transported by the lahar were chemically analysed for this work. Rocks show an andesitic composition with 58.5–61.7 wt.% SiO2 and 5.9–4.0 wt.% MgO. Contents of large ion lithophile elements (LILE), rare-earth elements (REE) and Zr are nearly constant through the compositional range. No significant Eu anomaly is present, but the samples show Nb-anomaly relative to LILE and high-field strength elements (HFSE). Nd- and Sr-isotopic compositions of these samples range from 143Nd/144Nd = 0.51291 to 0.51287 and 87Sr/86Sr = 0.70399 to 0.70422. Comparison of Popocatépetl products with volcanic rocks from the nearby areas shows that the magmas in CMVB were generated in a heterogeneously veined-mantle source enriched in LILE, HFSE, and REE. Additional crustal assimilation as well as fractional crystallization could account for the great chemical variability of rocks in the CMVB. Statistical comparison of the geochemical compositions of the volcanic products ejected from 1994 to 2000 to those ejected during the 2001 event shows that most geochemical parameters (major- and trace-elements, normative minerals, Sr and Nd isotopic composition, as well some elemental ratios) present no statistically significant differences. Statistically significant differences in the mean only were computed for the major-elements SiO2, FeO, MgO, CaO, and K2O, as well as for the rare-earth elements Nd, Sm, Eu, Gd, Dy, Ho, Tm, and Yb.