Geochemistry of evolved magmas and their relationship to subduction-unrelated mafic volcanism at the volcanic front of the central Mexican volcanic belt.
Verma, Surendra P (1999) Geochemistry of evolved magmas and their relationship to subduction-unrelated mafic volcanism at the volcanic front of the central Mexican volcanic belt. Journal of Volcanology and Geothermal Research. 93; 1-2, Pages 151-171. 1999.
| Authors | Verma, Surendra P |
|---|---|
| Year | 1999 |
| Title | Geochemistry of evolved magmas and their relationship to subduction-unrelated mafic volcanism at the volcanic front of the central Mexican volcanic belt. |
| Source | Journal of Volcanology and Geothermal Research. 93; 1-2, Pages 151-171. 1999. |
| Publisher | Elsevier. Amsterdam, Netherlands. 1999. |
| Document type | Serial |
| ISSN | 0377-0273 |
| GeoRef | 2000-039414 |
| Keywords | alkaline-earth-metals; fractional-crystallization; geochemistry-; isotope-ratios; isotopes-; lead-; magmas-; mantle-; metals-; Mexican-volcanic-belt; Mexico-; mixing-; Nd-144-Nd-143; neodymium-; partial-melting; Pb-207-Pb-204; Pb-208-Pb-204; plate-tectonics; radioactive-isotopes; rare-earths; rifting-; Sr-87-Sr-86; stable-isotopes; strontium-; subduction-; volcanism- |
| DOI | 10.1016/S0377-0273(99)00086-4 |
Abstract
This study reports new geochemical and radiogenic isotope data on hy-normative Pleistocene to recent <40,000 years andesitic to dacitic volcanic rocks from Sierra de Chichinautzin SCN, located south of Mexico City, in the central part of the Mexican Volcanic Belt MVB. Their rare-earth element, Nb, Zr, and Y concentrations are generally lower than in mafic rocks from this area, which have been shown to be subduction-unrelated. The isotopic ratios of these evolved magmas show the following ranges: super 87 Sr/ super 86 Sr 0.70370-0.70469, super 143 Nd/ super 144 Nd 0.51278-0.51289, super 206 Pb/ super 204 Pb 18.64-18.72, super 207 Pb/ super 204 Pb 15.59-15.62, and super 208 Pb/ super 204 Pb 38.39-38.52. These isotopic ratios are generally similar to those for the associated mafic rocks, although some differences do exist between them, particularly for the super 87 Sr/ super 86 Sr ratios that are somewhat higher and super 143 Nd/ super 144 Nd that are slightly lower for the evolved rocks. The available geochemical evidence does not support the generation of the SCN evolved magmas by simple fractional crystallization FC or even by assimilation coupled with fractional crystallization AFC of such mafic magmas, nor by direct slab melting or indirect fluid transport to the mantle participation of the subducted Cocos plate. The viable mechanism seems to be that the most evolved andesitic and dacitic magmas in the SCN were produced by partial melting of a heterogeneous mafic granulite source in the lower crust. The magmas of intermediate compositions may reflect magma mixing processes between the most evolved andesitic and dacitic magmas generated in the lower crust and the mantle-derived mafic magmas basalt and basaltic trachy-andesite at the volcanic front of the central part of the MVB. These results have direct bearing to other volcanic areas with complex tectonic setting.