Reappraisal of the geology and geochemistry of Volcan Zamorano, central Mexico; implications for discriminating the Sierra Madre Occidental and Mexican volcanic belt provinces.
Verma, Surendra P; Carrasco, Nunez Gerardo (2003) Reappraisal of the geology and geochemistry of Volcan Zamorano, central Mexico; implications for discriminating the Sierra Madre Occidental and Mexican volcanic belt provinces. International Geology Review. 45; 8, Pages 724-752. 2003.
| Authors | Verma, Surendra P; Carrasco, Nunez Gerardo |
|---|---|
| Year | 2003 |
| Title | Reappraisal of the geology and geochemistry of Volcan Zamorano, central Mexico; implications for discriminating the Sierra Madre Occidental and Mexican volcanic belt provinces. |
| Source | International Geology Review. 45; 8, Pages 724-752. 2003. |
| Publisher | Winston & Son. Silver Spring, MD, United States. 2003. |
| Document type | Serial |
| ISSN | 0020-6814 |
| GeoRef | 2004-014286 |
| Keywords | absolute-age; andesites-; Ar-Ar; basalts-; Cenozoic-; dacites-; dates-; geochemistry-; Holocene-; igneous-rocks; ignimbrite-; Mexican-volcanic-belt; Mexico-; Miocene-; Neogene-; pyroclastics-; Quaternary-; sampling-; Sierra-Madre-Occidental; Tertiary-; volcanic-rocks; volcanism-; volcanoes-; Zamorano- |
| DOI | 10.2747/0020-6814.45.8.724 |
Abstract
We report new geological, super 40 Ar/ super 39 Ar geochronology, and geochemical data major and trace elements, and Sr, Nd, and Pb isotopic ratios on andesitic to dacitic rocks collected from Volcan Zamorano and on rhyolitic ignimbrites from the surrounding area. These data better constrain the relationship of two major volcanic provinces of Mexico: the mid-Tertiary Sierra Madre Occidental SMO and the Miocene to Recent Mexican Volcanic Belt MVB. Structurally, the SMO and MVB show different extensional styles. The SMO was affected by east-west extension mainly during the Oligocene and middle Miocene, whereas the MVB was affected by extensional deformation during middle-to-late Miocene and Plio-Quaternary times, although reactivation of the older structural systems, such as the NNW-SSE system, has occurred in more recent times. The new geological data from the study area are consistent with the super 40 Ar/ super 39 Ar dates. The andesitic and dacitic rocks from Volcan Zamorano are about 10 Ma. These rocks, along with nearby andesitic and basaltic volcanoes, mark a relatively early phase of the MVB. The basaltic to dacitic rocks show the following ranges for Sr, Nd, and Pb isotopic ratios: super 87 Sr/ super 86 Sr sub i 0.70362-0.70474; super 143 Nd/ super 144 Nd sub i 0.51258-0.51286; super 206 Pb/ super 204 Pb 18.38-18.81; super 207 Pb/ super 204 Pb 15.57-15.63; and super 208 Pb/ super 204 Pb 38.27-38.70. For SMO ignimbrites approximately 30-28 Ma cropping out in the Zamorano area, super 87 Sr/ super 86 Sr sub i are slightly higher 0.70407-0.70557, and super 143 Nd/ super 144 Nd sub i are somewhat lower 0.51250-0.51253. Pb-isotope ratios for these ignimbrites are also higher about 18.84-18.87, 15.65, and 38.78-38.82, respectively than for basaltic to dacitic rocks from Volcan Zamorano and the surrounding area. Most studied rocks from both provinces seem to contain a crustal component. The ignimbrites are chemically and isotopically similar to rhyolitic and ignimbritic rocks sampled from other areas of the SMO. Our study of Volcan Zamorano shows that the transition from SMO to MVB was rather sudden and not a gradual process.