Source contamination versus assimilation; an example from the Trans-Mexican volcanic arc.
Chesley, John; Ruiz, Joaquin; Righter, Kevin; Ferrari, Luca; Gomez, Tuena Arturo (2002) Source contamination versus assimilation; an example from the Trans-Mexican volcanic arc. Earth and Planetary Science Letters. 195; 3-4, Pages 211-221. 2002.
| Authors | Chesley, John; Ruiz, Joaquin; Righter, Kevin; Ferrari, Luca; Gomez, Tuena Arturo |
|---|---|
| Year | 2002 |
| Title | Source contamination versus assimilation; an example from the Trans-Mexican volcanic arc. |
| Source | Earth and Planetary Science Letters. 195; 3-4, Pages 211-221. 2002. |
| Publisher | Elsevier. Amsterdam, Netherlands. 2002. |
| Document type | Serial |
| ISSN | 0012-821X |
| GeoRef | 2002-028437 |
| Keywords | alkaline-earth-metals; assimilation-; asthenosphere-; Cenozoic-; concentration-; fractional-crystallization; geochemistry-; igneous-rocks; island-arcs; isotope-ratios; isotopes-; lithogeochemistry-; magma-contamination; magmas-; magmatic-differentiation; major-elements; mantle-; mantle-wedges; metals-; metasomatism-; Mexican-volcanic-belt; Mexico-; Michoacan-Guanajuato-volcanic-field; Neogene-; Os-188-Os-187; osmium-; plate-tectonics; platinum-group; Quaternary-; Re-Os; slabs-; Sr-87-Sr-86; stable-isotopes; strontium-; subduction-; Tertiary-; volcanic-fields; volcanic-rocks; volcanism- |
| DOI | 10.1016/S0012-821X(01)00580-5 |
Abstract
Volcanic samples representing a wide range of lithologies and compositions were collected from the Miocene to Quaternary age Michoacan-Guanajuato volcanic field MGVF in the Trans-Mexican volcanic belt TMVB. The samples were analyzed for major and trace elements, and super 87 Sr/ super 86 Sr and super 187 Os/ super 188 Os in an effort differentiate the importance of source contamination and assimilation in continental arc magmatism. Re concentrations in the MGVF samples range from 0.03 to 0.13 ppb and Os concentrations range from 0.05 to 0.001 ppb. The super 87 Sr/ super 86 Sr of the samples vary little, ranging from 0.7037 to 0.7047, despite a wide range in major element composition. However, the super 187 Os/ super 188 Os vary greatly, from 0.135 to 0.410. Decreasing Os concentration and increasing super 187 Os/ super 188 Os show a clear relation with indicators of fractionation such as MgO or Ni. A plot of super 187 Os/ super 188 Os versus Ba/Nb for all samples from the MGVF show two distinct trends: 1 a wide variation in Ba/Nb 50-200 associated with minor variations in super 187 Os/ super 188 Os approximately 0.135-0.145, and 2 increasing super 187 Os/ super 188 Os 0.145-0.40 associated with restricted Ba/Nb 35-70. These trends are best explained through a dynamic multi-component process. Fluids are released from the subducting slab, resulting in melting of the overlying asthenospheric wedge. The pristine fluids have high Ba and low Re and Os concentrations. The resulting melts have variable Ba/Nb, but unradiogenic super 187 Os/ super 188 Os. Superimposed upon these melts are both assimilation and fractional crystallization processes, which affect both the Ba/Nb and super 187 Os/ super 188 Os systems as they ascend into the lower crust.