Transcript ppt - SOEST
Arcs & continents Updates/questions - Wednesday review, midterm on April 2nd Topics: Systematics for: - Arcs - Some continental rocks Trace Elements: REEs Figure 14-2. After Wilson (1989) Igneous Petrogenesis. Kluwer. MORB-normalized Spider Diagrams Figure 14-3. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall. Data from Sun and McDonough (1989). Trace Elements Isotope Geochemistry Isotopes do not fractionate during partial melting of fractional melting processes, so will reflect the characteristics of the source OIBs only cross oceanic plate, limiting contamination (<-> continent); good estimate of mantle Sr Isotope Evolution Figure 9-13. After Wilson (1989). Igneous Petrogenesis. Unwin Hyman/Kluwer. Sm-Nd: Evolution opposite to Rb - Sr Ctl Crust (enriched) = hi 87Sr/86Sr, lo 143Nd/144Nd 147Sm143Nd by alpha decay half life 106 Ga Daughter more incompatible 143 Nd/144Nd = (143Nd/144Nd)o + (147Sm/144Nd)(elt-1) MORB Sr - Nd Isotopes Figure 13-12. Data from Ito et al. (1987) Chemical Geology, 62, 157-176; and LeRoex et al. (1983) J. Petrol., 24, 267-318. MORB+OIB: Sr - Nd Range in compositions Isotopes = mantle array Every composition by mixing end-members: DM -depleted DM mantle MORB EM 1&2 OIB (colors) enriched mantle HIMU - high m HIMU 238 204 = U/ Pb BSE 238U -> 206Pb So high 206Pb/204Pb EM2 EM1 A Model for Oceanic Magmatism Continental Reservoirs DM OIB EM and HIMU from crustal sources (subducted OC + CC seds) Figure 14-10. Nomenclature from Zindler and Hart (1986). After Wilson (1989) and Rollinson (1993). Arc Magmatism Volcanism in arc-shaped region of volcanoes Different because: Composition more diverse and silicic Basalt generally occurs in subordinate quantities Also more explosive than the quiescent basalts Strato-volcanoes are the most common volcanic landform Result of subduction: H2O melting Arc occurrence Structure of an Island Arc Major Elements and Magma Series A multi-stage, multi-source process NOAA Ocean Explorer Continental Arcs Andes arc: north, central, south Andes trace elements Granitoid Rocks Types of granites Melting and composition