Arcs & continentsArcs & continents

- Wednesday review, midterm on April 2ndWednesday review, midterm on April 2nd

Topics:Topics:

Systematics for:Systematics for:- ArcsArcs- Some continental rocksSome continental rocks

Updates/questionsUpdates/questions

Trace Elements: REEsTrace Elements: REEs

Figure 14-2. After Wilson (1989) Igneous Petrogenesis. Kluwer.

Enriched

Enriched

DepletedDepleted

MORB-normalized Spider DiagramsMORB-normalized Spider Diagrams

Figure 14-3. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall. Data from Sun and McDonough (1989).

Trace ElementsTrace Elements

Isotope GeochemistryIsotope Geochemistry Isotopes do not fractionate during partial Isotopes do not fractionate during partial

melting of fractional melting processes, so melting of fractional melting processes, so will reflect the characteristics of the sourcewill reflect the characteristics of the source

OIBs only cross oceanic plate, limiting OIBs only cross oceanic plate, limiting contamination (<-> continent); good contamination (<-> continent); good estimate of mantleestimate of mantle

Sr Isotope EvolutionSr Isotope Evolution

Figure 9-13. After Figure 9-13. After Wilson (1989). Igneous Wilson (1989). Igneous Petrogenesis. Unwin Petrogenesis. Unwin Hyman/Kluwer.Hyman/Kluwer.

Sm-Nd: Evolution opposite to Rb - SrSm-Nd: Evolution opposite to Rb - SrCtl Crust (enriched) = hi Ctl Crust (enriched) = hi 8787Sr/Sr/8686Sr, lo Sr, lo 143143Nd/Nd/144144NdNd

147147SmSm143143Nd Nd

by alpha decayby alpha decayhalf life 106 Gahalf life 106 Ga

Daughter moreDaughter more

incompatibleincompatible

143143Nd/Nd/144144Nd = (Nd = (143143Nd/Nd/144144Nd)Nd)oo

+ (+ (147147Sm/Sm/144144Nd)(eNd)(ett-1)-1)

MORB Sr - Nd IsotopesMORB Sr - Nd Isotopes

Figure 13-12.Figure 13-12. Data from Ito et al. (1987) Data from Ito et al. (1987) Chemical Geology, 62, 157-176; Chemical Geology, 62, 157-176; and LeRoex et al. (1983) and LeRoex et al. (1983) J. Petrol., 24, 267-318.J. Petrol., 24, 267-318.

MORB+OIB: Sr - Nd IsotopesMORB+OIB: Sr - Nd IsotopesRange in compositions = mantle arrayRange in compositions = mantle array

Every composition by mixing end-members:Every composition by mixing end-members:DM -depleted DM -depleted mantlemantleEM 1&2 -EM 1&2 -enriched mantleenriched mantleHIMU - high HIMU - high = = 238238U/U/204204PbPb

238238U -> U -> 206206PbPbSo high So high 206206Pb/Pb/204204PbPb

MORB

OIB (colors)}

DMDM

HIMUHIMU

EM1EM1

EM2EM2

BSEBSE

AA Model for Oceanic Magmatism Model for Oceanic Magmatism

DMDM

OIBOIB

ContinentalContinental

ReservoirsReservoirs

EM and HIMU from crustal sources (subducted OC + CC seds)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 MagmatismArc Magmatism

Volcanism in arc-shaped region of volcanoesVolcanism in arc-shaped region of volcanoes Different because:Different because:

Composition more diverse and silicicComposition more diverse and silicic Basalt generally occurs in subordinate quantitiesBasalt generally occurs in subordinate quantities Also more explosive than the quiescent basalts Also more explosive than the quiescent basalts Strato-volcanoes are the most common volcanic Strato-volcanoes are the most common volcanic

landformlandform Result of subduction: H2O meltingResult of subduction: H2O melting

Arc occurrenceArc occurrence

Structure of an Island ArcStructure of an Island Arc

Major Elements and Major Elements and Magma SeriesMagma Series

NOAA Ocean ExplorerNOAA Ocean Explorer

A multi-stage, multi-source processA multi-stage, multi-source process

Continental ArcsContinental Arcs

Andes arc: north, central, southAndes arc: north, central, south

Andes trace elementsAndes trace elements

Granitoid RocksGranitoid Rocks

Types of granitesTypes of granites

Melting and compositionMelting and composition