GEOL 5310 ADVANCED IGNEOUS AND METAMORPHIC PETROLOGY

Subduction-related Igneous Activity

and the Origin of Granite

November 16, 2009

Winter (2001) Figure 16-1. Principal subduction zones associated with orogenic volcanism and plutonism. Triangles are on the overriding plate. After Wilson (1989) Igneous Petrogenesis, Allen Unwin/Kluwer.

PRESENT-DAY SUBDUCTION ZONES

CHANGING MODELS OF ARC MAGMATISM

1960-70’s Arc magmas largely derived from subducted oceanic crust and sediment

1980-90’s Arc magmas largely derived from mantle wedge

1990’s- 2000’s both contribute, but wedge is dominant source

Winter (2001) Figure 16-2. Schematic cross section through a typical island arc after Gill (1981), Orogenic Andesites and Plate Tectonics. Springer-Verlag. HFU= heat flow unit (4.2 x 10-6

joules/cm2/sec)

STRUCTURE OF AN ISLAND ARC

VOLCANIC ROCKS OF ISLAND ARCS Complex tectonic situation and broad spectrum of volcanic

products High proportion of basaltic andesite and andesite Basalts common and an important part of the story

MAJOR ELEMENTS AND MAGMA SERIES

Figure 16-3. Data compiled by Terry Plank (Plank and Langmuir, 1988) Earth Planet. Sci. Lett., 90, 349-370.

CharacteristicSeries Convergent Divergent Oceanic ContinentalAlkaline yes yes yesTholeiitic yes yes yes yesCalc-alkaline yes

Plate Margin Within Plate

THOLEIITIC VS. CALC-ALKALINE MAGMA SERIES

Winter (2010) Figure 16.6. b. AFM diagram distinguishing tholeiitic and calc-alkaline series. Arrows represent differentiation trends within a series.

Figure 16.6. c. FeO*/MgO vs. SiO2 diagram distinguishing tholeiitic and calc-alkaline series. The gray arrow near the bottom is the progressive fractional melting trend under hydrous conditions of Grove et al. (2003).

Fractional Melting of Hydrous Mantle

K MAGMA SERIES IN ISLAND ARC BASALT - ANDESITE

Figure 16.6. a. K2O-SiO2 diagram distinguishing high-K, medium-K and low-K series. Large

squares = high-K, stars = med.-K, diamonds = low-K series from Table 16-2. Smaller symbols are identified in the caption. Differentiation within a series (presumably dominated by fractional crystallization) is indicated by the arrow. Different primary magmas (to the left) are distinguished by vertical variations in K2O at low SiO2. After Gill, 1981, Orogenic

Andesites and Plate Tectonics. Springer-Verlag.

Figure 16.5. Combined K2O - FeO*/MgO

diagram in which the Low-K to High-K series are combined with the tholeiitic vs. calc-alkaline types, resulting in six andesite series, after Gill (1981) Orogenic Andesites and Plate Tectonics. Springer-Verlag. The points represent the analyses in the appendix of Gill (1981).

BA

And

DIFFERENTIATION TRENDS FOR IAV

Figure 16-6. From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

Pl+Cpx FX

Early Fe-Ti Ox FX in Calc-Alk

CaPl NaPl

TRACE ELEMENT CHARACTERISTICS

Winter (2010) Figure 16-10.

Depleted MantleDepleted Mantle

Undepleted Mantle or Low % PM of DM?Undepleted Mantle or Low % PM of DM?

Low % PM of Undepleted mantle?Low % PM of Undepleted mantle?

GARNET in GARNET in source?source?

Figure 16-11a. MORB-normalized spider diagrams for selected island arc basalts. Using the normalization and ordering scheme of Pearce (1983) with LIL on the left and HFS on the right and compatibility increasing outward from Ba-Th. Data from BVTP. Composite OIB from Fig 14-3 in yellow.

TRACE ELEMENT CHARACTERISTICSHYDROUS MORB SOURCE, SELECTIVELY ENRICHED MORB SOURCE,

OR OIB SOURCE W/ HFS-COMPATIBLE RESIDUAL MINERAL? Hydrophilic

LIL ElementsNb(Ta)

Anomalies HFS Elements

PETROGENESIS OF ISLAND ARC MAGMAS

THERMAL MODEL FOR SUBDUCTION

Variables affecting isotherms in subduction zones:

• Rate of subduction• Age of the subduction

zone• Age of the subducting

slab• Flow in the mantle wedge• Frictional/shear heating

along the Wadati-Benioff zone

Other factors: dip of the slab endothermic metamorphic

reactions metamorphic fluid flow

Isotherms will be higher when: • convergence is slower• slab is younger (nearer to ridge)• arc is younger

Winter (2010) Figure 16-15. Cross section of a subduction zone showing isotherms (red-after Furukawa, 1993, J. Geophys. Res., 98, 8309-8319) and mantle flow lines (yellow- after Tatsumi and Eggins, 1995, Subduction Zone Magmatism. Blackwell. Oxford).

POTENTIAL SOURCES OF ARC MAGMAS

1. Crustal portion of the subducted slab

Altered oceanic crust (hydrated by circulating seawater, and metamorphosed in large part to greenschist facies)

Subducted oceanic and forearc sediments

Seawater trapped in pore spaces

2. Mantle wedge between slab and arc crust

3. Arc crust

4.Lithospheric mantle of subducting plate

5. Asthenosphere beneath slabWinter (2010) Figure 16-15. Cross section of a subduction zone showing isotherms (red-after

Furukawa, 1993, J. Geophys. Res., 98, 8309-8319) and mantle flow lines (yellow- after Tatsumi and Eggins, 1995, Subduction Zone Magmatism. Blackwell. Oxford).

Only Viable Sources

P-T-t PATHS FOR SUBDUCTED CRUST

Yellow paths = Yellow paths = various arc agesvarious arc ages

Subducted Crust

Figure 16-16. Subducted crust pressure-temperature-time (P-T-t) paths for various situations of arc age (yellow curves) and age of subducted lithosphere (red curves, for a mature ca. 50 Ma old arc) assuming a subduction rate of 3 cm/yr (Peacock, 1991, Phil. Trans. Roy. Soc. London, 335, 341-353).

Red paths = Red paths = different ages of different ages of subducted slabsubducted slab

Subduction rate of 3 cm/yr (length of each curve = ~15 Ma)

Winter (2010) Figure 16-16. Subducted crust pressure-temperature-time (P-T-t) paths for various situations of arc age (yellow curves) and age of subducted lithosphere (red curves, for a mature ca. 50 Ma old arc) assuming a subduction rate of 3 cm/yr (Peacock, 1991). Included are some pertinent reaction curves, including the wet and dry basalt solidi (Figure 7-20), the dehydration of hornblende (Lambert and Wyllie, 1968, 1970, 1972), chlorite + quartz (Delaney and Helgeson, 1978). Winter (2001). An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

D- Dehydration Zone - no melting; LIL-enriched fluids move into mantle wedge.

M – Partial melting of basaltic slab Mg andesite

MELTING OF SUBDUCTED CRUSTONLY FOR YOUNG CRUST AND ARCS

VISCOSITY AT SLAB-MANTLE INTERFACE

ENHANCING MANTLE FLOW AND T

Winter (2001) Figure 16.17. P-T-t paths at a depth of 7 km into the slab (subscript = 1) and at the slab/mantle-wedge interface (subscript = 2) predicted by several published dynamic models of fairly rapid subduction (9-10 cm/yr). ME= Molnar and England’s (1992) analytical solution with no wedge convection. PW = Peacock and Wang (1999) isoviscous numeric model. vK = van Keken et al. (2002a) isoviscous remodel of PW with improved resolution. vKT = van Keken et al. (2002a) model with non-Newtonian temperature- and stress-dependent wedge viscosity. After van Keken et al. (2002a) © AGU with permission.

Slab Surface

7 Km into Slab

No Mantle Flow

Isov

isco

sity

Mod

el

Var

iabl

e V

isco

sity

Mod

el

Figure 16-11b. A proposed model for subduction zone magmatism with particular reference to island arcs. Dehydration of slab crust causes hydration of the mantle (violet), which undergoes partial melting as amphibole (A) and phlogopite (B) dehydrate. From Tatsumi (1989), J. Geophys. Res., 94, 4697-4707 and Tatsumi and Eggins (1995). Subduction Zone Magmatism. Blackwell. Oxford.

MELTING OF HYDRATED MANTLE WEDGEMAIN SOURCE OF ARC MAGMAS

MELTING OF MANTLE WEDGEMAIN SOURCE OF ARC MAGMAS

Winter (2010) Figure 16.19

A

B

Melting at 3 main locationsT - Mantle TipA - Pargasite-out depth (~110km)B - Phlogopite-out depth (~200 km)

T

TT

Figure 16-11b. A proposed model for subduction zone magmatism with particular reference to island arcs. Dehydration of slab crust causes hydration of the mantle (violet), which undergoes partial melting as amphibole (A) and phlogopite (B) dehydrate. From Tatsumi (1989), J. Geophys. Res., 94, 4697-4707 and Tatsumi and Eggins (1995). Subduction Zone Magmatism. Blackwell. Oxford.

MELTING OF HYDRATED MANTLE WEDGEMAIN SOURCE OF ARC MAGMAS

Primary Magma= High-Mg (>8wt%) High-Al tholeiite from Garnet Lherzolite Source

From which more evolved tholeiitic and calc-alkaline magmas are formed by fractional crystallization?

SpGt

CONTINENTAL ARCS VS ISLAND ARCS

AFFECTS OF THICK DIFFERENTIATED CONTINENTAL CRUST

Thick sialic crust contrasts greatly with mantle-derived partial melts may produce more pronounced effects of contamination

Low density of crust may retard ascent causing stagnation of magmas and more potential for differentiation

Low melting point of crust allows for partial melting and crustally-derived melts

Subcontinental lithosphere may be more compositionally diverse that suboceanic lithosphere, especially if crust is old

TYPES OF CONTINENTAL ARCS

Destructivemore common where Continental crust is oldere.g. Andean Margin

Constructivemore common where Continental crust is younger e.g. Pacific NW

ANDEAN CONTINENTAL ARC

Gaps in volcanic activity• shallow subduction• overthickened slab

ANDEAN VOLCANIC COMPOSITIONSDISTRIBUTION OF ROCK TYPES

Lower Crust traps Mafic Magmas

Melting of Lower Crust generates Felsic Magmas

Island Arcs

Alkaline RocksNorthern Volcanic Zone• more andesitic to felsic• K-rich comps to east

Central Volcanic Zone• more andesitic to felsic• basalts rare• more staging beneath Precambrian crust

Southern Volcanic Zone• broad range of comps• K-rich comps to east• shallower subduction angle• Young continental crust especially to south

ANDEAN VOLCANIC COMPOSITIONSMAJOR ELEMENTS

ANDEAN VOLCANIC COMPOSITIONSTRACE ELEMENTS

SVZ - Shallower subduction angle melting of Gt-free mantle

CVZ – Assimilation of Precambrian crust and SCLM

Winter (2010) Figure 17.4. Chondrite-normalized REE diagram for selected Andean volcanics. NVZ (6 samples, average SiO2 = 60.7, K2O = 0.66, data from

Thorpe et al. 1984; Geist, pers. comm.). CVZ (10 samples, ave. SiO2 = 54.8, K2O = 2.77, data from Deruelle, 1982; Davidson, pers. comm.; Thorpe et al.,

1984). SVZ (49 samples, average SiO2 = 52.1, K2O = 1.07, data from Hickey et al. 1986; Deruelle, 1982; López-Escobar et al. 1981).

ANDEAN VOLCANIC COMPOSITIONSTRACE ELEMENTS

Negative Nb-Ta anomaly - similar to island arc pattern

CVZ – Assimilation of Precambrian crust and/or SCLM

Enriched LIL and mobile HFS dehydration of subducted slab and enrichment of mantle wedge

Winter (2010) Figure 17.5. MORB-normalized spider diagram (Pearce, 1983) for selected Andean volcanics. NVZ (6 samples, average SiO2 = 60.7, K2O =

0.66, data from Thorpe et al. 1984; Geist, pers. comm.). CVZ (10 samples, ave. SiO2 = 54.8, K2O = 2.77, data from Deruelle, 1982; Davidson, pers. comm.;

Thorpe et al., 1984). SVZ (49 samples, average SiO2 = 52.1, K2O = 1.07, data from Hickey et al. 1986; Deruelle, 1982; López-Escobar et al. 1981).

ANDEAN VOLCANIC COMPOSITIONSISOTOPIC COMPOSITIONS

Crustal Contamination

Winter (2010) Figure 17.6. Sr vs. Nd isotopic ratios for the three zones of the Andes. Data from James et al. (1976), Hawkesworth et al. (1979), James (1982), Harmon et al. (1984), Frey et al. (1984), Thorpe et al. (1984), Hickey et al. (1986), Hildreth and Moorbath (1988), Geist (pers. comm), Davidson (pers. comm.), Wörner et al. (1988), Walker et al. (1991), deSilva (1991), Kay et al. (1991), Davidson and deSilva (1992).

CONSTRUCTIVE CONTINENTAL ARCPACIFIC NW

Columbia Embayment - area of young crust and arc construction by rollback or trench jumping

Juan de Fuca Plate – Young, hot, bouyant;dehydrates quickly upon subduction

CASCADE MAGMA TYPES OVER TIME

Bimodal VolcanismGreater proportion of mafic compositions & bimodal volcanism

More akin to Continental Flood Basalt provinces

Interpreted to indicate mafic underplating leading to lower crustal melting in an extensional environment

CASCADES TRACE ELEMENT GEOCHEMISTRY

Deplete (MORB) and Enriched (OIB) Signatures

= Heterogeneous Mantle Wedge?

Nb-Ta anomaly not common

= Early shallow dehydration of hot slab?

CASCADES ISOTOPE GEOCHEMISTRY

Precambrian Crustal Signature87/86Srº > 0.706206/204Pbº > 18.9

GENERAL MODEL FOR CONTINENTAL ARC MAGMATISM

M-crustal MeltingA- AssimilationS- StorageH-Homogenization

Frontpiece from H.H. Read (1958) The Granite Controversy

ORIGIN OF GRANITES

PARTIAL MELTING VS. FRACTIONAL CRYSTALLIZATIONTHE SONJU LAKE – FINLAND GRANITE CONNECTION

Finland Granite

SLI

The Problem: Even very efficient fractional crystallization will create only 5-10% felsic magma

A FEW BROAD GENERALIZATIONS ABOUT GRANITES

1) Most granitoids of significant volume occur in areas where the continental crust has been thickened by orogeny, either continental arc subduction or collision of sialic masses. Many granites, however, may post-date the thickening event by tens of millions of years.

2) Because the crust is solid in its normal state, some thermal disturbance is required to form granitoids

3) Most workers are of the opinion that the majority of granitoids are derived by crustal anatexis, but that the mantle may also be involved. The mantle contribution may range from that of a source of heat for crustal anatexis, or it may be the source of material as well

Zoned zircon in a granite with older inherited (restite) core overgrown by new material from the felsic magma

ARC PLUTONIC

COMPLEXES- “GRANITE”

BATHOLITHS

FEEDER CHAMBERS TO CONTINENTAL

ARC VOLCANICS

GEOCHEMISTY OF ARC PLUTONIC COMPLEXES

MIMICS VOLCANIC COMPOSITIONS

Peruvian Coastal Batholith

NON-GENETIC CLASSIFICATIONS OF GRANITIC ROCKS

Chemistry-based

Mineralogy-based

COMPOSITE EMPLACEMENT OF “GRANITIC” BATHOLITHS

Tends toward more felsic compositions over time

Epizonal batholiths form mostly by roof collapse (stoping) or downdropping of the chamber floor

CRUSTAL ANATEXIS AT DIFFERENT CRUSTAL DEPTHS

GENETIC CLASSIFICATION OF GRANITIC ROCKS

BASED ON SOURCE ROCK/MODE OF ORIGIN

Table 18-3. The S-I-A-M Classification of Granitoids

Type SiO2 K2O/Na2O Ca, Sr A/(C+N+K)* Fe3+/Fe2+Cr, Ni 18O 87Sr/86Sr Misc Petrogenesis

M 46-70% low high low low low < 9‰ < 0.705 Low Rb, Th, U Subduction zoneLow LIL and HFS or ocean-intraplate

Mantle-derivedI 53-76% low high in low: metal- moderate low < 9‰ < 0.705 high LIL/HFS Subduction zone

mafic uminous to med. Rb, Th, U Infracrustalrocks peraluminous hornblende Mafic to intermed.

magnetite igneous sourceS 65-74% high low high low high > 9‰ > 0.707 variable LIL/HFS Subduction zone

high Rb, Th, Umetaluminous biotite, cordierite Supracrustal

Als, Grt, Ilmenite sedimentary sourceA high Na2O low var var low var var low LIL/HFS Anorogenic

77% high peralkaline high Fe/Mg Stable craton high Ga/Al Rift zone

High REE, ZrHigh F, Cl

* molar Al2O3/(CaO+Na2O+K2O) Data from White and Chappell (1983), Clarke (1992), Whalen (1985)

M-TYPE GRANITOIDSDIFFERENTIATES OF MAFIC MAGMAS

Type SiO2 K2O/Na2O Ca, Sr A/(C+N+K)* Fe3+/Fe2+Cr, Ni 18O

87Sr/86Sr Misc PetrogenesisM 46-70% low high low low low < 9‰ < 0.705 Low Rb, Th, U Subduction zone

Low LIL and HFS or ocean-intraplate

Mantle-derivedI 53-76% low high in low: metal- moderate low < 9‰ < 0.705 high LIL/HFS Subduction zone

mafic uminous to med. Rb, Th, U Infracrustalrocks peraluminous hornblende Mafic to intermed.

magnetite igneous source

high Rb, Th, Umetaluminous biotite, cordierite Supracrustal

Als, Grt, Ilmenite sedimentary sourceA high

high Ga/Al Rift zoneHigh REE, Zr

High F, Cl

I-TYPE GRANITOIDSREMELTING OF MAFIC UNDERPLATED

CRUSTType SiO2 K2O/Na2O Ca, Sr A/(C+N+K)* Fe3+/Fe2+

Cr, Ni 18O87Sr/86Sr Misc Petrogenesis

M 46-70% low high low low low < 9‰ < 0.705 Low Rb, Th, U Subduction zoneLow LIL and HFS or ocean-intraplate

Mantle-derived

mafic uminous to med. Rb, Th, U Infracrustalrocks peraluminous hornblende Mafic to intermed.

magnetite igneous source

high Rb, Th, Umetaluminous biotite, cordierite Supracrustal

Als, Grt, Ilmenite sedimentary sourceA high

high Ga/Al Rift zoneHigh REE, Zr

High F, Cl

Type

Low LIL and HFS or ocean-intraplate

Mantle-derivedI 53-76% low high in low: metal- moderate low < 9‰ < 0.705 high LIL/HFS Subduction zone

mafic uminous to med. Rb, Th, U Infracrustalrocks peraluminous hornblende Mafic to intermed.

magnetite igneous sourceS 65-74% high low high low high > 9‰ > 0.707 variable LIL/HFS Subduction zone

high Rb, Th, Umetaluminous biotite, cordierite Supracrustal

Als, Grt, Ilmenite sedimentary sourceA high

high Ga/Al Rift zoneHigh REE, Zr

High F, Cl

S-TYPE GRANITOIDSREMELTING OF SEDIMENTARY ROCKS

Type SiO2 K2O/Na2O Ca, Sr A/(C+N+K)* Fe3+/Fe2+Cr, Ni 18O

87Sr/86Sr Misc PetrogenesisM 46-70% low high low low low < 9‰ < 0.705 Low Rb, Th, U Subduction zone

Low LIL and HFS or ocean-intraplate

Mantle-derived

mafic uminous to med. Rb, Th, U Infracrustalrocks peraluminous hornblende Mafic to intermed.

magnetite igneous source

high Rb, Th, Umetaluminous biotite, cordierite Supracrustal

Als, Grt, Ilmenite sedimentary sourceA high

high Ga/Al Rift zoneHigh REE, Zr

High F, Cl

Type

Low LIL and HFS or ocean-intraplate

Mantle-derived

mafic uminous to med. Rb, Th, U Infracrustalrocks peraluminous hornblende Mafic to intermed.

magnetite igneous sourceS 65-74% high low high low high > 9‰ > 0.707 variable LIL/HFS Subduction zone

high Rb, Th, Umetaluminous biotite, cordierite Supracrustal

Als, Grt, Ilmenite sedimentary sourceA high

high Ga/Al Rift zoneHigh REE, Zr

High F, Cl

Dehydration Melting of Hydrous Mineral-bearing Rocks

A-TYPE GRANITOIDSANOROGENIC MELTING OF CONTINENTAL

INTERIORSType SiO2 K2O/Na2O Ca, Sr A/(C+N+K)* Fe3+/Fe2+

Cr, Ni 18O87Sr/86Sr Misc Petrogenesis

M 46-70% low high low low low < 9‰ < 0.705 Low Rb, Th, U Subduction zoneLow LIL and HFS or ocean-intraplate

Mantle-derived

mafic uminous to med. Rb, Th, U Infracrustalrocks peraluminous hornblende Mafic to intermed.

magnetite igneous source

high Rb, Th, Umetaluminous biotite, cordierite Supracrustal

Als, Grt, Ilmenite sedimentary sourceA high

high Ga/Al Rift zoneHigh REE, Zr

High F, Cl

Type

Low LIL and HFS or ocean-intraplate

Mantle-derived

mafic uminous to med. Rb, Th, U Infracrustalrocks peraluminous hornblende Mafic to intermed.

magnetite igneous source

high Rb, Th, Umetaluminous biotite, cordierite Supracrustal

Als, Grt, Ilmenite sedimentary sourceA high Na2O low var var low var var low LIL/HFS Anorogenic

77% high peralkaline high Fe/Mg Stable craton high Ga/Al Rift zone

High REE, ZrHigh F, Cl

GRANITES CREATED DURING CONTINENT-CONTINENT COLLISION (OROGENESIS)

POST-OROGENIC GRANTOIDSEXTENSIONAL

COLLAPSE

Post-Penokean granites

TECTONIC DISCRIMINATION DIAGRAMS FOR GRANITOIDS

Figure 18.9. Examples of granitoid discrimination diagrams used by Pearce et al. (1984, J. Petrol., 25, 956-983) with the granitoids of Table 18-2 plotted. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.