1. G EOL 5310 A DVANCED I GNEOUS AND M ETAMORPHIC P ETROLOGY Subduction-related Igneous Activity and the Origin of Granite November 16, 2009

2. 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. P RESENT -D AY S UBDUCTION Z ONES

3. C HANGING M ODELS OF A RC M AGMATISM 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

4. 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/cm 2 /sec) S TRUCTURE OF AN I SLAND A RC

5. V OLCANIC R OCKS OF I SLAND A RCS 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

6. M AJOR E LEMENTS AND M AGMA S ERIES Figure 16-3. Data compiled by Terry Plank (Plank and Langmuir, 1988) Earth Planet. Sci. Lett., 90, 349-370.

7. T HOLEIITIC VS. C ALC - ALKALINE M AGMA S ERIES 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. SiO 2 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

8. K M AGMA S ERIES I N I SLAND A RC B ASALT - A NDESITE Figure 16.6. a. K 2 O-SiO 2 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 K 2 O at low SiO 2. After Gill, 1981, Orogenic Andesites and Plate Tectonics. Springer-Verlag. Figure 16.5. Combined K 2 O - 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

9. D IFFERENTIATION T RENDS 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

10. T RACE E LEMENT C HARACTERISTICS Winter (2010) Figure 16-10. Depleted Mantle Undepleted Mantle or Low % PM of DM? Low % PM of Undepleted mantle? GARNET in source?

11. 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. T RACE E LEMENT C HARACTERISTICS H YDROUS MORB S OURCE, S ELECTIVELY ENRICHED MORB S OURCE, OR OIB S OURCE W / HFS- COMPATIBLE RESIDUAL MINERAL ? Hydrophilic LIL Elements Nb(Ta) Anomalies HFS Elements

12. P ETROGENESIS OF I SLAND A RC M AGMAS

13. T HERMAL M ODEL FOR S UBDUCTION 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).

14. P OTENTIAL S OURCES OF A RC M AGMAS 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 slab 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). Only Viable Sources

15. P-T-t P ATHS FOR S UBDUCTED C RUST Yellow paths = various 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 = different ages of subducted slab Subduction rate of 3 cm/yr (length of each curve = ~15 Ma)

16. 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 M ELTING OF S UBDUCTED C RUST O NLY FOR Y OUNG C RUST AND A RCS

17. V ISCOSITY AT S LAB -M ANTLE I NTERFACE E NHANCING M ANTLE F LOW 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 Isoviscosity Model Variable Viscosity Model

18. 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. M ELTING OF H YDRATED M ANTLE W EDGE M AIN S OURCE OF A RC M AGMAS

19. M ELTING OF M ANTLE W EDGE M AIN S OURCE OF A RC M AGMAS Winter (2010) Figure 16.19 A B Melting at 3 main locations T - Mantle Tip A - Pargasite-out depth (~110km) B - Phlogopite-out depth (~200 km) T T

20. 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. M ELTING OF H YDRATED M ANTLE W EDGE M AIN S OURCE OF A RC M AGMAS 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? Sp Gt

21. C ONTINENTAL A RCS VS I SLAND A RCS A FFECTS OF T HICK D IFFERENTIATED C ONTINENTAL C RUST  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

22. T YPES OF C ONTINENTAL A RCS Destructive more common where Continental crust is older e.g. Andean Margin Constructive more common where Continental crust is younger e.g. Pacific NW

23. A NDEAN C ONTINENTAL A RC Gaps in volcanic activity shallow subduction overthickened slab

24. A NDEAN V OLCANIC COMPOSITIONS D ISTRIBUTION OF R OCK T YPES Lower Crust traps Mafic Magmas Melting of Lower Crust generates Felsic Magmas

25. Island Arcs Alkaline Rocks Northern 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 A NDEAN V OLCANIC COMPOSITIONS M AJOR E LEMENTS

26. A NDEAN V OLCANIC COMPOSITIONS T RACE E LEMENTS 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 SiO 2 = 60.7, K 2 O = 0.66, data from Thorpe et al. 1984; Geist, pers. comm.). CVZ (10 samples, ave. SiO 2 = 54.8, K 2 O = 2.77, data from Deruelle, 1982; Davidson, pers. comm.; Thorpe et al., 1984). SVZ (49 samples, average SiO 2 = 52.1, K 2 O = 1.07, data from Hickey et al. 1986; Deruelle, 1982; López-Escobar et al. 1981).

27. A NDEAN V OLCANIC COMPOSITIONS T RACE E LEMENTS 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 SiO 2 = 60.7, K 2 O = 0.66, data from Thorpe et al. 1984; Geist, pers. comm.). CVZ (10 samples, ave. SiO 2 = 54.8, K 2 O = 2.77, data from Deruelle, 1982; Davidson, pers. comm.; Thorpe et al., 1984). SVZ (49 samples, average SiO 2 = 52.1, K 2 O = 1.07, data from Hickey et al. 1986; Deruelle, 1982; López-Escobar et al. 1981).

28. A NDEAN V OLCANIC COMPOSITIONS I SOTOPIC C OMPOSITIONS 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).

29. C ONSTRUCTIVE C ONTINENTAL A RC P ACIFIC 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

30. C ASCADE M AGMA T YPES OVER T IME Bimodal Volcanism Greater 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

31. C ASCADES T RACE E LEMENT G EOCHEMISTRY Deplete (MORB) and Enriched (OIB) Signatures = Heterogeneous Mantle Wedge? Nb-Ta anomaly not common = Early shallow dehydration of hot slab?

32. C ASCADES I SOTOPE G EOCHEMISTRY Precambrian Crustal Signature 87/86 Srº > 0.706 206/204 Pbº > 18.9

33. G ENERAL M ODEL FOR C ONTINENTAL A RC M AGMATISM M-crustal Melting A- Assimilation S- Storage H-Homogenization

34. Frontpiece from H.H. Read (1958) The Granite Controversy O RIGIN OF G RANITES

35. P ARTIAL M ELTING VS. F RACTIONAL C RYSTALLIZATION T HE S ONJU L AKE – F INLAND G RANITE C ONNECTION Finland Granite SLI The Problem: Even very efficient fractional crystallization will create only 5-10% felsic magma

36. A F EW B ROAD G ENERALIZATIONS A BOUT G RANITES 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

37. A RC P LUTONIC C OMPLEXES - “G RANITE ” B ATHOLITHS F EEDER C HAMBERS TO C ONTINENTAL A RC V OLCANICS

38. G EOCHEMISTY OF A RC P LUTONIC C OMPLEXES M IMICS V OLCANIC C OMPOSITIONS Peruvian Coastal Batholith

39. N ON -G ENETIC C LASSIFICATIONS OF G RANITIC R OCKS Chemistry-based Mineralogy-based

40. C OMPOSITE E MPLACEMENT OF “G RANITIC ” B ATHOLITHS Tends toward more felsic compositions over time Epizonal batholiths form mostly by roof collapse (stoping) or downdropping of the chamber floor

41. C RUSTAL A NATEXIS AT D IFFERENT C RUSTAL D EPTHS

42. G ENETIC C LASSIFICATION OF G RANITIC R OCKS B ASED ON S OURCE R OCK /M ODE OF O RIGIN

43. M-T YPE G RANITOIDS D IFFERENTIATES OF M AFIC M AGMAS

44. I-T YPE G RANITOIDS R EMELTING OF M AFIC U NDERPLATED C RUST

45. S-T YPE G RANITOIDS R EMELTING OF S EDIMENTARY R OCKS Dehydration Melting of Hydrous Mineral-bearing Rocks

46. A-T YPE G RANITOIDS A NOROGENIC M ELTING OF C ONTINENTAL I NTERIORS

48. G RANITES C REATED D URING C ONTINENT - C ONTINENT C OLLISION (O ROGENESIS )

49. P OST - O ROGENIC G RANTOIDS E XTENSIONAL C OLLAPSE Post- Penokean granites

50. T ECTONIC D ISCRIMINATION D IAGRAMS FOR G RANITOIDS 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.