chapter 17: continental arc magmatism potential differences with respect to island arcs: thick...

Chapter 17: Continental Arc MagmatismPotential differences with respect to Island Arcs:• Thick sialic crust contrasts greatly with mantle-

derived partial melts may more pronounced effects of contamination

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

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

Chapter 17: Continental Arc

Magmatism

Figure 17.1. Map of western South America showing the plate tectonic framework, and the distribution of volcanics and crustal types. NVZ, CVZ, and SVZ are the northern, central, and southern volcanic zones. After Thorpe and Francis (1979) Tectonophys., 57, 53-70; Thorpe et al. (1982) In R. S. Thorpe (ed.), (1982). Andesites. Orogenic Andesites and Related Rocks. John Wiley & Sons. New York, pp. 188-205; and Harmon et al. (1984) J. Geol. Soc. London, 141, 803-822. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.


Magmatism

Figure 17.2. Schematic diagram to illustrate how a shallow dip of the subducting slab can pinch out the asthenosphere from the overlying mantle wedge. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.


Magmatism

Figure 17.3. AFM and K2O vs. SiO2 diagrams

(including Hi-K, Med.-K and Low-K types of Gill, 1981; see Figs. 16-4 and 16-6) for volcanics from the (a) northern, (b) central and (c) southern volcanic zones of the Andes. Open circles in the NVZ and SVZ are alkaline rocks. Data from Thorpe et al. (1982,1984), Geist (personal communication), Deruelle (1982), Davidson (personal communication), Hickey et al. (1986), López-Escobar et al. (1981), Hörmann and Pichler (1982). Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

Chapter 17: Continental Arc Magmatism

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). Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.


Figure 17.5. MORB-normalized spider diagram (Pearce, 1983) for selected Andean volcanics. NVZ (6 samples, average SiO 2 = 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). Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.


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). Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

Chapter 17: Continental

Arc Magmatism

Figure 17.7. 208Pb/204Pb vs. 206Pb/204Pb and 207Pb/204Pb vs. 206Pb/204Pb for Andean volcanics plotted over the OIB fields from Figures 14-7 and 14-8. 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). Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.


Figure 17.8. 87Sr/86Sr, D7/4, D8/4, and d18O vs. Latitude for the Andean volcanics. 7/4 and 8/4 are indices of 207Pb and 208Pb enrichment over the NHRL values of Figure 17-7 (see Rollinson, 1993, p. 240). Shaded areas are estimates for mantle and MORB isotopic ranges from Chapter 10. 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). Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.


Figure 17.9. Relative frequency of rock types in the Andes vs. SW Pacific Island arcs. Data from 397 Andean and 1484 SW Pacific analyses in Ewart (1982) In R. S. Thorpe (ed.), Andesites. Wiley. New York, pp. 25-95. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.


Magmatism

Figure 17.10. Map of the Juan de Fuca plate-Cascade Arc system, after McBirney and White, (1982) The Cascade Province. In R. S. Thorpe (ed.), Andesites. Orogenic Andesites and Related Rocks. John Wiley & Sons. New York. pp. 115-136. Also shown is the Columbia Embayment (the western margin of pre-Tertiary continental rocks) and approximate locations of the subduction zone as it migrated westward to its present location (after Hughes, 1990, J. Geophys. Res., 95, 19623-19638). Due to sparse age constraints and extensive later volcanic cover, the location of the Columbia Embayment is only approximate (particularly along the southern half). Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.


Magmatism

Figure 17.11. Schematic cross sections of a volcanic arc showing an initial state (a) followed by trench migration toward the continent (b), resulting in a destructive boundary and subduction erosion of the overlying crust. Alternatively, trench migration away from the continent (c) results in extension and a constructive boundary. In this case the extension in (c) is accomplished by “roll-back” of the subducting plate. An alternative method involves a jump of the subduction zone away from the continent, leaving a segment of oceanic crust (original dashed) on the left of the new trench. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.


Figure 17.12. Time-averaged rates of extrusion of mafic (basalt and basaltic andesite), andesitic, and silicic (dacite and rhyolite) volcanics (Priest, 1990, J. Geophys. Res., 95, 19583-19599) and Juan de Fuca-North American plate convergence rates (Verplanck and Duncan, 1987 Tectonics, 6, 197-209) for the past 35 Ma. The volcanics are poorly exposed and sampled, so the timing should be considered tentative. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.


Figure 17.13a. Rare earth element diagram for mafic platform lavas of the High Cascades. Data from Hughes (1990, J. Geophys. Res., 95, 19623-19638). Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.


Figure 17.13b. Spider diagram for mafic platform lavas of the High Cascades. Data from Hughes (1990, J. Geophys. Res., 95, 19623-19638). Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.


Figure 17.14. Summary of 206Pb/204Pb from sulfides in Tertiary Cascade intrusives as a function of latitude. After Church et al. (1986), Geochim. Cosmochim. Acta, 50, 317-328. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.


Figure 17.15a. Major plutons of the North American Cordillera, a principal segment of a continuous Mesozoic-Tertiary belt from the Aleutians to Antarctica. From The Geologic Map of North America, GSA and USGS. The Sr 0.706 line in N. America is after Kistler (1990), Miller and Barton (1990) and Armstrong (1988). Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.


Figure 17-15b. Major plutons of the South American Cordillera, a principal segment of a continuous Mesozoic-Tertiary belt from the Aleutians to Antarctica. After USGS.


Figure 17.16. Schematic cross section of the Coastal batholith of Peru. The shallow flat-topped and steep-sided “bell-jar”-shaped plutons are stoped into place. Successive pulses may be nested at a single locality. The heavy line is the present erosion surface. From Myers (1975) Geol. Soc. Amer. Bull., 86, 1209-1220.


Figure 17.17. Harker-type and AFM variation diagrams for the Coastal batholith of Peru. Data span several suites from W. S. Pitcher, M. P. Atherton, E. J. Cobbing, and R. D. Beckensale (eds.), Magmatism at a Plate Edge. The Peruvian Andes. Blackie. Glasgow. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.


Magmatism

Figure 17.18. Chondrite-normalized REE abundances for the Linga and Tiybaya super-units of the Coastal batholith of Peru and associated volcanics. From Atherton et al. (1979) In M. P. Atherton and J. Tarney (eds.), Origin of Granite Batholiths: Geochemical Evidence. Shiva. Kent. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.


Magmatism

Figure 17.19. a. Initial 87Sr/86Sr ranges for three principal segments of the Coastal batholith of Peru (after Beckinsale et al., 1985) in W. S Pitcher, M. P. Atherton, E. J. Cobbing, and R. D. Beckensale (eds.), Magmatism at a Plate Edge. The Peruvian Andes. Blackie. Glasgow, pp. 177-202. . b. 207Pb/204Pb vs. 206Pb/204Pb data for the plutons (after Mukasa and Tilton, 1984) in R. S. Harmon and B. A. Barreiro (eds.), Andean Magmatism: Chemical and Isotopic Constraints. Shiva. Nantwich, pp. 235-238. ORL = Ocean Regression Line for depleted mantle sources (similar to oceanic crust). Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.


Magmatism

Figure 17.20. Schematic diagram illustrating (a) the formation of a gabbroic crustal underplate at an continental arc and (b) the remelting of the underplate to generate tonalitic plutons. After Cobbing and Pitcher (1983) in J. A. Roddick (ed.), Circum-Pacific Plutonic Terranes. Geol. Soc. Amer. Memoir, 159. pp. 277-291.


Figure 17.21. Isotopic age vs. distance across (a) the Western Cordillera of Peru (Cobbing and Pitcher, 1983 in J. A. Roddick (ed.), Circum-Pacific Plutonic Terranes. Geol. Soc. Amer. Memoir, 159. pp. 277-291) and (b) the Peninsular Ranges batholith of S. California/Baja Mexico (Walawander et al. 1990 In J. L. Anderson (ed.), The Nature and Origin of Cordilleran Magmatism. Geol. Soc. Amer. Memoir, 174. pp. 1-8).


Figure 17-22. Range and average chondrite-normalized rare earth element patterns for tonalites from the three zones of the Peninsular Ranges batholith. Data from Gromet and Silver (1987) J. Petrol., 28, 75-125. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.


Figure 17.23. Schematic cross section of an active continental margin subduction zone, showing the dehydration of the subducting slab, hydration and melting of a heterogeneous mantle wedge (including enriched sub-continental lithospheric mantle), crustal underplating of mantle-derived melts where MASH processes may occur, as well as crystallization of the underplates. Remelting of the underplate to produce tonalitic magmas and a possible zone of crustal anatexis is also shown. As magmas pass through the continental crust they may differentiate further and/or assimilate continental crust. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.


Figure 17-24. Pressure-temperature phase diagram showing the solidus curves for H2O-saturated and dry granite. An H2O-saturated

granitoid just above the solidus at A will quickly intersect the solidus as it rises and will therefore solidify. A hotter, H 2O-undersaturated

granitoid at B will rise further before solidifying. Note: the pressure axis is inverted to strengthen the analogy with the Earth, so a negative dP/dT Clapeyron slope will appear positive. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

chapter 17: continental arc magmatism potential differences with respect to island arcs: thick...

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