Chapter 17: Continental Arcs

Report
Chapter 17: Continental Arc Magmatism
Potential differences with respect to Island Arcs:
• Thick sialic crust contrasts greatly with mantlederived 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, 5370; 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.
Chapter 17:
Continental Arc
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.
Chapter 17:
Continental Arc
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), LópezEscobar 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; LópezEscobar et al. 1981). Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.
Chapter 17: Continental Arc Magmatism
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.
Chapter 17: Continental Arc Magmatism
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.
Chapter 17: Continental Arc Magmatism
Figure 17.8. 87Sr/86Sr, D7/4, D8/4,
and d18O vs. Latitude for the
Andean volcanics. D7/4 and D8/4
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.
Chapter 17: Continental Arc Magmatism
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.
Chapter 17:
Continental Arc
Magmatism
Figure 17.10. Map of the Juan de Fuca plateCascade 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.
Chapter 17:
Continental Arc
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.
Chapter 17: Continental Arc Magmatism
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.
Chapter 17: Continental Arc Magmatism
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.
Chapter 17: Continental Arc Magmatism
Figure 17.13b. Spider diagram for mafic platform lavas of the High Cascades. Data from Hughes (1990, J. Geophys. Res., 95, 1962319638). Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.
Chapter 17: Continental Arc Magmatism
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.
Chapter 17: Continental Arc
Magmatism
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.
Chapter 17: Continental Arc
Magmatism
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.
Chapter 17: Continental Arc Magmatism
Figure 17.16. Schematic cross section of the Coastal batholith of Peru. The shallow flat-topped and steepsided “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.
Chapter 17: Continental Arc Magmatism
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.
Chapter 17:
Continental Arc
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.
Chapter 17:
Continental Arc
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.
Chapter 17:
Continental Arc
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.
Chapter 17: Continental Arc Magmatism
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).
Chapter 17: Continental Arc Magmatism
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.
Chapter 17: Continental Arc Magmatism
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.
Chapter 17: Continental Arc Magmatism
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.

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