Chapte 16 Island Arc Magmatism Michigan Technological 16章岛弧岩浆密歇根科技.pptVIP

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Chapte 16 Island Arc Magmatism Michigan Technological 16章岛弧岩浆密歇根科技.ppt

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Chapte 16 Island Arc Magmatism Michigan Technological 16章岛弧岩浆密歇根科技

Chapter 16. Island Arc Magmatism Arcuate volcanic island chains along subduction zones Distinctly different from mainly basaltic provinces thus far Composition more diverse and silicic Basalt generally subordinate More explosive Strato-volcanoes most common volcanic landform Igneous activity is related to convergent plate situations that result in the subduction of one plate beneath another The initial petrologic model: Oceanic crust is partially melted Melts rise through the overriding plate to form volcanoes just behind the leading plate edge Unlimited supply of oceanic crust to melt Ocean-ocean ? Island Arc (IA) Ocean-continent ? Continental Arc or Active Continental Margin (ACM) Subduction Products Characteristic igneous associations Distinctive patterns of metamorphism Orogeny and mountain belts Structure of an Island Arc Volcanic Rocks of Island Arcs Complex tectonic situation and broad spectrum High proportion of basaltic andesite and andesite Most andesites occur in subduction zone settings Major Elements and Magma Series Tholeiitic (MORB, OIT) Alkaline (OIA) Calc-Alkaline (~ restricted to SZ) Major Elements and Magma Series a. Alkali vs. silica b. AFM c. FeO*/MgO vs. silica diagrams for 1946 analyses from ~ 30 island and continental arcs with emphasis on the more primitive volcanics Chapter 17: Continental Arc Magmatism Potential 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 Chapter 17: Continental Arc Magmatism Chapter 17: Continental Arc Magmatism Trace Elements REEs Slope within series is similar, but height varies with FX due to removal of Ol, Plag, and Pyx (+) slope of low-K ? DM Some even more depleted than