Arc Crustal Sections: One Roadmap to Integrating Geochemistry and Geophysics

1. Arc Crustal Sections: One Roadmap to Integrating Geochemistry and Geophysics (how to increase the petrological signal-to-noise ratio, and avoid that groundhog day feeling…?) George Bergantz University of Washington

2. 2 - 3 Science Questions: Essential Missing Piece- the Geology • Controls on architecture, a hierarchical perspective • Temporal changes: vol-comp-time • “Right” physical model/template? • Coupling with structure/rheology?

3. Successes: Integrating Volcanic-Plutonic Observations • Magmas obviously mantle-crust hybrids • aFC rules: eNd, NCI < .4, oxygen, other isotopes (few to 20% crust) • Compositional continuity at large scales, Compositional gaps within temporally related suites • Hybridization generally happens early and deep • Open system/complex crystal cargo at all scales Further progress requires spatial-temporal controls and arc sections

4. Some Arc Sections: • Kohistan (see Jagoutz poster, papers) • Talkeetna-Bonanza Arc (Vancouver Island) • North Cascades • Sierra Nevada/BC • Fiordland • Famatina (Argentina) Much agreement! Details have rarely served to address site-resolvable, specific *processes*

5. Famatinian arc: exposed along 1500 km of arc length, 600 km of plutonic section Early Ordovician (~40 my activity), 7 to ~30 km of continuous intact exposure Voluminous hydrous mafic magmas, regionally hyper-solidus contacts

6. Average magma flux rates km3/yr- low-pass filter (see Straub white paper) Large Silicic Provinces: Altiplano-Puna: 4x10-3 – 1.2x10-2 Central San Juan: 8x10-3 Sierra Nevada: 3 - 9x10-3 North Cascades: 3x10-3 Boulder, B.C. batholith: 6x10-3 – 1x10-2 Other Arc systems (but see Jicha, Singer): Klyuchevskoy: 3.2x10-2 Mt. Shasta: 6x10-3 Tatara-San Pedro: 6x10-5 Mt. Adams (field): 2.5x10-4 Ceboruco- Pedro: 1x10-4 Santorini: 4.6x10-4

7. Given open system processes, “duration” or “residence time” can be misleading concepts. (Grunder et al., 2008, Trans. Roy. Soc. Edin.)

8. What is the significance of the 4-5 m.y. trigger? (Grunder et al., 2008, Trans. Roy. Soc. Edin.)

9. Age relations Famatinian Arc, Valle Fertil section, Argentina

10. Time scales have dual nature: homogeneity at the large scale, heterogeneity at the small scale • Toba: chem oscillations in allanites > .4 M.y. before eruption; cycling of crystals through hyper-solidus domains • Fish Canyon: reverse mineral zoning, complex crystal compositions • Tuolumne Intrusive Suite: complexly zoned zircons, • Spirit Mtn., Mojave system: complex rejuvenation of intrusive sheets, zoned zircon Complicated!….but other than open systems processes, what general conclusions? Without in situ stratigraphic control, hard to know what it is telling us

11. ‘Right’ Physical Model? • Hot zone(Dufek and Bergantz, Annen et al.) : model driven, not constrained by direct geological observations. “Balloon+straw,” no assimilation or melt extraction physics • Mush column(Daly, Marsh, Bachmann et al.): Basedon crustal sections and physical model for aFC and extraction Both have features in accord with geochemical constraints

12. Famatinian arc: exposed along 1500 km of arc length, 600 km of plutonic section Early Ordovician (~40 my activity), 7 to ~30 km of continuous intact exposure Voluminous hydrous mafic magmas, regionally hyper-solidus contacts

13. Bachmann and Bergantz, 2008

14. Silicic Mushes? Persistent hyper-solidus state (Hildreth, 2004, J. Volc. Geotherm. Res., v. 136, p. 169)

15. Interplay of rheological/structural changes and other time scales? • Does it matter for compositional diversity? • What controls the fundamental change from largely horizontal regional tectonics/emplacement to vertical? Arc sections: Linking vol-comp-structure-time

16. Thanks