An Introduction of Aleutian Subduction Zone. Chuanmao Yang, Hong Yang, Meng Zhang, Wenzhong Wang 2016/04/29

Transcription

1 An Introduction of Aleutian Subduction Zone Chuanmao Yang, Hong Yang, Meng Zhang, Wenzhong Wang 2016/04/29

2 Outline General Introduction Formation history Structure from seismic study geochemical features

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4 Location West to Komandorsky Islands East to Alaska Peninsula WA CA EA Singer et al. JGR 2007

5 Seismicity, Slab geometry, convergence Velocity

6 Slabs of EA and CA Syracuse and Abers, 2006

7 B B'

8 Tectonic setting From Shillington, Donna J., et al, 2004 The locations of fracture zones in the subducting plate, together with the locations of the Bowers Ridge, transitions in upper plate composition (e.g., from oceanic to continental) and earthquake aftershock zones, have provided the basis for dividing the upper plate into four discrete segments : Rat, Adreanof, Four Mountains, and Cold Bay

9 Formation of Aleutian Subduction Zone

10 From Lizarralde, Daniel, et al At 59 Ma, both the Kula plate and the Pacific Plate were subducting in the Aleutian trench, and these two plates were separated by a transform fault. At 56 Ma, subduction jumped south, stranding a small piece of the Kula plate ( Aleutia ) on the North American plate. At 40 Ma, the Kula plate subducted entirely, and the direction of convergence shifted from north to north-northwest.

11 Seismic structure

12 Seismic structure km/s km/s km/s km/s From Shillington, Donna J., et al, 2004

13 Cross section of CA 40Ar-39Ar dating: oldest rock Ma Magma production rate km^3/km/my Jicha et al. Geology 2006

14 Seismic structure From Lizarralde et al. 2002

15 Western Aleutians (Yogodzinski et al., 2001) suggest a large slab window is beneath the westernmost Aleutians. (Levin et al., 2002) Depth:150km

16 The low-velocity anomaly indicates that subducted lithosphere is absent in the western Aleutians; It is significantly thinner and hotter than expected from the age of the Pacific lithosphere entering the mantle (Levin et al., 2005)

17 Plume Three parts: The lower part extending vertically through depths of ~900 to ~400 km The upper part rising obliquely to the north up to ~200 km depth The subsidiary part extending subhorizontally to the NW at depths above y300 km. (Gorbatov et al., 2001)

18 Slab portal Isosurface representation of shear-velocity model beneath western Aleutians, blue surface ( +1.2%); Red surface ( -1.2%) (Levin et al., 2005) The westernmost Aleutians are above an opening in a vertical barrier that divides the upper mantle beneath the Pacific and the North American plates from the Kuriles to Alaska.

19 (Koulakov et al., 2011)

20 Presence of a slab subducting down to km The subduction mechanism in the case of oblique motion remains unclear. (Koulakov et al., 2011)

21 Singer et al. JGR 2007

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26 Model of magmatism

27 Arc vs. continental crust Cai et al. EPSL 2015

28 Nd and Pb isotopes

29 Geochemical model of Aleutian Arc

30 Reference Shillington, Donna J., et al. "Composition and structure of the central Aleutian island arc from arc parallel wide angle seismic data." Geochemistry, Geophysics, Geosystems 5.10 (2004). Helffrich, George, and Geoffrey A. Abers. "Slab low-velocity layer in the eastern Aleutian subduction zone." Geophysical Journal International (1997): Lizarralde, Daniel, et al. "Crustal construction of a volcanic arc, wide angle seismic results from the western Alaska Peninsula." Journal of Geophysical Research: Solid Earth 107.B8 (2002). Ellen M. Syracuse and Geoffrey A. Abers,"Global compilation of variations in slab depth beneath arc volcanoes and implications", Geochemistry, Geophysics, Geosystems (2006) Koulakov et al.,slab shape in subduction zones beneath the Kurile Kamchatka and Aleutian arcs based on regional tomography results, Russian Geology and Geophysics 52 (2011)

31 Levin et al., Slab portal beneath the western Aleutians, Geology 2005 Gorbatov et al., Seismic evidence for a mantle plume oceanwards of the Kamchatka Aleutian trench junction, Geophys. J. Int. (2001) 146, Jicha et al., Revised age of Aleutian Island Arc formation implies high rate of magma production, Geology (2006) Y. Cai et al., Distinctly different parental magmas for calc-alkaline plutons and tholeiitic lavas in the central and eastern Aleutian arc, EPSL(2015) Singer et al., Along-strike trace element and isotopic variation in Aleutian Island arc basalt: Subduction melts sediments and dehydrates serpentine, JGR (2007) Yogodzinski et al., Subduction controls of Hf and Nd isotopes in lavas of the Aleutian island arc, EPSL (2010) Volk, Geological review of the Alaska-Aleutian Arc and exploration of 3D subduction zone modeling, MS, (2015)