Aleutian

North Pacific subduction system

53

±

2

Ma

Polarity reversal

A250P

Schematic tectonic reconstruction of the Aleutian SZI event (modified from Domeier et al., 2017). The collision of the Olutorsky arc with the trench of the south-dipping subduction of the Eurasia plate below the Pacific Plate is suggested to have caused a flip in subduction polarity, initiating the new Aleutian subduction zone. Shown are the new subduction zone (pink line), other active (solid purple lines) and inactive (dashed purple lines) subduction zones, spreading ridges (solid red lines), and transform faults (red dashed lines).

The Aleutian subduction zone initiation event formed today’s active Aleutian trench. The onset of the subduction zone likely occurred at around 53 Ma (Davis et al., 1989; Jicha et al., 2006) when the Pacific and Kula plates began to subduct northward, and at some point, under the overriding continental plates of northeast Siberia and North America.

The Aleutian SZI event was possibly instigated as a subduction polarity reversal associated with the arrival of an intraoceanic arc (Olutorsky arc) to the Okhotsk-Chukotka-Beringian margin of northeastern Asia and northwestern North America (Scholl, 2007; Domeier et al., 2017; Vaes et al., 2019), and therefore may have formed close to (i.e., at a distance of around 300 km) a pre-existing convergent plate boundary. Vaes et al. (2019) have speculated that the Aleutian trench may have exploited a pre-existing transform boundary in a possible backarc behind the Olutorsky arc. Those authors have furthermore pointed out that arc volcanics with ages of 54.4 Ma to 50.2 Ma have been dredged from the Beringian margin (Davis et al., 1989), and note that the Aleutian SZI event could also be seen as the outboard jump of that Beringian subduction zone.


The oldest rocks in the Aleutian arc are andesites dredged from Murray Canyon (Jicha et al., 2006) and primitive basaltic rocks from Medny Island, both of which are 46 Ma (Minyuk and Stone, 2009).


In the model of Müller et al. (2016), the Aleutian SZI event occurs at 55 Ma, by the outboard (southward) jump of a pre-existing Kamchatka-Alaska subduction zone; this jump ranges from less than 100 km in the east to ~500 km in the west. The Olutorsky arc is not implemented in this model (nor is any other intra-oceanic arc in this region at this time), but instead a regional plate reorganisation event is temporally paired to subduction of the Izanagi ridge. This plate reorganisation occurs at 55 Ma, and includes both a re-direction of the Pacific plate (from NW-directed to N-directed) and an acceleration of the Kula plate’s northward drift.


Seismic tomography reveals a slab attached to the trench and reaching a maximum depth of around 700 km (van der Meer et al. 2018).

Seismic tomography VoteMap (Shephard et al., 2017) analysis of the Aleutian SZI event.

Aleutian SZI event as reconstructed in the model of Müller et al. (2016). Pink dashed (solid with teeth) line shows the Aleutian trench 1 Myr before (at) SZI time in the model. Purple (red) lines show segments of neighbouring subduction zones (ridges and transforms) that lie within some radius of the Aleutian trench (pink line); the brightness of the colours reflects 3 different distance thresholds of 250, 500 and 1000 km.

Davis, A. S., Pickthorn, L. G., Valuer, T. L., Marlow, M. S. (1989). Petrology and age of volcanic-arc rocks from the continental margin of the Bering Sea: implications for Early Eocene relocation of plate boundaries. Canadian Journal of Earth Sciences, 26(7), 1474-1490.


Domeier, M., Shephard, G. E., Jakob, J., Gaina, C., Doubrovine, P. V., & Torsvik, T. H. (2017). Intraoceanic subduction spanned the Pacific in the Late Cretaceous–Paleocene. Science advances, 3(11), eaao2303.


Jicha, B. R., Scholl, D. W., Singer, B. S., Yogodzinski, G. M., & Kay, S. M. (2006). Revised age of Aleutian Island Arc formation implies high rate of magma production. Geology, 34(8), 661-664.


Minyuk, P. S., & Stone, D. B. (2009). Paleomagnetic determination of paleolatitude and rotation of Bering Island (Komandorsky Islands) Russia: Comparison with rotations in the Aleutian Islands and Kamchatka. Stephan Mueller Special Publication Series, 4, 329-348.


Müller, R. D., Seton, M., Zahirovic, S., Williams, S. E., Matthews, K. J., Wright, N. M., Shephard, G. E., Maloney, K. T., Barnett-Morre, N., Hosseinpour, M., Bower, D. J., Cannon, J. (2016). Ocean Basin Evolution and Global-Scale Plate Reorganization Events Since Pangea Breakup. Annual Review of Earth and Planetary Sciences, 44, 107-138.


Scholl, D. W. (2007). Viewing the tectonic evolution of the Kamchatka-Aleutian (KAT) connection with an Alaska crustal extrusion perspective. Washington DC American Geophysical Union Geophysical Monograph Series, 172, 3-35.


Shephard, G.E., Matthews, K.J., Hosseini, K., Domeier, M. (2017). On the consistency of seismically imaged lower mantle slabs. Scientific Reports 7.


Vaes, B., van Hinsbergen, D.J.J., & Boschman, L.M. (2019). Reconstruction of Subduction and Back-Arc Spreading in the NW Pacific and Aleutian Basin: Clues to Causes of Cretaceous and Eocene Plate Reorganizations. Tectonics, 38(4), 1367-1413.


van der Meer, D. G., van Hinsbergen, D. J., & Spakman, W. (2018). Atlas of the underworld: Slab remnants in the mantle, their sinking history, and a new outlook on lower mantle viscosity. Tectonophysics, 723, 309-448.

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