Crustal structure along the Aleutian island arc: New insights from receiver functions constrained by active‐source data

Abstract

[1] Moho depth and Vp/Vs estimates from stacking phases of receiver functions along the Aleutian island arc give new constraints on its composition and structure. They expand on the current understanding of island arcs and their relationship to continental crust production. We also present an approach for including constraints from active-source data in receiver function analysis in a region with sparse data coverage to complement this analysis. Moho depth averages 37.5 km with an average uncertainty of 2.5 km along the entire arc. Excluding the westernmost island of Attu yields an average crustal thickness of 38.5 6 2.9 km. The Vp/Vs ratio decreases moving eastward along the arc with an average value of 1.80 in the western and central portion of the arc built on oceanic crust, but 1.63 in the eastern section built on continental crust. This may reflect tectonic and compositional changes along the arc. However, overall the arc appears more mafic than continental crust. Near-constant crustal thickness, despite significant compositional changes, may indicate that nonmagmatic processes such as erosion and isostasy act to regulate arc thickness. Additionally, strong conversions from an upper crustal magma chamber are observed beneath Akutan Island, confirming and clarifying the geometry of the magma body inferred from other techniques. They indicate a volcanic body much larger than the eruptive edifice, a feature that must persist between eruptive cycles.

Seismicity and structure of Akutan and Makushin Volcanoes, Alaska, using joint body and surface wave tomography

“…Both our low‐velocity region and that of Janiszewski et al . [] lie above and east/northeast of the inflation source at 10.6–18.0 km depth (95% confidence interval) modeled by Lu et al . [].…”

“…The location of this low‐velocity area corresponds to low‐ V p , low‐ V s , and high‐ V p / V s layers modeled by Janiszewski et al . [] to fit receiver functions beneath and east of Akutan's caldera, indicating that it is potentially magma rich. Petrologic analyses of melt inclusions from material erupted at Akutan indicate that in an eruption 1600 years B.P., magma began crystallizing between 4.6 km and the surface [ Zimmer , ], supporting the possibility of a slightly deeper magma source.…”

“…There are at least seven secondary eruptive sites on Makushin's flanks active since the middle to late Pleistocene, several of which have been active in the Holocene, although none historically [ McConnell et al ., ]. Although Akutan and Makushin are located west of the apparent break in the continental shelf off of Alaska, they are formed on relatively thick crust (33–39 km [ Janiszewski et al ., ]) with shallow water depths surrounding the islands (<100 m [ Amante and Eakins , ]).…”

Downdip variations in seismic reflection character: Implications for fault structure and seismogenic behavior in the Alaska subduction zone

“…Because there is uncertainty in identifying the continental Moho of the overriding plate in our data set (and in data from many other subduction zones), we also consider an alternative interpretation for the base of the crust. If the shallower band of reflections is unrelated to the lower crust and the Moho of the overriding plate, we can simply assume that the Moho is flat and extrapolate from the crustal thickness determined onshore by receiver functions [ Janiszewski et al , ]. In this case, the continental Moho in our study region would be ~40 km in depth and intersect the middle of the thick band of reflections around 150 km landward from the trench (Figure a).…”

The Record of the Transition From an Oceanic Arc to a Young Continent in the Talamanca Cordillera

“…Therefore, a combination of subducted slab input in the form of a melt (Kelemen, Yogodzinski, et al, 2003) and the subsequent fractional crystallization of the arc primary magmas (Kay et al, 1990;Kay & Kay, 1994), yielded a composition very close to upper continental crust (Kay et al, 1990, and data in Figure 12a), but still not as enriched as the Talamanca suite ( Figure 12a). The crustal thickness along the Aleutian arc is relatively thick~35-40 km (Holbrook et al, 1999;Janiszewski et al, 2013;Van Avendonk et al, 2004). P wave velocities range from 4.3 to 7.7 km/s (Holbrook et al, 1999;Van Avendonk et al, 2004).…”