Building a magnetic view of Alaska

Crustal structure across the central Alaska Range: Anatomy of a Mesozoic collisional zone

“…One possible control of this response may be the varying compositions between the sections of the suture zone. Variability in composition across the sections of the Alaska Range suture zone is supported by our estimates of Vp/Vs (Figures 6a and 6b) Vp/Vs calculations of Eberhart‐Phillips et al [2006] (Figures 7a and 7b), the overall pattern of magnetic potential (Figure 3b) [ Saltus et al , 1997, 1999; Brunstein , 2002; Glen et al , 2007; Saltus et al , 2007], and regional geologic mapping (Figure 3a) [e.g., Jones et al , 1982; Csejtey et al , 1992; Ridgway et al , 1997; Trop and Ridgway , 1997; Ridgway et al , 2002]. The observed variability in crustal structure across the Alaska Range suture zone is likely controlled by the differing compositions of the terranes involved, which have influenced how each section has responded to precollisional, syncollisional, and postcollisional deformation.…”

Common depth of slab‐mantle decoupling: Reconciling diversity and uniformity of subduction zones

“…This interpretation is supported by high‐amplitude, long‐wavelength positive magnetic anomalies and negative gravity anomalies in the Cascadia fore arc [ Blakely et al , 2005]. Serpentinization of the fore‐arc mantle wedge has also been inferred from seismic observations in Nankai (50–70%) [ Kamiya and Kobayashi , 2000; Seno et al , 2001], Kyushu (20–30%) [ Xia et al , 2008], northern Chile (0–12%) [ Graeber and Asch , 1999; Carlson and Miller , 2003], and Costa Rica (15–25%) [ DeShon and Schwartz , 2004; Carlson and Miller , 2003], from magnetic and gravity anomalies in Alaska [ Saltus et al , 1999], and from the presence of serpentine mud volcanoes in the fore‐arc region of the Izu and Mariana margins [ Fryer , 1996]. The presence of a serpentinized fore‐arc mantle wedge is proposed to explain the lack of velocity contrast between the continental crust and the underlying mantle in SC Chile [ Groß et al , 2008].…”

An Origin for the Linear Magnetic Anomalies on Mars through Accretion of Terranes: Implications for Dynamo Timing

“…These accreted terranes have several origins: oceanic crust, oceanic arcs, distal parts of continental edges, rift remainders, or oceanic plateaus (Coney et al 1980). The sources of the Alaskan anomalies have a significant thickness on a crustal scale (Saltus et al 1999), the same as that proposed for Terra Cimmeria and Terra Sirenum based on magnetization intensity (Connerney et al 1999, Nimmo 2000. Moreover, starting from magnetic features common to several global magnetic maps of Mars, Purucker (2002) suggests that the southern boundary between magnetic and nonmagnetic terranes is sharp for longitudes between 120 • and 240 • E (corresponding to strongly magnetized crust) and gradational for other longitudes.…”

“…Dohm et al (2002) has mapped numerous macrostructures that have similar trends and appear to correlate with some of the anomalies. Importantly, the magnetic character shown by the southern continental margin of Alaska has been considered (Saltus et al 1999) as a typical example for what is to be expected in any region on Earth that undergoes convergent margin processes. If plate tectonics operated on early Mars, then terrane accretion would be anticipated.…”

“…In this note we show that the characteristics of the magnetic lineations in Terra Cimmeria and Terra Sirenum can be fairly explained as the result of a process of collision in a zone of crustal destruction, causing continental accretion, like the one that took place in the west coast of North America in Jurassic to early Tertiary time (e.g., Coney et al 1980), which produced a distinctive pattern of magnetic anomalies (Saltus et al 1999). We also discuss the implications of this hypothesis for the temporal evolution of both martian crustal dynamics and magnetic field.…”