Crustal thickness

Figure 18. Plot of versus crustal thickness (from Gill 1981) for each arc studied (averages...

Crustal thickness in the LAP is slightly greater than in Tuscany, increasing across the Apennine chain up to about 35 km, and decreasing towards the Adriatic Sea (Scarascia et al. 1994 Piromallo and Morelli 2003). By... 

The Emici-Roccamonfina zone has a crustal thickness of about 30 km. The uppermost mantle is characterised by a thin layer of material with relatively low S-wave velocity (Vs = 3.95 km/sec), which passes into a thick lid that has higher S-wave velocities (Vs = 4.40-4.65 km/sec). This upper mantle structure is unique in the circum-Tyrrhenian area (Panza et al. 2004 Chap. 10). 

Crustal thickness in the Sicily volcanic province is about 20 to 25 km (Boccaletti et al. 1984 Him et al. 1997 Nicolich 2001, and references therein). The lithosphere shows variable thickness from about 50 km beneath the Ustica island, to 60 km beneath the Sicily Channel and some 70 km in the Etna and Iblei area (Calcagnile et al. 1982). Heath flow is about 50 to 70 mW/m2 at the regional scale but is higher than 80-100 mW/m2 in the areas affected by recent magmatism (Della Vedova et al. 2001). 

Figure 7.4. A sedimentation diagram for a hypothetical Devonian-age carbonate sequence. The curve for the sequence gives its inferred position relative to sea level and land surface elevation since the time of its sedimentation. Schematic subsurface isotherms are also presented based on estimates of crustal thickness and hypothetical heat flow values related to plate movements and igneous activity. [Adapted from Siever s (1979) representation of the Esopus Formation.]...

Klein E. M. and Langmuir C. H. (1987) Global correlations of ocean ridge basalt chemistry with axial depth and crustal thickness. J Geophys. Res. 92, 8089-8115. 

Reference Age Setting, (uplift originf Current crustal thickness (km) Maximum depth (km) Middle crust lithologies Lower crust lithologies... 

Shaw et al., 1986 Gupta et al, 1991 Jaupart et al., 1998 Gao et al., 1998). The value of Shaw et al. (1986) for the Canadian Shield is not consistent with the heat flow data. Thus, one may not apply one estimate for one province to another province. A further difficulty is that the crustal thickness varies significantly. For example, the crust of the North China craton is thinner than average (—35 km Gao et al., 1998). 

Canales J. P., Detrick R. S., Bazin S, Harding A. J., and Orcutt J. A. (1998) Off-axis crustal thickness across and along the East Paciflc Rise within the MELT area. Science 280, 1218-1221. 

Figure 2 The ocean crust reference section used in this paper, using a standard Penrose style ophiolite assemblage (Penrose Conference Participants, 1972) and a crustal thickness after White etal.(l992) and C. Z. Mutter and J. C. Mutter (1993). Various modeling parameters used are also indicated, including densities and fluxes, the approximate positions of drill holes discussed in this paper, and some typical extreme alteration environments found...

White R. S., McKenzie D., and O Nions R. K. (1992) Ocean crustal thickness from seismic measurements and rare earth element inversions. J. Geophys. Res. 97, 19683-19715. 

Thus, all three explanations for the genesis of continental crust require delamination of garnet granulite, eclogite and/or pyroxenite. Moreover, recent, dynamical calculations support the hypothesis that delamination is possible—even likely—where Moho temperatures exceed —750 °C, where crustal thicknesses reach 30 km or more, and where ultramafic cumulates are present (Jull and Kelemen, 2001). The base of arc crust fulfills all of these criteria. Finally, our data on the Talkeetna arc section, and more limited data on the Kohistan arc section, support the hypothesis that substantial proportions of pyroxenite, and perhaps also garnet granulite, were removed by viscous delamination from the base of the arc crust. 

---