Page 51 - Whole Earth Geophysics An Introductory Textbook For Geologists And Geophysicists

33 leads to

Boundaries Plate Along Lithosphere Asthenosphere LN SSE rises. is ; N \ or pressure because lithosphere and volcanism) that generation of magma Ophiolite Basalt _ Sediments mst foseie illustrating decompression rift zone showing that magma magma.

Manifestations Bound oD Ae a) Hot asthenosphere Pressure drop causes partial metting. ¢) No change in temperature asthenosphere do not change (= No depth. illustrating the GY (Hot) Decompressed) Midocean ridge Continental

a) Divergent Plate “ Volcanism Melting Asthenosphere Volcanism (Hot, Volcanism at divergent plate boundaries. a) through continental crust, enriching the silica content of the
)) Lithosphere subducts.
ca Schematic cross-section of Earth Ridge Rift the development of an ophiolite sequence. b)
nt Fluids rise as the plate's Water.
io crust Is heated. Hotspot volcanism oe originate from deep mante or manile/core Crust cso
boundary.

2.23 Mid-Ocean Oceanic / oY Continental 2.24 initially melt
FIGURE volcanism. a) Z b) FIGURE melting and must

Boundary to moderate size occur large earthquakes normally normal originate astheno- shown commonly melt a therefore low- 2.24a). basalt to it The high form-

Plate km to moderate size earthquakes at plate. is Volcanism their at (Fig. 2.23c). Some vol- may that hot on melting, as minerals partial the C); silica) is relatively (Fig. rocks of pillows make not does crust. lower silica), (30%

Transform =700 overriding plates. Very of the descending remain drop hotspots in pressure partial in High-silica (Appendix (30% (50%). produces igneous forming that the peridotite

kin Shallow earthquakes of small boundaries. materials pressure over (Fig. 2.23d). drop increase of tapidly, composition
700 b) upper portion or ride The 2.7). minerals asthenosphere silica asthenosphere sequence cool comprising essentially

«ute descending and the plate because rise plates boundary an causes (Fig. higher melted floor silica) gabbro, still
Boundary interiors, where mantle/core boundaries phase than of of somewhat partially ocean same dikes below

* boundaries (see also map view, Fig. 2.19). c) Small the convergent boundaries temperature the Volcanism diagram low-silica the characteristic (50% of is

Tectonics Plate Size Occurrence of earthquakes at plate boundaries. a,b) together, and at greater depths in or divergent plate no significant or Boundary the peridotite ridges, a in the onto the of intrusive remains

Plate Moderate boundaries occur at shallow depths in with transform is plate in mantle deep Plate divergent at on arrow temperatures the off composition mid-ocean resulting pour out Material forms material that

Chapter2 a) Divergent Earthquakes: Small to Very Large along divergent and transform plate plates lock the associated absent from depths; there occurs canism the from Divergent sphere rising the by bold melt lower at that comes basalt/gabbro At magma, silica that Lavas silica). (50% surface the density

32. ¥% %3 FIGURE 2.22 convergent occur where