That portion of the Earth's surface overlying the Mohorovičić discontinuity, and with an average density of 2 700–3 000 mg/m3. The thickness is variable, mostly 30–40 km, except for areas of recent mountain building where the thickness can be 70 km. The crust comprises two layers, but the boundary between them is poorly defined. The upper layer is of granitic composition with surface enrichment in radiogenic and other lithophile elements, and has an average density of 2 700 mg/m3. The lower layer was previously considered to be of gabbroic composition but is now thought to be quartz diorite in granulite metamorphic grade.
Subjects: Earth Sciences and Geography.