Adakites—the key to understanding LILE depletion in granulites

A catalytic delamination-driven model for coupled genesis of Archaean crust and sub-continental lithospheric mantle

“…High-SiO 2 adakites have SiO 2 > 60%, MgO < 4%, TiO 2 < 0.9%, high Sr (<1000 ppm), high contents of LREE (light rare earth elements) and LILE (large ion lithophile elements), and low Y (<20 ppm) and HREE (heavy rare earth elements). High-SiO 2 adakites are thought to have formed by multistage devolatilization and melting of unusually young (hot) oceanic crust as it subducts (Drummond and Defant, 1990;Drummond et al, 1996;Kepezhinskas et al, 1997;Rollinson and Tarney, 2005;Martin et al, 2005). The high Mg#, Cr, and Ni of some high-SiO 2 adakites is attributed to reaction with the mantle wedge (Kay, 1978;Carroll and Wyllie, 1989;Calmus et al, 2003;Martin et al, 2005).…”

The Laxford Shear Zone: an end-Archaean terrane boundary?

“…The gneisses of 520 the Assynt terrane were most probably formed from magmas derived by melting of a 521 subducting slab (Rollinson and Tarney, 2005), whereas the chemistry of the 522 Rhiconich gneisses is more like that of modern-day calc-alkaline igneous rocks, and 523 the most likely origin for the magmas is in the mantle wedge above the subducting 524 slab. The geochemistry thus does indicate that there were differences in the process of 525 crust formation to the north and south of the Laxford Shear Zone (Rollinson, 1996).…”

“…These 564 geochemical differences are considered to be igneous rather than metamorphic 565 (Rollinson and Tarney, 2005). 566…”

Origin of High Electrical Conductivity in the Lower Continental Crust: A Review

“…What about the depletion of LILE? Many recent studies have shown that not all granulites are depleted in LILE (Rollinson and Tarney 2005; and references therein). Therefore, the depletion of some LILE in individual granulites is probably just a feature inherited from the original protoliths, but not a general result due to granulite-facies metamorphism.…”