摘要
The term adakite was originally pro- posed to define silica-rich, high Sr/Y and La/Yb vol- canic and plutonic rocks derived from melting of the basaltic portion of oceanic crust subducted beneath volcanic arcs. It was also initially believed that ada- kite only occurs in convergent margins where young and thus still hot oceanic slabs are being subducted, but later studies have proposed that it also occurs in other arc settings where unusual tectonic conditions can lower the solidus of older slabs. Currently, ada- kite covers a range of arc rocks ranging from pristine slab melt, to adakite-peridotite hybrid melt, to melt derived from peridotite metasomatized by slab melt. Adakite studies have generated some confusions because (1) the definition of adakite combines com- positional criteria with a genetic interpretation (melt- ing of subducted basalt), (2) the definition is fairly broad and relies on chemistry as its distinguishing characteristic, (3) the use of high pressure melting experiment results on wet basalts as unequivocal proofs of slab melting and (4) the existence of ada- kitic rocks with chemical characteristics similar to adakites but are clearly unrelated to slab melting. Other studies have shown that adakitic rocks and a number of the previously reported adakites are pro- duced through melting of the mafic lower crust or ponded basaltic magma, high-pressure crystal frac- tionation of basaltic magma and low-pressure crystal fractionation of basaltic magma plus magma mixing processes in both arc or non-arc tectonic environ- ments. Despite the confusing interpretations on the petrogenesis of adakite and adakitic rocks, their in- vestigations have enriched our understanding of material recycling at subduction zones, crustal evolu- tionary processes and economic mineralization.
The term adakite was originally proposed to define silica-rich, high Sr/Y and La/Yb volcanic and plutonic rocks derived from melting of the basaltic portion of oceanic crust subducted beneath volcanic arcs. It was also initially believed that adakite only occurs in convergent margins where young and thus still hot oceanic slabs are being subducted, but later studies have proposed that it also occurs in other arc settings where unusual tectonic conditions can lower the solidus of older slabs. Currently, adakite covers a range of arc rocks ranging from pristine slab melt, to adakite-peridotite hybrid melt, to melt derived from peridotite metasomatized by slab melt. Adakite studies have generated some confusions because （1） the definition of adakite combines compositional criteria with a genetic interpretation （melting of subducted basalt）, （2） the definition is fairly broad and relies on chemistry as its distinguishing characteristic, （3） the use of high pressure melting experiment results on wet basalts as unequivocal proofs of slab melting and （4） the existence of ada- kitic rocks with chemical characteristics similar to adakites but are clearly unrelated to slab melting. Other studies have shown that adakitic rocks and a number of the previously reported adakites are produced through melting of the mafic lower crust or ponded basaltic magma, high-pressure crystal fractionation of basaltic magma and low-pressure crystal fractionation of basaltic magma plus magma mixing processes in both arc or non-arc tectonic environments. Despite the confusing interpretations on the petrogenesis of adakite and adakitic rocks, their investigations have enriched our understanding of material recycling at subduction zones, crustal evolutionary processes and economic mineralization.
关键词
岩石成因论
板块融合
交代作用
榴辉岩
角闪岩
太古代
安山岩
玄武岩
俯冲带
岩浆作用
adakite, slab melting, metasomatism, eclogite, amphibolite, Archean TTG, magnesian andesite, high-Nb basalt, subduction zone, arc magmatism.
作者简介
email： pcastillo@ucsd.edu
