Silica-undersaturated spinel granulites in the Daqingshan complex of the Khondalite Belt, North China Craton: Petrology and quantitative P–T–X constraints

摘要: Abstract The Da’nangou silica-undersaturated spinel-bearing granulites in the Daqingshan Complex of Khondalite Belt, North China Craton, occurred within quartzo-feldspathic rocks or interlayered with garnet–cordierite–biotite gneiss. These preserve a distinct mineral assemblage spinel + garnet + biotite + K-feldspar + plagioclase ± sillimanite reaction textures that are useful for deciphering metamorphic evolution Belt. Quantitative pressure, temperature, and bulk composition constraints on development preservation characteristic granulite facies assessed reference to calculated phase diagrams. Combined studies assemblages, relations spinel P – T X pseudosections NCKFMASH system, origin protoliths these reveal assemblages formed mainly high-variance fields. indicate restricted only conditions extremely low Si iron enrichment high Al. A clockwise is inferred from pseudosection observed microtextures involving near-isothermal decompression decompressional cooling stages, which comparable metapelitic Complex. history can be subdivided into following successive stages. peak biotite + garnet + K-feldspar + plagioclase + sillimanite + liquid was stable at ∼830 °C ∼10.5 kbar. During post-peak stage ∼870 °C ∼8 kbar, partial melting introduced by biotite dehydration events occurred, followed melt extraction taking SiO 2 alkali elements, restitic Al–Fe-rich remains. coarse-grained therefore produced dehydration-melting reactions: biotite + garnet + sillimanite→spinel + K-feldspar + liquid biotite + sillimanite ± quartz→spinel + liquid. Symplectic rimming garnet breakdown garnet + sillimanite + liquid→spinel + K-feldspar + plagioclase as cooling. after ∼800 °C ∼6.5 kbar, further broken down consumption had not been segregated, give rise biotite + plagioclase symplectites related reactions garnet + spinel + liquid→biotite + plagioclase garnet + liquid→biotite + plagioclase ± quartz. Such were likely occur exhumation processes continental subduction–collision, indicated path.