Continental Suture Zone Research Articles

Petrotectonics of Sulu-Dabie metamorphic belt,Central and East China

The Sulu-Dabieshan metamorphic belt separates the North China and Yangtze cratons. This metamorphic belt is further divided into three petrological-tectonic units which are respectively equivalent to a root zone of an Andean-type magmatic arc (northern Dabie terrane), continental collision suture zone (southern Dabie terrane) and metamorphosed cover sediments of the Yangtze continental margin (Susong metamorphic complex). They are regularly located in the space from north to south in Dabieshan and roughly from northwest to southeast in Sulu region in spite of being strongly reconstructed by the Tan-Lu Fault. The occurrence of the Mesozoic granites and alkali dike swarm are also regular in the space. They occur in the Dabie area, especially in the northern Dabie terrane. These facts support a suggestion that there was subduction of the Yangtze Plate under the North China Plate or obduction of the North China Plate over the Yangtze Plate. Up to now, no evident remnant of old occean crust has been identified. Ultrahigh pressure metamorphic (UHPM) rock-bearing southern terrane is possibly a root of continent-continent collision zone representing a suture between the North China and Yangtze Plates. The fact that UHPM lenses were tectonically emplaced into not-high pressure metamorphic host gneisses indicates deeply subducted rocks uplifted to middle-upper crust after continental collision. The UHPM rocks and related rocks occurring on the surface at the moment suffered at least two stages of uplifting and exhumation.

Geochemistry and origin of Archean granites from the Black Hills, South Dakota

The Little Elk Granite (2549 Ma) and granite at Bear Mountain (BMG) (~2.5 Ga) of the Black Hills formed as a result of a collisional event along the eastern margin of the Wyoming Province during the late Archean. Geochemical modelling and Nd isotopic data indicate that the Little Elk Granite was generated by the partial melting of a slightly enriched (εNd = −1.07 to −3.69) granodioritic source that had a crustal residence time of at least 190 Ma. The medium-grained to pegmatitic, peraluminous, leucocratic BMG was produced by melting a long-lived (>600 Ma), compositionally variable, enriched (εNd = −7.6 to −12.3) crustal source. This produced a volatile-rich, rare-earth-element-poor magma that experienced crystal–melt–volatile fractionation, which resulted in a lithologically complex granite.The production of volatile-rich granites, such as the BMG and the younger Harney Peak Granite (1715 Ma), is a function of the depositional and post-depositional tectonic environment of the sedimentary source rock. These environments control protolith composition and the occurrence of dehydration and melting reactions that are necessary for the generation of these volatile-rich leucocratic granites. These types of granites are commonly related to former continental–continental accretionary boundaries, and therefore their occurrence may be used as signatures of ancient continental suture zones.