Petrogenesis of Jurassic granites linked to crustal growth above the subduction zone in the Lesser Xing'an Range (LXR), NE China

Popular opinion holds that continental crust growth occurs principally by subduction due to the fluid-fluxed melting of the mantle, however, whether the formation of granites above subduction zones is closely related to crustal growth remains unclear. Zircon U-Pb dating combined with zircon Hf-O isotopes from granite may be used to investigate this issue. Here, we present whole-rock geochemical, geochronological and zircon Hf-O isotope compositional analyses of the Cuigang monzogranite, Dongan syenogranite and Luming monzogranite above the subduction zone in the Lesser Xing'an Range (LXR) of the Songliao Block, eastern Central Asian Orogenic Belt, to reveal the petrogenesis of these three plutons and Mesozoic crust-mantle interactions in the LXR. These plutons yield zircon U-Pb ages of 191 +/- 1 Ma, 177 +/- 1 Ma and 177 +/- 1 Ma with zircon epsilon Hf(t), TDM2 and delta 18O values of 1.2-+4.2,969-1308 Ma and 5.5-6.2; 2.4-+5.7, 907-1178 Ma and 4.7-6.6; and 3.0-+5.9,914-1410 Ma and 5.0-6.5, respectively. These values and the whole-rock geochemical compositions of the granites imply that significant heat and mass from the mantle were involved in the formation of the Cuigang, Luming and Dongan granites during the subduction of the oceanic plate. It may be linked to significant crustal growth in the LXR during the Early Jurassic, corresponding to widespread crust-mantle interactions as recorded by zircon Hf and whole-rock Nd and Pb isotopes of granitoids in the Songliao Block. Combining our results with prior lines of evidence from lithogeochemistry, geophysics, numerical simulation and frequency variations in global detrital zircon age and associated O isotope data, we infer that crustal growth may commonly trigger fluid-fluxed melting of pre-existing crust to generate granitic magmas above subduction zones.

Automated summary

Through analysis of the geochemical, geochronological, and zircon Hf-O isotope compositions of the Cuigang monzogranite, Dongan syenogranite, and Luming monzogranite in the Lesser Xing'an Range of the Songliao Block, it is discovered that these plutons are related to mantle heat and mass, and may be linked to widespread crust-mantle interactions during the Early Jurassic.