Inhomogeneous crust-mantle interaction and Triassic tectonic escape of a Proterozoic microplate: A tale of the Bikou Terrane

摘要: Abstract Compressional stress in collisional orogenic belts open a free boundary for the lateral extrusion of rigid blocks. Here we trace history tectonic escape Proterozoic microplate and associated inhomogeneous crust-mantle processes from magmatic records Bikou Terrane, which is largest microblock located among North China Block, South Block Songpan-Ganzi Orogenic Belt. Zircon U-Pb geochronology indicates that Triassic granitoid intrusions Terrane emplaced at 220–210 Ma. Petrographical, whole-rock geochemical isotopical features suggest granitoids derived partial melting lower crust, with contribution mafic magma subcontinental lithospheric mantle. Compared Yangba pluton northeastern five southwestern display relatively REE concentrations, more negative Eu anomalies (δEu = 0.24–0.93), Nb/Ta Zr/Hf ratios values 14–20 37–45. Furthermore, they higher (87Sr/86Sr) i 0.7050 to 0.7075 eNd(t) −9.4 −4.7. These imply granitic were primary crust lesser input mantle materials than pluton, indicating interaction Terrane. We calculated Moho depth northeast southwest as ~60 km ~ 40–50 km, respectively. propose escaped southwestward Late following transition regime compression NE-SW NW-SE, addition slab break-off east west. The resulted inhomogenous interaction.