This paper reports an understanding of the origin of the Tonglu volcanic-intrusive rocks on the basis of further studies. U-Pb age determinations of single zircon show that the Tonglu volcanic-intrusive rocks are the products of Early Cretaceous volcanic activities (134.4~134.9Ma). The rhyolitic, rhyodacitic and quartz dioritic magmas, from upper to lower in the shallow magma chamber, have similar Rb-Sr and Sm-Nd isotopic initial values, (87Sr/86Sr)(i)=0.708~0.709. ε(Nd)(t) = -5.27~-6.56, and have similar high field strong elements (HFSE) ratio (e. g. Zr/Nb=10.1~13.1). These indicate that various volcanic-intrusive rocks in the Tonglu basin were comagmatic. The existence of 'compositional undercooling border' outside the porphyroclastic potassium feldspars in the rhyodacite suggests that the crystallization of acidic magma inside the dome crust was slower than that of acidic lava flow. Rb-Sr and Sm-Nd isotopes, Mg/(Mg+Fe) and Na/(Na+Ca) ratios of the intermediate igneous enclaves in central hypabyssal intrusive rocks in the basin indicate that these igneous enclaves are the products of immiscibility of the lower quartz dioritic magma in the chamber.
|Number of pages||9|
|Journal||Acta Petrologica Sinica|
|Publication status||Published - 1999|
- Compositional undercooling
- Early cretaceous
- Immiscibility of magma
- Tonglu volcanic-intrusive rocks