Petrogenesis of the microcrystalline-dioritic enclaves from Jiuling granitoids in the eastern segment of Jiangnan Orogen and constraints on magma source materials

Numerous dark enclaves with different shapes are found in Jiuling Neoproterozoic granitoids.Precise LAICP-MS U-Pb dating was conducted on zircons extracted from two microcrystalline enclave samples,yielding crystallization ages of 822.6±5.8 Ma and 822.2±6.2 Ma,respectively.The consistent ages within analytical errors with the host granitoids suggested that they were the products of the same magmatism.The microcrystalline-dioritic enclaves commonly show plastic forms and contain similar plagioclase megacrysts to the host rocks,and both of the enclaves and host granitoids showed a complex composition and structural imbalance in plagioclases.Furthermore,the apatites with a euhedral acicular shape occurred widely in the microcrystalline-dioritic enclaves.All of these petrographic features above imply magma mixing is involved in their diagenesis.The enclaves and host granitoids show a marked zircon trace element difference and Hf isotopic signatures without correlation in zircon trace element pairs but form their own system between enclaves and host granitoids.Additionally,most of the zircons show extremely high εHf (t) with εHf (t) =3.54?11.94 from the southern samples,and εHf (t) =1.0?9.09 from the central region.Some zircons with the higher εHf (t) are similar to the zircons from the juvenile island arc in the eastern segment of Jiangnan Orogen.Integrated geological and Hf isotopic characteristics suggest microcrystalline-dioritic enclaves were derived from the partial melting process of the Mesoproterozoic crust which enriched juvenile island arc materials and mixed with the granitic magma that remelted from the Mesoproterozoic continental crust which relatively enriched ancient sediments and mixed with the host granitoid in diagenesis.

Sulfur determination by laser ablation high resolution magnetic sector ICP-MS applied to glasses, aphyric lavas,and micro-laminated sediments

Sulfur(S) is an important element for understanding redox processes, ore formation, environmental chemistry, volcanism and climate. Here, we present a method for in situ S concentration measurement by LA-ICP-MS at the50–100 lm length scale using a 213 nm laser ablation set up coupled to a single-collector magnetic sector ICP-MS with high resolution capabilities. Analyses were performed in medium mass resolution(m/Dm = 3000) mode, which allows for the separation of32 S and34S from molecular interferences. S is simultaneously analyzed along with all major and minor elements so that a priori knowledge of an internal standard concentration is not necessary; this allows for in situ bulk analysis of aphyric groundmass in volcanic rocks or other fine-grained samples. The primary limitation in analyzing S by laser ablation was found to be long-term instrumental drift in fractionation of elemental S relative to other elements,presumably due to drift in laser dynamics. A method for correcting for such fractionation over time was implemented.After correcting for such drift, measurements of homogeneous basaltic glasses are reproducible to within 10 % for high concentration samples([500 ppm) and to within 20 % for low concentration samples(\200 ppm). The applicability of the method was demonstrated using natural and synthetic glasses, aphyric lavas, and micro-laminated sediments.