Zulkarnain, Iskandar. “Geochemical Signature of Mesozoic Volcanic and Granitic Rocks in Madina Regency Area, North Sumatra, Indonesia, and Its Tectonic Implication”. Indonesian Journal on Geoscience, vol. 4, no. 2, June 2009, pp. 117-31, doi:10.17014/ijog.4.2.117-131.