DISCUSSION OF PAPERS PUBLISHED IN PREVIOUS PARTS OF THE QUARTERLY JOURNAL

Abstract

From Mr C. N. Okezie: The writer recently mapped a small portion (about 200 square miles) of the basement complex of the Kafanchan area, in the Nigerian Younger Granite province. He also mapped a very small Younger Granite stock, the Nok granite, within this area. As a result of this work it became apparent to the writer that the trends of some intrusive Older Granites, their consanguineous granitic pegmatite dykes and sills, and the few basic dykes found in the area appear to have been controlled by four main structural planes of weakness in the basement rocks. These planes are the roughly north-south schistosity and foliation and three inferred sets of master-joints striking roughly nw–se, ne–sw , and e -w. Careful examination of the Younger Granite complexes of this province as seen on the 1 : 2 000 000 geological map of Nigeria or on pl. vii of the Society’s Memoir .No . 1 shows also that these four planes of weakness appear to have exercised a significant control in the emplacement of the Younger Granites. This is shown by the fact that groups of these complexes are often aligned while individual complexes are often elongated parallel to any one of these four directions. The position is illustrated as follows: Aligned complexes (1) Banke-Kudaru-Rishua-Kerku-Nok-Afu (N-S) (2) Banke-Liruei-Suku-Tongolo-Dagga Allah-Kwandon-Kaya-Kofayi ( nw-se ) (3) Kwandon-Kaya-Jos-Bukuru-Vom-Kagoro ( ne -sw) (4) Burra-Ningi-Kila-Wurji-Fagam ( e -w) (5) Zuku-Saiya-Shokobo-Jere-Sanga-Buji-Jos-Bukuru-Rop ( n-s ) (6) Sara-Fier-Sha-Kaleri-South-Mada-Afu ( ne-sw ) Elongated complexes (1) Liruei, Kwandon-Kaya, Kofayi ( nw-se ) (2) Afu, Fagam ( ne -sw) (3) Sara–Fier, Nok, Rishua, Kudaru ( n––s ) (4)