Geological Survey Bulletin Volume 1448, PT. 9

Geological Survey Bulletin Volume 1448, PT. 9

By (author) 

List price: US$13.03

Currently unavailable

Add to wishlist

AbeBooks may have this title (opens in new window).

Try AbeBooks


This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. Excerpt: ...objections to this idea are numerous. (1) Anomalies investigated in composite gneiss unit 2 were caused by magnetite in migmatitic rocks associated with plutonic rocks or by magnetite in biotitequartz diorite gneiss; the itabirite-quartzite-iron silicate assemblage was not found. (2) The original depositional environments of the two units seem incompatible--a shelf origin is probable for itabirite rocks; a eugeosynclinal origin is probable for composite gneiss unit 2. Itabirite could have been incorporated into composite gneiss unit 2 during a thorough reworking, but it does not seem probable that the boundary between gneiss unit 2 and the leucocratic gneiss then would be the abrupt feature it is. More important, reworked itabirite would be expected also in quartz diorite gneiss unit 1, which is adjacent to the itabirite province and which has the same fold style as gneiss unit 2. Itabirite has not been found in quartzdiorite gneiss unit 1. The problem of restriction of the iron-formation to the itabirite province is not resolved, but a study of the movement of faults, discussed in (a), might resolve the problem. AGE PROVINCES Hurley, White, and Fairbairn (1971) made whole-rock Rb-Sr age determinations on a few rocks from Liberia as part of a reconnaissance study to outline intracratonic age provinces in several of the more ancient regions of the continental crust. Their interpretation shows three age provinces for Liberia: The Liberian age province (about 2,700 m.y. old), the Eburnean age province (about 2,000 m.y. old), and the Pan-African age province (about 550 m.y. old). A 2,230-m.y. date was determined for gneiss on the western flank of Jide Mountain. A 2,070-m.y. date was obtained by Hurley and others (1971) from graphitic gneiss of composite...
show more

Product details

  • Paperback | 30 pages
  • 189 x 246 x 2mm | 73g
  • United States
  • English
  • black & white illustrations
  • 1236877209
  • 9781236877208