The Greer Lake leucogranite, Manitoba, and the origin of lepidolite-subtype granitic pegmatites |
| |
Authors: | Petr erný Morgan Masau Bruce E Goad Karen Ferreira |
| |
Institution: | aGeological Sciences, University of Manitoba, Winnipeg, MB, Canada R3T 2N2 bGeology and Geophysics, University of New Orleans, New Orleans, LA 70148, USA cInukshuk Exploration Inc., 21861 44A Avenue, Langley, BC, Canada V3A 8E1 |
| |
Abstract: | The Archean Greer Lake leucogranite intruded metabasalts of the Bird River Greenstone Belt in the southwestern part of the Superior Province of southeastern Manitoba. The considerably evolved, multiphase, peraluminous, B-, P-, and S-poor leucogranite (K/Rb 132 to 24) was probably generated by fault-friction-assisted anatexis of dominantly metatonalitic rocks and subsequent differentiation. The leucogranite produced interior, transitional, non-crosscutting pods of barren, beryl-columbite- and lepidolite-subtype pegmatites that solidified from local segregations of highly fractionated residual melt. Steep fractionation gradients characterize the granite-to-pegmatite transition, most conspicuously so in the case of the most evolved, Li, Rb, Cs, Be, Mn, Sn, Nb-Ta, F-rich, lepidolite-subtype pod AC #3 (with K/Rb ≥ 16 and Cs 330 ppmwt in accessory K-feldspar, ≥2.5 and ≤11,200 ppmwt, respectively, in lepidolite, Cs ≤28,000 ppmwt in beryl, and Ta/(Ta+Nb) at. ≤ 0.95 in manganotantalite). The Greer Lake example documents beyond any doubt the igneous derivation of lepidolite-subtype pegmatites from a plutonic parent. Most cases of generally very scarce lepidolite-subtype pegmatites obscure this relationship, as the volatile-rich, highly fluid melts stable to relatively low temperatures commonly migrate to great distances from their plutonic sources. |
| |
Keywords: | Leucogranite Granitic pegmatite Lepidolite Petrology Geochemistry Petrogenesis |
本文献已被 ScienceDirect 等数据库收录! |
|