Nm. Halden et Bj. Fryer, Geochemical characteristics of the Eden Lake Complex: evidence for anorogenic magmatism in the Trans-Hudson orogen, CAN J EARTH, 36(1), 1999, pp. 91-103
The Eden Lake Complex intrudes granitic rocks located between the Lynn Lake
and Leaf Rapids tectonic domains in the Reindeer Zone of the Trans-Hudson
orogenic terrane in northern Manitoba. It consists of a number of magmatic
phases. Of particular interest are aegirine-bearing monzonites and late rar
e earth element (REE)- and fluorine-enriched pegmatites. The aegirine monzo
nite ranges in SiO2 content from 51 to 76 wt.%, showing a continuous fracti
onation trend from low to high silica. The CaO, Fe2O3T, and MgO contents ar
e low (about 1-6 wt.%), TiO2 contents range from 0.8 to about 0.1 wt.%, and
total alkalis range from about 11 to 13 wt.%. The early evolution of the c
omplex was influenced by pyroxene fractionation; during the later stages, K
-feldspar fractionation had an increasing effect on the bulk composition of
the magma. Accumulation of K-feldspar has obscured the tectonic signature
of the complex, but elevated REE, high field strength element, and fluorine
contents are consistent with an A-type granitoid association. The complex
is associated with REE-bearing pegmatites. Total REE contents in the monzon
ites range from 1000 ppm in low-silica phases to 20 ppm in high-silica phas
es, with La/Lu-CN values ranging from 80 to 25. REE patterns reflect the fr
actionation of K-feldspar, pyroxene, and minor amounts of titanite, apatite
, and zircon. Y/Nb and Yb/Ta values (relatively constant at similar to 1 an
d 1.5, respectively) are consistent with derivation from a depleted- mantle
source enriched in REE; moreover, positive epsilon(Nd) values of 0.3-1.7 (
with an assumed age of 1750 Ma) are consistent with derivation from an init
ially light rare earth element (LREE)-depleted source. Elevated Sigma REE c
ontents and LREE-enriched characteristics of the complex suggest the source
region was altered prior to generation of the magma(s).