cycle detritus from highly differentiated granitoids similar to those from the Aldan Shield. © 2000 Elsevier Science B.V. All rights reserved.
Keywords
:
Proterozoic; Shales; Trace elements; Rare earth elements; Provenance
1. Introduction
The mineralogical and chemical composition of fine-grained sedimentary rocks are commonly
used as a sensitive indicator of provenance and weathering conditions and only in a few cases as a
tool of tectonic setting Ronov and Migdisov, 1971; Cullers et al., 1975, 1979; Taylor and
McLennan, 1985, 1991; Bhatia and Crook, 1986; Roser and Korsch, 1986, 1988; Ronov et al.,
1990; Cullers, 1994b; Cox and Lowe, 1995; Cox et al., 1995; Nesbitt et al., 1996; Cullers and Berend-
sen, 1998; Cullers, 2000. On a global scale, mu- drock chemistry reflects the average composition
of continental crust Taylor and McLennan, 1985. Most mudrocks, however, form in re-
stricted basin environments in specific tectonic settings that reflect the composition of the source
rocks Cox and Lowe, 1995. Elements concen- trated in basic rocks e.g. Sc, Cr, Co and ele-
ments concentrated in silicic rocks La, Th, REE, REE patterns, and Eu-anomaly size have been
used for provenance and tectonic determinations of mudrocks Cullers, 1994b; Mongelli et al.,
1996. Of course these signatures of the source rock may be modified by weathering, hydraulic
sorting and diagenesis Cullers et al., 1987; Condie et al., 1995; Nesbitt et al., 1996.
Although few studies deal with effects of basi- nal tectonic settings controlling the chemical com-
position of mudrocks, it is generally assumed that in more stable and evolved intracratonic settings
mudrocks are more homogenized and represent the average composition of continental crust in
the region Ronov et al., 1974; Bhatia, 1985; Taylor and McLennan, 1985; Cox and Lowe,
1995. Recent studies of the influence of grain-size and transportation distance in a given tectonic
environment on the chemical composition of sedi- ments show that some major element and trace
element concentrations and ratios, including REE patterns and negative Eu-anomaly size, are similar
to the source rock in mudrocks compared with the more variable chemical composition of sand-
stones in the same sedimentary sequences Cullers et al., 1975; Cullers, 1988, 1994a,b; Mongelli et
al., 1996. Thus, mudrock compositions provide more information not only about weathering con-
ditions and sediment recycling, but also regional tectonic settings compared with the more variable
composition of associated sandstones Bhatia, 1983; Bhatia and Crook, 1986; Roser and Korsch,
1988; Sochava et al., 1994; Cullers, 1995.
The specific aims of this paper are as follows: 1 to examine secular variations in mudrock com-
position of
a single
sedimentary unit
the Lakhanda Group, 1.05 – 1.01 Ga on the edge of a
mature craton and 2 to examine the effect of the input of the composition of the sediment as a
result of the changing tectonic evolution.
2. Geology
