Northeastern Section - 36th Annual Meeting (March 12-14, 2001)
Paper No. 15-0
Presentation Time: 8:30 AM-12:00 PM

WHOLE-ROCK GEOCHEMICAL ANALYSIS OF THE STRAITS SCHIST, WESTERN CONNECTICUT

ROBERTS, Todd M. and DIETSCH, Craig, Geology Department, Univ of Cincinnati, 500 Geology/Physics, Cincinnati, OH 45221-0013, tmroberts77@hotmail.com

The whole-rock geochemistry of high-grade Silurian-Devonian metasediments of the Connecticut Valley Zone of western CT and MA have been analyzed using XRF spectrometry. Analyzed rocks include The Straits Schist (DSt), its basal member (Stb), and its upper Southington Mountain member (DSts) (Table 1). Immobile Th and Ti, and high field strength elements (U, Y, Nb, and Zr) were used to evaluate protoliths. The bottom of the sequence is composed of shallow water carbonates finely interbedded with sandstone. The Straits is chemically similar to pelitic and psammitic shales and was deposited as a sandy shale fining upward into an Al-rich shale. The upper part of the sequence, DSts, is a graphite-rich schist with high U levels, characteristic of deep-water black shales. Based on field relations and chemical discrimination diagrams, this sequence of rocks is conformable and is interpreted as arc-derived sediments deposited in the distal extension of a subsiding basin.
ppm Mo Nb Zr Y Sr U Rb Cr V Ti (wt. %) Ba Th
DSts 3.428 19.285 253.027 40.105 28.921 4.471 155.991 95.897 131.362 1.122 618.409 18.296
DSt 2.996 14.960 184.252 34.525 83.907 2.100 147.728 97.605 134.807 0.963 663.524 15.063
Basal 0.853 10.325 130.249 20.846 88.653 0.012 92.083 73.400 71.882 0.514 482.282 7.864
Weight % Fe Mn Ti Si Al Ca K P Mg Na LOI Weight %
DSts 7.405 0.103 1.078 70.641 14.437 0.085 2.808 0.106 1.871 1.496 0.005 100.035
DSt 7.036 0.157 0.992 66.135 17.070 1.122 3.258 0.174 2.253 1.860 0.006 100.063
Basal 5.970 0.116 1.092 60.023 16.594 5.679 2.565 0.149 4.458 3.343 0.002 99.991
Table 1: Average whole-rock geochemistry of the Southington Mountain member (DSts; n=3,2), The Straits Schist (DSt; n=17,16), and its basal member (Stb; n=4,2).

 

Northeastern Section - 36th Annual Meeting (March 12-14, 2001)
General Information for this Meeting
Session No. 15--Booth# 7
Hydrogeology and Geochemistry (Posters)
Sheraton Burlington: Lake Champlain Exhibition Hall
8:30 AM-12:00 PM, Tuesday, 13 March 2001


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