Age and origin of the Cortlandt Complex,New York: Implications from Sm-Nd data |
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| Authors: | Michael A Domenick Asish R Basu |
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| Institution: | (1) Department of Geological Sciences, University of Rochester, 14627 Rochester, NY, USA;(2) Branch of Isotope Geology US Geological Survey, Federal Center Denver, Box 25046, 80225 Colorado, USA |
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| Abstract: | Sm-Nd systematics for nine whole-rock samples of hornblende norites, pyroxenites and a lamprophyre from various parts of the Cortlandt Complex were analyzed. Six of these samples from the central and eastern parts of the complex give an isochron age of 430±34 (2 ) Ma with an 
Nd value of –2.9±0.5, and the other three samples from the western part, including the lamprophyre, define a similar age of 394±33 (2) Ma but with a distinctly different
Nd value of –1.4±0.4. The two different initial 143Nd/144Nd ratios corresponding to these -values are interpreted to reflect continental crustal contamination of the lamprophyric parental liquid prior to final emplacement and crystal fractionation to produce the different rock types of the complex. The intrusion age of 430 Ma for the complex clearly post-dates the major metamorphic event of the Taconic orogeny. The Nd-isotopic data also suggest a relationship between the Cortlandt Complex and a belt of lamprophyric dike rocks to the west, known as the Beemerville trend, which cuts across the metamorphic trends of the Taconic (Ratcliffe 1981). |
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