Origin and Source Evolution of the Leucite Hills Lamproites: Evidence from Sr-Nd-Pb-O Isotopic Compositions |
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| Authors: | MIRNEJAD H; BELL K |
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| Institution: | 1 GEOLOGICAL SURVEY OF CANADA 601 BOOTH STREET, OTTAWA, ONTARIO, CANADA K1A 0E8
2 OTTAWA–CARLETON GEOSCIENCE CENTRE, DEPARTMENT OF EARTH SCIENCES, CARLETON UNIVERSITY OTTAWA, ONTARIO, CANADA K1S 5B6 |
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| Abstract: | Whole-rock major and trace element and O, Sr, Nd and Pb isotopicdata are reported for 3·0–0·89 Ma lamproitesfrom the Leucite Hills, Wyoming, USA. The two main groups oflamproites, madupitic lamproites and phlogopite lamproites,are geochemically distinct and cannot be related to one anotherby either fractional crystallization or crustal contamination.It seems likely that the geochemical differences between thesetwo rock types are related to variations in source mineralogyand depth of partial melting. The high Mg-number and large ionlithophile element abundances and negative  Nd values of thelamproites indicate a mantle source that has experienced stagesof both depletion and enrichment. The negative Nb, Ta and Tianomalies in mantle-normalized trace element diagrams and lowtime-integrated U/Pb, Rb/Sr and Sm/Nd ratios of both lamproitegroups and other Cenozoic igneous rocks from the Wyoming ArcheanProvince indicate an ancient metasomatic enrichment (>1·0Ga) of the mantle source associated with the subduction of carbonate-bearingsediments. Other chemical characteristics of the Leucite Hillslamproites, especially their high K2O and volatile contents,are attributed to more recent metasomatism (<100 Ma) involvinginflux from upwelling mantle during back-arc extension or plumeactivity. KEY WORDS: isotopes; lamproites; metasomatism; Leucite Hills; Wyoming |
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| Keywords: | : isotopes lamproites metasomatism Leucite Hills Wyoming |
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