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Thompson, R. N., Velde, D., Leat, P. T., Morrison, M. A., Mitchell, J. G., Dickin, A. P., Gibson, S. A. (1997) Oligocene lamproite containing an Al-poor, Ti-rich biotite, Middle Park, northwest Colorado, USA. Mineralogical Magazine, 61 (407) 557-572 doi:10.1180/minmag.1997.061.407.08

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Reference TypeJournal (article/letter/editorial)
TitleOligocene lamproite containing an Al-poor, Ti-rich biotite, Middle Park, northwest Colorado, USA
JournalMineralogical MagazineISSN0026-461X
AuthorsThompson, R. N.Author
Velde, D.Author
Leat, P. T.Author
Morrison, M. A.Author
Mitchell, J. G.Author
Dickin, A. P.Author
Gibson, S. A.Author
Year1997 (August)Volume61
Issue407
PublisherMineralogical Society
Download URLhttps://rruff.info/doclib/MinMag/Volume_61/61-407-557.pdf+
DOIdoi:10.1180/minmag.1997.061.407.08Search in ResearchGate
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Mindat Ref. ID194Long-form Identifiermindat:1:5:194:2
GUID0
Full ReferenceThompson, R. N., Velde, D., Leat, P. T., Morrison, M. A., Mitchell, J. G., Dickin, A. P., Gibson, S. A. (1997) Oligocene lamproite containing an Al-poor, Ti-rich biotite, Middle Park, northwest Colorado, USA. Mineralogical Magazine, 61 (407) 557-572 doi:10.1180/minmag.1997.061.407.08
Plain TextThompson, R. N., Velde, D., Leat, P. T., Morrison, M. A., Mitchell, J. G., Dickin, A. P., Gibson, S. A. (1997) Oligocene lamproite containing an Al-poor, Ti-rich biotite, Middle Park, northwest Colorado, USA. Mineralogical Magazine, 61 (407) 557-572 doi:10.1180/minmag.1997.061.407.08
In(1997, August) Mineralogical Magazine Vol. 61 (407) Mineralogical Society
Abstract/NotesAbstractA small 33 ± 0.8 Ma lamproite pluton is exposed in the midst of a 23–26 Ma basalt-rhyolite province in Middle Park, NW Colorado. It contains abundant phlogopite phenocrysts in a fine-grained groundmass of analcime pseudomorphs after leucite, biotite, potassic richterite, apatite, ilmenite and accessory diopside. The phlogopite phenocryst cores contain ∼4 wt.% TiO2, 1% Cr2O3 and 0.2% BaO. The smallest groundmass biotites have normal pleochroism but compositions unlike any previously reported, with ∼2% Al2O3, ∼8% TiO2 and F <1.5%. Apart from those elements affected by leucite alteration, both the elemental and isotopic composition of this lamproite are close to those of the Leucite Hills, Wyoming. Its Nd-isotopic model age (TDM = 1.6 Ga) is outside the Leucite Hills range but within that of other Tertiary strongly potassic magmatism in the region underlain by the Wyoming craton. Evidence from both teleseismic tomography and the mantle xenoliths within other western USA mafic ultrapotassic igneous suites shows that the total lithospheric thickness beneath NW Colorado was probably ∼150–200 km at 33 Ma, when the Middle Park lamproite was emplaced. This is an important constraint on tectonomagmatic models for the Cenozoic evolution of this northernmost part of the Rio Grande rift system.


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