Xenoliths of phlogopite-bearing rocks in kimberlites of Yakutia
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Phlogopite
Xenolith
Xenolith
Phlogopite
Lapilli
Diatreme
Country rock
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Phlogopite
Country rock
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Dharwar Craton
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Diatreme
Phlogopite
Xenolith
Breccia
Phenocryst
Ultramafic rock
Mineral redox buffer
Diopside
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Cluster analysis of 458 pyroxenes from kimberlites, associated xenoliths and diamonds has allowed recognition of 5 chemically distinct orthopyroxene groups and 10 distinct clinopyroxene groups from the $$TiO_{2}, Al_{2}O_{3}, Cr_{2}O_{3}$$, FeO, MgO, CaO, and $$Na_{2}O$$ contents. Names assigned to these groups convey their distinctive chemical features. Because many groups contain cases from both kimberlite and xenoliths, some kimberlite pyroxenes may derive from fragmented xenoliths. However from size alone, large discrete orthopyroxene crystals, discrete sub-calcic diopside nodules and low-Cr diopsides intergrown with ilmenite are apparently not xenolithic; nor are the minute diopside crystals growing in the kimberlite matrix. Pyroxene inclusions in diamonds and pyroxenes coexisting with diamond in eclogite and peridotite xenoliths range widely in chemical composition.
Xenolith
Diopside
Pyroxene
Ilmenite
Peridotite
Pyrope
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Phlogopite
Xenolith
Lapilli
Diatreme
Country rock
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Phlogopite
Xenolith
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Phlogopite
Xenolith
Phenocryst
Diatreme
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Five known kimberlites intrude Lower Permian sedimentary rocks in Riley County, Kansas. Structural studies show that these kimberlites were emplaced in Late Cretaceous (post-Dakota sandstone) time. Four K-Ar age determinations on altered phlogopite from two of the kimberlites vary between $$204 \pm 20$$ m.y. and $$380 \pm 40$$ m.y. The phlogopite, therefore, crystallized much earlier than the time of emplacement of the kimberlite pipes and, in a sense, may be regarded as xenocrystic. Both the $$*Ar^{40}$$ and total K content are low due to the altered nature of the phlogopite. The pre-emplacement ages are consistent with a low temperature of injection, possibly as low as 100°-200° C, which explains the lack of pyrometamorphic contact effects in the Permian country rocks.
Phlogopite
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