Macrocrystal phlogopite Rb–Sr dates for the Ekati property kimberlites, Slave Province, Canada: evidence for multiple intrusive episodes in the Paleocene and Eocene

Acid-Leached phlogopite Rb-Sr isochron ages of the Kotakonda and Mudalbid kimberlites in the Narayanpet kimberlite field northwest of the Cuddapah basin, south India are 1085±14 and 1099±12 Ma, respectively. These concordant ages are much younger than the recently reported K-Ar and 40 Ar- 39 Ar ages of 1363±48 and 1402±5 Ma, respectively for the former kimberlite, and support our earlier conclusion that the south Indian kimberlites erupted episodically close to 1090 Ma ago. Three lamproites-one each from Ramannapeta at the northeastern margin and Chelima and Zangamarajupalle within the Cuddapah basin-give distinctly different Rb-Sr ages of 1224±14, 1354±17 and 1070±22 Ma, respectively. While the Rb-Sr age of the Ramannapeta lamproite is also younger than an earlier reported K-Ar age of 1381±18 Ma, it is the same as that of many spatially close alkaline complexes like at Elchuru and Kunavaram. The ages for the Chelima and Zangamarajupalle rocks are only tentative, as these rocks contain a large secondary carbonate component with its Sr isotopic composition genetically unrelated to that of their phlogopites.

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Citations (31)

A Rb‐Sr Isochron Age For A Kimberlite From the Recently Discovered Lac De Gras Field, Slave Province, Northwest Canada

The Journal of Geology (1997)

W J Davis B A Kjarsgaard

A Rb‐Sr phlogopite macrocryst‐whole rock isochron age of 47.5 ± 0.5 Ma is reported for a kimberlite from the recently discovered Lac de Gras field in the Slave Province, northwestern Canada. This is the youngest reliably dated kimberlite occurrence in the world and correlates closely in time with emplacement of kimberlites in Tanzania and Yakutia, indicating a widespread kimberlite emplacement event on three different cratons in the Eocene.

Phlogopite

Isochron dating

10.1086/515942

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Citations (32)

Supplemental Material: Reconciling seismic structures and Late Cretaceous kimberlite magmatism in northern Alberta, Canada

Yunfeng Chen

Summary of northern Alberta kimberlite emplacement ages.<br>

10.1130/geol.s.12298556.v1

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Blueball, a new kimberlite from Arkansas

Geol. Soc. Am., Abstr. Programs; (United States) (1985)

P. A. Salpas L. A. Taylor John W. Shervais

Kimberlites provide direct observation of the upper-mantle/lower-crust by their constituent minerals and inclusions. Blueball is a previously unreported kimberlite from Scott County, Arkansas. It is unrelated to the Murfreesboro kimberlite and is composed of phenocrysts of phlogopite and olivine (serpentinized), along with spinels, in a ground mass of calcite and phlogopite, with minor perovskite and apatite. Phlogopites are compositionally homogeneous, often with euhedral spinel inclusions, and occur as embayed and corroded laths (2 mm). Si+Al are insufficient to fill tetrahedral sites. Reverse pleochroism suggests that Fe/sup 3 +/ or Ti may occupy the remaining tetrahedral sites, similar to other kimberlitic phlogopites. Besides inclusions, spinel also occurs as discrete, anhedral grains with skeletal and atoll habits. Compositions of the two occurrences are the same. These have Mg-Al-chr cores and Mg-Al-mt rims (2-5 um). Based on mineral compositions, as well as whole-rock REE data, Blueball is a true kimberlite. Blueball minerals are compositionally similar to those from kimberlites occurring in other stable cratons (e.g., South Africa); they are dissimilar from those in kimberlites at plate margins (e.g., the Appalachians) indicating heterogeneity in the mantle underlying different tectonic regimes.

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Phenocryst

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Constraints on kimberlite ascent mechanisms revealed by phlogopite compositions in kimberlites and mantle xenoliths

Lithos (2015)

Andrea Giuliani David Phillips Vadim S. Kamenetsky Karsten Goemann

Phlogopite

Xenolith

10.1016/j.lithos.2015.11.013

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Citations (136)

Major- and trace-element compositional variation of phlogopite from kimberlites and carbonatites as a petrogenetic indicator

Lithos (2009)

Ekaterina P. Reguir Anton R. Chakhmouradian N. M. Halden V. G. Malkovets Panseok Yang

Phlogopite

Carbonatite

Trace element

Phenocryst

10.1016/j.lithos.2009.05.023

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Citations (80)

Kimberlite age in the Arkhangelsk Province, Russia: Isotopic geochronologic Rb–Sr and 40Ar/39Ar and mineralogical data on phlogopite

Petrology (2016)

Yu. О. Larionova Л. В. Сазонова Nataliya Lebedeva А. А. Носова V.V. Tretyachenko

Phlogopite

Xenolith

Phenocryst

Diatreme

10.1134/s0869591116040020

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Citations (39)

The Significance of K-Ar Dates on Altered Kimberlitic Phlogopite from Riley County, Kansas

The Journal of Geology (1969)

Douglas G. Brookins

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

10.1086/627412

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Citations (13)