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Mantle Xenoliths from the Southeastern Slave Craton: Evidence for Chemical Zonation in a Thick, Cold Lithosphere 总被引:7,自引:3,他引:7
We present the first data on the petrology of the mantle lithosphereof the Southeastern (SE) Slave craton, Canada. These are basedon petrographic, mineralogical and geochemical studies of mantlexenoliths in Pipe 5034 of the Cambrian Gahcho Kué kimberlitecluster. Major types of mantle xenoliths include altered eclogite,coarse garnet or spinel peridotite, and deformed garnet peridotite.The peridotites belong to the low-temperature suite and formedat T=6001300°C and P= 2580 kbar in a thick(at least 220250 km), cool lithosphere. The SE Slavemantle is cooler than the mantle of other Archaean cratons andthat below other terranes of the Slave craton. The thick lithosphereand the relatively cool thermal regime provide favourable conditionsfor formation and preservation of diamonds beneath the SE Slaveterrane. Similar to average Archaean mantle worldwide, the SESlave peridotite is depleted in magmaphile major elements andcontains olivine with forsterite content of 9193·5.With respect to olivine composition and mode, all terranes ofthe Slave mantle show broadly similar compositions and are relativelyorthopyroxene-poor compared with those of the Kaapvaal and Siberiancratons. The SE Slave spinel peridotite is poorer in Al, Caand Fe, and richer in Mg than deeper garnet peridotite. Thegreater chemical depletion of the shallow upper mantle is typicalof all terranes of the Slave craton and may be common for thesubcontinental lithospheric peridotitic mantle in general. Peridotiticxenoliths of the SE Slave craton were impregnated by kimberliticfluids that caused late-stage recrystallization of primary clinopyroxene,spinel, olivine and spinel-facies orthopyroxene, and formationof interstitial clinopyroxene. This kimberlite-related recrystallizationdepleted primary pyroxenes and spinel in Al. The kimberliticfluid was oxidizing, Ti-, Fe- and K-rich, and Na-poor, and introducedserpentine, chlorite, phlogopite and spinel into peridotitesat P < 35 kbar. KEY WORDS: kimberlite xenolith; lithosphere; mantle terrane; chemical zoning; thermobarometry; Slave craton 相似文献
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Primitive Magma From the Jericho Pipe, N.W.T., Canada: Constraints on Primary Kimberlite Melt Chemistry 总被引:12,自引:7,他引:5
We report the first estimates of primary kimberlite melt compositionfrom the Slave craton, based on samples of aphanitic kimberlitefrom the Jericho kimberlite pipe, N.W.T., Canada. Three samplesderive from the margins of dykes where kimberlite chilled againstwall rock (JD51, JD69 and JD82) and are shown to be texturallyconsistent with crystallization from a melt. Samples JD69 andJD82 have geochemical characteristics of primitive melts: theyhave high MgO (2025 wt %), high mg-numbers (8688),and high Cr (13001900 ppm) and Ni (8001400 ppm)contents. They also have high contents of CO2 (1017 wt%). Relative to bulk macrocrystal kimberlite, they have lowermg-numbers and lower MgO but are enriched in incompatible elements(e.g. Zr, Nb and Y), because the bulk kimberlite compositionsare strongly controlled by accumulation of mantle olivine andother macrocrysts. The compositions of aphanitic kimberlitefrom Jericho are similar to melts produced experimentally bypartial melting of a carbonate-bearing garnet lherzolite. Onthe basis of these experimental data, we show that the primarymagmas from the Jericho kimberlite could represent 0·70·9%melting of a carbonated lherzolitic mantle source at pressuresand temperatures found in the uppermost asthenosphere to theSlave craton. The measured CO2 contents for samples JD69 andJD82 are only slightly lower than the CO2 contents of the correspondingexperimental melts; this suggests that the earliest hypabyssalphase of the Jericho kimberlite retained most of its originalvolatile content. As such these samples provide a minimum CO2content for the primary kimberlite magmas from the Slave craton. KEY WORDS: kimberlite; melt; primitive; primary magma; Slave craton 相似文献
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正1 Introduction Salt lakes are very interesting natural objects which can be found in different places in the world.Russia is not an exception.Climate conditions are various in Russia,but the climate is not very hot.In Russia there are a lot of places where salt lakes are spread.One of them is the Tuva region where lakes with different compositions are 相似文献
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