Silicate–natrocarbonatite liquid immiscibility in 1917 eruption combeite–wollastonite nephelinite, Oldoinyo Lengai Volcano, Tanzania: Melt inclusion study

Sharygin, Victor V.; Kamenetsky, Vadim S.; Zaitsev, Anatoly N.; Kamenetsky, Maya B.

doi:10.1016/j.lithos.2012.01.021

Cited by 50 publications

(26 citation statements)

References 66 publications

(140 reference statements)

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“…The bulk rock composition of the FT-A material is very similar to recent nephelinitic products of Oldoinyo Lengai (Dawson, 1962;Klaudius and Keller, 2006). Of the three most recent explosive eruptions recorded from this volcano [1917, 1966-1967-2008Dawson (2008) and Keller et al (2010)], the erupted material has consisted of peralkaline melilite-bearing nephelinites (Dawson et al, 1992;Mitchell and Dawson, 2007;Keller et al, 2010;Sharygin et al, 2012). The mineral assemblage and also the mineral chemistry, e.g.…”

Section: Volcanic Source Of the Footprint Tuffmentioning

confidence: 63%

The Lake Natron Footprint Tuff (northern Tanzania): volcanic source, depositional processes and age constraints from field relations

Balashova

Mattsson

Hirt

et al. 2016

J Quaternary Science

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The Engare Sero Footprint Site, situated on the southern shore of Lake Natron in northern Tanzania, has been reported to host one of the best preserved sets of fossilized hominid footprints in the world. However, until now there has been no detailed characterization and age determination of the footprint‐bearing strata (the Footprint Tuff). Here, we combine field observations with geochemical and mineralogical analyses and measurements of the anisotropy of magnetic susceptibility to constrain depositional processes, the role of reworking and the volcanic source for the Footprint Tuff. We find that the footprint‐bearing horizon consists of volcanic ash‐fall that has been slightly reworked by water, and that this was produced during a voluminous eruption of the Oldoinyo Lengai volcano. The unit, which covered the footprints and helped to preserve them, consists of the wind‐blown material from the same eruption, mixed together with locally derived detrital material. We can constrain the ash horizon to be of Holocene age, based on: (i) the location of the Footprint Tuff within the regional stratigraphy, (ii) previous age determination of an ash layer that can be correlated with the Footprint Tuff and (iii) the regional climatological history of the area. The ash horizon was probably deposited around 11000‐10500 years ago, but could potentially be even younger than this.

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Section: Volcanic Source Of the Footprint Tuffmentioning

confidence: 63%

The Lake Natron Footprint Tuff (northern Tanzania): volcanic source, depositional processes and age constraints from field relations

Balashova

Mattsson

Hirt

et al. 2016

J Quaternary Science

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“…It is noteworthy that these experimental melts are extremely rich in alkalis (10-19 wt.% Na 2 O+K 2 O; Na 2 O  K 2 O). Their closest natural analogues are carbonate globules documented at the Kerimasi and Oldoinyo Lengai carbonatite volcanoes (Tanzania), which were interpreted to have evolved from carbonated nephelinitic magma by immiscibility (Guzmics et al, 2012;Sharygin et al, 2012). In both instances, phosphorus shows a clear preference for the carbonate phase (3.2-7.7 wt.% P 2 O 5 ) relative to the associated silicate melt ( 2.3 wt.% P O ).…”

Section: Phosphorus In Carbonatites: General Observationsmentioning

confidence: 99%

Apatite in carbonatitic rocks: Compositional variation, zoning, element partitioning and petrogenetic significance

Chakhmouradian

Reguir

Zaitsev

et al. 2017

Lithos

Self Cite

174

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Apatite-group phosphates are nearly ubiquitous in carbonatites, but our understanding of these minerals is inadequate, particularly in the areas of element partitioning and petrogenetic interpretation of their compositional variation among spatially associated rocks and within individual crystals. In the present work, the mode of occurrence, and major-and trace-element chemistry of apatite (sensu lato) from calcite and dolomite carbonatites, their associated cumulate rocks (including phoscorites) and hydrothermal parageneses were studied using a set of 80 samples from 50 localities worldwide. The majority of this set represents material for which no analytical data are available in the literature. Electron-microprobe and laser-ablation mass-spectrometry data (~600 and 400 analyses, respectively), accompanied by back-scattered-electron and cathodoluminescence images and Raman spectra, were used to identify the key compositional characteristics and zoning patterns of carbonatitic apatite. These data are placed in the context of phosphorus geochemistry in carbonatitic systems and carbonatite evolution, and compared to the models proposed by previous workers. The documented variations in apatite morphology and zoning represent a detailed record of a wide range of evolutionary processes, both magmatic and fluid-driven. The majority of igneous apatite from the examined rocks is Cl-poor fluorapatite or F-rich hydroxylapatite ( 0.3 apfu F) with 0.2-2.7 wt.% SrO, 0-4.5 wt.% LREE 2 O 3 , 0-0.8 wt.% Na 2 O, and low levels of other cations accommodated in the Ca site (up to 1000 ppm Mn, 2300 ppm Fe, 200 ppm Ba, 150 ppm Pb, 700 ppm Th and 150 ppm U), none of which show meaningful correlation with the host-rock type. Silicate, (SO 4) 2and (VO 4) 3anions, substituting for (PO 4) 3-, tend to occur in greater abundance in crystals from calcite carbonatites (up to 4.2 wt.% SiO 2 , 1.5 wt.% SO 3 and 660 ppm V). Although (CO 3) 2groups are very likely present in some samples, Raman micro-spectroscopy proved inconclusive for apatites with small P-site deficiencies and other substituent elements in this site. Indicator REE ratios sensitive to redox conditions (Ce, Eu) and hydrothermal overprint (Y) form a fairly tight cluster of values (0.8-1.3, 0.8-1.1 and 0.6-0.9, respectively) and may be used in combination with trace-element abundances for the development of geochemical exploration tools. Hydrothermal apatite forms in carbonatites as the product of replacement of primary apatite, or is deposited in fractures and interstices as euhedral crystals and aggregates associated with typical late-stage minerals (e.g., quartz and chlorite). Hydrothermal apatite is typically depleted in Sr, REE, Mn and Th, but enriched in F (up to 4.8 wt.%) relative to its igneous precursor, and also differs from the latter in at least some of key REE ratios [e.g., shows (La/Yb) cn  25, or a negative Ce anomaly]. The only significant exception is Sr(REE,Na)-rich replacement zones and overgrowths on igneous apatite from some dolomite(-bearing) carbonati...

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“…Once immiscibility occurs, the drive for efficient segregation of natrocarbonate is the density contrast between the two immiscible liquids. It is inferred from heating-stage experiments on phenocryst-hosted silicate glass inclusions with carbonate globules from Oldoinyo Lengai that the onset of immiscibility occurs at temperatures >1130 °C (Sharygin et al 2012). Therefore, a comparison of melt density between the average natrocarbonate and average nephelinite erupted from Oldoinyo Lengai (Table 6; Keller et al 2010), is made at 1150 °C as a function of pressure in Fig.…”

Section: Application To Natrocarbonatite Liquidsmentioning

confidence: 99%

The compressibility of CaCO3–Li2CO3–Na2CO3–K2CO3 liquids: application to natrocarbonatite and CO2-bearing nephelinite liquids from Oldoinyo Lengai

O'Leary

Lange

2015

Contrib Mineral Petrol

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dense than the average melt density (~2.67 g/cm 3 ) calculated for associated Mg-poor nephelinite liquids at the same conditions and volatile-free. However, the dissolution of 10.1 wt% H 2 O and 8.7 wt% CO 2 in the average nephelinite melt (based on volatile contents reported in the literature for these magmas) reduces its density to ~2.14 g/ cm 3 at 1150 °C and 1 GPa, eliminating the buoyancy contrast with the natrocarbonate melt. In turn, it is highly likely that the natrocarbonatite melts contained significant amounts of dissolved H 2 O and, as an example, the addition of 10 wt% H 2 O lowers the melt density by ~14 % to ~1.88 g/cm 3 , and therefore re-establishes a large density contrast with the volatile-rich nephelinite melts.

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Silicate–natrocarbonatite liquid immiscibility in 1917 eruption combeite–wollastonite nephelinite, Oldoinyo Lengai Volcano, Tanzania: Melt inclusion study

Cited by 50 publications

References 66 publications

The Lake Natron Footprint Tuff (northern Tanzania): volcanic source, depositional processes and age constraints from field relations

The Lake Natron Footprint Tuff (northern Tanzania): volcanic source, depositional processes and age constraints from field relations

Apatite in carbonatitic rocks: Compositional variation, zoning, element partitioning and petrogenetic significance

The compressibility of CaCO3–Li2CO3–Na2CO3–K2CO3 liquids: application to natrocarbonatite and CO2-bearing nephelinite liquids from Oldoinyo Lengai

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