Wyomingite

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The Wyomingit is a fairly rare magmatic to the Lamproiten belonging rock. It comes from the upper mantle and is characterized by its ultrapotassic character.

Name and initial description

Wyomingite is named after its place of origin, the US state of Wyoming . Its type locality is in the Leucite Hills . The rock was first scientifically described by Charles Whitman Cross in 1897 . Cross originally regarded it as a variety of leucitite , the mineral constituents of which , embedded in a glassy matrix, were composed of clinopyroxene , mica and leucite .

definition

The Wyomingite is now defined as Diopside-Leucite-Phlogopite-Lamproit and is therefore one of the Phlogopite-Lamproites .

mineralogy

Phenocrystals or microphenocrystals in Wyomingite are:

In the base mass there are primarily leucite , as well as magnetite and rarely amphibole ( Richterite ). Accessories are apatite , priderite and wadeit . Calcite occurs secondary.

Wyomingites are mineralogically very similar to Orendites , but differ in their glassy matrix and the lack of sanidine . In their chemical composition they are almost identical to Orenditen. The mineralogical differences can be explained by a different depth range of the crystallization, different cooling rates or different p H 2 O pressure conditions in the magma chamber.

Wyomingites usually form the cooled edge of Orenditic lava flows.

Chemical composition

Main and trace elements

Oxide
weight percent 		Wyomingit
bandwidth		 Wyomingite Wyomingit
Circle Mesa		 Trace element
ppm 		Wyomingit
bandwidth		 Wyomingite Wyomingit
Circle Mesa
SiO 2 49.6-55.2 48.94 55.1 Cr 260-440 900 343
TiO 2 2.4-2.6 1.76 2.73 Ba 4430-7030 8100 6240
Al 2 O 3 8.8-10.6 12.44 9.87 Sr 2070-2930 3800 1830
Fe 2 O 3 4.1-5.3 4.28 4.28 V 75-97 600 90
FeO 3.71 Ni 200-312 70 226
MnO 0.062-0.066 0.10 0.06 Co 16.8-24.0 50 21st
MgO 5.7- 8.7 5.84 6.28 Cu 190 35
CaO 2.6-6.6 4.77 4.11 Zn 110 67
Na 2 O 0.4-2.6 2.17 0.98 Rb 239-319 288
K 2 O 7.8-12.6 11.01 11.5 Nd 102-160 96.8
P 2 O 5 1.2-2.2 0.47 1.29 Zr 1270 159
LOI 1.97 3.23 Pb 27 32
Mg # 0.74-0.81 0.76 0.73 Th 13.7
K / Na 3.19-12.74 3.34 7.73
K / Al 0.96-1.29 0.96 1.26
(Na + K) / Al 1.03-1.69 1.25 1.43

Sources: Mirnejad and Bell (2006) and Vollmer and colleagues (1984).

The Wyomingites belong to the alkali rocks . They are peralkalic with (Na + K) / Al> 1, mostly perpotassic with K / Al> 1 and ultrapotasic with K / Na> 3. Your Mg # magnesium numbers are increased (0.73 to 0.76).

Isotope ratios

The isotope ratios listed follow Mirnejad and Bell (2006):

Isotopes Circle Mesa
87 Sr / 86 Sr 0.7056683-0.705741
143 Nd / 144 Nd 0.511870-0.511940
206 Pb / 204 Pb 17,182-17,227
207 Pb / 204 Pb 15.462-15.4467
208 Pb / 204 Pb 37.258-37.320
δ 18 O 8.65-8.72

Occurrence

Individual evidence

  1. ↑ Cross, CW: Art. XVI - Igneous rocks of the Leucite Hills and Pilot Butte, Wyoming . In: American Journal of Science . Vol. 4, 4th Series. New Haven 1897, p. 115-141 .
  2. ↑ Mitchell, RH and Bergman, SC: Petrology of Lamproites . Springer Science & Business Media, 1991, ISBN 978-1-4613-6688-1 , doi : 10.1007 / 978-1-4615-3788-5 .
  3. ↑ Mirnejad, H. and Bell, K .: Origin and Source Evolution of the Leucite Hills Lamproites: Evidence from Sr-Nd-Pb-O Isotopic Compositions . In: Journal of Petrology . tape 47 , 2006, p. 2463-2489 , doi : 10.1093 / petrology / eg1051 .
  4. ↑ Vollmer et al.: Nd and Sr isotopes in ultrapotassic volcanic rocks from the Leucite Hills, Wyoming . In: Contrib. Mineral. Teal Volume = 87 . 1984, p. 359-368 .
  5. ↑ Mirnejad, H. and Bell, K .: Isotopic analysis of mineral phases to unravel the origin of altered volcanic rocks: an example from the Leucite Hills lamproites . In: Iranian Journal of Crystallography and Mineralogy . No. 2, 1385, 2006, pp. 472-486 .