Madupit
Madupites are quite rare igneous rocks belonging to the lamproites . They come from the upper mantle and are characterized by their ultrapotassic character.
etymology
The word madupit is derived from madúpa , a word from the Shoshone language meaning sweet water . This Indian name refers to the Sweetwater County in southwest Wyoming , in which the type locality ( Pilot Butte in the Leucite Hills ) of the sub-volcanic rock is located.
Initial description
The madupit was first scientifically described by Charles Whitman Cross in 1897 .
mineralogy
At that time, Cross had considered the rock to be a melanocratic variety of leucitite , which essentially consisted of diopside and phlogopite pheocrystals. The glassy base material was similar in its composition to the minerals nepheline and leucite .
Madupit lamproite
In the course of the redefinition of the lamproite, Madupit is now called Diopside Madupit Lamproit. The Madupite lamproites or Madupite lamproites form a separate group within the lamproites alongside the transitional Madupite lamproites and the phlogopite lamproites. In contrast to the phlogopite lamproites, which are characterized by phlogopite phenocrystals , the poikilitic phlogopite is also found in the matrix of the madupite lamproites. In addition to the madupite , the madupite lamproites also include the jumillite , an olivine-diopside Richterite-madupite-lamproit, and the volgidite , a diopside-leucite-Richterite-madupite-lamproit. They are geochemically related to the transition madupite lamproites, but mineralogically, unlike them, they do not contain leucite phenocrystals.
Madupites are related to and also associated with Orendites and Wyomingites , but have a more basic composition and differ in their radioisotope ratios .
Main and trace elements
Oxide weight percent |
Madupit bandwidth |
Madupit Badger’s Teeth |
Madupit Pilot Butte |
Madupit Middle Table Mountain |
Trace element ppm |
Madupitit bandwidth |
Madupit Badger’s Teeth |
Madupit Pilot Butte |
Madupit Middle Table Mountain |
---|---|---|---|---|---|---|---|---|---|
SiO 2 | 43.6-47.4 | 41.9-43.9 | 41.4-45.3 | 47.4-48.3 | Cr | 463-559 | 469-489 | 444-560 | 408-415 |
TiO 2 | 2.3-2.5 | 2.16-2.29 | 2.05-2.28 | 2.37-2.55 | Ba | 4950-9750 | 8171-12500 | 7212-11690 | 6451-8453 |
Al 2 O 3 | 7.7-9.1 | 7.72-8.36 | 7.20-7.64 | 8.63-9.12 | Sr | 4198-6003 | 5250-6223 | 3814-7233 | 2965-3051 |
Fe 2 O 3 | 5.9-6.7 | 5.58-5.94 | 5.89-6.41 | 4.61-4.72 | V | 50-110 | 65-129 | 21-109 | 114-119 |
FeO | Ni | 175-209 | 109-148 | 104-161 | 115-156 | ||||
MnO | 0.099-0.125 | 0.09-0.11 | 0.12-0.13 | 0.8-0.10 | Co | 26-30 | 24-27 | 26-30 | 24-25 |
MgO | 8.9-10.5 | 9.3-10.5 | 10.6-12.2 | 8.87-9.09 | Cu | 28-38 | 37-45 | 28-39 | |
CaO | 8.5-11.7 | 10.0-12.3 | 11.0-12.7 | 8.78-9.34 | Zn | 64-97 | 68-116 | 61-115 | |
Na 2 O | 0.8-1.0 | 0.90-1.23 | 0.48-1.67 | 0.96-1.08 | Rb | 187-233 | 31-52 | 26-120 | 47-80 |
K 2 O | 7.6-10.2 | 4.74-8.14 | 5.13-8.69 | 7.29-9.57 | Nd | 259-325 | 286-300 | 265-300 | 200-208 |
P 2 O 5 | 1.8-3.0 | 2.84-3.01 | 1.63-2.39 | 1.30-1.60 | Zr | 1210 | 140-788 | 253-850 | 737-808 |
LOI | 5.42-9.05 | 4.48-6.96 | 4.48-6.79 | Pb | 57 | 31-52 | 26-120 | 47-80 | |
K / Na | 6.73-7.14 | 3.47-4.36 | 3.43-7.08 | 4.99-5.84 | |||||
K / Al | 1.07-1.21 | 0.66-1.05 | 0.77-1.23 | 0.91-1.14 | |||||
(Na + K) / Al | 1.22-1.39 | 0.86-1.30 | 0.88-1.59 | 1.10-1.33 |
Sources: Mirnejad and Bell (2006) and Vollmer and colleagues (1984).
The Madupite belong to the alkali stones . They are predominantly peralkalic with (Na + K) / Al> 1, mostly also perpotassic with K / Al> 1 and ultrapotasic with K / Na> 3. They are also low-silicon, mafic to ultramafic rocks with sometimes very high MgO and CaO content. Their Al 2 O 3 values are low. Their total iron is higher than that of the phlogopite lamproites.
In the case of trace elements, compared to other lamproites, they show accumulations of barium , strontium , thorium and rare earths , especially LREE. Nickel is depleted and its K / Rb ratio is low. Compared to the phlogopite lamproites, LILE and HFSE are increased. As with other lamproites, there are negative spikes on niobium , tantalum, and titanium .
According to Mitchell and Bergman 1991, these findings suggest that madupites are derived from phlogopite lamproites.
Isotope ratios
Isotopes | Badger's Teeth | Pilot Butte | Middle Table Mountain |
---|---|---|---|
87 Sr / 86 Sr | 0.70534-0.70551 | 0.70545-0.70563 | 0.70551 |
143 Nd / 144 Nd | 0.51197-0.51204 | 0.51208-0.51211 | 0.51206-0.51209 |
206 Pb / 204 Pb | 17.436-17.457 | 17.542-17.583 | 17.534-17.535 |
207 Pb / 204 Pb | 15.473-15.484 | 15.489-15.508 | 15.491-15.496 |
208 Pb / 204 Pb | 37.272-37.463 | 37.480-37.523 | 37.501-37.512 |
δ 18 O | 8.21-8.37 | 8.66-8.93 | 8.80-8.86 |
In terms of isotope ratios, madupite and madupite lamproites also clearly differ from the phlogopite lamproites (or orendites) and show higher 143 Nd / 144 Nd and somewhat lower 87 Sr / 86 Sr ratios. Their lead isotope ratios are generally somewhat higher. In the isotope diagram 143 Nd / 144 Nd versus 87 Sr / 86 Sr, madupite lamproites come to lie in the enriched quadrant, just like all other lamproites. In general, two trends can be identified: a steep trend depleted in 87 Sr / 86 Sr and a flat trend towards 87 Sr / 86 Sr -rich crust components. The madupite and phlogopite lamproites of the Leucite Hills as well as the lamproites of Smoky Butte are on the steep trend, whereby Smoky Butte is extremely depleted in ϵ Nd and lead isotopes. The lamproites of Tuscany, southeast Spain and western Australia follow the flat trend. The Lamproit from Gaußberg in Antarctica occupies a middle position.
Occurrence
-
United States of America :
-
Wyoming :
- Badger's Teeth , Leucite Hills - Transitional Madupit-Lamproit
- Middle Table Mountain , Leucite Hills - Transitional Madupit-Lamproit
- Pilot Butte , Leucite Hills (type locality) - Madupit-Lamproit
-
Wyoming :
Individual evidence
- ↑ 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 .
- ↑ Mirnejad, H .: Isotope geochemistry, petrology, and source evaluation of the Leucite Hills lamproites, Wyoming. Ph.D. thesis . Carleton University, Ottawa, Ont. 2002.
- ↑ 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 .
- ↑ Vollmer u. a .: Nd and Sr isotopes in ultrapotassic volcanic rocks from the Leucite Hills, Wyoming . In: Contrib. Mineral. Teal Volume = 87 . 1984, p. 359-368 .
- ↑ Mitchell, RH and Bergman, SC: Petrology of lamproites . Plenum Press, New York, New York 1991.