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 Madupit from the type locality on the Pilot Butte from the west

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

Neodymium-strontium isotope diagram with the position of various lamproites

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

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.

[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] Mirnejad, H .: Isotope geochemistry, petrology, and source evaluation of the Leucite Hills lamproites, Wyoming. Ph.D. thesis . Carleton University, Ottawa, Ont. 2002.

[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 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 .

[5] Mitchell, RH and Bergman, SC: Petrology of lamproites . Plenum Press, New York, New York 1991.