Cancalit

The Cancalit is a very rare magmatic alkaline rocks with potassium supremacy that the Lamproiten is expected to more accurately the phlogopite Lamproiten . It occurs in the south-east Iberian volcanic province .

Occurrence and first description

The Cancarix volcano from the southwest, type locality of the Cancalit

The type locality of the Cancalit is the Cancarix volcano near Hellín in the province of Albacete in southeastern Spain . Its name is derived from the town of Cancarix . The rock was first scientifically described in 1967 by JM Fuster and colleagues.

mineralogy

After the lamproite was redefined by Mitchell and Bergman in 1991, the cankalite is now referred to as enstatite-sanidin-phlogopite-lamproit . The definition reflects the mineralogy that is crucial for the rock, in the case of Cancalite these are the minerals phlogopite , sanidine and enstatite ( orthopyroxene ). In addition to the titanium-rich phlogopite, the iron-rich sanidine and the enstatite, the minerals olivine (rich in the component forsterite ), Richterite ( amphibole with potassium and titanium), idiomorphic, prismatic diopside and leucite also appear . In addition, needle-shaped apatite , more rarely ilmenite , rutile and geikilite as well as accessory dalyite and aegirine .

The specific mineralogical composition and structural formation of the Cancalite, however, depend on the degree of crystallization . For example, olivine disappears in the holocrystalline interior of lamproite, but shows local accumulations in porphyry sectors associated with glassy lava parts (with a glassy to microcrystalline base mass). Phlogopite and diopside occur mainly in holocrystalline areas as hypidiomorphic to idiomorphic crystals, whereas amphibole and sanidine appear as interstices, which can also be poikilitic .

The crystallization proceeds via the early formations of olivine, diopside, and phlogopite to the late formed Richterite and Sanidin, which poikilitically surrounds the first mentioned minerals. In the final phase, dalyite and aegirine crystallized in cavities.

The idiomorphic, block-like, partly skeletal, 0.3 to 1.0 millimeter large sanidin takes up around 50 percent of the volume of the Cancalit. The xenomorphic olivine is corroded and surrounded by enstatite. It is also found in peridotic xenolites . The phlogopite is also corroded and shows legendary segregation (lattice-like intergrowth with rutile). The Richterite, which is up to 3 millimeters in size, fills gussets in the sanitary structure. It also displaces freely occurring phlogopite and diopside and encloses enstatite, with which it also forms adhesions. The rare ilmenite is fused with geikilite. Dalyit occurs in miaroles , in which it is surrounded by sanidine and amphibole. Aegirine appears in drusen and is interpreted as crystals of the vapor phase .

Olivine ( ol ), Akmit ( ac ), sodium metasilicate ( ns ) and potassium metasilicate ( ks ) act as characteristic standard minerals , the latter three being typical for peralkaline rocks. Another characteristic is the absence of normative leucite ( lc ).

Chemical composition

Main and trace elements

Oxide wt.%	Cancalit Cancarix volcano	Cancalit SP-723	Cancalit SP-725	Trace elements ppm	Cancalit Cancarix volcano	Cancalit SP-723	Cancalit SP-725
SiO 2	56.7	57.8	55.9	Cr	1039	757	810
TiO 2	1.54	1.58	1.49	Ni	151	601	470
Al 2 O 3	9.23	9.84	9.30	Zn	83.0
Fe 2 O 3	4.80 (dead)	4.75 (dead)	4.67 (dead)	Rb	676	111	110
FeO				Sr	864	746	696
MnO	0.08	0.07	0.08	Zr	768	978	962
MgO	12.1	10.2	11.8	Ba	1694	1893	1815
CaO	3.42	3.19	4.12	Ce	293	328	295
Na 2 O	0.78	1.02	1.08	Nd	186	214	188
K 2 O	9.11	9.20	8.93	Sm	34.5	40.2	35.9
P 2 O 5	1.14	1.18	1.24	Hf	23.8	23.7	23.9
LOI	0.26	0.79	1.22	Th	128	129	117
K / Na	7.67	5.92	5.45
K / Al	1.07	1.01	1.04
(Na + K) / Al	1.21	1.18	1.23

Source: S. Duggen and colleagues (2005)

The Cancalit is an ultrapotassic (K / Na> 3), intermediate alkaline rock with a peralkaline character (since (Na + K) / Al> 1). It is characterized by very high contents of MgO and K ₂ O , whereas Na ₂ O is clearly depleted. As with all lamproites, the incompatible elements are enriched in the trace elements , in particular the LILE rubidium and strontium , but also the HFSE thorium , cerium , zirconium , hafnium and the rare earths neodymium and samarium . The six-coordinate chromium also shows very high concentrations.

Isotope ratios

Isotopes	Ratio Cancalit	Cancalit SP-723	Cancalit SP-725
87 Sr / 86 Sr	0.718046	0.717426	0.717311
143 Nd / 144 Nd		0.512023	0.512014
206 Pb / 204 Pb	18.803		18.787
207 Pb / 204 Pb	15.689		15.710
208 Pb / 204 Pb	39.015		39.086

With the very high initial lead ratios, which overlap with the values ​​for oceanic sediments (especially with the values ​​of Atlantic shelf-edge sediments of northwest Africa), there are also similarities with lamproites of Tuscany and lamproic minets of the western Alps. In the diagram ⁸⁷ Sr / ⁸⁶ Sr compared to ²⁰⁶ Pb / ²⁰⁴ Pb, the similarity with the Atlantic sediments can be seen again, the relationship to the cordierite- bearing lavas of southeastern Spain and an approach to the enriched mantle reservoir EM 2 .

Individual evidence

1. ^ Fuster, JM et al.: Las rocas lamproíticas del SE de España . In: Estudios geológicos . Vol. 23. Instituto de Investigaciones Geológicos Lucas Mallada, Madrid 1967, p. 35-69 .
2. ↑ Mitchell, RH and Bergman, SC: Petrology of Lamproites . Plenum Press, New York 1991, ISBN 0-306-43556-X .
3. ↑ Linthout, K. et al.: First occurrence of dalyite in extrusive rock . In: Mineralogical Magazine . tape 368 , 1988, pp. 705-708 .
4. ↑ ^{a b} Duggen, S. et al .: Post-collisional transition from subduction to intraplate type magmatism in the westernmost Mediterranean: Evidence for continent-edge delamination of subcontinental lithosphere . In: Journal of Petrology . tape 46 , 2005, pp. 1155-1201 , doi : 10.1093 / petrology / egi013 .