Fortunit
The Fort Unit is a rare igneous rock , which the Lamproiten is expected. The alkaline rock with a predominance of potassium occurs in the south-east Iberian volcanic province .
First description and occurrence.
The fortunit was first scientifically described in 1893 by Ramon Adan de Yarza . There are three known occurrences of Fortunit, all of which are located near the eponymous southeastern Spanish city of Fortuna ( Murcia province ). Including the chimney filling of the Cabecicos Negros (3.5 kilometers southeast of Fortuna) and the two passages of El Tale (3.5 kilometers east of Fortuna) and Los Derramadores (2 kilometers east-southeast of Fortuna).
mineralogy
Adan de Yarza originally described the fortunite as a trachyte variety characterized by the presence of phlogopite and the orthopyroxen bronzite . According to the redefinition of lamproites by Mitchell and Bergman in 1991, the rock is now referred to as hyalo-enstatite-phlogopite-lamproit , so it belongs to the phlogopite-lamproites .
The fortunite consists of the phenocrystals olivine and phlogopite, which are embedded in a glassy to mesocrystalline base mass of 61 percent by volume. In addition, microphenocrystals of idiomorphic clinopyroxene and skeletal sanidine appear in the matrix , which crystallized during an early devitrification phase. Orthopyroxene is a substitute for olivine. Apatite and pseudobrookite act as accessories . Phlogopite, aluminum-rich spinel as well as ilmenite and rutile have an origin as xenocrystals . Occurring nickel sulfides are post-magmatic formations. The olivine, which occupies up to 24 percent by volume, is rich in the component forsterite (Mg # = 0.91) and often contains chromium-rich spinel. Phlogopite (Mg # = 0.90) with grain sizes up to more than 5 millimeters has a volume fraction of 10 percent. The pyroxenes reach 5 percent by volume.
Chemical composition
Main elements
Oxide wt.% |
Fortunit average |
Fortunit bandwidth |
Fortunit El Tale |
Fortunit Cabecicos Negros |
Fortunit Barqueros |
Fortunit Salmerón |
Fortunit 73A8 |
---|---|---|---|---|---|---|---|
SiO 2 | 56.05 | 53.36-57.51 | 59.14 | 56.4-57.1 | 55.32 | 56.88 | 58.77 |
TiO 2 | 1.35 | 0.95-1.86 | 1.46 | 1.35-1.54 | 1.63 | 1.52 | 1.35 |
Al 2 O 3 | 11.43 | 9.69-13.03 | 12.42 | 11.0-11.7 | 11.24 | 9.04 | 11.34 |
Fe 2 O 3 | 2.23 | 0.72-3.23 | 4.82 (dead) | 5.58-5.98 (dead) | 2.25 | 2.29 | 1.31 |
FeO | 3.31 | 1.31-4.82 | 3.40 | 2.79 | 3.49 | ||
MnO | 0.08 | 0.01-0.12 | 0.04 | 0.07 | 0.07 | 0.08 | 0.10 |
MgO | 9.27 | 5.20-11.81 | 5.96 | 8.93-9.23 | 9.48 | 11.56 | 8.05 |
CaO | 4.21 | 1.41-7.01 | 2.71 | 2.60-2.78 | 3.59 | 3.03 | 4.71 |
Na 2 O | 2.10 | 1.35-4.07 | 1.30 | 0.87-1.16 | 1.25 | 1.64 | 1.25 |
K 2 O | 6.14 | 3.52-9.15 | 8.73 | 7.84-8.48 | 6.88 | 8.45 | 7.87 |
P 2 O 5 | 0.81 | 0.30-1.57 | 1.14 | 0.75-0.86 | 0.72 | 1.08 | 2.22 |
LOI | 2.97 | 1.22-7.71 | 1.70 | 1.84-3.26 | 4.46 | 1.06 | 1.27 |
K / Na | 1.92 | 1.48-1.72 | 4.41 | 4.45-6.32 | 3.61 | 3.38 | 4.13 |
K / Al | 0.58 | 0.39-0.76 | 0.76 | 0.74-0.82 | 0.66 | 1.01 | 0.75 |
(K + Na) / Al | 0.88 | 0.62-1.27 | 0.93 | 0.74-0.95 | 0.85 | 1.31 | 0.93 |
Source: For analysis 73A8: Wagner, C. and Velde, D. (1986)
Fortunite is an intermediate rock that is oversaturated with silicon . It is also predominantly metaluminous with (Na + K) / Al <1 (rarely also peralkaline) and potassic to ultrapotassic (with K / Na> 3). It is one of the alkaline rocks with a predominance of potassium. The main elements MgO , CaO and Na 2 O have very low concentrations .
In the case of halides, fluorine has extremely high values of around 0.5 percent by weight - the highest concentrations ever measured for lamproites worldwide. The chlorine levels, on the other hand, are low, as are those of carbon dioxide and sulfur .
The Fortunit is a quartz normative rock ( Q = 2.27 percent by volume). The standardized feldspar components Or , Ab and An together come to 60.22, orthopyroxene ( En and Fs ) to 24.69 and clinopyroxene ( Di ) to 5.75 percent by volume. Imenite ( II ) is 2.57 and apatite ( Ap ) 1.88 percent by volume.
Trace elements
Trace elements ppm |
Fortunit average |
Fortunit bandwidth |
Fortunit El Tale |
Fortunit Cabecicos Negros |
Fortunit Barqueros |
Fortunit Salmerón |
---|---|---|---|---|---|---|
Cr | 531 | 495-568 | 629 | 543-582 | 583 | 523 |
Ni | 428 | 353-503 | 163 | 371-479 | 479 | 552 |
Zn | 82.0 | 110.9-138.7 | ||||
Rb | 489 | 478-501 | 828 | 753-903 | 500 | 528 |
Sr | 507 | 478-536 | 493 | 586-703 | 516 | 615 |
Zr | 541 | 413-669 | 753 | 594-687 | 678 | 856 |
Ba | 1164 | 806-1523 | 1587 | 1766-2096 | 1274 | 1722 |
Ce | 222 | 195-235 | 248 | 204 | ||
Nd | 141 | 127-152 | 163 | |||
Sm | 25.6 | 25.2-30.0 | 26.6 | |||
Hf | 20.6 | 15.6-17.9 | 19.8 | |||
Th | 92 | 85-100 | 112 | 75.2-106 | 106 | 129 |
The Fortunit is clearly enriched in incompatible elements , LILE , HFSE and rare earths all have high contents. Rubidium , zirconium and thorium in particular are very high . Nickel , lead and scandium have low concentrations .
Isotope ratios
Isotopes | Cabecicos Negros SP 044 |
Cabecicos Negros SP 049 |
Cabecicos Negros SP 050 |
---|---|---|---|
87 Sr / 86 Sr | 0.717689 | 0.717820 | 0.717928 |
143 Nd / 144 Nd | 0.512039 | 0.512045 | 0.512035 |
206 Pb / 204 Pb | 18.764 | ||
207 Pb / 204 Pb | 15.706 | ||
208 Pb / 204 Pb | 39.122 |
With the isotope ratios 143 Nd / 144 Nd is constantly low, but 87 Sr / 86 Sr is significantly increased and approaches the values of upper crustal rocks . With these two parameters, a correspondence with the crustal rocks in the Tuscan Magma Province and with the conditions in the Italian western Alps can be observed. In contrast to the madupites and orendites , which belong to the association of the interior of the plate, Fortunite follow a flat trend of orogenetically influenced association. In comparison with the other lamproites in southeastern Spain, their 87 Sr / 86 Sr values are above those of the Jumillite (J) - Fortunites are therefore somewhat more crustally contaminated - but still clearly below the Verite (V); with the Cancalites (C) they are almost indistinguishable and practically identical.
In the lead ratios (206 and 207), which overlap with the values for oceanic sediments, there is also a correspondence with the lamproites of Tuscany and the lamproic minets of the western Alps (206). The very high lead ratios of 207 Pb / 204 Pb and 208 Pb / 204 Pb are also striking . The lead ratio of 206 Pb / 204 Pb, however, is the lowest among the lamproites of south-east Spain.
Temporal development and dating
The intermontane Fortuna Basin was transgressed by the sea from the lower Tortonian (about 10 million years ago BP) and initially calcarenites, bioclastic limestone and marl sedimented. With progressive deepening followed 500 to 600 meters thick turbidites and marls, the Fortuna marls . From the Messinian onwards, in connection with the salinity crisis of the Mediterranean, evaporites were deposited, which were bordered by reefs and fluvial sediments at the edge. The final pelvis development up to the Pliocene then took place detritically.
The Fortunitganges of Derramadores and El Tale intruded below the Lower Gypsum into the Fortuna marl. Their intrusion age should correspond to the Ar-Ar age of 7.1 ± 0.11 million years BP found by Kuiper and colleagues. However, the Cabecicos Negros fortunites penetrated stratigraphically nearly 200 meters higher and intruded at the base of the Ramblada Salada gypsum. Since the intrusion occurred at the same time as the sedimentation, they are inevitably much younger than the tunnels that only ascended to the Fortuna marl. They may have the age of 6.16 ± 0.3 million years BP found by Bellon and colleagues (1983) using the K-Ar method.
Individual evidence
- ↑ Adan de Yarza, R .: Roca eruptiva de Fortuna (Murcia) . In: Boletin de la Commissión del Mapa Geológico de España . Vol. 20. Madrid 1893, pp. 349-353 .
- ↑ Mitchell, RH and Bergman, SC: Petrology of Lamproites . Plenum Press, New York 1991, ISBN 0-306-43556-X .
- ^ Wagner, C. and Velde, D .: The mineralogy of K-richterite-bearing lamproites . In: American Mineralogist . Volume 71, 1986, pp. 17-37 .
- ↑ Conticelli, S. et al .: Trace elements and Sr-Nd-Pb isotopes of K-rich, shoshonitic and calc-alkaline magmatism of the Western Mediterranean Region: Genesis of ultrapotassic to calc-alkaline magmatic associations in a post-collisional geodynamic setting . In: Lithos . tape 107 , 2009, p. 68-92 .
- ↑ Kuiper et al .: 40 Ar / 39 Ar for the lamproite volcanism of Cabezos Negros, Fortuna basin (Eastern Betics, SE Spain) . In: Palaeogeogr. Paleoclimatol. Palaeoecol.
- ↑ Bellon, H. et al.: Chronologie du magmatisme néogène des Cordillères bétiques (Espagne méridionale) . In: Bull. Soc. Géol. Ms. Band 7 (25) (2) , 1983, pp. 205-217 .