Islamic Azad University Ahar Branch, Iran
m-advay@iau-ahar.ac.ir
The studied area is located in NW of Iran and 20 Km nearby Shabestar city. This area is limited to Mishow mountains and Marand city from the North, to Heris village and Sharafkhane city from the South, to the Tasuj city from the West, and to Shabestar city from the South-East. Based on classification of Iran structural zones, this area is located to Central Iran and/or West Alborz-Azerbaijan zones. Lithological unites in this area include Kahar, Barut, Dorud, and Routeh formations, then, Cretaceous limestones and Miocene conglomerate. The studied granites are intruded to Kahar formation and caused to recrystallization of Soltaniyeh formation and also is covered by Permian sedimentary rocks. So, the stratigraphical age of the granites is attributed to Post Camberian and Pre-Permian.
Major minerals in this granite are alkali feldspar and quartz and minor minerals are plagioclase, biotite, zircon, apatite. Chlorite, kaolinite, seresite and muscovite are the secondary and alteration products of these rocks.
Based on alumina saturation index (ASI) the studied granites have metaluminous to weak-peraluminous character.
REE diagram of these granites indicate that these rocks are generated from plagioclase-bearing fractionated source. The strong negative anomaly of Eu in REE diagram indicates the presence of plagioclase in the source materials or differentiation of plagioclase during evolution of the magma.
Multi element diagram (normalized to ORG) indicate that they have crustal source. Negative anomaly of Ba and enrichment of Rb and Th relative to Ta and Nb is an indicator of crustal origin for the rocks. The studied granites have WPG character and they are counted as A-type granites.
SHRIMP method dating of zircons yield 306±34 Ma for crystallization of them and subsequently for cooling of the studied granite.
It seems that the studied granites are probably formed by partial melting of tonalitic- granodioritic source in an extensional tectonic setting.
The first discovery of combeite and pectolite in kamafugitic rocks of Central Italy
Nikolaeva A.T.
V.S. Sobolev Institute of Geology and Mineralogy sb ras, Novosibirsk, Russia
atnikoleva@gmail.com
The considered Сupaello volcano is part of the Intra-mountain Ultra-alkaline Province (IUP) of Central Italy characterized by kamafugitic and carbonatitic magmatism. This district consists of diatremes, maars and tuff rings [11]. IUP magmatic centers, such as the San-Venanzo (SV) volcano, the Colle Fabbri (CF) stock, and the Сupaello volcano are found in the Pleistocene/Quaternary continental tectonic depressions which cross cut the Pliocene Apennine thrust-fold system. The Cupaello volcano is located along the eastern border fault of the Rietti basin, Central Italy. This is represented by lava flow about 700 m long, 60-200 m wide, and up to 6 m thick [1,2,10].
The lava flow is composed of kalsilite melilitite (local name - cupaellite). The rock consists of phenocrysts of clinopyroxene, phlogopite and fine grains of melilite. Groundmass is represented by clinopyroxene, melilite, kalsilite, olivine, monticellite, perovskite, opaque minerals, and glass.
The chemical composition of kalsilite melilitite (cupaellite) is drastically SiO2 undersaturated (~ 43,8 wt.%), has a low content of Al2O3 (~ 7,4 wt.%) and alkalis (4.4 wt.% K2O and 0.27 wt. % Na2O), and a high content of MgO (~ 11,3 wt.%), FeO (~ 6,7 wt.%), and CaO (~ 15.4 wt.%). This composition is very close to that of the SV olivine melilitites [1], but compared to the CF melilitolite contains less Al2O3 and CaO (about 11 wt.% and 38 wt. % in CF melilitolite, respectively).
Clinopyroxene phenocrysts in this rock have a short-columnar and prismatic habit. Their composition is diopside (Mg # 95) and similar to that of the SV clinopyroxene, and has more FeO and Al2O3 compared to the CF clinopyroxene [12]. Phlogopite phenocrysts are corroded in the rock. Their chemical composition is characterized by high TiO2 (up to 2.3 wt.%) and Mg/Mg+Fe value (86-94). Melilite grains are euhedral in the rock. Their composition contains about 86% akermanite, up to 2% gehlenite, and about 12% Na-melilite components. This is similar to the SV melilite composition and very different from the CF melilite composition. Kalsilite from the groundmass is different from the SV kalsilite [1] due to a high content of FeO.
Combeite and pectolite was found in primary silicate-carbonate completely crystallized inclusions which are present in clinopyroxene phenocrysts. Previously, considered minerals were not detected among rock-forming minerals of carbonatite and kamafugite rocks of IUP. Inclusions in the clinopyroxene from kalsilite melilitite have a rounded, irregular, close to the prismatic form. Their size varies from 10-15 mμ to 50 mμ. The content of inclusions is represented by fine-grained aggregates of colorless, light green and brownish daughter minerals. Among the latter, with the exception of combeite (Na4Ca3[Si6O16](OH, F)2) and pectolite (Ca2NaH[SiO3]3), are present carbonates and sulphates of Ba, K, and Ca, phlogopite, and opaque minerals (Fig.).
Combeite is a rare mineral of alkaline rocks, but, nevertheless, it is typical magmatic mineral in combeite-, and wollastonite-bearing nephelinites from Oldoinyo Lengai volcano in Tanzania [7]. In these rocks combeite was found as phenocrysts, coronas around wollastonite and clinopyroxene [3], as well as globular patches in the groundmass of rock [5]. In addition, it was found in melilite-bearing rock – kugdite [9] as a daughter phase of melt inclusions present in the olivine and perovskite from Krestovskaya intrusion (Polar Siberia). The composition of combeite is characterized by 49-51 wt.% SiO2, 26-27 wt.% CaO, and 18-20 wt.% Na2O. Its stoichiometric formula, Na4, 39Ca3, 49[Si6, 06O16](OH, F)2, is different from the standard one due to the fact that we have not detected F. The calculated Na/Na+Ca ratio is 0,55-0,57. Its composition is similar to that of Oldoinyo Lengai combeite (Tanzania), differing from it in low content of FeO (0,2-0,23 wt.% vs. 8 wt.%) and the presence of K2O (0,61-0,67 wt.%). With a certain degree of conditionality it can be assumed that formation of combeite in the Italian kalsilite melilitite and in the Oldoinyo Lengai nephelenite has occurred under similar physico-chemical parameters.
Fig. Daughter phases of combeite (comb) and pectolite (pct) in silicate-carbonate inclusions from clinopyroxene (cpx).
The pectolite is a very rare mineral in primary magmatic rocks. It is occasionally found in tinguaites, mikrofoyaites, phonolites, and different nepheline syenites [4]. Pectolite is also observed as a reaction rim of mantle xenoliths in Gahcho Kue' kimberlites in Canada [6], in the melt inclusion from Cr-diopside of Inagli Deposit [8], as well as a crystallite and daughter phase of melt inclusions in pyroxenites and kugdites of Krestovskaya intrusion [9]. Chemical composition of pectolite is characterized by ~ 50 wt.% SiO2, ~ 30 wt.% CaO, and ~ 9 wt.% Na2O, its stoichiometric formula is Ca2,04Na1,14[Si3,19O8]OH. This composition is similar to that of pectolite from melilite-bearing rocks of Krestovskaya intrusion.
Thus, discovery of pectolite and combeite among crystalline phases in melt inclusions from clinopyroxene in melilitites suggests that initial melt was enriched in Ca and alkalis during clinopyroxene crystallization, and Na was predominant over K among alkalis. In addition, it can be assumed that the physico-chemical conditions of rock crystallization were quite comparable to those of rock crystallization of the Oldoinyo Lengai volcano.
References:
1. Cundari A., Ferguson A.K. (1991) Petrogenetic relationships between melilitite and lamproite in Roman Comagmatic Region: the lavas of S. Venanzo and Cupaello. Contrib Mineral Petrol 107: 343-357.
2. Gallo F., Giammetti F., Venturelli G., Vernia L. (1984) The kamafugitic rocks of S. Venanzo and Cupaello, Central Italy. Neues Jahrb Mineral Monatsh 5: 198-210.
3. Dawson J.B., Smith J.V., Steele I.M. (1989) Combeite (Na2.33Ca1.74others0.12)Si3O9 from Oldoinyo Lengai, Tanzania. Journal of Geology 97:365–372.
4. Deer W.A., Howie R.A., Zussman J. (1963) Rock-forming minerals 2 – Chain Silicates. Longmans, London (in Rus).
5. Donaldson C.H., Dawson J.B., Kanaris-Sotiriou R., Batchelor R.A., Walsh J.N. (1987) The silicate lavas of Oldoinyo Lengai, Tanzania. Neues Jahrbuch für Mineralogie. Abhandlungen 156: 247–279.
6. Hetman C.M., Scott Smith B.H., Paul J.L., Winter F. (2004) Geology of the Gahcho Kue´ kimberlite pipes, NWT, Canada: root to diatreme magmatic transition zones. Lithos 76: 51– 74.
7 .Klaudius J., Keller J. (2006) Peralkaline silicate lavas at Oldoinyo Lengai, Tanzania. Lihos 91: 173–190.
8. Naunov V.B., Kamenetsky V.S., Thomas R., Kononkova N.N., Ryzhenko B.N. (2008) Inclusions in silicate and sulfate melts in chrome diopside from the Inagli Deposit, Yakutia, Russia. Geochemistry International 46(6): 554-564.
9. Panina L.I., Sazonov A.M., Usol’tseva L.M. (2001) Melilite- and monticellite-bearing rocks of Krestovskaya intrusion (Polar Siberia) and their genesis. Russian Geology and Geophysics 42(9): 1314 – 1332.
10. Stoppa F., Cundari A. (1995) A new Italian carbonanite occurrence at Cupaello (Rieti) and its genetic significance. Contrib Mineral Petrol 122: 275-288.
11. Stoppa F., Lavecchia G. (1992) Late Pleistocene ultra-alkaline magmatic activity in the Umbria – Latium region (Italy): An overview. Journal of Volcanology and Geothermal Research 52: 277 – 293.
12. Stoppa F., Sharygin V.V. (2009) Melilitolite intrusion and pelite digestion by high temperature kamafugitic magma at Colle Fabbri, Spoleto, Italy. Lithos 112: 306-320.