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Experience of Petrochemical Typification of Acid Volcanic Rocks from Different Geodynamic Settings A

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Experience of Petrochemical Typification of Acid Volcanic Rocks from Different Geodynamic Settings A ISSN 18197140, Russian Journal of Pacific Geology, 2013, Vol. 7, No. 3, pp. 212–216. © Pleiades Publishing, Ltd., 2013. Original Russian Text © A.V. Grebennikov, V.K. Popov, A.I. Khanchuk, 2013, published in Tikhookeanskaya Geologiya, 2013, Vol. 32, No. 3, pp. 80–85. Experience of Petrochemical Typification of Acid Volcanic Rocks from Different Geodynamic Settings A. V. Grebennikov, V. K. Popov, and A. I. Khanchuk Far East Geological Institute, Far East Branch, Russian Academy of Sciences, pr. Stoletiya Vladivostoka 159, Vladivostok, 690022 Russia email: [email protected] Received November 16, 2012 Abstract—A classification diagram was empirically developed for acid volcanic rocks formed in modern geo dynamic settings and reflects their peculiar chemical features. The testing of the binary diagram Al2O3/(CaO + Tot MgO) – Fe2O3 /(CaO + MgO) for the Late Cretaceous (Pimorsky, Siyanovsky, Kamensky, and Levosobo levsky) and Paleogene (Bogopolsky) Volcanic Complexes of East Sikhote Alin demonstrated its high effi ciency for deciphering the tectonic settings of ancient acid volcanism. Keywords: geochemical classification, geodynamic settings, petrogenic elements, rhyolites DOI: 10.1134/S1819714013030044 INTRODUCTION STUDY RESULTS A great number of diagnostic (discriminant) dia According to the tectonic and geochemical (for basalts) reconstructions of the Mesozoic–Cenozoic grams have been developed on the basis of the evolution of the Asian continental margin, the Late geochemical composition of acid magmatic rocks for Cretaceous volcanic rocks were formed during sub deciphering the geodynamic settings of magmatism. duction, while the Paleogene rocks were derived in a The most frequently applied classification diagrams transform plate margin setting [16, 18]. Previous (Pearce et al., 1984; Batchellor and Bowden, 1985; works on the geochemical typification of Late Creta Harris et al., 1986; Whalen et al., 1987; Maniar and ceous and Paleogene acid volcanic rocks from East Piccoli, 1989; Velikoslavinsky, 2003; and others) were Sikhote Alin (using the aforementioned diagnostic constructed exclusively for granitic rocks. The chemi diagrams for granitic rocks) led to ambiguous results cal identity of intrusive and volcanic rocks formed in [4]. In most geochemical discriminant diagrams, the subduction and withinplate settings was demon data points of the volcanic complexes of different ages occupy uncertain positions, plotting simultaneously in strated only in [2]. However, special studies of the the fields of the island and continental volcanic arc validity of these diagrams for volcanic analogues (dac granitoids, as well as in the field of collisional and ites and rhyolites) have not been conducted yet. Some withinplate granitoids. In this relation, we attempted reseachers [7] demonstrated that the application of to construct discriminant petrochemical diagrams for these diagrams to acid volcanic rocks may lead to the acid volcanic rocks. In particular, the fields of Late invalid conclusions. We encountered this problem Cretaceous and Paleogene ignimbrites of East Sikhote during the study of Late Cretaceous and Paleogene Alin are well distinguished in the diagrams (CaO + ignimbrites of East Sikhote Alin [14]. Thus, a search MgO)–(K2O + Na2O) and (CaO + MgO)–(FeO + for reliable geodynamic interpretations of petro Fe2O3) (Fig. 1). However, deciphering the geodynamic geochemcial data on acid volcanic rocks has remained settings of the ancient acid volcanism can be solved only on the basis of generalization of the data on sim an urgent problem. The main problem in the system ilar rocks formed in modern suprasubduction, plate atics of acid magmatic rocks consists in the variability sliding (transform plate margin), withinplate, and and convergence of the petrogeochemical composi spreading settings. The volcanism of collisional zones tion due to their polygenous origin and intense chem was generated by the sliding of the lithospheric plates ical interaction with other rocks (and melts). Finally, during and after their collision. this may lead to the obliteration of the petrochemical The detection of petrochemical parameters was signatures of acid volcanic rocks of different geody caused by the behavior of the trace elements in the namic settings. acid melts. We agree with the conclusions in [29] that 212 EXPERIENCE OF PETROCHEMICAL TYPIFICATION OF ACID VOLCANIC ROCKS 213 (a) (b) 140 80 120 60 100 molecular molecular , 3 40 1 O, O 2 80 2 2 60 20 3 O + Na 2 40 0 FeO + Fe K 20 0 20406080 020406080 CaO + MgO, molecular CaO + MgO, molecular Fig. 1. Diagrams: (a) (Na2O + K2O)–(CaO + MgO) (molecular); (b) (Fe2O3 + FeO)–(CaO + MgO) (molecular). Data points of acid volcanic rocks: (1) Turonian–Santonian Primorskaya Unit; (2) Campanian–Maastrichtian Siyanovsky, Kamensky, and Levosobolevsky Volcanic Complexes; (3) Paleocene–Eocene Bogopolsky Volcanic Complex. the existing geochemical classifications of granitic the data points of the rocks with insignificant overlap rocks based on trace and minorelement abundances ping define four main fields. The first field (I) includes cannot unambiguously identify the magmatic source volcanic rocks related to islandarc and continental– or tectonic setting. Minor elements in acid melts, margin suprasubduction magmatism. They include unlike those in basalts, usually reveal incompatible dacites and rhyolites from the Cascades (USA) [33], behavior [25]. REE, U, Th, and Zr are usually incor ignimbrites from the volcanic front of the Andean belt porated in such accessory minerals as apatite, zircon, (Argentina, Bolivia, and Chile) [10, 28, 39, 40, 42], titanite, orthite, and monazite, while Nb and Y are and ignimbrites of Kamchatka (the Uzon and Semy accumulated in oxides and amphiboles. Correspond achik Volcanoes) [9]. The second field (II) comprises ingly, their contents are determined by the crystalliza volcanic rocks from intra and continental transform tion as a function of the extensive parameters (oxygen plate margins. They are represented by rhyolites of and water fugacity). Crustal contamination affects the extrusive domes and lava piles of Californiantype concentrations of trace elements to a greater extent Coso province in California in the United States [22], than those of petrogenic oxides. Thus, the use of as well as by rhyolites from the western coast of Amer minor elements and their ratios as factors of the classi ica (about 30 manifestations in Nevada, Utah, and fication of granitic rocks often cannot provide unam Idaho in the United States) [27] and the Yellowstone biguous identification of the magmatic source or geo supercaldera (Wyoming, USA) [26, 31, 41]. The third dynamic setting. field (III) encloses data on the withinplate alkaline rocks, in particular, ignimbrites from the East African Diagrams were constructed on the basis of 600 pub rift system [38, 43], as well as pantellerites and comen lished chemical analyses of diversefacies acid volca dites from the Paektusan Volcano (Korea–China nic rocks (tuffs, ignimbrites, lavas, and extrusive bod boundary) [13], acid volcanic glasses and breccias ies) formed in different geodynamic settings. The data from the Kergelen plateau (Indian Ocean) [24, 37], set included only acid volcanic rocks (SiO2 > 67 wt %) rhyolitic domes of the Red Sea [21], and rhyolites of unaltered by secondary processes with L.O.I. < 4 wt %. oceanic islands (Easter, Socorro, Ascension, Bouvet, Rocks representing fragments of glasses, fiamme, and and others) [23, 36]. The fourth field (IV) is formed by end members of highly differentiated melts and liquid acid volcanics from spreading zones: rhyolites from immiscibility products were omitted. The composition the Alcedo Volcano (Galapagos Islands) [30] and Ice was calculated to 100% water free. The molecular land [6, 34, 35]. Thus, distinguished fields I–IV corre amounts were calculated using the standard tech spond to the composition of the acid volcanic rocks of niques [20]. modern geodynamic settings. Numerous triangle and binary petrochemical dia grams were empirically compiled to obtain the most The next step involved plotting the data points of Tot the Late Cretaceous ignimbrites of the Siyanovsky, informative Al2O3/(CaO + MgO) – Fe2O3 /(CaO + Levosobolevsky, Kamensky, and Primorsky Com MgO) diagram (Fig. 2). In our opinion, the propor plexes and the Paleogene ignimbrites of the Bogopol tions of Al, Fe, and sum of thermophile cations (Ca sky Complex (East Sikhote Alin) in the diagram. The and Mg) may serve as the major petrochemical criteria data set included our original [5, 32] and literature [1, for distinguishing between the rocks of different geo 3, 8, 11, 12, 15, 19] data, as well as materials from geo dynamic settings. As is seen in the presented diagram, logical reports. In the developed diagram (Fig. 2), the RUSSIAN JOURNAL OF PACIFIC GEOLOGY Vol. 7 No. 3 2013 214 GREBENNIKOV et al. (a) 100 (b) 100 III III molecular molecular 10 10 IV IV /(CaO + MgO), /(CaO + MgO), 1 1 II 3 3 Tot Tot O O 2 2 Fe Fe II 1 I I 0.1 0.1 2 1 10 100 1 10 100 Al2O3/(CaO + MgO), molecular Al2O3/(CaO + MgO), molecular tot Fig. 2. Diagrams: (a, b) Al2O3/(CaO + MgO)–Fe2O3 /(CaO + MgO) (molecular). Fields I–IV are separated by lines taking their origin at the points with the following coordinates: (a) 1–0.5, 1000–60; 10–0.1; 10–100; (b) 1–0.22, 100–7; 1–100; 9–0.1. (I) Zones of islandarc and continentalmargin suprasubduction magmatism: rhyolites of Kamchatka (the Uzon and Semyachik Volcanoes); Andean rhyolites (Chile, Bolivia, Argentina); rhyolites
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