Nalazite se na CroRIS probnoj okolini. Ovdje evidentirani podaci neće biti pohranjeni u Informacijskom sustavu znanosti RH. Ako je ovo greška, CroRIS produkcijskoj okolini moguće je pristupi putem poveznice www.croris.hr
izvor podataka: crosbi

The clinopyroxene crystallization pressure variations from the Alpine volcanic associations of the Dinarides (CROSBI ID 480179)

Prilog sa skupa u zborniku | sažetak izlaganja sa skupa | međunarodna recenzija

Balen, Dražen ; Pamić, Jakob The clinopyroxene crystallization pressure variations from the Alpine volcanic associations of the Dinarides // PANCARDI 2000 Abstracts / Bruno Tomljenović, Dražen Balen & Bruno Saftić (ur.). Zagreb: Hrvatsko geološko društvo, 2000. str. 155-x

Podaci o odgovornosti

Balen, Dražen ; Pamić, Jakob

engleski

The clinopyroxene crystallization pressure variations from the Alpine volcanic associations of the Dinarides

The Dinarides, which can be traced along strike for about 700 km, form a complex fold belt which is composed of several Alpine large lithological associations originating by complex processes of rifting, opening (spreading), subduction and collision. All these evolutionary stages were accompanied by magmatic processes which produced plutonic and volcanic rock associations each of them with specific chemical composition. These differences are particularly valid for geochronologically various volcanic associations, which originated in different geotectonic settings. In all these volcanic associations varieties of basic and intermediate composition contain, as a rule, clinopyroxenes as major femic minerals. For that reason, the chemical composition of the clinopyroxenes from the Mesozoic and Tertiary volcanic associations of the Dinarides have been studied in detail as a key rock-forming mineral. The study is based on microprobe chemical analyses and clinopyroxene geobarometry of magmatic rocks (geobarometer based on crystal-structure modeling of unit cell dimension using chemical composition - NIMIS, 1995 and 1999 ; NIMIS & ULMER, 1998). The clinopyroxene composition varies from augite to diopside according to MORIMOTO (1989) classification diagram. Some of the clinopyroxenes are discontinuously zoned which suggests that crystallization of the cores started at the greater depths than calculated ones. All calculated pressures are referring to temperature of 900 °C. Within the Alpine cycle of the Dinarides the following volcanic associations with clinopyroxenes can be distinguished: 1) The Permian-Triassic andesite-dacite calc-alkaline association largely represented by metabasalts (spilites), metaandesites (keratophyres) and metadacites (quartz keratophyres) with subordinate basalts of tholeiitic affinity related to Alpine rifting processes (starting in the Middle/Late Permian and ending in the Middle Norian with the peak in the Ladinian). The volcanics are interlayered with fossiliferous Late Permian to Middle Norian sedimentary rocks (PAMIĆ, 1984). Pressure of clinopyroxene (augite) crystallization is between 14.3 and 16.5 (ą 2.0) kbars. 2) Jurassic tholeiitic basalts associated with diabases, gabbros and ultramafic rocks of the Dinaride Ophiolite Zone are included into ophiolite mélange. The ophiolites were emplaced (obducted) as the result of suprasubduction which took place in Late Jurassic/Early Cretaceous times. The basalts are largely spilites interlayered with Jurassic sedimentary rocks. K-Ar ages of the associated ophiolites range between 185 and 160 Ma, also indicating Jurassic age (PAMIĆ & TOMLJENOVIĆ, 2000). The chemistry of basalts can be correlated with E-type MORBs or back-arc basin tholeiites (LUGOVIĆ et al., 1991 ; TRUBELJA et al., 1995). Clinopyroxene (mainly augite but some of cpx fall along the boundary with diopside) crystallization pressure varies between 8.7 and 10.6 (ą 1.8) kbars. 3) Cretaceous-Early Paleogene tholeiitic basalts largely transformed into spilites and associated with diabases, gabbros and ultramafics of the Vardar Zone originated most probably in back-arc basin environments. The ophiolites, originated by secondary accretion, were emplaced by Late Eocene secondary obduction related to main collision stage and uplift of the Dinarides. Whole-rock K-Ar ages obtained on mafic ophiolites range from 110-66 Ma (PAMIĆ, 1997) whereas LUGOVIĆ et al. (1991) obtained on ultramafics a Sr-Nd age of 136ą15 Ma indicating Early Cretaceous age. 4) Bimodal basalt-rhyolite (ignimbrite) association of the Vardar Zone originated in trench parts of the back-arc basin. The basalts and rhyolites originated by fractional crystallization of primitive tholeiite basalt with slight alkalic signatures. On rhyolites and associated comagmatic granites a Sr- isochron age of 71.5 Ma was obtained (PAMIĆ et al., 1988) whereas K-Ar ages of 70-60 Ma were produced on basalts. Clinopyroxene (augite) pressure crystallization is 10.2 (ą 1.8) kbars for both 3) and 4) associations. 5) Postorogenic (post-collisional) Tertiary volcanics, which can be separated into five groups, were probably genetically related to subduction processes in terms of slab breakoff model (von BLANCKENBURG & DAVIES, 1995 ; DAVIES & von BLANCKENBURG, 1995): a) Early Oligocene shoshonites with subordinate high-K calc-alkaline andesites on which K-Ar age ranges between 36.15-28.52 Ma (ALTHERR et al., 1995 ; KNEŽEVIĆ et al., 1991 ; PAMIĆ et al., 2000). A calculated pressure for clinopyroxenes (augite) varies between 7.1 and 9.4 (ą 2.0) kbars. The clinopyroxenes are discontinuously zoned which suggests that crystallization of their cores started at greater depths. Maximal calculated value of clinopyroxene (augite) crystallization pressure is 11.6 (ą 2.0) kbars. b) Egerian-Eggenburgian (25.9-22.8 Ma) andesites and dacites with subordinate basalts of tholeiite to calc-alkaline affinity, which originated by fractional crystallization from primary tholeiite basalt magma (PAMIĆ & BALEN, 2000). The clinopyroxene (augite) pressure varies between 5.1 and 8.2 (ą 1.9) kbars. These two formations were related to Oligocene transpressional processes, whereas three next volcanic formations were related to the rifting stage of Neogene evolution of the Pannonian Basin (PAMIĆ, 1997). c) Karpatian (16.8-15.4 Ma) trachyandesites (shoshonites) from primary magma which originated by partial melting of the upper mantle wedge. Pressure of crystallization for Karpatian clinopyroxenes (diopside) is 10.0 (ą 2.0) kbars. d) Most differentiated Badenian (14.5-12.4 Ma) basalts, basaltic andesites, andesites, dacites and rhyolites of tholeiite-calc-alkaline affinity originated by fractional crystallization of primary tholeiite basalt melt of the upper mantle wedge source. Clinopyroxenes (augite and diopside) show maximal pressure variations spanned between 10.9 and 18.3 (ą 2.0) kbars. e) Post-Badenian (11.6-8.4 Ma) basalts and alkali basalts of tholeiitic affinity originated by partial melting of the upper mantle wedge. The crystallization pressure value for their augite and diopside is 10.0 (ą1.8) kbars. The calculated clinopyroxene crystallization pressure variations show, to some extent, various degrees of "guesstimation" regarding to many variables that could interfere with each other. However, although this is an early stage report, results are dispersed into two main groups: one with slightly elevated pressures and depths of crystallization that can be ascribed to rifting processes and second one with pressures around 10 kbars that correspond to melting in subduction related environments.

clinopyroxene; Dinarides; pressure; geobarometry; Alpine cycle

nije evidentirano

nije evidentirano

nije evidentirano

nije evidentirano

nije evidentirano

nije evidentirano

Podaci o prilogu

155-x.

2000.

objavljeno

Podaci o matičnoj publikaciji

PANCARDI 2000 Abstracts

Bruno Tomljenović, Dražen Balen & Bruno Saftić

Zagreb: Hrvatsko geološko društvo

Podaci o skupu

PANCARDI 2000

predavanje

01.10.2000-03.10.2000

Dubrovnik, Hrvatska

Povezanost rada

Geologija