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NEGRO A. DAL; CARBONIN S.; SALVIULO G.; PICCIRILLO E. M.; CUNDARI A. 《Journal of Petrology》1985,26(4):1027-1040
A clinopyroxene suite from leucitebearing lavas locatedin the Sabatini district of the Roman Volcanic Region has beeninvestigated by singlecrystal Xray diffractionmethods combined with electron probe microanalysis. The main aim of the study was to obtain crystallographic datanecessary to evaluate intracrystaUine orderdisorder relationshipsin natural clinopyroxenes and related equilibriadisequilibriaphenomena in different hostrock types. Generally, the polyhedral site configurations of the clinopyroxenesinvestigated are interdependent and follow specific variationtrends related to specific hostrock types. The majorvariations are found in the tetrahedron and the octahedron;while the polyhedron M2 is essentially unchanged and occupiedby(Ca+Na). The degree of MgFe2+; ordering in M1M2, respectively,depends on the configuration of these sites, particularly M2,and is generally lower in latecrystallized (rim) clinopyroxenesthan in the corresponding highertemperature (core) fromthe same crystals. This is' attributed to configuration relationshipsunfavourable to the MgFe2+ ordering and largely dependingon the occupancy of M2. Polygenetic, earlycrystallized clinopyroxenes, occasionallywith resorbed margins, indicate crystal-liquid disequilibriarelated to crystal andor magma mixing processes. 相似文献
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The petrogeny of the leucite-bearing rocks occurring in theRoman and Birunga volcanic regions is reappraised using previouslypublished data. It is shown by means of Principal Latent VectorVariation Diagrams (Le Maitre, 1968) that the chemical analysesof rocks from the two provinces form complementary suites withina well defined trend, which can be interpreted in terms of low-pressurecrystal differentiation. The potential role of the basic compositionsof the trend as parent material is examined in the light ofrecent experimental evidence and a possible evolutionary modelis proposed involving polybaric crystallization. 相似文献
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A clinopyroxene suite from Somma-Vesuvius clinopyroxenite cjectaand mcgacrysts has been investigated by single crystal X-raydiffraction combined with electron probe microanalysis. Theaim of the study was to characterize the intracrystalline configurationof the clinopyroxenes and delineate their possible parentalliquid(s). Vesuvius megacrysts and nodule clinopyroxenes show the initialsignature of the leucitite (sensu lato) magmawhile Somma clinopyroxenes are characteristic of leucite phonolitemagma. The crystal chemical variations demonstrate that thespecimens investigated had originated by shallow-level crystallizationof leucitite and its derivatives, under reducing conditions.T-site (Si + Al) deficiency, typical of clinopyroxene from lamproitesis reported in some specimens from the Roman Volcanic Regionfor the first time. Intracrystalline Mg-Fe2+ ordering in M1-M2 appears to be configuration-dependent,yielding the largest KD variation in the clinopyroxene fromphonolite. This is contrary to expectation. 相似文献
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