Petrogenesis of Potassic Basalts from Northeast China: New Constraints from Trace Elements in Olivine     

ZHANG Liuyi  LI Ni  Dejan PRELEVIC 《《地质学报》英文版》2015,89(4):1418-1419

<正>This study used trace elements in olivine as a new petrogenetic indicator to further constrain the petrogenesis of potassic basalts from the Erkeshan-Wudalianchi-KeluoXiaogulihe potassic volcanic field(EWKX for short)in the Songliao Basin of NE China,with a combination of the previous olivine and whole-rock geochemical data.We  相似文献   

Origin of Minette by Mixing of Lamproite and Dacite Magmas in Veliki Majdan, Serbia   总被引：6，自引：1，他引：5  

PRELEVIC  D.; FOLEY  S. F.; CVETKOVIC  V.; ROMER  R. L. 《Journal of Petrology》2004,45(4):759-792

Composite dykes consisting of leucominette and dacite as wellas discrete dykes and flows of minette and lamproite composition,occur in the Veliki Majdan area, western Serbia. This area ispart of the Serbian Tertiary magmatic province, which consistsof numerous small occurrences of ultrapotassic igneous rocks.The composite dykes have leucominette margins (up to 150 cmthick) enclosing a central part of dacite up to 100 m in width.Between these two lithologies, a decimetre-sized transitionzone may occur. Petrography, mineral chemistry and bulk-rockgeochemistry, including Sr, Nd and Pb isotopes, provide evidencethat the minettes and leucominettes formed by hybridizationbetween a felsic magma similar in composition to dacite anda mantle-derived lamproitic magma. The leucominettes and minettescontain all phenocryst types (biotite, plagioclase, quartz)present in the dacites, but in partly resorbed and reacted form.The mica displays a great diversity of resorption textures asa result of partial dissolution, incipient melting and phlogopitization,suggesting superheating of the felsic melt during hybridization;the mineral modes and mineral compositions of the leucominettesand minettes resemble those in the lamproites. A model for themodification of lamproite melt towards minette is presentedin which minette is formed by mixing of lamproite and <30%felsic magma. The lack of any significant correlation betweenPb isotopic ratios and some of the ‘mixing-indices’(SiO₂, Zr, Zr/Nb, ¹⁴³Nd/¹⁴⁴Nd_i) recognized in the hybridizationmodel for the Veliki Majdan dykes may be a result of similarityof the Pb-isotopic signature in the two end-members. Highlyphlogopitized biotite xenocrysts in the minettes are ascribedto the retention of volatile components after magma mixing andcrystallization of a new generation of phlogopite from the hybridizedmagma. The magma-mixing model explains the reverse zoning andresorption features of phlogopite macrocrysts commonly recognizedin calcalkaline lamprophyres elsewhere. Therefore, this mixingmechanism may be globally applicable for the origin of minettesassociated with calcalkaline granitic plutonism in post-orogenicsettings. KEY WORDS: Serbia; lamproites; micas; phlogopitization; calcalkaline lamprophyres; superheating; magma mixing  相似文献   

Tertiary Ultrapotassic Volcanism in Serbia: Constraints on Petrogenesis and Mantle Source Characteristics   总被引：5，自引：1，他引：4  

PRELEVIC  D.; FOLEY  S. F.; ROMER  R. L.; CVETKOVIC  V.; DOWNES  H. 《Journal of Petrology》2005,46(7):1443-1487

The Serbian province of Tertiary ultrapotassic volcanism isrelated to a post-collisional tectonic regime that followedthe closure of the Tethyan Vardar Ocean by Late Cretaceous subductionbeneath the southern European continental margin. Rocks of thisprovince form two ultrapotassic groups; one with affinitiesto lamproites, which is concentrated mostly in the central partsof the Vardar ophiolitic suture zone, and the other with affinitiesto kamafugites, which crops out in volcanoes restricted to thewestern part of Serbia. The lamproitic group is characterizedby a wide range of ⁸⁷Sr/⁸⁶Sr_i (0·70735–0·71299)and ¹⁴³Nd/¹⁴⁴Nd_i (0·51251–0·51216), whereasthe kamafugitic group is isotopically more homogeneous witha limited range of ⁸⁷Sr/⁸⁶Sr_i (0·70599–0·70674)and ¹⁴³Nd/¹⁴⁴Nd_i (0·51263–0·51256). ThePb isotope compositions of both groups are very similar (²⁰⁶Pb/²⁰⁴Pb18·58–18·83, ²⁰⁷Pb/²⁰⁴Pb 15·62–15·70and ²⁰⁸Pb/²⁰⁴Pb 38·74–38·99), falling withinthe pelagic sediment field and resembling Mesozoic flysch sedimentsfrom the Vardar suture zone. The Sr and Nd isotopic signaturesof the primitive lamproitic rocks correlate with rare earthelement fractionation and enrichment of most high field strengthelements (HFSE), and can be explained by melting of a heterogeneousmantle source consisting of metasomatic veins with phlogopite,clinopyroxene and F-apatite that are out of isotopic equilibriumwith the peridotite wall-rock. Decompression melting, with varyingcontributions from depleted peridotite and ultramafic veinsto the final melt, accounts for consistent HFSE enrichment andisotopic variations in the lamproitic group. Conversely, themost primitive kamafugitic rocks show relatively uniform Srand Nd isotopic compositions and trace element patterns, andsmall but regular variations of HFSE, indicating variable degreesof partial melting of a relatively homogeneously metasomatizedmantle source. Geochemical modelling supports a role for phlogopite,apatite and Ti-oxide in the source of the kamafugitic rocks.The presence of two contrasting ultrapotassic suites in a restrictedgeographical area is attributable to the complex geodynamicsituation involving recent collision of a number of microcontinentswith contrasting histories and metasomatic imprints in theirmantle lithosphere. The geochemistry of the Serbian ultrapotassicrocks suggests that the enrichment events that modified thesource of both lamproitic and kamafugitic groups were relatedto Mesozoic subduction events. The postcollisional environmentof the northern Balkan region with many extensional episodesis consistent at regional and local levels with the occurrenceof ultrapotassic rocks, providing a straightforward relationshipbetween geodynamics and volcanism. KEY WORDS: kamafugite; lamproite; Mediterranean; Serbia; mantle metasomatism; veined mantle; petrogenesis  相似文献