Petrogenetic significance of ocellar camptonite dykes in the Ditrău Alkaline Massif, Romania
Introduction
Camptonitic alkaline lamprophyres are usually associated with alkaline syenite-gabbro plutons (e.g. Monteregian Hills, Canada). In many occurrences, such as Borralan (Scotland), Lovozero and Khibina (Kola Peninsula, Russia), and Sokli (Finland) (Rock, 1991 and references therein) they are the most primitive or the only primitive rocks, or represent the only primitive melts to penetrate throughout some provinces (e.g. Monteregian; Iberian, Gorringe Bank). As such, lamprophyres have now been equated with parental melts for a wide range of igneous suites generated repeatedly in time and space (Mitchell, 1994, Rock, 1991). Alkaline lamprophyres are widely recognised at divergent margins (rift valleys, triple junctions) and in intra-plate (oceanic islands, hot-spots) tectonic settings, and they are genetically associated with alkali basaltic magmatism (e.g. Kerr et al., 2010, Orejana et al., 2008, Tappe et al., 2006). Alkaline lamprophyres are more typical of uncontaminated, primary mantle-derived rocks generated at considerable depths (100–150 km) (e.g. Bédard, 1994, Bernard-Griffiths et al., 1991). They frequently contain carbonate ocelli which may suggest the presence of CO2 in their upper-mantle source. Thus their study can put additional constrains on the role of CO2–H2O-rich fluids during mantle metasomatism (Bouabdli et al., 1988, Hidas et al., 2010).
Numerous camptonite dykes occur in the northern part of the Ditrău Alkaline Massif, Eastern Carpathians (Romania), intruding hornblendite, diorite, nepheline syenite, syenite, and granite. Petrogenetically, neither of the lamprophyres has been studied, although they are widely reported in previous papers on the geology of the massif (Kräutner and Bindea, 1998, Streckeisen, 1954, Streckeisen, 1960, Streckeisen and Hunziker, 1974); only a few studies have dealt with the petrography and mineralogy of the lamprophyres and a few have given some whole-rock chemical data (Anastasiu and Constantinescu, 1982, Mauritz, 1912, Streckeisen, 1954, Vendl, 1926) but no interpretation of their origin.
This paper provides new data on mineralogy, mineral chemistry and major, trace, and rare-earth element whole-rock chemistry, as well as on the Sr–Nd isotopic compositions of the Ditrău camptonites, a set of mafic alkaline volatile-rich intrusions that cross-cut the Ditrău Alkaline Massif. The camptonites have the potential to provide important information on the mantle geochemistry beneath the region of their emplacement and on the origin of parental melts of the massif.
Section snippets
Geological setting
The Ditrău Alkaline Massif in the Eastern Carpathians (Romania) is a Mesozoic alkaline igneous complex (19 km long and 14 km wide, ca. 200 km2 in size on the surface, Pál-Molnár, 2000). In the structural system of the Alpine–Carpathian–Dinaric region it belongs to the Dacia Mega-Unit (Fig. 1A). The massif intrudes Variscan metamorphic rocks which can be identified in the Alpine Bucovinian Nappe, Eastern Carpathians (Săndulescu, 1984). These Variscan nappes are built up by the Bretila lithogroup
Field relations and samples
Lamprophyre intrusions are quite common in the whole area of the Ditrău Alkaline Massif. They cross-cut the main intrusions of the massif, hornblendite, nepheline syenite and syenite, and granite, and are themselves cut by alkali feldspar syenite dykes and veins (Fig. 2). The lamprophyre dykes have sharp contact with the host rocks and some of them show very thin chilled margins. Locally all the rocks are more or less altered. Some lamprophyres are disintegrated mostly at the margins of the
Analytical methods
Eighteen lamprophyres were selected for whole-rock chemical analyses, seven samples were analysed for their mineral composition and four were analysed for Sr and Nd isotope compositions. The samples were selected to cover the range of mineralogical varieties of the lamprophyres in a representative way.
Minerals were analysed with a Cameca SX50 electron microprobe in wavelength-dispersion mode at the Department of Geosciences, Uppsala University, Sweden, using a beam current of 15 nA and an
Petrography
The lamprophyres are fine grained with a typical hypocrystalline porphyritic and panidiomorphic texture, but mineralogically they differ from each other. There are clinopyroxene-bearing and clinopyroxene-free varieties. Major components of both types are amphibole, biotite and plagioclase. Olivine is totally decomposed to green or colourless secondary amphibole in radiating nests. According to their mineral assemblage, the studied lamprophyres are camptonites (Le Maitre, 2002, Rock, 1991). A
Mantle source and enrichment processes
The Ditrău lamprophyres compositionally resemble basanites and trachy-basalts, although they seem to present volatile-rich equivalents of these rocks (e.g. Rock, 1991). They contain kaersutite or hastingsite, Ti-rich annite, albite, oligoclase, andesine, apatite, titanite and magnetite in the groundmass with silicate–carbonate or silicate ocelli ± Al–Fe-diopside phenocrysts and pilitic pseudomorphs after olivine. They are significantly enriched in volatile elements (H2O, CO2), in LILE and in LREE.
Conclusions
Camptonite dykes intrude a wide range of igneous rock of the Ditrău Alkaline Massif, namely hornblendite, diorite, syenite, nepheline syenite and granite. Two amphibole populations are present in the lamprophyres with steady reduction in Yb/Eu, CaO and FeOt and similar crystallisation conditions. Camptonite-I contains kaersutite formed under 7–9 kbar and 755–838 °C, while hastingsite formation in camptonite-II shows 6–9 kbar and 666–779 °C. In turn, fractionation of olivine and clinopyroxene are
Acknowledgements
We are grateful to Carl-Magnus Mörth (ICP-MS), Birgitta Boström and Klára Hajnal (ICP-AES) at Stockholm University for their help with the analyses. We thank Ǻke Johansson at the Swedish Museum of Natural History in Stockholm for his technical support in TIMS analyses and for his constructive comments on isotopic results. Hans Harrysson at Uppsala University is acknowledged for technical assistance during the analytical work on the microprobe. Special thanks to Csaba Szabó at the Lithosphere
References (84)
- et al.
The effects of pressure and temperature on the partitioning of Ti, Sr and REE between amphibole, clinopyroxene and basanitic melts
Chemical Geology
(1994) - et al.
Trace element and Nd–Sr isotopic composition of ultramafic lamprophyres from the East Antarctic Beaver Lake area
Chemical Geology
(2001) - et al.
Petrogenesis of Devonian lamprophyre and carbonatite minor intrusions, Kandalaksha Gulf (Kola Peninsula, Russia)
Lithos
(1996) Mesozoic east North American alkaline magmatism: Part 1. Evolution of Monteregian lamprophyres, Québec, Canada
Geochimica et Cosmochimica Acta
(1994)- et al.
Isotopic study (Sr, Nd, O and C) of lamprophyres and associated dykes from Tamazert (Morocco): crustal contamination processes and source characteristics
Earth and Planetary Science Letters
(1991) - et al.
Geochemistry of Mesozoic alkaline lamprophyres and related rocks from the Tamazert massif, High Atlas (Morocco)
Lithos
(1988) - et al.
Petrogenetic processes in the ultramafic, alkaline and carbonatitic magmatism in the Kola Alkaline Province: A review
Lithos
(2005) - et al.
Fluid evolution in the nepheline syenites of the Ditrău Alkaline Massif, Transylvania, Romania
Lithos
(2007) Liquid immiscibility and melt segregation in alkaline lamprophyres from Labrador
Lithos
(1984)Vein-plus-wall-rock melting mechanisms in the lithosphere and the origin of potassic alkaline magmas
Lithos
(1992)
Trace element partition coefficients for clinopyroxene and phlogopite in an alkaline lamprophyre from Newfoundland by LAM-ICP-MS
Geochimica et Cosmochimica Acta
Coexisting silicate melt inclusions and H2O-bearing, CO2-rich fluid inclusions in mantle peridotite xenoliths from the Carpathian–Pannonian region (central Hungary)
Chemical Geology
Sm–Nd isotopic evolution of chondrites and achondrites. II
Earth and Planetary Science Letters
Late Cretaceous alkaline sills of the south Tethyan suture zone, Pakistan: initial melts of the Réunion hotspot?
Lithos
The Lesvos mafic–ultramafic complex, Greece: Ophiolite or incipient rift?
Lithos
Clinopyroxene composition as a method of identification of the magmatic affinities of paleo-volcanic series
Earth and Planetary Science Letters
Some remarks on the movement of small melt fractions in the mantle
Earth and Planetary Science Letters
Tectonic setting of basaltic rocks determined using trace element analyses
Earth and Planetary Science Letters
Interpretation of crystalline spheroidal structures in igneous rocks
Lithos
Post-collisional Tertiary-Quaternary mafic alkalic magmatism in the Carpathian–Pannonian region: a review
Tectonophysics
Nb and Ta incorporation and fractionation in titanian pargasite and kaersutite: crystal-chemical constraints and implications for natural systems
Earth and Planetary Science Letters
The influence of crystal settling on the compositional zoning of a thin lamprophyre sill: A multi-method approach
Lithos
Multiple origin of clinopyroxenes in alkali basaltic rocks
Lithos
The origin of ocean-island basalt end-member compositions: trace element and isotopic constrains
Earth and Planetary Science Letters
Determination of ultra-low Nb, Ta, Zr, and Hf concentrations and the chondritic Zr/Hf and Nb/Ta ratios by isotope dilution analyses with multiple collector ICP-MS
Chemical Geology
Nb/Ta, Zr/Hf and REE in the depleted mantle: implication for the differentiation history of the crust–mantle system
Earth and Planetary Science Letters
Magmatism and the geodynamics of basin formation
Sedimentary Geology
Tectostructural position of the foidic rocks in the Romanian Carpathians
Revue Roumaine de Geologie Geophysique et Geographie Serie, Geologie
Some clinopyroxenes from ultramafic inclusions in Dreiser Weiher, Eifel
Contributions to Mineralogy and Petrology
Petrology of the alkaline magmatism from the Cretaceous North-Pyrenean Rift Zone (France and Spain)
European Journal of Mineralogy
Genesis of carbonate aggregates in lamprophyres from the northeastern Transdanubian Central Range, Hungary: Magmatic or hydrothermal origin?
Mineralogy and Petrology
Geotectonica terenurilor metamorfice din Romania
Petrogenesis of Cenozoic basalts from Mongolia: evidence for the role of asthenospheric versus metasomatized lithospheric mantle sources
Journal of Petrology
Comparative amphibole chemistry of the Monteregian and White Mountain alkaline suites, and the origin of amphibole megacrysts in alkali basalts and lamprophyres
Mineralogical Magazine
Calcic amphibole equilibria and a new amphibole-plagioclase geothermometer
Contributions to Mineralogy and Petrology
Structura geoloică a masivului de roci alcaline de la Ditrău
Buletin St. Revue Roumaine de Géologie, Géophysique
Petrology of ocellar lamprophyres from western Otago, New Zeland
Journal of Petrology
Middle-late Triassic 40Ar/39Ar hornblende ages for early intrusions within the Ditrau alkaline massif, Rumania: Implications for Alpine rifting in the Carpathian orogen
Geologica Carpathica
Partition coefficients for rare-earth elements between calcic amphibole and Ti-rich basanitic glass at 1.5 Gpa, 1100 degrees C
Mineralogical Magazine
Cretaceous alkaline lamprophyres from northeastern Czech Republic: geochemistry and petrogenesis
Geologische Rundschau
Minor and trace element partitioning between immiscible ocelli-matrix pairs from lamprophyre dykes and sills, Monteregian Hills petrographic province, Quebec
Contributions to Mineralogy and Petrology
Evidence of liquid immiscibility in alkaline ultrabasic dikes at Callander Bay Ontario
Journal of Petrology
Cited by (37)
Paleoproterozoic calc-alkaline lamprophyres from the Sidhi Gneissic complex, India: Implications for plate tectonic evolution of the Central Indian Tectonic Zone
2021, Precambrian ResearchCitation Excerpt :They are characterised by porphyritic-panidiomorphic texture comprising hydrous mafic phenocryst (amphiboles and micas) with feldspars always restricted to the groundmass (Rock, 1991). Being the small-volume melt products of deeper parts of the earth’s mantle, their bulk-rock geochemistry serve as proxy for assessing relative contributions from asthenosphere and/or lithosphere of the underlying mantle domains around the world (Ulrych et al., 2014; Batki et al., 2014; Garza et al., 2013). Lamprophyres are known to occur in diverse tectonic regimes and can be important for geodynamic interpretations (Krmíček et al., 2016; Vichi et al., 2005).