Petrogenetic significance of ocellar camptonite dykes in the Ditrau Alkaline Massif, Romania

Camptonite dykes intrude the rift-related Mesozoic igneous body of the Ditrău Alkaline Massif, Eastern Carpathians, Romania. We present and discuss mineral chemical data, major and trace elements, and the Nd isotopic compositions of the dykes in order to define their nature and origin. The dykes are classified as the clinopyroxene-bearing (camptonite–I) and clinopyroxene-free (camptonite–II) varieties. Camptonite–I consists of aluminian–ferroan diopside phenocrysts accompanied by kaersutite, subordinate Ti-rich annite, albite to oligoclase and abundant calcite–albite ocelli. Camptonite–II comprises K-rich hastingsite to magnesiohastingsite, Ti-rich annite, albite to andesine, abundant accessory titanite and apatite, and silicate ocelli filled mainly with plagioclase (An4-34). Age-corrected 143Nd/144Nd ratios vary from 0.51258 to 0.51269. The high εNd values of +4.0 to +6.1 which are consistent with intra-plate composition, together with light rare earth element (LREE), large ion lithophile element (LILE) and high field strength element (HFSE) enrichment in the camptonites is ascribed to the formation of small melt batches of a metasomatised sub-lithospheric mantle source. The presence of an asthenospheric ‘high μ’ ocean island basalt (HIMU–OIB)-type mantle component in the source region has also been revealed. A 1–4% degree of partial melting of an enriched garnet lherzolite mantle source containing pargasitic amphibole followed by fractionation is inferred to have been involved in the generation of the camptonites. They are deduced to be parental melts to the Ditrău Alkaline Massif

Mezozóos alkáli magmatizmus a Kárpát régióban: a Ditrói Alkáli Masszívum petrogenezise = Mesozoic alkaline magmatism in Carpathian region: petrogenesis of the Ditró Alkaline Massif

A Ditrói Alkáli Masszívum a Keleti-Kárpátok központi kristályos kőzettömegébe nyomult be, és ezekkel a metamorf kőzetekkel együtt vett részt az alpi tektonikai eseményekben. Szerkezetileg a Bukovinai takaróhoz tartozik, annak négy prekambriumi, kora paleozóos litológiai egységével érintkezik. A terepi (térképezési), petrográfiai, geokémiai, izotóp-geokémiai, cirkonmorfológiai, fluidzárvány és mikrotermometriai, raman spektroszkópiai valamint kormeghatározási vizsgálatok és adatok alapján a Ditrói Alkáli Masszívum kialakulása egy kontinentális autonom magmás aktivizációhoz köthető. A magmatizmus a kontinentális kéreg kialakulása utáni, az intruzó a platform alapzatát átszelő mélytörések mentén alakult ki. Ez a magmatizmus sokféle alkáli (miaszkitos) kőzetegyüttest produkált. A Tarnica Komplexum Kőzetei (peridotitok, gabbrók), a nefelinszienitek és gránitok közel azonos időben keletkezett, komagmás kőzetek. Ez a magmás tevékenység a középső-triász extenziós tektonikai környezetben, a dél-európai passzív kontinentális szegélyen, köpenyeredetű magma felemelkedésével indult. A Bukovinai-Géta mikrokontinensnek az európai platformtól a jurában történő elszakadásával, a Civcin - Severin riftrendszer mentén egy újabb, köpeny eredetű, intrúzió jött létre. Az így keletkezett szienitek az első magmás folyamat kogenetikus kőzeteivel keveredve egy sor hibrid kőzetet eredményeztek (dioritok, monzonitok). | The formation of the Ditró Alkaline Massif can be related to continental magmatic activation. The process started in the Middle Triassic at the Southern passive edge of the European continent in an extensional tectonic environment by the uplift of mantle origin magma, producing various types of petrologic associations. The rocks of the Tarnica Complex (nepheline syenites and granites) are comagmatic as they were formed almost simultaneously. By the Jurassic detachment of the Bukovina-Géta microcontinent from the European platform a new, mantle origin intrusion developed. The mixing of syenites of this formation with the rocks of the first magmatic phase resulted various hybrid rocks

Origin of mafic and ultramafic cumulates from the Ditrău Alkaline Massif, Romania

Mafic–ultramafic cumulates enclosed in gabbroic-dioritic rocks form part of the Mesozoic Ditrău Alkaline Massif in the Eastern Carpathians, Romania. The poikilitic olivine- and pyroxene-rich and nearly mono mineralic hornblendite rocks display typical cumulate textures with early crystallised olivine (Fo75–73), diopside and augite. In the early stages of their genesis the amphibole was intercumulus whilst in later stages it acquired cumulus status as the fractionating magma evolved. Using major and trace element compositions of minerals and whole-rock samples the origin of these cumulates is determined and the parental magma composition and depth of emplacement are calculated. Cumulus clinopyroxene has more primitive composition than intercumulus amphibole suggesting closed system fractionation for the evolution of poikilitic olivine- and pyroxene-rich cumulates. The evolution of the amphibole-rich mesocumulates is more clearly the result of closed system crystallisation dominated by the precipitation of clinopyroxene and amphibole cumulus crystals. Lamprophyre dykes of the Ditrău Alkaline Massif are proposed to reflect multiple basanitic parental magma batches from which the cumulus olivine and clinopyroxene crystallised. Relative to these dykes the calculated equilibrium melts for intercumulus amphibole in the cumulates was more primitive whilst that for the cumulus amphibole was more evolved. The calculated crystallisation temperature and pressure of ~1000–1050 °C and ~0.7 GPa, based on the composition of the amphiboles, indicate crystallisation at lower crustal depths. Rare earth element compositions are consistent with an intra-plate tectonic setting

Insights into the evolution of an alkaline magmatic system: An in situ trace element study of clinopyroxenes from the Ditrău Alkaline Massif, Romania

Clinopyroxene is a major constituent in most igneous rock types (hornblendite, diorite, syenite, nepheline syenite, camptonite, tinguaite and ijolite) of the Ditrău Alkaline Massif, Eastern Carpathians, Romania. Phenocryst and antecryst populations have been distinguished based on mineral zoning patterns and geochemical characteristics. Major and trace element compositions of clinopyroxenes reflect three dominant pyroxene types including primitive high-Cr Fe-diopside, intermediate Na-diopside-hedenbergite and evolved high-Zr aegirine-augite. Clinopyroxenes record two major magma sources as well as distinct magma evolution trends. The primitive diopside population is derived from an early camptonitic magma related to basanitic parental melts, whilst the intermediate diopside-hedenbergite crystals represent a Na-, Nb- and Zr-rich magma source recognised for the first time in the Ditrău magmatic system. This magma fractionated towards ijolitic and later phonolitic compositions. Field observations, petrography and clinopyroxene-melt equilibrium calculations reveal magma recharge and mingling, pyroxene recycling, fractional crystallisation and accumulation. Repeated recharge events of the two principal magmas resulted in multiple interactions between more primitive and more fractionated co-existing magma batches. Magma mingling occurred between mafic and felsic magmas by injection of ijolitic magma into fissures (dykes) containing phonolitic (tinguaite) magma. This study shows that antecryst recycling, also described for the first time in Ditrău, is a significant process during magma recharge and demonstrates that incorporated crystals can crucially affect the host magma composition and so whole-rock chemical data should be interpreted with great care