Formation de skarns et histoire de la cristallisation magmatique en bordure d'une intrusion monzodioritique (Ciclova-Oravita, Banat, Roumanie)
(2004)
Files
Katona.pdf
Restricted Access - Adobe PDF
- 33.54 MB
Details
- Authors
- Supervisors
- Abstract
- The calkalkaline intrusion of Ciclova-Oravita (Banat, Romania), was emplaced in the marly limestones series of Upper jurassic and lower Cretaceous age during a tectonic episode of tensional character which followed the Austrian (Upper Cretaceous) compressive tectonic phase. The skarns which occur in its contacts, show ore mineralisations (mainly copper), associated with a late stage developement of andradite. These ore bearing stages are well documented in the literature. The earlier stages, characterized by the predominance of vesuvianite and grossularitic garnet would not be especially interesting, were it not for the relicts of earlier stages they include, among which gehlenite rich melilite is certainly the most remarkable mineral, but which contain also monticellite, clintonite, ellestadite, etc. This mineralogy is typical of very high temperature skarns, two other occurrences of which only are known in the Carpato - Balkanic belt (in the Apuseni Mountains), but which remain almost completely unknown in the contacts of the Europenean Hercynian belt for instance, may correspond to the well established fact that Ciclova - Oravita intrusion, (and those of Apuseni Mountains as well) is more basic - dioritic and even locally gabbro-dioritic to monzodioritic, than most other banatitic intrusions (commonly composed almost only of granodiorites). The mineralogic and petrogenetic study of these skarns has therefore been focalized on the early stages of reaction between the magma and its wall rocks including the already cristallized outer parts of the intrusion (endoskarns) and on the evolution of these rocks. Based on a detailed examination of the textures associated with a systematic analysis of the minerals and their zoning, we tried to restitute the skarn zonation now only partly preserved, partly rubbed out by the action of the fluids of the later hydrothermal stages. From inner to outer regions those parts which have been preserved include, the melilite rocks when they exist, the anorthite + Al-rich clinopyroxene skarns, and the anorthite + wollastonite + diopside skarns, which were developed succesively through a reaction of the magma at different stages in the history of its cristallization with Ca-rich fluids, under essentially variable CO2 pressure (because this reaction produces both CO2 and H2O). A number of textural observations within the intrusion, at the contact of the skarns, testify of their development before the end of the magmatic crystalization. This organisation changed in time, through the developement and progress of various metasomatic fronts related, at the gabbro and dioritic stages, to the infiltration of calcic fluids through this system, and at the pegmato-monzonitic stage (not to be confused with the pegmatitic stage proper), through flow, in the opposite direction, of aqueous fluids rich in Si, Fe and alkalies. These fluids originated from the intrusion near the end of its cristallisation. A wollastonite K-feldspar front separates the region in which the skarns developped under the influence of the calcic external fluid, from the region in which the silicious and alkalies-rich fluids of internal origin has been dominant. The composition and aspect of the clinopyroxenes change sharply at this front. This interpretation is illuminated and completed by the results concerning the evolution of the intrusive rocks. They commenly contains mineral witnesses of a beginning of their cristallization at depth (PH2O > 3-4 kbar), which enables to determine the degree of evolution of the magmas at the time of their ascension
- Affiliations
Citations
Katona, I. (2004). Formation de skarns et histoire de la cristallisation magmatique en bordure d’une intrusion monzodioritique (Ciclova-Oravita, Banat, Roumanie). https://hdl.handle.net/2078.5/124180