Diageneza klastycznych utworów karbońskich w obszarze mazowieckim oraz północnej części obszaru lubelskiego na tle ich historii pogrążeniowo-termicznej

Abstract

Diagenesis of the Carboniferous clastic sediments of the Mazowsze region and the northern Lublin region related to their burial and thermal history.S u m m a r y. This paper presents an attempt to combine analysis of diagenetic processes affecting Carboniferous sediments in the SE Poland (Mazowsze and northern part of Lublin region) to their burial and thermal history. For this reason results of petrographic study, analysis of paleotemperatures from fluid inclusion and K/Ar dating of diagenetic fibrous illite were confronted with 1–D maturity modelling calibrated with vitrinite reflectance data (VRo). The main diagenetic processes of the Carboniferous sediments are compaction and cementation especially by: quartz, kaolinite and carbonates (siderite, dolomite, Fe–dolomite, ankerite, Fe–calcite). Fluid inclusions in quartz rims indicate representative temperatures of its growth in a range of 60 oC to 150 oC. Homogenisation temperatures of inclusions from Fe–dolomite and ankerite cement indicate its growth in temperatures ranging between 60–129 oC. Both mentioned above cements are followed in the succession by diagenetic illite; for Mazowsze region its K/Ar dates range from 205,4 ± 4,2 Ma (late most Triassic — early–most Jurassic) to 167,3 ± 3,3 Ma (Bathonian). These measurements were indirectly used as thermochronological data for modelling. In the Mazowsze region thermal modelling based on VRo profiles does not reveal any palaeothermal events. This is due to the fact that the recent burial is not significantly different from the Late Cretaceous maximum one. However incorporation of palaeotemperatures from fluid inclusion analysis together with results of dating of diagenetic illite into thermal history modelling clearly shows presence of Early to Middle Jurassic thermal event. Similar process was independently revealed from maturity modelling for the southern part of Kujawy segment of the Polish Basin (Poprawa et al., 2002), i.e. directly to the NW of analysed area. This event correlates with tectonic phase, expressed by acceleration of subsidence and development of a system of extensional or transtensional faults. It is concluded that the mechanism of heat transport could be related to tectonically induced migration of hot fluids from deeper part of the Palaeozoic sedimentary cover. In the northern part of Lublin region and in the Mazowsze region the Variscan thermal history did not result with depth–depended VRo profiles. Instead sub-vertical or inverted maturity profiles are observed. According to model of Żywiecki (2003) this could be explained by migration of hot fluids from Kock zone, being a site of Carboniferous magmatic activity. Conducted research shows that integration of analysis of inorganic diagenetic processes and maturity modelling allows for more precise reconstruction of thermal history. Therefore this has also potential in calibration of hydrocarbon generation/expulsion modelling.