Fluid Migration and Rock Interactions during Dolomitisation of the Dinantian Irish Midlands and Dublin Basin

Abstract

Lower Carboniferous carbonate rocks of the southern Irish Midlands and the Dublin Basin record a complex history of dolomitisation involving multiple fluid sources. At least one regional migration of fluid in both the south Midlands and the Dublin Basin is interpreted based on regional dolomite cement correlation in units as young as Asbian (Supra-Waulsortian). This cement paragenetically predates ost main-stage Zn-Pb mineralisation. O isotope and fluid inclusion data appear to reflect stratigraphic and geographic controls on fluid type. δ18O values for the Sub-Waulsortian are the most negative (-10 PDB) in the Dublin Basin. Waulsortian δ18O values are also most negative (-10 PDB) in the Dublin Basin and in the south Midlands, near the Rathdowney Trend. The δ18O values for the Supra-Waulsortian are the most negative (-10 PDB) from the Rathdowney Trend southeast towards the Leinster granite. If the patterns of the increasing δ18O values reflect cooling along their respective flow paths. Then the distinct patterns noted in each stratigraphic interval require multiple fluids from multiple sources. In contrast, a single fluid and source affecting the entire stratigraphic section should yield a similar pattern throughout. Analysis of fluid inclusion data also suggests that three, chemically and thermally, distinct fluids precipitated dolomite, and those fluids in the Supra-Waulsortian are at slightly higher temperature and are less saline than their counterparts in the Waulsortian and Sub-Waulsortian. The patterns of the δ18O values could reflect other processes besides cooling, such as differences in fluid-rock interaction, or introduction of multiple chemically distinct fluids at different times and loci throughout the diagenetic hydrothermal history. Stable isotopes alone cannot definitively answer questions regarding the localised versus regional flow, or distinguish fluid sources from water-rock reactions. However, using these isotopes and other geochemical data we propose a hybrid model of fluid flow, incorporating both regional as well as localised fluid flow, occurring during the dolomitisation of the Dinantian rocks of Ireland.

Meeting Name

3rd International Conference on Fluid Evolution, Migration and Interaction in Sedimentary Basins and Orogenic Belts (2000: Jul. 12-14, Barcelona, Spain)

Department(s)

Geosciences and Geological and Petroleum Engineering

Keywords and Phrases

Carboniferous; Dolomite; Fluid Flow; Fluid Inclusions; Isotopes; Zn-pb; Dolomitisation; Geographic Controls; Ireland; Kinetic Model; Mineralization; Rock; Granite; Petrology; Stratigraphy; Exploratory Geochemistry; Diagenesis; Water-Rock Interaction

Geographic Coverage

Ireland

International Standard Serial Number (ISSN)

0375-6742

Document Type

Article - Conference proceedings

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2000 Elsevier, All rights reserved.

Publication Date

01 Jun 2000

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