I am currently looking for parameters to know if 87Sr/86Sr data is reliable for chemostratigrahy in marbles, and/or parameters to know if those marbles have had some post-depositional modifications.
I have found some articles that have unaltered ratio ranges, as
Bartley et al. (2001), Brand and Veizer (1980), and Kah et al. (1999, 2001).
Does anyone know any other articles that assess this problem?
Dear Elisa,
One has to be careful using isotopic ratios to interpret geological history. The term marble is generally used for metamorphosed limestones. Perhaps you are unaware about the process Isochron Translation which modifies isotopic composition during isotopic resetting associated with metamorphism. You are invited to read my paper "Isochron Translation and a Geological Criterion to Declare an Isochron" which could be useful to you to understand how isotopic compositions of your rocks may have changed.
LRK Perera
L. R. K. Perera, thank you! I will certainly read your paper.
Dear Mrs. Oliveira da Costa,
the term chemostratigraphy in context with Sr isotopes should only be used for un-metamorphosed calcareous sediments. In this situation for some parts of the geological record it makes sense, whereas for others in makes not sense for overlaps.
DILL, H.G. and HENJES-KUNST, F. (2007) Strontium (87Sr/ 86Sr) - and calcium (44Ca/ 40Ca -44Ca/ 42Ca) isotope ratios of the Miocene Dam Formation in Qatar: Tools for stratigraphic correlation and environment analysis.- GeoArabia, 12: 61-76.
Under metamorphic conditions even at low grade stage you cannot be sure whether some alteration of the isotope ratio has been taken place or not. Whenever (metamorphic) mobilisation occurs and is reflected in the structure you must take into consideration an alteration of the original isotope ratio so that chemostratigraphy is not recommended to be conducted.
H.G.Dill
The following author/paper has used this method combined with other chemistry to filter out samples with compositions which are inferred as being unaffected. It fundamentally relies initially on selecting pure carbonate samples with no metamorphic silicate minerals, the formation of which contributes to altered isotopic signatures by reaction.
Chemostratigraphy as a Tool for Determining Depositional Ages of Metamorphosed Carbonate Rocks Prior to Supercontinent Formation
- April 2015
- Journal of the Indian Institute of Science 95(2)
- 📷M. Satish-Kumar
Geoff Grantham, thank you very much. It seems exactly what I was looking for.
Dear Mrs. Da Costa,
marble is rarely a stand-alone lithology but alternates with other calcareous metasediments such as calsilicates and/ or para-amphibolites. Even minerals indicative of evaporitic parent rocks such a scapolite-bearing calcsiilicates may occur. Have you already drafted such a lithostraphic column and used prior to the isotope studies the wide range of trace elements relevant for calcareous depositional environments. You can distil a lot out of these chemical values in combination with the metamorphic host minerals.
H.G.Dill
Dear Harald G. Dill
First, thank you for helping me.
The marbles I am concerned about are indeed in a metamorphic complex that has several lithologies. However, multiple deformation phases probably make impossible to reconstruct a lithostratigraphic column. To be more precise, I am not studying the marbles of the complex, but the metapelites and some acid metavulcanics. I made this question because previous works done in the marbles use isotopes in order to constrain the depositional age of them, and since those works obtained different depositional ages I was hoping to find parameters to know which of those works got more reliable results.
Elisa da Costa
Dear Mrs. Da Costa,
I wrote two papers which are available for download and which deal with chemical facies analyses of metamorphic rocks (HT medium to high-grade) in context with metamorphic mobilization. Maybe you can find some hints for your own studies.
DILL, H.G. (2019) Coupling restites and mobilizates – Geological and litho-chemical investigations of paired belts of calcsilicate fels and quartzite (SE German Basement) - Quo vadis David London´s pegmatology ?.- Ore Geology Reviews 105: 636-662.
DILL, H.G. (2018) Geology and chemistry of Variscan-type pegmatite systems (SE Germany) - With special reference to structural and chemical pattern recognition of felsic mobile components in the crust.- Ore Geology Reviews 92: 205-239.
DILL, H.G. and KOLB, J. (2019) Carbonate-related metallic and non-metallic mineralization within and proximal to granites (Fichtelgebirge Pluton, Germany): “Mantle-crust marker mineralization”.- Ore Geology Reviews 104: 46-71.
With kind regards
H.G.Dill
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