Dear All,
I am looking to find out the optimum point of some factor in regard to the geochemical study of ophiolitic rocks, especially pillow basalts, to detect whether it is an E-, N-MORB, or IOB basalt, including:
- The optimum number of samples for a reliable test
- The distance between sampling locations and samples in each location
Generally, I am looking for a standard method for studying the origin of an ophiolite, even if the isotop geochemistry is required. It would be appreciated if expertise can help me with this question.
The sample spacing can easily be defined after a careful geological and petrological mapping. If you come to the conclusion that the rock suite is rather honogeneous you can expand the distance between the sampling sites vice versa you may be forced to reduce the distance. There is no rule of thumbs. It is also the scope of your study that matters. For an overview the spacing can be wider for a rock-chip program coming close to what might be called mineral exploration , random sampling would be a no-go and shorter distances a must. It also depends on the tectonic/geodynamic situation. Is it a complete ophiolite suite or a dis-membered one caused by strong tectonics?
HGD
Hi Mr. Rojhani,
For study about rock genesis, I would suggest to take at the least one sampling point for each lithological unit. However, if you found variations within the same lithological unit, it's better to sample each variation.
Lithological unit/variation is more important than dimension/distance between sampling point.
For each sample, you will need to take two hand-sized speciment, one for microscopic observation (thin section + polished section if needed), one for chemical analysis (XRF, ICP-MS, stable isotope).
Dear Saefudin Juhri
Thanks for your reply and for sharing your information.
Best regatds,
Harald G. Dill
Dear Harald G. Dill,
Thanks for your answer. The pillow basalts associated with pelagic sediments have been mapped as basic volcanic (continental), and crop out only on a limited area, 6*3 km, faulted against younger turbidites and covered by Cretaceous carbonate and siliciclastics. What I want to perform now is an examination that to what extent they are related to the other ophiolitic bodies in the same suture.
Best regards,
Sample all variations at your study area, samples need to be homogenous. Do not mix different samples. Heterogenous samples are not recommended to be samples. You can also sample at a large area if the rocks are same or if you dont see the variation. You can sample at a small area as long as the rocks keeping changing... Best
Mzee Nyirongo
Dear Miss/Mr Mzee nyirongo,
Thanks for your information and reply. Another question comes after this guide:
What about a single coherent ophiolitic body? In case, ICP-MS is statistics, what is the least number of required samples for a coherent cropped out ophiolitic basalts/peridotite, to make a meaningful interpretation? Is, then, 5 samples enough for example?
Best regards,
Emad
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