Dear authors,

Thank you for your responses to the reviewer’s (R#) comments. At this time, I would like to invite you to submit a revised manuscript (moderate revisions to undergo further review by editor and further comment by R2 and R4). In addition to the specific changes you have detailed in your responses, I would encourage you to consider the following:

- See comments made by R1, R3 and R4. Expand the discussion/comparison of the Keller and Bacon approach for modelling age data in the context of volcanic terrains.

- Comments R1 & R3. Inter-chronometer comparison can be complex owing to systematic uncertainties but there are many cases in the literature where Ar/Ar and U-Pb ages are consistent in dating the same eruptive events (including optimisation model approach). Your response to R1 alludes to the fact that the optimisation approach is the only set of parameters that provides quantitative uncertainty estimates and addresses the 40K decay constant and at the moment there is lack of agreement in the Ar/Ar community about the best parameters to use for age calculation. However, this does not preclude discussion of the potential differences between the Ar/Ar and U-Pb data in the current case study, see below.

- Given the reviewer appetite for further discussion, the disagreement between the Deccan Trap Ar/Ar and U-Pb datasets actually provides the ideal opportunity (upper Ambenali) for you to frame discussion of potential issues with the geology of the region (R3), as well as discussion of systematic uncertainties in the Ar/Ar system (R1, R2, R3, R4) and also potential for inaccuracies in the approach of using zircon from red boles to constrain the age of over- and under-lying lava flows (R3). I agree with much of your response to R3 concerning your approach and such a discussion will be direct benefit to the readers of this work. But ultimately, all things equal, you cannot escape the fact that if you want to know about the timing of lava flow emplacement, then dating the basalt is the logical/simplest approach. This comment aligns with the wise words of R2 about adopting multi-chronometer approaches to resolving the distribution of time in such geological settings – even though the precision of the Ar/Ar plagioclase technique may not approach that of the U-Pb zircon in this case study, it does not mean there is not valuable information to be gleaned from the Ar/Ar data. As R3 highlights and your response acknowledges, both data sets measure very different things and made very different assumptions.

- Discussion of the Ar/Ar systematics/technique requires careful consideration concerning the accuracy of comments/assertions made (e.g., R1) about the use of multi-grains aliquots of plagioclase. Although there is discussion of age variation within sanidines found in, for example, Mesa Falls Tuff (Ellis et al., 2017) or Bishop Tuff (Mark et al., 2017; Andersen et al., 2017), these explosive eruptions vary from the lava flows associated with the Deccan Traps and the plagioclase recovered from the lava rather than an explosive deposit. Similarly, the comments made by R2 concerning the utilisation and difficulty of plagioclase for Ar/Ar geochronology are correct. However, absolutely the use of more modern mass spectrometers (R1) that allow for improved measurements of minor isotopes (e.g., 36Ar) or low-K samples would allow for improved analytical precision. Such measurements however do not address the systematic uncertainties associated with the technique, see discussion above.

- I completely agree revision of the manuscript to honour the original intent of Dr Sprain is appropriate, as is adoption of a constructive approach/tone towards building better models for eruption rates of the Deccan Traps. The fact that results agree significantly more than they disagree is the big take home message here. This should absolutely be emphasised further in the revised manuscript. Taking the opportunity to clarify use of ‘eruptive flux’ by Sprain et al. can only serve the community in a positive way.

I appreciate that some of the changes suggested will indeed change the scope of this contribution but three of the reviewers have advocated for this. In addition, I completely agree with your comment concerning student uptake and I have found that in my reading of this manuscript with students’ clarity concerning the differences in the geochronological approaches against a backdrop of cutting-edge measurements and discussion of complexity in local geology, is highly desirable.

I look forward to receiving your revised manuscript and thank you for submitting to Geochronology.

Darren Mark
14th October 2020

Apologies for the delay in coming back to you with the current manuscript. Courtney Sprain has spent considerable time reviewing the revised manuscript and I would ask that you respond to the minor issues she has raised. I would pay particular attention to the few places that it is suggested wrong information is provided and carefully consider the arguments presented about the use of multi-aliquot plagioclase. For sure, the main limitation here is the amount fo K with respect to the Ar/Ar dating system. I look forward to progressing the manuscript following this round of revisions. DM

I am happy with all edits etc. and the document can proceed to publication.

Dear Blair
your paper is now in good shape and ready for publication. However Figs 3 and 6 are low resolution and very hard to read. Can you be so kind and resubmit high-res versions of these figures
Kind regards
KLaus