see attached

The manuscripts aims at presenting a workflow for detrital rutile provenance studies, based on U-Pb LA dating and trace elemental analysis.

Rutile geochemical data and LA U-Pb data are presented for reference materials (with R-10 rutile used as primary) and detrital samples from Anatolia as the case study to validate the workflow. Testing different common Pb correction approaches is one of the aims of the study.

Starting from the introduction, the authors seem unaware that rutile is an established provenance proxy. If U-Pb dating of detrital rutile was not a widespread technique until perhaps 10-15 year ago (particularly by laser ablation, primarily due to the lack of available reference materials at the time), it is nowadays established and routinely applied in combination with bulk and other single grain methods.

I have identified several issues regarding the U-Pb rutile data, summarised as follows (see detailed comments in the annotated manuscript):

- the data handling of the reference materials (unreported scatter in the measured and corrected isotopic ratios of the reference materials, inconsistency between uncertainties before and after the correction, lack of representation of the data as Concordia diagrams)

- the sample dataset which should serve as the case study to validate the workflow (rejection of >50% of the initial analysis due to “anomalous spiky patterns”, followed by further rejections due to large 7/6 uncertainty, leaving with only 30% of the initial data, with no possibility to carry out provenance interpretation at the sample level due to too small n per sample; last but not least vast majority of these remaining data being largely discordant despite the different common Pb correction approached used

- attempted provenance analysis based on such a largely discordant dataset, with age modes identified in the KDEs distributions of up to 60% discordant data and unsupported claim that the KDEs distributions of variably discordant data are similar hence meaningful, and can be used to constrain provenance

All the above cannot be taken as an example for best practice and certainly not recommended as a part of a workflow to be followed by others. Therefore I am afraid I cannot recommend the publication of the manuscript in its current form.

The large amount of work and effort behind the manuscript is appreciated (analytical work, data handling, care in drafting a range of informative figures), however the LA U-Pb sample dataset is affected by problems likely starting with the analytical set-up hence cannot serve as a case study, nor can the discordant data support any provenance interpretation.

I would suggest to either: i) reconsider the LA U-Pb analytical protocol and data handling/uncertainty propagation before repeating LA U-Pb dating on the same samples to integrate the existing geochemical data (which I have not reviewed in detail); ii) select a different set of samples to validate the workflow.

In any case the manuscript requires substantial restructuring and rewriting, hence a new submission is recommended.

Kind regards,

Laura Bracciali

I was asked to review the manuscript entitled “An expanded workflow for detrital rutile provenance studies: An application from the Neotethys Orogen in Anatolia” by Mueller et al., where the authors have tackled the issues related with detrital rutile provenance, mainly those arising from U-Pb dating, to provide a new workflow to be more widely applied by others. They further explore their data in view of the Neotethys orogen in Anatolia.

Objectively, I think the manuscript is interesting, mostly well-written and logic, overall, with good figures, but does not bring elements of novelty concerning rutile U-Pb geochronology. The authors have a biased starting point: “most people apply a U threshold before U-Pb rutile dating”. It is true that some authors have done it, but digging in the literature, it is not that frequent anymore. Some may do it, to avoid having to deal with very complicated datasets, where very little Pb is radiogenic, but most analyse all grains up to about 150 grains per sample, give or take. Then, that may discard some data.

I liked how detailed the authors present their common-Pb corrections, which is useful to the community. But again, this is not expanding a workflow, it is mostly literature review applied to a dataset and explored a bit further. 

My main concern related to U-Pb data acquisition/treatment came from the rather large number of discarded rutile grains, due to inclusions, lamellae, etc. In the end, they discarded many rutile grains. How did it affect or biased the final dataset? In these circumstances, how robust is it to average all samples and plot them together, especially in a dynamic sedimentary environment? What about source variability through time weighted on each of your sample populations (n)? Figure A3 is clear in illustrating the issue here.

The geochemistry is used, but PCA is not really adding anything new or rather interesting. I do not see the purpose of keeping it in its current form. I am afraid that by stating strongly very early on that you would be "expanding the workflow" of rutile in provenance studies, but then not combining it well with TE systematics is misleading.     

My suggestion, if you will, is that you make a full twist and turn of your manuscript. Place the focus on using detrital rutile in reconstructing convergent margin evolution, using Anatolia and your sample set. I recommend you acquire more data (more grains) to overcome the reduced number of dates you have from each individual sample. Focus first on your case study, then move on into the rutile dating challenges affecting provenance, and how your approach can enhance the level of information we obtain from U-Pb rutile dating and from convergent settings. This requires major rewriting, but you can reuse most of your very nice figures. Unfortunately, I do not recommend publication in its current form, but you should feel encouraged to a re-submission.  

I added a few more comments below, summarising parts of my assessment, and more detailed comments can be found in the annotated .pdf file.

Section 2.1.

Provenance: Don’t place all the focus on Nb-Cr and Zr thermometry. You can be more concise in your sentences and ideas, and then you could highlight how other more recent tools can be effectively used in provenance studies (see my comments in the pdf). I also find that this subsection’s title is not suitable. You should re-think better how 2.1 related to the other subsection under section 2 and propose an improved structure and matching headings. You have provenance in 2, and then a “synopsis”, followed by “challenges” that actually just relate to U-Pb. So, in my view you are emphasising the application of detrital rutile geochronology as a provenance tool. This is fine, but the subheadings need to clarify this.

Sections 2.3.1 and 2.3.2

You should provide at least a short review on the ²⁰⁴Pb-based correction of common Pb. You can discuss why it is sometimes very difficult to apply it, but omitting it is not satisfactory in a paper meant to cover common Pb corrections.

I suggest you include a figure with two panels, in one showing a common Pb-bearing analysis and the corresponding corrected age using the ²⁰⁸Pb correction and in the second the 207. These can the theoretical if you will, but you can add arrows and annotations illustrating the assumptions.

Section 6.2. Careful with rushing into conclusions. While it may be true that in your dataset your U<4ppm is vastly metamafic, this does not necessarily imply lower T. For a robust assessment of lower Ts, you need to rely on your metapelitic detrital grains. Rephrase.

Section 6.3

If you are not exploring your data further, I would remove it, as it is not bringing anything really new, and it does not add to any relevant information to your main objective. Since they are detrital grains, I would have difficulty to saying much more.

If you decide to follow my suggestion of major rewriting, you could do a bit more work on detrital rutile trace element geochemistry, try to interpret their chemistries a bit more, and then it would be fine to use the PCA as a starting point of such a subsection.

I hope you find my assessment fair, even if against your best expectations, and consider my comments as a means to improve your current work.

Best wishes, 

Inês