is it precambrian

I am asking, not proposing. Some people suggest it is an intrusion of Tertiary age!

Early Miocene, when evaporation was high, sea level dropping.

Precambrian sir

Shahzaib; The generation of trap should not be controlled by sea level changes. Volcanism is much more deeply seated.

Ihtisham, Eocambrian has been proposed by most authors for the trap.

My question is searching for field evidence, that is 1) are there any studies, apart from those of SH Faruqi, that suggest that the Khewra Trap is an intrusion rather than a flow, and 2) if it is an intrusion, what are the youngest rocks that it intrudes.

Thank you, James, for useful suggestion of trying radiometric dates. 

The rock is not tholeiite. It is ultrapotassic (lamproitic), but one can always hope to have some zircon for dating. The young age, i.e., Tertiary, was suggested by only one author and I think he did not specify the age.

Qasim,

I would be very much interested to date the zircos, apatitie etc by LA-ICP-MS. Do you have mineral separate?  Or just send the rock we will include them in my next analytical session

That will be great, Munazzam.

I do not have separated minerals, but can send a couple of samples. By the way, how long will it take you to do the analyses after you have the samples? Please do not think I am rushing you. The issue is that I have XRF analyses, EPMA data and petrography ready to send to a journal. But I can wait for a reasonable length of time to incorporate your data and, of course, you as an author in the paper.

Cheers,

Qasim

Mineral separation will take some time, also, I need to schadule for a lab time at Arizona yet.  It will not take less than 3-4 months as Arizona lab is too busy. How many samples you want to analyse? I think three or four samples would be good.

Let me talk with lab manager if I could sneek in these samples earlier in someone else's session.

Qasim Jan saheb, 

     As you know I am a man of soft rocks. However, while describing the Neoproterozoic Salt Range Formation (SRF) in my book (under printing), I sifted through the literature to deal with the so called ‘Khewra Trap’, as well. I was looking for a kind of petrological description as yours, wow! Most of the authors have referred to Mosebach (1956), who probably did not deal with the age, and described it as an effusive rock. But as I understand the Trap is a hypabyssal emplacement, may be at a shallower depth. He suggested the name “Khewrite”, which is a better term as there is a formation by the name of  Khewra Sandstone. I do not have the paper. 

     On a different note, the following information may be of interest to you, and others. A deep exploratory well drilled in the southeastern corner of Pakistan drilled two mafic sills below a depth of 3600 m. The shallower one is a massive emplacement of several sills in clastic host rock with a net thickness of more than 50 m. The deeper one is of much less thickness. Their K–Ar ages are 250 +/-6 Ma, and 222+/- 3 Ma, respectively. These emplacements are of Hawaiite theme, as mentioned in the well report. The igneous intrusions are probably related to the rift–drift phase of the Indian Plate at a very early stage. Dr. Fuzail Siddiqui has shown a great interest in that, and I am in the process to get the permission to study the samples stored in the Petroleum Ministry archives. So, K–Ar method would be a useful tool for dating the Trap. 

     Hitherto, only two igneous episodes have been reported in the sedimentary sequences of the Indus Basin (south of the Khairabad–Punjal Thrust), as under: 

     1. Khaskheli basaltic intermittent flows across Maastrichtian–Danian, supported by the fossil assemblage in the host rock. The K–Pg boundary falls within.

     2. Khewrite’s (Khewra Trap) random emplacements near the top of SRF. The wells drilled in eastern Potwar, and had penetrated SRF, do not report the presence of igneous minerals. The age is not known so far; waiting for your findings! 

     3. The massive mafic sills of mainly Triassic age drilled in the exploratory well, as mentioned above. However, I have interpreted that the region is not part of the Indus Basin. Will be presenting a paper, on the subject, in the PAPG–SPE Technical Conference in Islamabad to be held in October.

Thank you Nusrat, for your detailed response. I and SH Faruqi published petrographic and geochemical account of the Khewra trap in1995 and the summary I gave here is from that (the paper is available on ResearchGate). I also published a refined extended abstract in HKT workshop held in Germany over two years ago. Mosbach paper was published in Neues Jb Min Abh in 1956. Martin published a brief account on the trap in 1965 (GSP Rec 8(2)). Both these papers are commented upon in our paper, but I can send you the hard copies.

Your report of the alkaline (hawaiite) sills is interesting but may not be related to the Salt Range trap. Southeastern corner of Pakistan takes us towards Nagar Parkar which contains alkali olivine basalt dykes in Neoproterozoic granite. I assume that these basaltic dykes are also Neoproterozoic. I would be a little restrained in considering the K-Ar dates as magmatic; they may well be cooling dates and younger than the age of formation. The northwestern edge of the Iniian plate (present day northern Pakistan and Kashmir) does have Late Paleozoic-Triassic magmatism (Panjal traps, mafic dykes, and alkaline complexes) that I and Karim (1990) related to rifting (paper available on ResearchGate). However, we did not consider the rifting to have stretched that far south or, for that matter, to have a N-S trend.

I would like to attend the PAPG-SPE conference and listen to what you say if I am in Pakistan on those days.

Regards,

Qasim

Thank you Qasim Jan Saheb,

So, if we consider that the N-S rifting stretch is not expected then what could be the genesis for such a massive magmatic intrusion, and at two different times. Regarding the K-Ar dating, the age difference of magma emplacement and the eventual cooling is too small in terms of geological time. Can't we take it as the closest possible date?

Some details available with me for Kashmir volcanics/subvolcanics are as under:

The  subvolcanics emplaced in sedimentary rocks are also reported from Kashmir and Zanskar-Spiti region, which are sandwiched between the Nilawahan Group and the overlying Zaluch Group; these subvolcanics  are confined to Kungurian to Midian (275 Ma and younger) Stages (Bhargava, 2008). However, the Marvi mafic sill in Pakistan, was intruded at the base of Permian.. Regarding Panjal volcanics Bhargava (2015) mentions “…a  Kungurian Stage to Middle Permian age was assigned to the Panjal Volcanic by Bhargava (2008), which now has been confirmed by radiometric date of ca 289 ± 3 Ma (Shellnutt et al., 2011).”  

Will check about your papers on RG.

I have the geochemistry and petrology done, but have been lazy to submit the paper. Perhaps in mid-December when I am free from a terrible routine continuing for nearly three months.

Thanks for your interest.

Qasim

Dear Prof Qasim Jan, Nusrat K Siddiqui and Munazzam Mehar,

My PhD work related to the spatio-temporal evolution of Kohat Potwar fold-thrust belts of Pakistan, I have collected samples from the entire Salt Range (Khewra, Karoli, Pail, Sakesar, Nammal, Zaluch, and Daud Khail sections) and Kohat. I used Apatite Helium and Fission track dating methods to document cooling ages. Interestingly Precambrian Samples gave similar AFT ages like Permain Samples around between 200-250 Ma. The ages are obviously partially reset but having similar ages was not expected. We conducted extensive thermal modeling of data and every model showed a cooling event in Late Paleozoic. We concluded that the Late Paleozoic rifting event reported In Kashmir, Zanskar and Peshawar effected the Salt Range. In my opinion, the trap is most probably related to Late Paleozoic rifting episode considering similar age magmatism in Kashmir.

I collected a small Khewra trap sample that is still sitting at my desk, It was not tempting to be tried for apatite. If Munazzam is interested i could try to separate zircons that will be no more than 3 days job, I would be free to do in December. The paper is in the final phase of review in Terra Nova, we are expecting a reply this week. If positive I will send you a copy. However, my thesis will be available online soon as I am defending thesis on 20th November.

Hammad Ghani, this is a good information. Thank you.

I am about to submit a paper on the petrography, and major and trace element geochemistry of the Khewra trap. I would be interested in quoting your tentative age. With discovery of Permian dykes in the Nagar Parkar (see our paper, Rehman et al, 2019, Island Arc) I am also tempted to the idea of Permian. SH Faruqui had long ago advocated a much younger than Eoccambrian age for the trap.

I would like to have more communication with you on the samples you collected. Where are you based currently? Can I have your e-mail? Mine is

Best, Qasim

Dear Prof Qasim Jan

I read your paper recently shared by prof Hafeez, so kind of him. It is very interesting to note important Permian events occurring in "southern" India. I am at Potsdam now will be visiting Pakistan in mid-January. Did you read Hughes 2019 paper? they published U-Pb ages from Cambrian strata of the Salt Range and linked source to sink relationship.

Sure we can discuss further. My email id is [email protected]

Thank you for the prompt answer.

I am away from library and Islamabad is shut. If it is not much of a bother, can you please send me the paper of Hughs?

Best

Humaad Ghani. The post popped-up after a long time. Can you share the summarized findings of your thesis. Regards.

My email.

[email protected]