Dear Sukunta,

Not all A-type granites are continental, therefore I would not want to endorse your statement that their formation is linked to ''attainment of stability and sufficient rigidity of the continental crust". Those classifying as A2 type on Nb-Y-Ga and Nb-Y-Ce diagrams include granitoids formed in different tectonic environments (Abey, 1992).

But coming to your basic question, I do not know the oldest granitoid that has been considered as A-Type.

Thanks Prof. Jan for your comment. I agree with you and modified the statement.

Dear Sukanta,

I found a reference for you, describing 3.30 Ga old A2-type granites-rhyolites from Brazil.

Zincone et al., 2016. Lithos 266, 414-434.

Cheers!!

Thanks Prof. Jan.

Now waiting for other's response.

If was aware about. It seems that you have enough knowledge, Your polite comportment its reflect well...

I think we do not know to give such a response: which you do not aware it.

If you practice an examination procedure, its better to do with your students

Dear Mr. Horvath,

I was aware of the Zincone et al. paper, but did not know that the granite reported by them is the oldest A-type granite of the world. I thank Prof. Jan again for pointing out this fact.

Best.

Sukanta

Please note that I only provided a reference to an Archean A-type granitoid association. I am not sure if it is the oldest reported.

Seeking the oldest A-type granites, that is anorogenic, and anhydrous is interesting, as the oldest Archean granitoids are TTGs, which are regarded as the oldest generated crust, though the issue is debated for subduction-related (crust generation) vs intracontinental preservation. The oldest material on the earth is the Jack Hills zircons disseminated in some sedimentary rocks, presumably the crust which recycled back into mantle. So most of the Archean, perhaps was orogenic period, with four or five major crust generation episodes.

To me, most of the Archean granitization is related to the subduction related, only place where abundant water was available, post-orogenic extension-related granites, as if in Archean would be scarce, if not absent

Thanks Dr. Ali Mahar for your response.

In the Neoprotrozoic Nubian Shield of Egypt, The A2 appear to be oldest than A1 as indicated by the current studies by me on A-type granites from the Eastern Desert of Egypt.

A1-granite in Egypt is related to major structures that crosscut the African plate.

It is easily recognizable by mineral properties and petrographic study as well as chemical analyzes. Generally, It is one of the most important rocks due to it contains high concentrations of rare metal deposits. Its estimated age is Triassic or above.

.

Dear Sukanta

In the Amazonian craton, Carajás Province, there are important occurrences of A2-type granitoides ages between 1.9 to 1.8 Ga (see Dall' Agnoll et al., 2004, 2005, 2007). In the archean of this same province, there are A2-type granitoids with ages 2.76-2.73 Ga (see Feio and Dall'Agnol, 2012; Dall'Agnol et all., 2017). To the south, Juruena and Tapajos provinces, A2-type granitoids ages 1.88-1.76 Ga and 1.6-1.10 Ga in Rondônia state (Scandolara et al., 2013).

Regards,

Jaime Scandolara