Saint Mark’s Monastery, Jerusalem, № 169 mostly contains homilies in Garšūnī, but at the beginning (ff. 4v-8r) there is an excerpt, in Syriac, from the Chronicle of Michael the Great, book 11 of chapter 20, on the Council of Manazkert (or Manzikert; see here for other forms of the name) convened in 726 by Catholicos Yovhannēs Ōjnec’i the Philosopher with Syriac Orthodox Patriarch Athanasios III. The title is “On the Unity Effected by Patriarch Athanasios and Catholicos John of the Armenians against the Heresy of Maximos that has Spread Abroad, and the Negation of the Phrase ‘Who was crucified for us.'” Neither Michael nor the title Chronicle are specifically mentioned here, however. This manuscript was copied outside of Amid/Diyarbakır; the date in the colophon seems to be 1092 AG, which is certainly wrong and probably a mistake for 2092 AG, so May 1781.
My friend and colleague, Ed Mathews, in his Armenian Commentary on Genesis attributed to Ephrem the Syrian, CSCO 573, (Louvain, 1998), pp. xlvii-xlviii, briefly discusses this council as follows:
It is fairly well known that a council of Manazkert, referred to by a number of historians, was convened in 726, by the great Armenian Kat‘ołikos Yovhannēs Ōjnec‘i, also known as the Philosopher (Arm., իմաստասէր) in order to quiet this dispute and come to some sort of union with the Syrian Church. This council was attended by a number of Armenian bishops and six Syrian bishops to try to effect a union between the two churches, and particularly, to find some common ground whereby each might suppress the more radical branch of Monophysitism as practiced by followers of Julian of Halicarnassus, who maintained the incorruptibility of the body of Christ. The Armenian historians, Step‘annos Asołik, Samuēl Anec‘i, Step‘annos Ōrbelian, and Kirakos Ganiakec‘i do little more than mention the council at all and, like the other historians just mentioned, seems far more interested in the personal appearance of Ōjnec‘i, being enthralled with his elaborate garments and even more with his gold-speckled beard. Clearly then, this council left no real lasting impression in the Armenian church.
As for Syriac sources on this council, as Mathews points out, Barhebraeus’ subsequent account (Chron. Eccl. 1.299-304) is based on that in Michael’s Chronicle, and there is also Dionysius b. Ṣalibi’s Against the Armenians. The bishop of Ḥarrān, Symeon of the Olives, associated with the Monastery of Mor Gabriel, attended the Council (cf. Brock “Fenqitho of the Monastery of Mor Gabriel in Tur ‘Abdin,” Ostkirchliche Studien 28 (1979): 168-182, here 177).
On the name of the place itself, Մանազկերտ, see Hübschmann, Die altarmenische Ortsnamen, 328, 330, 449-450, and Toumanoff, Studies in Christian Caucasian History, p. 218, n. 253, who points to the name of the Urartian king Menua as the source of the place-name. We may also note the important battle fought there in 1071, with the Byzantine army defeated by the Seljuks.