3-Discussion
In the following paragraphs, the two contrasting views proposed on the
nature of the eastern Anatolian crust are discussed based on geological,
geophysical, and geochemical data;
1-an ophiolitic mélange-accretionary complex forms the basement, which
was developed during the demise of the Neo-Tethyan Ocean. Later, it was
trapped between the approaching continents (Fig 6A) (Şengör and Kidd
1979; Şengör et al. 2008).
2- The entire eastern Anatolia is underlain by an old and thick
continental crust (Fig 6 B) (Topuz et al., 2017).
Both views listed above were based on inconclusive evidence. The
following critical data set are needed to provide verifications for the
two hypotheses:
a-detailed geological data to examine the applicability of the view on
the regional scale, including comparative data to correlate the eastern
Anatolian geology with the neighboring tectonic belts (i.e., with the
Southeastern Anatolian Orogenic Belt to the south and the Pontide Belt
to the north to provide evidence how each hypothesis fits with the
geology and tectonic evolution of the neighboring regions in a
time-space reference.
b-geophysical data, particularly seismic data, to enlighten the nature
of the basement.
The hypothesis proposed by Topuz et al. (2017), is based on the
observations basically from two metamorphic rock inliers in eastern
Anatolia (Fig 2) and the following interpretations; on the SE Anatolia
and Pontide
1- ‘’Metagranite obtained from the metamorphic rock outcrops have a Late
Ordovician–Early Silurian protolith and were therefore connected with
the Menderes Massif of western Anatolia, which displays a similar
protolith”.
The old metamorphic minerals obtained from eastern Anatolia’s
metamorphic inliers are expected to be similar to those obtained from
the Menderes Massif because the metamorphic massifs of Western, Central,
and SE Anatolian orogenic belts share the Pan African-Gondwanan origin
(Şengör and Yılmaz 1981).
2- ‘’Multiple continental fragments separated by oceanic accretionary
complexes are absent in eastern Anatolia”.
This interpretation dismisses the essential characteristics of the
Anatolian orogen, including the eastern Turkey where the orogen was
developed by accretions of small continental fragments following the
closure of the separating oceans (Şengör and Yılmaz 1981; Yılmaz and
Şengör,1985; Dercourt et al. 1986; Dilek, 2006; Robertson et al. 2012;
Barrier et al. 2018; McNab et al. 2018). Regional heating generated
during the plate reorganization is stated to have caused major obduction
of these ophiolites (Hassig et al. 2013, 2016 a, b; Roland 2020).
3- ‘’the metamorphic mineral assemblages that crop out in the
metamorphic rocks of the region, display medium to high T metamorphisms,
but not high-pressure metamorphism”.
This interpretation disregards the critical geological data obtained
from the neighboring orogenic belts (see the two accompanying papers in
this volume on the Pontide and SE Anatolian orogenic belts by Yılmaz et
al.). Particularly the recent studies on the SE Anatolian metamorphic
massifs indicate that the ophiolitic rocks and the Bitlis Massif
underwent an initial HP metamorphism, followed by an HT metamorphic
phase during the Late Cretaceous-Early Eocene period (Roland et al.
2012; Oberhansli et al. 2012; 2014; Pourteau et al. 2013; Awalt and
Whitney 2018; Yılmaz 2019). The Bitlis Massif, a fragment of continental
crust involved in northward subduction together with the oceanic
lithosphere (the Berit metaophiolite; Yılmaz 2019) under the Eastern
Anatolia where, they were buried down to 35-65 km at depths (Oberhansli
et al., 2014). Their exhumation occurred mainly during the Early Eocene
period (Roland et al., 2012; Oberhansli et al., 2014; Yılmaz, 2019). A
transgressive sequence was deposited above the elevated metamorphic
massifs during the Middle Eocene (Yiğitbaş 1989; Yiğitbaş and Yılmaz
1996; Yılmaz 1993; Yılmaz 2019). The metamorphic massifs were then
thrust over the ophiolitic mélange during the Late Eocene before they
were tectonically emplaced as a giant nappe package onto the Arabian
Plate in the Late Miocene (Yılmaz 2019). Consequently, the southeast
Anatolian metamorphic massifs represent allochthonous belts (Fig 7B)
resting tectonically on the Late Cretaceous-Middle Eocene metamorphic
ophiolites (the Kızılkaya Metamorphics and the Berit Metaophiolite), and
non-metamorphic ophiolites (The Göksun Ophiolite) and an accretionary
complex (Fig 7B) extending from the eastern Anatolia (Fig 7A). Tens of
kilometers of the nappe transport of the metamorphic massifs may be
estimated from the Muş region in the North to the Sason region in the
South (Figs 7A and B) (Yılmaz 2019 and the references therein).