Outcrops, isotopic ages, terranes and the undesirable fate of tectonic interpretations

Abstract

This paper embodies a criticism of the recent proliferation of papers reporting high-quality isotopic ages combined with extremely poor tectonic interpretations resulting from an absence or non-consideration of high-quality geological mapping and ignorance of the basic tenets of tectonics, particularly of the comparative anatomy of mountain ranges. It appears that some geologists began to think that chronology (not even chronostratigraphy) alone is sufficient for understanding the geological history of a region. This seems a result of the mistaken belief that one kind of data can yield the clues to the entire geological history of an area. The kind of data chosen has become a matter of the most recent fashion, a sort of 'methodomania,' not what is required by the geological nature of the region under investigation. The appreciation that geological data are woefully incomplete and inadequate in most cases (even where superb geological maps exist) to generate perfect reconstructions is being lost. This brings with it the grave danger of impoverishing our conceptual repertoire of geological structures and evolutionary paths of tectonic entities such as orogens, taphrogens and keirogens leading to poor interpretations bereft of any sound geological basis.Erde, wie wir sie jetzt vor uns gewahr werden. Auch hier ist eine genetische Betrachtung wünschenswert. Alles, was wir entstanden sehen, und eine Succesion dabei gewahr werden, davon verlangen wir dieses successive Werden einzusehen. So wie die wahre Geschichte über-haupt nicht das Geschehene aufzählt, sondern wie sich das Geschehene auseinander entwickelt und darstellt. (Johann Wolfgang von Goethe) Wenn in der Zeichnung der Welt-und Länderkarten die Landesnatur dargestellt wird, so sollte dieß immer nur mit Bewußtsein der bestimmten Hypothese geschehen, wie dieß Absichtlich von einem Buache, Gatterer, v. Zimmermann, Fr. Schulz, Reichard, und nicht ohne Nutzen für die Wissenschaft, durchgeführt und von Zeune nach allen Seiten beleuchtet ist. Aber durch das in seiner Thätigkeit ohne Bewußtsein, nur blind folgende Heer der Nachahmer geht auch dieser Nutzen wieder verloren, und es tritt statt des Bildes der Natur ein Zerrbild hervor, welches die physikalische Erdkunde eben so als Quelle verwerfen sollte, wie die Physiognomik schon unrichtig gezeichnete Schattenrisse keiner Aufmerksamkeit würdig hält. (Carl Ritter) La rupture entre l'homme et la terre, c'est aussi la rupture entre l'homme et lui-même. (Gustave Thibon) 1

Evolution of the Greater Caucasus Basement and Formation of the Main Caucasus Thrust, Georgia

“…The ages of ~230‐190 Ma observed along the MCT in Kazbegi correspond with similar ages observed along sutures in East Asia and Iran (e.g., Kapp et al, ; Mirnejad et al, ; Pullen et al, ) typically associated with accretion of the Cimmerian continental ribbon on the margin of Laurasia (Metcalfe, ; Şengör, ). Although Triassic‐Jurassic deformation and accretionary complexes have been identified in Turkey, debate persists regarding whether Cimmerian collision extended as far west as the Caucasus or whether such deformation reflects subduction accretion beyond the western edge of the Cimmerian fragment (Şengör, ; Topuz et al, ; Topuz et al, ), which has only been confidently traced as far west as northern Iran (e.g., Alavi, ; Natal'in & Şengör, ; Zanchetta et al, ). In this study, we do not observe any clear evidence in the Caucasus region for Triassic‐Jurassic accretion of the Cimmerian ribbon, which if present would lie to the south of the crystalline massifs in the Lesser Caucasus, given the likely shared Carboniferous accretion of both the Greater Caucasus core and Lesser Caucasus massifs to Laurussia.…”

A Preliminary Framework for Magmatism in Modern Continental Back‐Arc Basins and Its Application to the Triassic‐Jurassic Tectonic Evolution of the Caucasus

“…Such correlations are based upon two lines of evidence: similar Paleozoic magmatic/metamorphic histories in crystalline rocks of the Lesser Caucasus and Pontides (e.g., Okay & Topuz, 2016;Rolland et al, 2016) and similar Jurassic-Cretaceous stratigraphic sections (e.g., Yilmaz et al, 2000). Many aspects of the Triassic-Jurassic evolution of the Pontides remain subjects of debate beyond the scope of this study, including whether Triassic deformation is best explained by continental collision or seamount accretion (e.g., Şengör, 2013;Topuz et al, 2013) and whether Triassic-Jurassic subduction beneath the Pontides was north-directed, south-directed, or both (e.g., van Hinsbergen et al, 2020). However, a key difference between the Lesser Caucasus and Pontides is the lack of Late Triassic accretionary complexes and coeval high-pressure/low-temperature metamorphism in the Lesser Caucasus, which are well-documented in the Pontides (e.g., Okay, 2000;Okay et al, 2002Okay et al, , 2006Topuz et al, 2014).…”

“…Debate persists in the western Tethyan realm regarding the presence of the Cimmerian continental ribbon and Paleotethyan suture west of Iran (e.g., Şengör, 2013; Topuz et al., 2013). In our model, there is no Triassic‐Jurassic Cimmerian collision/Paleotethyan suture in the Caucasus and thus locally no distinction between Paleotethyan and Neotethyan subduction (Figure 8).…”