Neotectonic mountain uplift and geomorphology

Abstract

Mountains are topographic features caused by erosion after vertical uplift or mountain building. Mountain building is often confused with orogeny, which today means the formation of structures in fold belts. The common assumption that folding and mountain building go together is generally untrue. Many mountains occur in unfolded rocks, granites and volcanic rocks, so there is no direct association of folding and mountain building. In those places where mountains are underlain by folded rocks the folding pre-dates planation and uplift. The age of mountains is therefore not the age of the last folding (if any) but the age of vertical uplift. Since mountains are not restricted to folded rocks, lateral compression is not required to explain the uplift.
 A compilation of times of uplift of mountains around the world shows that a major phase of tectonic uplift started about 6 Ma, and much uplift occurred in the last 2 Ma. This period is known as the Neotectonic Period. It is a global phenomenon including mountains on passive continental margins, and those in deep continental interiors. Several hypotheses of mountain building have problems with this timing. Some fail by being only able to make mountains out of folded rock at continental margins. Many translate the vertical uplift into lateral compression, but vertical uplift alone can create mountains.
 The Neotectonic Period has important implications for geomorphology, climate and global tectonics. In geomorphology it does not fit into conventional theories of geomorphology such as Davisian or King cycles of erosion. Neotectonic uplift might initiate several cycles of erosion, but most planation surfaces are much older than the Neotectonic Period. The increasing relief associated with Neotectonic uplift affected rates of erosion and sedimentation, and also late Cenozoic climate.
 The Neotectonic Period does not fit within plate tectonics theory, in which mountains are explained as a result of compression at active margins: mountains in other locations are said to have been caused by the same process but further back in time. This is disproved by the young age of uplift of mountains in intercontinental and passive margin positions. Subduction is supposed to have been continuous for hundreds of millions of years, so fails to explain the world-wide uplifts in just a few million years.
 Geomorphologists should be guided by their own findings, and refrain from theory-driven hypotheses of plate collision or landscape evolution.

Wheeler’s dilemma revisited: first Oecophylla–Lasius syninclusion and other ants syninclusions in the Bitterfeld amber (late Eocene)

“…The second hypothesis assumes the presence of rather high mountains in the places where amber forests grow. However, such regional mountains at that time were only in Scandinavia, and these were much lower than now, as their secondary uplift wasn't until the Neogene (Ollier, Pain, 2019). Daley (1972), examining this climatic mixture in the late Eocene flora of southern England, rejected the two elevations hypothesis as such mountains would have had to exceeded 2000 m above sea level, incompatible with paleotopographic reconstructions.…”

An Analytical Review of the Recent Crustal Uplifts, Tectonics, and Seismicity of the Caucasus Region

“…Regarding the mechanism of mountain building on a planetary scale [43], researchers believe that plate tectonic theories are not entirely consistent. The authors consider that vertical uplifts can form mountain ranges independently, without the influence of lateral horizontal stresses.…”

Tectonic evolution of a sequence of related late Permian transtensive coal-bearing sub-basins, Mongolia: A global wrench tectonics portrait

“…Many parts of the Altai Range consist of flattopped mountains exposing uplifted erosion surfaces; the youthfulness of the topography may suggest that uplift has occurred during the last few million years (e.g., Cunningham, 1998). For more than a century, a strong body of evidence has accumulated to show that the formation of present-day continental mountain ranges and elevated plateaus are recent phenomena (for discussions and references, see Ollier, 1992Ollier, , 2006Ollier and Pain, 2000;Hay et al, 2002). In addition, Ewing and Ewing (1967) and Storetvedt (1997Storetvedt ( , 2003Storetvedt ( , 2015 have argued that uplift of mid-ocean ridges falls in the same category.…”

“…The origin of both continental mountains and mid-ocean ridges can be regarded as a united global dynamo-tectonic expression and a provisional late stage in the episodic and perpetual alteration of the crust. There is no "folding mountain", Ollier (2006) stated -implying that the term orogeny is a misnomer. Keller et al (1998), who studied the crustal structure of the Rocky Mountains, did not find a connection between topography and predicted thickened crust -thus putting a big question mark on the conventional term of orogenesis.…”