NATURE

Natural Geological Processes

The Tian-Shan Mountain Range

Deciphering the interactions between Tectonics and Surface Processes (erosion, sedimentation).

The Tian Shan is a 2500 km long, up to 7400 m high, range extending through western China, Kazakhstan, and Kyrgyzstan. This range belongs to the larger Central Asian Orogenic Belt (CAOB) extending from the Urals to the Pacific across the East European, Siberian North China, and Tarim cratons. The Tian Shan range resulted from the amalgamation of a number of terranes during the Paleozoic. The Late Devonian to Early Carboniferous collision between the Tarim and Central Tian Shan blocks was followed by a Late Carboniferous‐Early Permian collision between the Tarim‐Central Tian Shan block and a series of island arcs currently exposed in the Northern Tian Shan. Compressive structures generated during these collision phases were then reworked by late Paleozoic strike‐slip shear zones such as the Main Tian Shan Shear Zone (MTSZ) in the central Tian Shan. This shearing phase, induced either by northward or northwestward motion and clockwise rotation of the Tarim block, seems to have ended in Late Permian to Early Triassic, around 245 Ma.

The present‐day topography of the range results from crustal shortening related to the ongoing India‐Asia collision that started in early Tertiary times. Several intermontane basins, such as the Yili basin, the Turpan basin, and the Bayanbulak basin, are preserved within the interior of the Tian Shan range. The sedimentary series within these basins are typically composed of largely undeformed Tertiary detrital sediments deposited over faulted and folded Jurassic strata which lie unconformably over strongly deformed Paleozoic rocks (Jolivet et al. 2010). Link to the Tian-Shan Project Post (coming soon …).

The Taiwan Arc-Continent Collision Range

Studying Arc-Continent Collision and Active Fault Seismic Cycle

Arc-continent collision and arc accretion along most continental margins mark the early episodes of mountain building. In the collision belts that can be studied in continental domains, the finite deformation exposed is very complex as a result of a long geologic history, generally involving numerous superimposed tectonic events.  To better understand the mechanics of mountain building, it is therefore fundamental to analyze the deformation processes acting currently in growing orogens.
The young Taiwan orogen has been the subject of study for many years, mainly on land. The geodynamic setting of the arc-continent collision is well-defined and the general kinematics are well-determined. The island itself represents the emerging part of a southward-propagating collisional orogen located between the Eurasian and Philippine Sea plates. South of the island, the initial stages of the collision between the Luzon volcanic arc and the Chinese continental platform can be observed (Lundberg et al., 1997; Huang et al., 1997). To the north, the island of Taiwan corresponds to a mature stage of collision and arc accretion, resulting in a 4-km-high mountain belt. A portion of the evolving collision complex is underwater to the east of the island (Malavieille et al., 2002). Link to the Taiwan Project Post (coming soon …).

The Sicilian Fold-and-Thrust Belt

Investigating Mountain Building and Subduction Zone Geodynamics

The Apennine-Sicilian-Maghrebian fold-and-thrust belt originated from the subduction of the Eastern Tethys and later collision of drifted continental blocks against the African and Apulian paleomargins. From North to South, the Sicilian Fold-and-Thrust Belt (SFTB) is divided into 4 tectono-stratigraphic domains: (1) the Calabro-Peloritani terrane, drifted from the European margin, (2) the remnants of the Alpine Tethys accretionary Wedge (ATW) related to the subduction of the Tethys, (3) the folded and thrusted platform (Panormide) and basinal (Imerese-Sicanian) series of the off scrapped African margin, and (4) the African foreland (Hyblean). Unfortunately, scarce good-quality seismic lines and outcrops of key tectono-stratigraphic units make the structure and dynamic evolution of SFTB controversial. First, this study provides through a review of the tectono-stratigraphic evolution of the Sicilian orogen, the major remaining issues concerning: (1) the occurrence of inferred Alpine Tethys units far from the region where the remnants of the ATW outcrop (Nebrodi Mountains); both, in a forearc position above the Peloritani block to the North and in an active foreland context along the present-day southern front of the belt; and (2) the diverging tectonic styles, from stacked large-scale tectonic nappes to foreland imbricated thrust systems rooted into a main basal décollement (Henriquet et al. 2020). Link to the Sicily Project Post

Active Margins and Seamount Subduction

Investigating Active Margin Deformations Induced by Seamount and Volcanic ridge subduction.

The subduction of oceanic highs, seamounts, volcanic chains, or oceanic plateaus, involves a vigorous deformation of the upper plate. Numerous bathymetric and seismic records show that deformation depends on several parameters such as the nature of the asperity, the structure and the dip of the oceanic plate, and also the geology and the tectonic regime of the overriding plate. Many authors have studied these problems, especially in the western Pacific Ocean. These studies of large seamount subduction, like the Daiichi– Kashima in the Japan Trench, the Erimo at the Japan– Kuril Trench junction, the Bougainville in the New Hebrides Trench, and several seamounts in the Middle America Trench have played a major role in the evaluation of deformation from a subducting asperity. Generally, the first indication of a subducting seamount is given by an anomaly in the morphology of the margin like a re-entrant, a scarp or an uplifted bulge. In the Mediterranean ridge, it is even possible to observe directly the top of the Bannock seamount due to the high dissolution rate, around the subducting seamount, of the evaporitic sediments forming the accretionary wedge. Link to the Seamount Subduction Project Post.