Dissimilar age and provenance of the Nindam and Jurutze volcaniclastic formations, Zanskar Gorge, Ladakh (India)

2021 ◽  
Author(s):  
Goran Andjic ◽  
Renjie Zhou ◽  
Tara N. Jonell ◽  
Jonathan C. Aitchison
Keyword(s):  
Detrital Zircon ◽  
Tectonic Evolution ◽  
Alternative Model ◽  
Early Eocene ◽  
Convergent Margins ◽  
Geochemical Composition ◽  
Age Gap ◽  
Volcaniclastic Rocks ◽  
Forearc Basins ◽  
Early Cenozoic

<p>Pre-early Eocene volcaniclastic rocks exposed in the Indus Suture Zone (Ladakh, India) are key to deciphering the complex magmatic and tectonic evolution of the convergent margins that existed between India and Eurasia. Several hypotheses exist regarding the provenance of the middle Cretaceous to early Cenozoic Jurutze and Nindam formations yet there is presently no consensus. Leading models propose that: (a) they were either formed in neighbouring sub-basins at one convergent margin consisting of the Kohistan-Ladakh-Dras arc; or (b) they became stratigraphically superposed after the collision between the Kohistan-Ladakh and Dras arcs. Here we present new U-Pb detrital zircon, major and trace element geochemical, and petrographic datasets from the Nindam and Jurutze formations that support a disparate provenance and thus necessitate an alternative model. The Jurutze Fm. has a geochemical composition typical of arcs built on continental crust, whereas the Nindam Fm. presents a geochemical signature compatible with that of an intraoceanic arc. The significant age gap between these formations (>20 m.y.) in the Zanskar Gorge further precludes the possibility that the Jurutze Fm. was deposited on top of the Nindam Fm. We propose that the Nindam and Jurutze formations were deposited in distinct forearc basins and explore scenarios for their formation at separate convergent margins, i.e. the separate Kohistan-Ladakh and Dras arcs, respectively.</p>

Cenozoic tectonic evolution of the Pamir-Tian Shan convergence zone: evidence from detrital zircon U-Pb provenance analysis

2020 ◽  
Author(s):  
Yingying Jia ◽  
Christoph Glotzbach ◽  
Todd Ehlers ◽  
Lixing Lü
Keyword(s):  
Tarim Basin ◽  
Detrital Zircon ◽  
Tectonic Evolution ◽  
Middle Miocene ◽  
Source Area ◽  
Convergence Zone ◽  
Late Cenozoic ◽  
Crustal Shortening ◽  
Early Cenozoic ◽  
Tian Shan

<p><span>The Pamir is an along-strike continuation of the Tibet-Himalaya orogen and penetrated ~300 km into the Tarim and Tajik basins in Cenozoic times. This northward indentation led to regional paleoenvironmental changes and facilitated northward transport of the far-field stress from the India-Asia plate boundary. Due to the compressional stress from the India-Asia boundary and Cenozoic lithosphere delamination, the Pamir underwent intense exhumations, which well recorded its Late Cenozoic mountain building processes. However, the very rapid Late Cenozoic exhumation also erased earlier cooling records and hinders a clear understanding of the Early Cenozoic tectonic evolution of Pamir. Thus, the onset and magnitude of the northward movement of Pamir are loosely constrained (Eocene-Late Oligocene) and long debated. In particular, the Early Cenozoic tectonic evolution of Pamir is unclear.</span></p><p><span>Provenance study of sediments in the adjacent sediment basins is a widely used method to reconstruct the tectonic-geomorphologic evolution of a mountain range. We carried out paleocurrent measurements and detrital zircon analysis of the Cretaceous-Pliocene sediments in the northern Pamir-Tian Shan convergence zone. Our study area, the Tierekesazi section, is located immediately south to the southern Tian Shan and is evolved in the present foreland basin of the southwestern Tian Shan. The provenance data show that the Tian Shan was the primary source area of the northwestern Tarim basin in the Cretaceous. The appearance of the Triassic-Jurassic detrital zircon grains and northward paleo-flow directions in the Eocene (~41 Ma) to Middle Miocene sediments suggest the Pamir became an important source area of the northwestern Tarim basin. Combining with the regional crustal shortening and paleoclimate data, we speculate that the northward indentation of the Pamir initiated before ~41 Ma. In contrast with the northward movement and Middle-Late Miocene accelerated exhumation of the Pamir, the source area of the studied section shifted back to the Tian Shan after the Middle Miocene. It consists with the Middle-Late Miocene uplift of the southwestern Tian Shan. Simultaneously, the crustal shortening of Pamir propagated to its northern foreland. Newly formed fold-and-thrust zones probably blocked the sediment transport from Pamir to the Tierekesazi section, and the present-day east flowing drainage system in the Pamir-Tian Shan convergence zone was established. We infer, in this period, the Pamir likely reached its present position, which is consistent with the appearance of an extreme arid climate in the Tarim basin.</span></p>

Evolution of Orogenic Plateaus at Subduction Zones - Sinking and raising the southern margin of the Central Anatolian Plateau

2018 ◽  
Author(s):  
David Fernández-Blanco
Keyword(s):  
Tectonic Evolution ◽  
Subduction Zones ◽  
Inversion Tectonics ◽  
High Discharge ◽  
Anatolian Plateau ◽  
Surface Uplift ◽  
Southern Margin ◽  
Wide Range ◽  
Forearc Basins ◽  
Orogenic Plateaus

Orogenic plateaus have raised abundant attention amongst geoscientists during the last decades, offering unique opportunities to better understand the relationships between tectonics and climate, and their expression on the Earth’s surface.Orogenic plateau margins are key areas for understanding the mechanisms behind plateau (de)formation. Plateau margins are transitional areas between domains with contrasting relief and characteristics; the roughly flat elevated plateau interior, often with internally drained endorheic basins, and the external steep areas, deeply incised by high-discharge rivers. This thesis uses a wide range of structural and tectonic approaches to investigate the evolution of the southern margin of the Central Anatolian Plateau (CAP), studying an area between the plateau interior and the Cyprus arc. Several findings are presented here that constrain the evolution, timing and possible causes behind the development of this area, and thus that of the CAP. After peneplanation of the regional orogeny, abroad regional subsidence took place in Miocene times in the absence of major extensional faults, which led to the formation of a large basin in the northeast Mediterranean. Late Tortonian and younger contractional structures developed in the interior of the plateau, in its margin and offshore, and forced the inversion tectonics that fragmented the early Miocene basin into the different present-day domains. The tectonic evolution of the southern margin of the CAP can be explained based on the initiation of subduction in south Cyprus and subsequent thermo-mechanical behavior of this subduction zone and the evolving rheology of the Anatolian plate. The Cyprus slab retreat and posterior pull drove subsidence first by relatively minor stretching of the crust and then by its flexure. The growth by accretion and thickening of the upper plate, and that of the associated forearc basins system, caused by accreting sediments, led to rheological changes at the base of the crust that allowed thermal weakening, viscous deformation, driving subsequent surface uplift and raising the modern Taurus Mountains. This mechanism could be responsible for the uplifted plateau-like areas seen in other accretionary margins. ISBN: 978-90-9028673-0

scholarly journals Paleoclimate and precipitation seasonality of the Early Eocene McAbee megaflora, Kamloops Group, British Columbia

2016 ◽  
Vol 53 (6) ◽  
pp. 591-604 ◽  
Author(s):  
Cale A.C. Gushulak ◽  
Christopher K. West ◽  
David R. Greenwood
Keyword(s):  
British Columbia ◽  
North American ◽  
Leaf Size ◽  
Early Eocene ◽  
Precipitation Seasonality ◽  
Two Samples ◽  
Fossil Site ◽  
Fossil Floras ◽  
Climate Analysis ◽  
Early Cenozoic

Early Eocene fossil floras from British Columbia are a rich resource for reconstructing western North American early Cenozoic climate. The best known of these floras reflect cooler (MAT ≤ 15 °C) upland forest communities in contrast to coeval (MAT ≥ 18 °C) forests in lowland western North American sites. Of particular interest is whether Early Eocene climates were monsoonal (highly seasonal precipitation). The McAbee site is a 52.9 ± 0.83 Ma 0.5 km outcrop of bedded lacustrine shale interbedded with volcanic ash. In this report two historical megaflora collections that were collected independently from different stratigraphic levels and (or) laterally separated by ∼100–200 m in the 1980s (University of Saskatchewan) and 2000s (Brandon University) are investigated to (i) assess whether they represent the same leaf population, (ii) assess whether a combined collection yields more precise climate estimates, and (iii) reconstruct paleoclimate to assess the character of regional Early Eocene precipitation seasonality. Combined, the two samples yielded 43 dicot leaf morphotypes. Analysis of leaf size distribution using ANOVA showed no difference between the two samples, and thus they were combined for climate analysis. Climate analysis using leaf physiognomy agrees with previous estimates for McAbee and other regional megafloras, indicating a warm (MAT ∼8–13 °C), mild (CMMT ∼5 °C), moist (MAP > 100 cm/year) ever-wet, non-monsoonal climate. Additionally, we recommend that climate analyses derived from leaf fossils should be based on samples collected within a stratigraphically constrained quarry area to capture a snapshot of climate in time rather than time-averaged estimates derived from multiple quarry sites representing different stratigraphic levels within a fossil site.

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