scholarly journals Cenozoic uplift of the Central Andes in northern Chile and Bolivia—reconciling paleoaltimetry with the geological evolution

2016 ◽  
Vol 53 (11) ◽  
pp. 1227-1245 ◽  
Author(s):  
Simon Lamb
Keyword(s):  
Lower Crust ◽  
Central Andes ◽  
Crustal Thickening ◽  
Direct Result ◽  
Western Margin ◽  
Crustal Shortening ◽  
Eastern Cordillera ◽  
Surface Uplift ◽  
Geological Evolution ◽  
History Of

The Cenozoic geological evolution of the Central Andes, along two transects between ∼17.5°S and 21°S, is compared with paleo-topography, determined from published paleo-altimetry studies. Surface and rock uplift are quantified using simple 2-D models of crustal shortening and thickening, together with estimates of sedimentation, erosion, and magmatic addition. Prior to ∼25 Ma, during a phase of amagmatic flat-slab subduction, thick-skinned crustal shortening and thickening (nominal age of initiation ∼40 Ma) was focused in the Eastern and Western Cordilleras, separated by a broad basin up to 300 km wide and close to sea level, which today comprises the high Altiplano. Surface topography at this time in the Altiplano and the western margin of the Eastern Cordillera appears to be ∼1 km lower than anticipated from crustal thickening, which may be due to the pull-down effect of the subducted slab, coupled to the overlying lithosphere by a cold mantle wedge. Oligocene steepening of the subducted slab is indicated by the initiation of the volcanic arc at ∼27–25 Ma, and widespread mafic volcanism in the Altiplano between 25 and 20 Ma. This may have resulted in detachment of mantle lithosphere and possibly dense lower crust, triggering 1–1.5 km of rapid uplift (over ≪5 Myrs) of the Altiplano and western margin of the Eastern Cordillera and establishing the present day lithospheric structure beneath the high Andes. Since ∼25 Ma, surface uplift has been the direct result of crustal shortening and thickening, locally modified by the effects of erosion, sedimentation, and magmatic addition from the mantle. The rate of crustal shortening and thickening varies with location and time, with two episodes of rapid shortening in the Altiplano, lasting <5 Myrs, that are superimposed on a long-term history of ductile shortening in the lower crust, driven by underthrusting of the Brazilian Shield on the eastern margin.

scholarly journals Constraints on the paleoelevation history of the Eastern Cordillera of Colombia from its palynological record

Geosphere ◽  
2021 ◽  
Author(s):  
Peter Molnar ◽  
Lina C. Pérez-Angel
Keyword(s):  
Probability Distributions ◽  
Objective Assessment ◽  
Probability Density Functions ◽  
Fossil Pollen ◽  
Density Functions ◽  
Fossil Plants ◽  
Eastern Cordillera ◽  
Surface Uplift ◽  
Complete Knowledge ◽  
History Of

We attempted to make an objective assessment of whether fossil pollen assemblages from the Sabana de Bogotá require surface uplift of ~2000 m since 6–3 Ma, as has been argued. We relied on recently published elevation ranges of plants for which fossil pollen has been found in sites 2000–2500 m high in the Sabana de Bogotá. The elevation ranges of fossil plants do not overlap, suggesting that those ranges may be too narrow. By weighting these elevation ranges by percentages of corresponding fossil pollen and summing them, we estimated probability density functions for past elevations. These probability distributions of past elevations overlap present-day elevations and therefore do not require surface uplift since deposition of the pollen. Fossil pollen assemblages include pollen from some plant taxa for which we do not know present-day elevation ranges, and therefore, with a more complete knowledge of elevation distributions, tighter constraints on elevations should be obtainable. The elevation of the oldest assemblage, from Tequendama, which lies at the southern edge of the Sabana de Bogotá and is thought to date from 16 to 6 Ma, is least well constrained. Although our analysis permits no change in elevation since the pollen was deposited, we consider 1000–2000 m of elevation gain since 15 Ma to be likely and consistent with an outward growth of the Eastern Cordillera.

scholarly journals Post-collisional crustal thickening and plateau uplift of southern Tibet: Insights from Cenozoic magmatism in the Wuyu area of the eastern Lhasa block

2020 ◽  
Author(s):  
Lu-Lu Hao ◽  
Qiang Wang ◽  
Andrew C. Kerr ◽  
Jin-Hui Yang ◽  
Lin Ma ◽  
...  
Keyword(s):  
Lower Crust ◽  
Temporal Distribution ◽  
Crustal Thickening ◽  
Indian Plate ◽  
Hf Isotopes ◽  
Southern Tibet ◽  
Tectonic Model ◽  
Surface Uplift ◽  
Thin Crust ◽  
Cenozoic Magmatism

The nature and timing of post-collisional crustal thickening and its link to surface uplift in the eastern Lhasa block of the southern Tibetan plateau remain controversial. Here we report on Cenozoic magmatism in the Wuyu area of the eastern Lhasa block. The Eocene (ca. 46 Ma) trachyandesites and trachydacites show slight fractionation of rare earth elements (REE), slightly negative Eu and Sr anomalies, and relatively homogeneous Sr-Nd and zircon Hf isotopes (87Sr/86Sr(i) = 0.7050−0.7063, εNd(t) = −0.92 to −0.03, εHf(t) = +2.6 to +4.8). Previous studies have suggested Neo-Tethys oceanic slab break-off at 50−45 Ma; thus, the Wuyu Eocene magmatism could represent a magmatic response to this slab break-off and originate from relatively juvenile Lhasa crust. The Miocene (ca. 15−12 Ma) dacites and rhyolites have adakitic affinities, e.g., high Sr (average 588 ppm), Sr/Y (29−136), and La/Yb (30−76) values, low Y (4−12 ppm) and Yb (0.4−0.9 ppm) contents, and variable Sr-Nd and zircon Hf isotopes (87Sr/86Sr(i) = 0.7064−0.7142, εNd(t) = −11.7 to −3.7, εHf(t) = −3.2 to +4.5). Their more enriched Sr-Nd-Hf isotopes relative to the Eocene lavas indicate that they should be derived from mixed Lhasa lower crust comprising juvenile crust, ultrapotassic rocks, and probably Indian lower crust-derived rocks. This study has also revealed the transformation from Eocene juvenile and thin crust with a thickness of &lt;40 km to Miocene mixed and thickened crust with a thickness of &gt;50 km. Combined with published tectonic data, we suggest that both lithospheric shortening and magma underplating contributed to eastern Lhasa block post-collisional crustal thickening. Given the spatial-temporal distribution of eastern Lhasa block magmatism and regional geology, we invoke a post-collisional tectonic model of steep subduction of the Indian plate and subsequent westward-propagating plate break-off beneath the eastern Lhasa block, which caused the surface uplift.

A Discussion on the evolution of the Precambrian crust - Tectonic displacements and thermal activity in two contrasting Proterozoic mobile belts from Greenland

1973 ◽  
Vol 273 (1235) ◽  
pp. 513-533 ◽  
Keyword(s):  
Plate Tectonics ◽  
Regional Metamorphism ◽  
The Other ◽  
Crustal Thickening ◽  
Thermal Activity ◽  
Crustal Shortening ◽  
Granite Intrusion ◽  
Igneous Activity ◽  
History Of ◽  
The One

The Proterozoic Nagssugtoqidian and Ketilidian mobile belts are comparable in scale with those of the Phanerozoic rather than those of the Archaean. These two Proterozoic belts differ from one another both in the tectonic displacements which gave rise to them, and in their thermal activities as expressed by igneous and metamorphic characteristics. Similar differences between modern tectonic belts have been interpreted in terms of plate tectonics. The Nagssugtoqidian is characterized by considerable crustal shortening, very limited igneous activity, and high-pressure regional metamorphism which may be related to crustal thickening resulting from both ductile and brittle overthrusting of the Nagssugtoqidian rocks over the Archaean foreland. Evidence of crustal shortening in the Ketilidian is limited, but vertical and transcurrent movements are important. Widespread igneous activity throughout the active history of the belt resulted in the formation of mainly acid volcanic supracrustal rocks and widespread granite intrusion. The appinite suite is also well represented. Metamorphism is mainly of low-pressure type. A tentative comparison can be made between the Alpine and Nagssugtoqidian belts on the one hand, and Andean and Ketilidian belts on the other.

scholarly journals Thrusting, exhumation, and basin fill on the western margin of the South China block during the India-Asia collision

2020 ◽  
Vol 133 (1-2) ◽  
pp. 74-90 ◽  
Author(s):  
Kai Cao ◽  
Philippe Hervé Leloup ◽  
Guocan Wang ◽  
Wei Liu ◽  
Gweltaz Mahéo ◽  
...  
Keyword(s):  
Structural Analysis ◽  
South China ◽  
Hanging Wall ◽  
Crustal Thickening ◽  
South China Block ◽  
Thrust Belt ◽  
Western Margin ◽  
Crustal Shortening ◽  
Fold And Thrust Belt ◽  
Early Cenozoic

Abstract The pattern and timing of deformation in southeast Tibet resulting from the early stages of the India-Asia collision are crucial factors to understand the growth of the Tibetan Plateau, but they remain poorly constrained. Detailed field mapping, structural analysis, and geochronological and thermochronological data along a 120 km section of the Ludian-Zhonghejiang fold-and-thrust belt bounding the Jianchuan basin in western Yunnan, China, document the early Cenozoic tectonic evolution of the conjunction between the Lanping-Simao and South China blocks. The study area is cut by two major southwest-dipping brittle faults, named the Ludian-Zhonghejiang fault and the Tongdian fault from east to west. Numerous kinematic indicators and the juxtaposition of Triassic metasedimentary rocks on top of Paleocene strata indicate thrusting along the Ludian-Zhonghejiang fault. Similarly, structural analysis shows that the Tongdian fault is a reverse fault. Between these structures, fault-bounded Permian–Triassic and Paleocene rocks are strongly deformed by nearly vertical and upright southwest-vergent folds with axes that trend nearly parallel to the traces of the main faults. Zircon and apatite (U-Th)/He and apatite fission-track data from a Triassic pluton with zircon U-Pb ages of 237–225 Ma in the hanging wall of the Ludian-Zhonghejiang fault, assisted by inverse modeling, reveal two episodes of accelerated cooling during 125–110 Ma and 50–39 Ma. The Cretaceous cooling event was probably related to crustal thickening during the collision between the Lhasa and Qiangtang terranes. The accelerated exhumation during 50–39 Ma is interpreted to record the life span of the fold-and-thrust belt. This timing is corroborated by the intrusive relationship of Eocene magmas of ca. 36–35 Ma zircon U-Pb age into the fold-and-thrust belt. Early Cenozoic activity of the deformation system controlled deposition of alluvial-fan and braided-river sediments in the Jianchuan basin, as evidenced by eastward and northeastward paleoflows and terrestrial clasts derived from the hanging wall of the Ludian-Zhonghejiang thrust. Since 39 Ma, decreasing cooling rates likely reflect cessation of activity on the fold-and-thrust belt. Early Cenozoic compressive deformation on the western margin of the South China block together with geological records of contraction in central, northern, and eastern Tibet document Eocene upper-crustal shortening located in the Himalaya, Qiangtang terrane, and northern plateau margins together with contractional basin development in the intervening Lhasa, Songpan-Garze, and Kunlun terranes, coeval with or shortly after the onset of the India-Asia collision. This suggests that moderate crustal shortening affected a large part of Tibet in a spaced way, contrary to models of homogeneous crustal thickening soon after the collision, and prior to the main crustal thickening, propagating progressively from south to north. This complex deformation pattern illustrates the complexity of Asian crustal rheology, which contrasts with assumptions in existing geodynamic models.

Evolution of the Paran drainage basin and its relation to the Plio-Pleistocene history of the Arava Rift western margin, Israel

2000 ◽  
Vol 49 (4) ◽  
pp. 215-238 ◽  
Author(s):  
Hanan Ginat ◽  
Yoav Avni ◽  
Zvi Garfunkel ◽  
Hanan Ginata ◽  
Yosef Bartov
Keyword(s):  
Drainage Basin ◽  
Western Margin ◽  
History Of

Hastings Donnan and Pnina Werbner (eds). Economy and Culture in Pakistan: Migrants and Cities in a Muslim Society. London: Macmillan. 1991. 268 pp.

1992 ◽  
Vol 31 (3) ◽  
pp. 325-328
Author(s):  
Ziaul Haque
Keyword(s):  
Urban Areas ◽  
Political System ◽  
Direct Result ◽  
The Political ◽  
Economic Factors ◽  
Population Movements ◽  
Social Fabric ◽  
History Of ◽  
Political Divide ◽  
Different Parts

Modem economic factors and forces are rapidly transforming the world into a single society and economy in which the migration of people at the national and international levels plays an important role. Pakistan, as a modem nation, has characteristically been deeply influenced by such migrations, both national and international. The first great exodus occurred in 1947 when over eight million Indian Muslims migrated from different parts of India to Pakistan. Thus, from the very beginning mass population movements and migrations have been woven into Pakistan's social fabric through its history, culture and religion. These migrations have greatly influenced the form and substance of the national economy, the contours of the political system, patterns of urbanisation and the physiognomy of the overall culture and history of the country. The recent political divide of Sindh on rural/Sindhi, and urban/non-Sindhi, ethnic and linguistic lines is the direct result of these earlier settlements of these migrants in the urban areas of Sindh.

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