Eocene thickening without extra heat in a collisional orogenic belt: A record from Eocene metamorphism in mafic dike swarms within the Tethyan Himalaya, southern Tibet

2021 ◽  
Author(s):  
Yuhua Wang ◽  
Lingsen Zeng ◽  
Li-E Gao ◽  
Zhenyu Chen ◽  
Sanzhong Li
Keyword(s):  
Large Scale ◽  
High Mountain ◽  
Southern Tibet ◽  
Crustal Rocks ◽  
Flow Estimation ◽  
Environmental Consequences ◽  
Slab Breakoff ◽  
Orogenic Belts ◽  
Lower Crustal ◽  
Tethyan Himalaya

Knowledge of the nature of the earliest metamorphism experienced by collisional orogenic belts is essential for reconstruction of tectonic processes that build high mountain chains and their environmental consequences. Understanding the metamorphic nature of Eohimalayan-phase orogeny of the Himalayan orogen, one of the typical examples of orogenic belts worldwide, could provide some important constraints to test different tectonic models (shallow continental subduction vs. slab breakoff) for the early phases of the development of large-scale orogenic belts. As exhumed middle- to lower-crustal rocks in the Kangmar gneiss dome, the garnet amphibolites with a protolith age of 176.4 ± 3.6 Ma experienced a phase of metamorphism at 47.2 ± 1.8 Ma with an increase in pressure as well as temperature from 3−5 kbar and 550−600 °C to over ∼11 kbar and 650 °C. This suggests that the middle- to lower-crustal rocks experienced heating at least by ∼50 °C while they underwent compression and thickening. Heat-flow estimation further demonstrates that the self-produced heat was high enough to achieve the observed pressure-temperature conditions recorded by the garnet amphibolite. Therefore, an additional heat supply is not required during early Eocene metamorphism. A breakoff of the leading part of the subducting Indian continental slab, if it occurred, should be younger than ca. 47 Ma.

Timing and kinematics of the Variscan orogenic cycle at the Moldanubian periphery of the central Bohemian Massif

2021 ◽  
pp. jgs2021-096
Author(s):  
M. Machek ◽  
I. Soejono ◽  
J. Sláma ◽  
E. Žáčková
Keyword(s):  
Bohemian Massif ◽  
Large Scale ◽  
Content Type ◽  
Crustal Rocks ◽  
Tectonic Events ◽  
Dextral Shear ◽  
Supplementary Material ◽  
Orogenic Cycle ◽  
Back Arc ◽  
Lower Crustal

The high-grade complexes along the northern Moldanubian periphery of the central Bohemian Massif provide an outstanding structural record of all episodes of the Variscan collisional evolution. Kinematics and timing of orogenic processes have been examined by structural and microstructural study of middle and lower crustal rocks combined with xenotime and monazite geochronology. Four distinct tectonic events have been identified in the studied units. A first relict sub-horizontal fabric S1 associated with the HP/HT metamorphism is developed only in the lower crustal rocks and was related to back-arc extension or lower crustal flow in a supra-subduction domain. This fabric was at c. 340 Ma completely reworked to the sub-vertical foliation S2 by the major collisional thickening leading to the lower and middle crust juxtaposition. Thereafter, the extensional collapse of thickened orogenic system caused strong refolding to the HT sub-horizontal fabric at c. 325 Ma. The region was subsequently affected by the NNE–SSW oriented horizontal shortening related to the dextral shearing and clockwise rotation of crustal blocks adjacent to the large scale dextral shear zone, the Elbe Zone. It led to the fragmentation and reorientation of the Moldanubian margin to the current position.Supplementary material:https://doi.org/10.6084/m9.figshare.c.5708800.v1

Study on the precipitation gradient characteristics in the high mountains of southern Tibet

2021 ◽  
Author(s):  
Chen Zeng ◽  
Fan Zhang
Keyword(s):  
Large Scale ◽  
Monsoon Season ◽  
Precipitation Amount ◽  
High Mountain ◽  
The Tibetan Plateau ◽  
Strongly Correlated ◽  
Southern Tibet ◽  
Rain Gauges ◽  
Set Up ◽  
High Elevations

<p>Precipitation usually is the main source of river discharge in the high mountain headwater areas and therefore as a key parameter in hydrological modelling. However, spatiotemporal distribution of precipitation in the remote high mountain headwater areas on the Tibetan Plateau (TP) has been poorly described due to the scarce meteorological stations located in high elevations. A series of rain gauges were set-up in three catchments of the southern TP to study their precipitation (liquid) gradient (PG) characteristics under different precipitation intensity grades (PIG) during the monsoon season (July to September) from 2013 to 2016. Results showed that the average PG varied during 0.71 to 0.82 mm·100 m<sup>-1</sup> in the three study catchments for the total (non-intensity-graded) precipitation during the monsoon, and varied up to 2.4 times under different PIGs. Besides, PGs were all strongly correlated to precipitation amounts in the three study catchments, these patterns were relatively persistent among different years but varied among different catchments. Generally, the correlations between PG and precipitation amount showed a steep positive slope under fine precipitation grade but became flat or even negative with stronger PIG. We concluded that the precipitation in southern Tibet was influenced more by valley-scale convection than by large-scale vapor circulation during the monsoon season.</p>

Towards Control of an Estuary

1987 ◽  
Vol 19 (9) ◽  
pp. 155-174
Author(s):  
Henk L. F. Saeijs
Keyword(s):  
Shallow Water ◽  
Storm Surge ◽  
Salt Marshes ◽  
Large Scale ◽  
Western Europe ◽  
Oxygen Depletion ◽  
Negative Effects ◽  
Intertidal Flats ◽  
Environmental Consequences ◽  
Short Time

The Delta Project is in its final stage. In 1974 it was subjected to political reconsideration, but it is scheduled now for completion in 1987. The final touches are being put to the storm-surge barrier and two compartment dams that divide the Oosterschelde into three areas: one tidal, one with reduced tide, and one a freshwater lake. Compartmentalization will result in 13% of channels, 45% of intertidal flats and 59% of salt marshes being lost. There is a net gain of 7% of shallow-water areas. Human interventions with large scale impacts are not new in the Oosterschelde but the large scale and short time in which these interventions are taking place are, as is the creation of a controlled tidal system. This article focusses on the area with reduced tide and compares resent day and expected characteristics. In this reduced tidal part salt marshes will extend by 30–70%; intertidal flats will erode to a lower level and at their edges, and the area of shallow water will increase by 47%. Biomass production on the intertidal flats will decrease, with consequences for crustaceans, fishes and birds. The maximum number of waders counted on one day and the number of ‘bird-days' will decrease drastically, with negative effects for the wader populations of western Europe. The net area with a hard substratum in the reduced tidal part has more than doubled. Channels will become shallower. Detritus import will not change significantly. Stratification and oxygen depletion will be rare and local. The operation of the storm-surge barrier and the closure strategy chosen are very important for the ecosystem. Two optional closure strategies can be followed without any additional environmental consequences. It was essential to determine a clearly defined plan of action for the whole area, and to make land-use choices from the outset. How this was done is briefly described.

Magmatic and tectonic emplacement of the Pukaskwa batholith, Superior Province, Ontario, CanadaThis article is one of a series of papers published in this Special Issue on the theme of Geochronology in honour of Tom Krogh.

2011 ◽  
Vol 48 (2) ◽  
pp. 187-204 ◽  
Author(s):  
Gary P. Beakhouse ◽  
Shoufa Lin ◽  
Sandra L. Kamo
Keyword(s):  
Partial Melting ◽  
Abrupt Change ◽  
Superior Province ◽  
Density Inversion ◽  
Tectonic Processes ◽  
Slab Breakoff ◽  
Greenstone Belts ◽  
Lower Crustal ◽  
Basaltic Crust ◽  
Structural Dome

The Neoarchean Pukaskwa batholith consists of pre-, syn-, and post-tectonic phases emplaced over an interval of 50 million years. Pre-tectonic phases are broadly synvolcanic and have a high-Al tonalite–trondhjemite–granodiorite (TTG) affinity interpreted to reflect derivation by partial melting of basaltic crust at lower crustal or upper mantle depths. Minor syn-tectonic phases slightly post-date volcanism and have geochemical characteristics suggesting some involvement or interaction with an ultramafic (mantle) source component. Magmatic emplacement of pre- and syn-tectonic phases occurred in the midcrust at paleopressures of 550–600 MPa and these components of the batholith are thought to be representative of the midcrust underlying greenstone belts during their development. Subsequent to emplacement of the syntectonic phases, and likely at approximately 2680 Ma, the Pukaskwa batholith was uplifted as a structural dome relative to flanking greenstone belts synchronously with ongoing regional sinistral transpressive deformation. The driving force for vertical tectonism is interpreted to be density inversion (Rayleigh–Taylor-type instabilities) involving denser greenstone belts and underlying felsic plutonic crust. The trigger for initiation of this process is interpreted to be an abrupt change in the rheology of the midcrust attributed to introduction of heat from the mantle attendant with slab breakoff or lithospheric delamination following the cessation of subduction. This process also led to partial melting of the intermediate to felsic midcrust generating post-tectonic granitic phases at approximately 2667 Ma. We propose that late density inversion-driven vertical tectonics is an inevitable consequence of horizontal (plate) tectonic processes associated with greenstone belt development within the Superior Province.

scholarly journals Lower-crustal earthquakes in southern Tibet are linked to eclogitization of dry metastable granulite

2018 ◽  
Vol 9 (1) ◽  
Author(s):  
Feng Shi ◽  
Yanbin Wang ◽  
Tony Yu ◽  
Lupei Zhu ◽  
Junfeng Zhang ◽  
...  
Keyword(s):  
Southern Tibet ◽  
Crustal Earthquakes ◽  
Lower Crustal

scholarly journals Large-scale atmospheric forcing and topographic modification of precipitation rates over High Asia – a neural-network-based approach

2015 ◽  
Vol 6 (1) ◽  
pp. 61-81 ◽  
Author(s):  
L. Gerlitz ◽  
O. Conrad ◽  
J. Böhner
Keyword(s):  
Neural Network ◽  
High Resolution ◽  
Spatial Resolution ◽  
Large Scale ◽  
Local Scale ◽  
Predictor Variables ◽  
High Mountain ◽  
Target Area ◽  
Monthly Precipitation ◽  
Highly Nonlinear

Abstract. The heterogeneity of precipitation rates in high-mountain regions is not sufficiently captured by state-of-the-art climate reanalysis products due to their limited spatial resolution. Thus there exists a large gap between the available data sets and the demands of climate impact studies. The presented approach aims to generate spatially high resolution precipitation fields for a target area in central Asia, covering the Tibetan Plateau and the adjacent mountain ranges and lowlands. Based on the assumption that observed local-scale precipitation amounts are triggered by varying large-scale atmospheric situations and modified by local-scale topographic characteristics, the statistical downscaling approach estimates local-scale precipitation rates as a function of large-scale atmospheric conditions, derived from the ERA-Interim reanalysis and high-resolution terrain parameters. Since the relationships of the predictor variables with local-scale observations are rather unknown and highly nonlinear, an artificial neural network (ANN) was utilized for the development of adequate transfer functions. Different ANN architectures were evaluated with regard to their predictive performance. The final downscaling model was used for the cellwise estimation of monthly precipitation sums, the number of rainy days and the maximum daily precipitation amount with a spatial resolution of 1 km2. The model was found to sufficiently capture the temporal and spatial variations in precipitation rates in the highly structured target area and allows for a detailed analysis of the precipitation distribution. A concluding sensitivity analysis of the ANN model reveals the effect of the atmospheric and topographic predictor variables on the precipitation estimations in the climatically diverse subregions.

scholarly journals Evaluating Predictor Strategies for Regression-Based Downscaling with a Focus on Glacierized Mountain Environments

2017 ◽  
Vol 56 (6) ◽  
pp. 1707-1729 ◽  
Author(s):  
Marlis Hofer ◽  
Johanna Nemec ◽  
Nicolas J. Cullen ◽  
Markus Weber
Keyword(s):  
Large Scale ◽  
Global Radiation ◽  
Local Scale ◽  
Forecast Skill ◽  
Model Complexity ◽  
High Mountain ◽  
European Alps ◽  
Limited Information ◽  
Mountain Environments ◽  
Measuring Site

AbstractThis study explores the potential of different predictor strategies for improving the performance of regression-based downscaling approaches. The investigated local-scale target variables are precipitation, air temperature, wind speed, relative humidity, and global radiation, all at a daily time scale. Observations of these target variables are assessed from three sites in close proximity to mountain glaciers: 1) the Vernagtbach station in the European Alps, 2) the Artesonraju measuring site in the tropical South American Andes, and 3) the Mount Brewster measuring site in the Southern Alps of New Zealand. The large-scale dataset being evaluated is the ERA-Interim dataset. In the downscaling procedure, particular emphasis is put on developing efficient yet not overfit models from the limited information in the temporally short (typically a few years) observational records of the high mountain sites. For direct (univariate) predictors, optimum scale analysis turns out to be a powerful means to improve the forecast skill without the need to increase the downscaling model complexity. Yet the traditional (multivariate) predictor sets show generally higher skill than the direct predictors for all variables, sites, and days of the year. Only in the case of large sampling uncertainty (identified here to particularly affect observed precipitation) is the use of univariate predictor options justified. Overall, the authors find a range in forecast skill among the different predictor options applied in the literature up to 0.5 (where 0 indicates no skill, and 1 represents perfect skill). This highlights that a sophisticated predictor selection (as presented in this study) is essential in the development of realistic, local-scale scenarios by means of downscaling.

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