oalib
Search Results: 1 - 10 of 100 matches for " "
All listed articles are free for downloading (OA Articles)
Page 1 /100
Display every page Item
Continental Flood Basalts and Rifting: Geochemistry of Cenozoic Yemen Volcanic Province  [PDF]
M. A. Mattash, L. Pinarelli, O. Vaselli, A. Minissale, M. Al-Kadasi, M. N. Shawki, F. Tassi
International Journal of Geosciences (IJG) , 2013, DOI: 10.4236/ijg.2013.410143
Abstract:

Rift formation is a crucial topic in global tectonics. The Yemen rift-related area is one of the most important provinces, being connected to the rifting processes of the Gulf of Aden, the Red Sea and Afar Triangle. In this paper, a review of the Yemen volcanic province and its relations with the Red Sea rifting are presented. Tertiary continental extension in Yemen resulted in the extrusion of large volumes of effusive rocks. This magmatism is divided in the Oligo-Miocene Yemen Trap Series (YTS) separated by an unconformity from the Miocene-Recent Yemen Volcanic Series (YVS). Magmas of the YTS were erupted during the synrift phase and correlate with the first stage of sea-floor spreading of the Red Sea and the Gulf of Aden (30 - 15 Ma), whereas the magmas of the YVS were emplaced during the post rift phase (10 - 0 Ma). A continental within plate character is recognized for both the YTS and YVS basalts. The YTS volcanic rocks are contemporaneous with, and geochemically similar to, the Ethiopian rift volcanism, just as the volcanic fields of the YVS are geochemically alike to most of the Saudi Arabian volcanics. YTS and YVS have analogous SiO2 ranges, but YVS tend to have, on average, higher alkalis and MgO contents than YTS. Fractional crystallization processes dominate geochemical variations of both series. Primitive magmas (MgO

Calibration of a transient transport model to tritium measurements in rivers and streams in the Western Lake Taupo catchment, New Zealand
M. A. Gusyev,M. Toews,U. Morgenstern,M. Stewart
Hydrology and Earth System Sciences Discussions , 2012, DOI: 10.5194/hessd-9-9743-2012
Abstract: Here we present a general approach of calibrating transient transport models to tritium concentrations in river waters developed for the MT3DMS/MODFLOW model of the Western Lake Taupo catchment, New Zealand. Tritium is a time-dependent tracer with radioactive half-life of 12.32 yr. In the transport model, the tritium input (measured in rain) passes through the groundwater system, and the modelled tritium concentrations are compared to the measured tritium concentrations in the river outlets for the Waihaha, Whanganui, Whareroa, Kuratau and Omori river catchments from 2000–2007. For the Kuratau River, tritium was also measured between 1960 and 1970, which allowed us to fine-tune the transport model. In order to incorporate all surface flows from rivers to small streams, an 80 m uniform grid cell size was selected in the steady-state MODFLOW model for the model area of 1072 km2. The groundwater flow model was first calibrated to groundwater levels and stream flow observations. Then, the transport model was calibrated to the measured tritium concentrations in the river waters. The MT3DMS model results show good agreement with the measured tritium values in all five river catchments. Finally, the calibrated MT3DMS model is applied to simulate groundwater ages that are used to construct groundwater age distributions for the river catchments.
Calibration of a transient transport model to tritium data in streams and simulation of groundwater ages in the western Lake Taupo catchment, New Zealand
M. A. Gusyev, M. Toews, U. Morgenstern, M. Stewart, P. White, C. Daughney,J. Hadfield
Hydrology and Earth System Sciences (HESS) & Discussions (HESSD) , 2013,
Abstract: Here we present a general approach of calibrating transient transport models to tritium concentrations in river waters developed for the MT3DMS/MODFLOW model of the western Lake Taupo catchment, New Zealand. Tritium has a known pulse-shaped input to groundwater systems due to the bomb tritium in the early 1960s and, with its radioactive half-life of 12.32 yr, allows for the determination of the groundwater age. In the transport model, the tritium input (measured in rainfall) passes through the groundwater system, and the simulated tritium concentrations are matched to the measured tritium concentrations in the river and stream outlets for the Waihaha, Whanganui, Whareroa, Kuratau and Omori catchments from 2000–2007. For the Kuratau River, tritium was also measured between 1960 and 1970, which allowed us to fine-tune the transport model for the simulated bomb-peak tritium concentrations. In order to incorporate small surface water features in detail, an 80 m uniform grid cell size was selected in the steady-state MODFLOW model for the model area of 1072 km2. The groundwater flow model was first calibrated to groundwater levels and stream baseflow observations. Then, the transient tritium transport MT3DMS model was matched to the measured tritium concentrations in streams and rivers, which are the natural discharge of the groundwater system. The tritium concentrations in the rivers and streams correspond to the residence time of the water in the groundwater system (groundwater age) and mixing of water with different age. The transport model output showed a good agreement with the measured tritium values. Finally, the tritium-calibrated MT3DMS model is applied to simulate groundwater ages, which are used to obtain groundwater age distributions with mean residence times (MRTs) in streams and rivers for the five catchments. The effect of regional and local hydrogeology on the simulated groundwater ages is investigated by demonstrating groundwater ages at five model cross-sections to better understand MRTs simulated with tritium-calibrated MT3DMS and lumped parameter models.
Calibration of a transient transport model to tritium data in streams and simulation of groundwater ages in the western Lake Taupo catchment, New Zealand
M. A. Gusyev,M. Toews,U. Morgenstern,M. Stewart
Hydrology and Earth System Sciences (HESS) & Discussions (HESSD) , 2013, DOI: 10.5194/hess-17-1217-2013
Abstract: Here we present a general approach of calibrating transient transport models to tritium concentrations in river waters developed for the MT3DMS/MODFLOW model of the western Lake Taupo catchment, New Zealand. Tritium has a known pulse-shaped input to groundwater systems due to the bomb tritium in the early 1960s and, with its radioactive half-life of 12.32 yr, allows for the determination of the groundwater age. In the transport model, the tritium input (measured in rainfall) passes through the groundwater system, and the simulated tritium concentrations are matched to the measured tritium concentrations in the river and stream outlets for the Waihaha, Whanganui, Whareroa, Kuratau and Omori catchments from 2000–2007. For the Kuratau River, tritium was also measured between 1960 and 1970, which allowed us to fine-tune the transport model for the simulated bomb-peak tritium concentrations. In order to incorporate small surface water features in detail, an 80 m uniform grid cell size was selected in the steady-state MODFLOW model for the model area of 1072 km2. The groundwater flow model was first calibrated to groundwater levels and stream baseflow observations. Then, the transient tritium transport MT3DMS model was matched to the measured tritium concentrations in streams and rivers, which are the natural discharge of the groundwater system. The tritium concentrations in the rivers and streams correspond to the residence time of the water in the groundwater system (groundwater age) and mixing of water with different age. The transport model output showed a good agreement with the measured tritium values. Finally, the tritium-calibrated MT3DMS model is applied to simulate groundwater ages, which are used to obtain groundwater age distributions with mean residence times (MRTs) in streams and rivers for the five catchments. The effect of regional and local hydrogeology on the simulated groundwater ages is investigated by demonstrating groundwater ages at five model cross-sections to better understand MRTs simulated with tritium-calibrated MT3DMS and lumped parameter models.
Temperature-Dependent Newtonian Rheology in Advection-Convection Geodynamical Model for Plate Spreading in Eastern Volcanic Zone, Iceland  [PDF]
Md. Tariqul Islam, Erik Sturkell
Journal of Geoscience and Environment Protection (GEP) , 2015, DOI: 10.4236/gep.2015.35003
Abstract:

Geodynamic process as advection-convection of the Mid-Atlantic Ocean Ridge (MAR), that is exposed on land in Iceland is investigated. Advection is considered for the plate spreading velocity. Geodetic GPS data during 2000-2010 is used to estimate plate spreading velocity along a profile in the Eastern Volcanic Zone (EVZ), Iceland striking N102E, approximately parallel to the NUVEL-1A spreading direction between the Eurasian and North American plates. To predict subsurface mass flow patterns, temperature-dependent Newtonian rheology is considered in the finite-element models (FEM). All models are considered 2-D with steady-state, incompressible rheology whose viscosity depends on the subsurface temperature distribution. The thickness of lithosphere along the profile in the EVZ is identified by 700C isotherm and 1022 Pa s iso-viscosity, those reach 50 ± 3 km depth at distance of 100 km from rift axis. Geodetic observation and model prediction results show the ~90% of spreading is accommodated within ~45 km of the rift axis in each direction. Model predicts ~8.5 mm.yr-1 subsidence at the surface of rift center when magmatic plumbing is inactive. The rift center (the highest magmatic influx is ~11 mm.yr-1) in model shifts ~10 - 20 km west to generate observed style surface deformation. The spreading velocity, isotherm and depth of isotherm are the driving forces resulting in the surface deformation. These three parameters have more or less equal weight. However, as the center of deformation in the EVZ shifts and most of the subsidence takes place in the volcanic system that is currently the active which is the located of plate axis.

Role of sedimentation in continental rifting from comparing two narrow rift valleys the Salton Trough and Death Valley-California  [PDF]
Musa Hussein, Laura F. Serpa, Aaron A. Velasco, Diane Doser
Natural Science (NS) , 2011, DOI: 10.4236/ns.2011.311119
Abstract: To unravel the forces and better understand the processes that drive continental rifting, and to understand the role of sedimentation in promoting the rifting process, we compare; the different geological features of two narrow rifts, the Salton Trough and Death Valley, California. According to our models, the Moho is 22 km deep to the southwest of the Salton Sea on US-Mexico border and it deepens to 30 km in the region west of the Salton Trough. In Death Valley, the Moho is 24 km deep in the central part of the basin and it deepens to 32 km outside of the basin. The dome shaped Moho in both rifts is suggested to be primarily the product of magmatic activity in the lower crust and upper mantle. Death Valley is narrow rift in the initial stage of rifting with several sedimentary basins 2 - 4 km deep. In Death Valley magmatic (thermal) forces appears to drive the rifting process. The Salton Trough is wider than Death Valley and is moving toward sea floor spreading. The depth of the sedimentary basins ranges from 8 - 10 km and a combination of thermal and sedimentation appears to drive rifting processes in the Salton Trough.
Cenozoic bimodal volcanic rocks of the West Qinling: Implication for the genesis and nature of the rifting of north-south tectonic belt
西秦岭新生代双峰式火山作用及南北构造带成因初探

YU XueHui,MO XuanXue,ZHAO ZhiDan,HE WenYan,LI Yong,
喻学惠
,莫宣学,赵志丹,和文言,李勇

岩石学报 , 2011,
Abstract: Presenting the analysis data of whole rock chemistry, REE and trace element and Sr, Nd, Pb isotopes of the rhyolite, and 27 isotopic dating of the Cenozoic bimodal volcanic rocks from West Qinling. The studies showed that the Cenozoic bimodal volcanic rocks like to East Africa rift, consisted of kamafugite, carbonatite, shoshonite, rhyolite and/or trachyte. The age of the bimodal volcanic rocks is from 23Ma to 7.1Ma determined by isotopic dating of K/Ar and 39Ar/40Ar. The 87Sr/86Sr=0.704031~0.70525, 206Pb/2...
Rifting process and formation mechanisms of syn-rift stage prolongation in the deepwater basin, northern South China Sea
DongDong Dong,ShiGuo Wu,GongCheng Zhang,ShengQiang Yuan
Chinese Science Bulletin , 2008, DOI: 10.1007/s11434-008-0326-1
Abstract: Based on the latest seismic and geological data, tectonic subsidence of three seismic lines in the deepwater area of Pearl River Mouth Basin (PRMB), the northern South China Sea (SCS), is calculated. The result shows that the rifting process of study area is different from the typical passive continental margin basin. Although the seafloor spreading of SCS initiated at 32 Ma, the tectonic subsidence rate does not decrease but increases instead, and then decreases at about 23 Ma, which indicates that the rifting continued after the onset of seafloor spreading until about 23 Ma. The formation thickness exhibits the same phenomenon, that is the syn-rift stage prolonged and the post-rift thermal subsidence delayed. The formation mechanisms are supposed to be three: (1) the lithospheric rigidity of the northern SCS is weak and its ductility is relatively strong, which delayed the strain relaxation resulting from the seafloor spreading; (2) the differential layered independent extension of the lithosphere may be one reason for the delay of post-rift stage; and (3) the southward transition of SCS spreading ridge during 24 to 21 Ma and the corresponding acceleration of seafloor spreading rate then triggered the initiation of large-scale thermal subsidence in the study area at about 23 Ma.
Post-Rifting Magmatism and the Drowned Reefs in the Xisha Archipelago Domain Post-Rifting Magmatism and the Drowned Reefs in the Xisha Archipelago Domain  [PDF]
WANG Hongli,ZHAO Qiang,WU Shiguo,WANG Dawei,WANG Bin
- , 2018,
Abstract: Fourteen isolated drowned reefs have been identified around the Xisha Uplift by multibeam and seismic data. The drowning processes of these reefs can be divided into three different stages, which correspond to three different accelerated tectonic subsidence periods. The drowning of the Xisha reefs is the result of the combined action of tectonic subsidence and sea level fluctuations, and the tectonic subsidence rate had to remain above 0.2 mm yr~(-1 )for a long time. Three abrupt accelerated tectonic subsidence events that occurred in the late Miocene, Pliocene and early Quaternary in the Xisha Uplift were closely related to the thermal subsidence processes after three stages of post-rifting magmatism. The magmatism of the middle Miocene and the following thermal subsidence resulted in the drowning of reefs in the northwestern Xisha uplift(Zone A). During the early Pliocene, massive magmatic intrusions and volcanic eruptions occurred in the Xisha Uplift. Then, the subsequent thermal subsidence started the drowning process of reefs in the northeastern and western regions of the Xisha Uplift(Zone B and C). During the early Quaternary, large-scale magmatism also occurred in the Xisha Uplift. The subsequent thermal subsidence resulted in a new rapid tectonic subsidence, which caused the reefs in the southern and southeastern regions of the Xisha Uplift to drown(Zone D and E)
The propagation of seafloor spreading in the southwestern subbasin, South China Sea
JiaBiao Li,WeiWei Ding,ZiYin Wu,Jie Zhang,ChongZhi Dong
Chinese Science Bulletin , 2012, DOI: 10.1007/s11434-012-5329-2
Abstract: On the basis of the summary of basic characteristics of propagation, the dynamic model of the tectonic evolution in the Southwestern Subbasin (SWSB), South China Sea (SCS), has been established through high resolution multi-beam swatch bathymetry and multi-channel seismic profiles, combined with magnetic anomaly analysis. Spreading propagates from NE to SW and shows a transition from steady seafloor spreading, to initial seafloor spreading, and to continental rifting in the southwest end. The spreading in SWSB (SCS) is tectonic dominated, with a series of phenomena of inhomogeneous tectonics and sedimentation.
Page 1 /100
Display every page Item


Home
Copyright © 2008-2017 Open Access Library. All rights reserved.