The Oligocene Afro-Arabian flood volcanic province contains significant silicic pyroclastic rocks (】60000 km^3 constituting up to 20%of the volcanic stratigraphy).Rhyolitic tephras,synchronous with the Afro-Arabian s...The Oligocene Afro-Arabian flood volcanic province contains significant silicic pyroclastic rocks (】60000 km^3 constituting up to 20%of the volcanic stratigraphy).Rhyolitic tephras,synchronous with the Afro-Arabian silicic pyroclastic rocks,are found in Indian Ocean ODP holes 711A.They are geoche-mically akin to the Afro-Arabian silicic pyroclastic rocks.This suggests that the tephras originated from Afro-Arabian silicic eruptions and represents more distal fallout of this volcanism.The temporal coin-展开更多
The high-MgO ultramafic volcanic rocks in the NW Ad Dhala province are classified as meimechite according to the IUGS classification scheme.This province represents the southeastern outcrops of the Yemen Volcanic Grou...The high-MgO ultramafic volcanic rocks in the NW Ad Dhala province are classified as meimechite according to the IUGS classification scheme.This province represents the southeastern outcrops of the Yemen Volcanic Group(YVG),which constitutes part of the AfroArabian continental large igneous province(LIP) and located within the boundary of the Afar mantle plume.In this study,we present the chemical compositions of olivine and Cr-spinel in meimechite rocks from Bagah Village in NW Ad Dhala province,aiming to characterize the genesis and partial melting conditions and to estimate the crystallization temperatures of these high-MgO rocks.Olivine crystals are characterized by high forsterite,ranges from Mg-rich core(up to Fo_(89.69)) to relatively Fe-rich rim(down to Fo_(78.57)),high CaO,MgO and MnO whereas Cr-spinel crystals have high TiO_(2) and Cr# values ranging from 0.49 to 0.63 which indicate that they are crystallized from primary magma and are typical of volcanic olivine and Crspinel that formed in intraplate tectonic setting.Olivine and Cr-spinel compositional data and primary melt composition(MgO ~ 23 wt.%) are compatible with the derivation of studied meimechite rocks from peridotite mantle source by small degrees of partial melting under conditions of high temperature and pressure at great depths,mostly within the garnet stability field.Also,these data provide a compelling indicator for the important role of upwelling Afar mantle plume in the genesis of these high-MgO ultramafic volcanic rocks.Finally,based on the different olivine-liquid equilibrium methods and Al-in-olivine thermometer approach the estimated crystallization temperature ranges from 1450 to 1490℃,and mantle potential temperature(Tp) ranges from 1617 to 1677℃,at high pressure(3-4.8 GPa).These high temperatures substantiate the existence of the Afar thermal mantle plume and its important role in the genesis of the studied meimechite rocks.展开更多
This application note discusses the preliminary results of paleomagnetics studies of several incisions of the Paleozoic period the territory of Armenia and neighboring regions （Minor Caucasus）. It is supposed that b...This application note discusses the preliminary results of paleomagnetics studies of several incisions of the Paleozoic period the territory of Armenia and neighboring regions （Minor Caucasus）. It is supposed that before the Permian period the Armenian-lranian Mezocontinent was uniform with Afro-Arabia and only at the end of the late Paleozoic the formed Mesozoic ocean separated these areas from each other. A result of application of the complex laboratory investigations were identified from samples of primary magnetization the direction of which corresponds to the time of formation of the studied rocks. On the basis of paleomagnetic researches of Triassic, Permian, Devonian, Carbonian rocks a preliminary conclusion has been made about the dipole configuration of the geomagnetic field throughout Paleozoic. The comparison of the obtained data to paleomagnetic definitions of African, Arabian plates, Europe and the Siberian platform leads to the conclusion that the Minor Caucasus existed separately from the present general lithosphere blocks of Greater Caucasus and Europe.展开更多
文摘The Oligocene Afro-Arabian flood volcanic province contains significant silicic pyroclastic rocks (】60000 km^3 constituting up to 20%of the volcanic stratigraphy).Rhyolitic tephras,synchronous with the Afro-Arabian silicic pyroclastic rocks,are found in Indian Ocean ODP holes 711A.They are geoche-mically akin to the Afro-Arabian silicic pyroclastic rocks.This suggests that the tephras originated from Afro-Arabian silicic eruptions and represents more distal fallout of this volcanism.The temporal coin-
文摘The high-MgO ultramafic volcanic rocks in the NW Ad Dhala province are classified as meimechite according to the IUGS classification scheme.This province represents the southeastern outcrops of the Yemen Volcanic Group(YVG),which constitutes part of the AfroArabian continental large igneous province(LIP) and located within the boundary of the Afar mantle plume.In this study,we present the chemical compositions of olivine and Cr-spinel in meimechite rocks from Bagah Village in NW Ad Dhala province,aiming to characterize the genesis and partial melting conditions and to estimate the crystallization temperatures of these high-MgO rocks.Olivine crystals are characterized by high forsterite,ranges from Mg-rich core(up to Fo_(89.69)) to relatively Fe-rich rim(down to Fo_(78.57)),high CaO,MgO and MnO whereas Cr-spinel crystals have high TiO_(2) and Cr# values ranging from 0.49 to 0.63 which indicate that they are crystallized from primary magma and are typical of volcanic olivine and Crspinel that formed in intraplate tectonic setting.Olivine and Cr-spinel compositional data and primary melt composition(MgO ~ 23 wt.%) are compatible with the derivation of studied meimechite rocks from peridotite mantle source by small degrees of partial melting under conditions of high temperature and pressure at great depths,mostly within the garnet stability field.Also,these data provide a compelling indicator for the important role of upwelling Afar mantle plume in the genesis of these high-MgO ultramafic volcanic rocks.Finally,based on the different olivine-liquid equilibrium methods and Al-in-olivine thermometer approach the estimated crystallization temperature ranges from 1450 to 1490℃,and mantle potential temperature(Tp) ranges from 1617 to 1677℃,at high pressure(3-4.8 GPa).These high temperatures substantiate the existence of the Afar thermal mantle plume and its important role in the genesis of the studied meimechite rocks.
文摘This application note discusses the preliminary results of paleomagnetics studies of several incisions of the Paleozoic period the territory of Armenia and neighboring regions （Minor Caucasus）. It is supposed that before the Permian period the Armenian-lranian Mezocontinent was uniform with Afro-Arabia and only at the end of the late Paleozoic the formed Mesozoic ocean separated these areas from each other. A result of application of the complex laboratory investigations were identified from samples of primary magnetization the direction of which corresponds to the time of formation of the studied rocks. On the basis of paleomagnetic researches of Triassic, Permian, Devonian, Carbonian rocks a preliminary conclusion has been made about the dipole configuration of the geomagnetic field throughout Paleozoic. The comparison of the obtained data to paleomagnetic definitions of African, Arabian plates, Europe and the Siberian platform leads to the conclusion that the Minor Caucasus existed separately from the present general lithosphere blocks of Greater Caucasus and Europe.
