A typical section of ophiolite at Tangga in Lhaze district shows the sequential association of ophiolite from north to south as follows: basal tectonized harzhurgitc,altered basalt, and red radiolarian chert. The ophi...A typical section of ophiolite at Tangga in Lhaze district shows the sequential association of ophiolite from north to south as follows: basal tectonized harzhurgitc,altered basalt, and red radiolarian chert. The ophiolites, late Cretaceous in age, arelithologically similar to the current models of oceanic crust and upper mantle, representing the slice of Tethys ocean basin. At Chongdui, about 20 km southeast of Xigaze, a thick sequence of trench turbidite is recognized associated with pillow lava and submarine volcanic conglomerate. The trench turbidite is well. layered with a suit of rhythmical deposits of graded bedding.The coarse-grained ophiolitic greywacke is generally at the base of each rhythm and gives its way upward to the gabbroid greywacke and finer material, while the chert and volcanic tuff rest at the top, showing good rhythmic pattern of Bouma cycle.Because it has not been documented before.it is named “the Chongdui Formation”after the place. It is also late Cretaceous in age. At the same place it is found that the basal serpentinite overthrusts northwards on the trench turbidite. There, the basal ultramafic rock dips southwards in contrast to the northward dipping of the turbidites, showing thrust drag at contact. Because the trench sediments mark the margin of Eurasia continent, it is suggested that the ophiolites are emplaced tectonically along the suture zone where Indian continent and Eruasia continent are welded together. A four-stage model is proposed to expblin the plate history for Himalayan geology.展开更多
A garnet lherzolite xenolith hosted in olivine nephelinite from Xilong,Zhejiang Province ,southeastern China, shows clear evidence of modal metasomatism involving a special sanidine-olivine-diopside(SOD) association w...A garnet lherzolite xenolith hosted in olivine nephelinite from Xilong,Zhejiang Province ,southeastern China, shows clear evidence of modal metasomatism involving a special sanidine-olivine-diopside(SOD) association which was produced by replacement of primary orthopyroxene.The fluid responsible for the measomatism was a silica-undersaturated vapour,rich in K,Ba,Sr and Ti.It is suggested that the SOD assemblage is the product of metasomatism of a depleted lherzolite precursor,and formed in the upper mantle prior to entrainment and eruption.展开更多
文摘A typical section of ophiolite at Tangga in Lhaze district shows the sequential association of ophiolite from north to south as follows: basal tectonized harzhurgitc,altered basalt, and red radiolarian chert. The ophiolites, late Cretaceous in age, arelithologically similar to the current models of oceanic crust and upper mantle, representing the slice of Tethys ocean basin. At Chongdui, about 20 km southeast of Xigaze, a thick sequence of trench turbidite is recognized associated with pillow lava and submarine volcanic conglomerate. The trench turbidite is well. layered with a suit of rhythmical deposits of graded bedding.The coarse-grained ophiolitic greywacke is generally at the base of each rhythm and gives its way upward to the gabbroid greywacke and finer material, while the chert and volcanic tuff rest at the top, showing good rhythmic pattern of Bouma cycle.Because it has not been documented before.it is named “the Chongdui Formation”after the place. It is also late Cretaceous in age. At the same place it is found that the basal serpentinite overthrusts northwards on the trench turbidite. There, the basal ultramafic rock dips southwards in contrast to the northward dipping of the turbidites, showing thrust drag at contact. Because the trench sediments mark the margin of Eurasia continent, it is suggested that the ophiolites are emplaced tectonically along the suture zone where Indian continent and Eruasia continent are welded together. A four-stage model is proposed to expblin the plate history for Himalayan geology.
文摘A garnet lherzolite xenolith hosted in olivine nephelinite from Xilong,Zhejiang Province ,southeastern China, shows clear evidence of modal metasomatism involving a special sanidine-olivine-diopside(SOD) association which was produced by replacement of primary orthopyroxene.The fluid responsible for the measomatism was a silica-undersaturated vapour,rich in K,Ba,Sr and Ti.It is suggested that the SOD assemblage is the product of metasomatism of a depleted lherzolite precursor,and formed in the upper mantle prior to entrainment and eruption.
