The Lesser Himalaya in central Nepal consists of greenschist\|facies metasedimentary rocks, which are overthrust by the amphibolite\|facies rocks of the Higher Himalaya along the Upper Main Central Thrust (UMCT). Desp...The Lesser Himalaya in central Nepal consists of greenschist\|facies metasedimentary rocks, which are overthrust by the amphibolite\|facies rocks of the Higher Himalaya along the Upper Main Central Thrust (UMCT). Despite a number of works on metamorphism of the MCT zone and the Higher Himalaya, the low\|grade metamorphic rocks to the south of the MCT zone have not been studied yet.In the present study, an attempt was made to constrain the metamorphic events and thermal structure of the whole Lesser Himalaya by means of white mica (Ms) compositions. About 600Ms grains in 48 metapelitic samples from the Lesser Himalaya were analysed by the EPMA. Compositional zoning in individual Ms grains was checked by means of X\|ray compositional mapping. There exist wide intersample, intrasample and within grain compositional variations in Ms in the samples from the Lesser Himalaya. Sheared Ms phenocrysts in pegmatites and gneisses have compositions very close to that of the ideal muscovite. Detrital Ms show wide variation in phengite content, most of which are poor in phengite content, and are most probably derived from older higher\|grade metamorphic rocks.展开更多
New monazite U\|Pb geochronological data from the Everest region suggest that 20～25Ma elapsed between the initial India—Asia collision and kyanite\|sillimanite grade metamorphism. Our results indicate a two\|phase m...New monazite U\|Pb geochronological data from the Everest region suggest that 20～25Ma elapsed between the initial India—Asia collision and kyanite\|sillimanite grade metamorphism. Our results indicate a two\|phase metamorphic history, with peak Barrovian metamorphism at (32 2±0 4)Ma and a later high\|temperature, low\|pressure event (620℃, 400MPa) at (22 7±0 2)Ma.. Emplacement and crystallization of the Everest granite subsequently occurred at 20 5～21 3Ma. The monazite crystallization ages that differ by 10Ma are recorded in two structurally adjacent rocks of different lithology, which have the same post collisional p—T history.. Scanning electron microscopy reveals that the younger monazite is elaborately shaped and grew in close association with apatite at grain boundaries and triple junctions, suggesting that growth was stimulated by a change in the fluid regime. The older monazite is euhedral, is not associated with apatite, and is commonly armoured within silicate minerals. During the low\|pressure metamorphic event, the armouring protected the older monazites, and a lack of excess apatite in this sample prevented new growth. Textural relationships suggest that apatite is one of the necessary monazite\|producing reactants, and spots within monazite that are rich in Ca, Fe, Al and Si suggest that allanite acted as a preexisting rare earth element host. We propose a simplified reaction for monazite crystallization based on this evidence.展开更多
The oxidative desulphurization process of coal with different metamorphism degrees treated by an air-steam mixture has been studied.It has been shown that the pyrite present in black coal and anthracite is oxidized wi...The oxidative desulphurization process of coal with different metamorphism degrees treated by an air-steam mixture has been studied.It has been shown that the pyrite present in black coal and anthracite is oxidized with the sulphur dioxide formation,and the process chemical mechanism does not depend on the quality of organic matter.The medium-metamorphized coal,capable of turning into a plastic state and cake in the range of investigated temperatures(350～450 ℃),is desulphurized with the greatest difficulty.The chemical mechanism dealing with the transformations of pyritic sulphur present in brown coal differs from similar processes taking place in black coal and anthracite,because FeS2 is converted with hydrogen sulphide formation at desulphurization.展开更多
The Arun mega\|antiform, a large N—S structure transversal to the tectonic trend of the E Nepal Himalaya, is a tectonic window offering a complete section of the Himalayan nappe pile, from the Lesser Himalayan zone t...The Arun mega\|antiform, a large N—S structure transversal to the tectonic trend of the E Nepal Himalaya, is a tectonic window offering a complete section of the Himalayan nappe pile, from the Lesser Himalayan zone to the Tethyan Himalaya. At the northern end of the Arun tectonic window (ATW), the Ama Drime—Nyonno Ri range of south Tibet exposes a section of that portion of the Main Central Thrust (MCT) zone and Lesser Himalayan Crystallines (LHC) which elsewhere in Nepal is concealed below the overlying Higher Himalayan Crystalline (HHC) nappe (Fig. 1). As throughout the Himalaya at the structural level of the MCT, the ATW is characterized by an inverted metamorphic field gradient characterized by a progression from chlorite to sillimanite grade from low to high structural levels of the nappe pile. Metamorphic peak temperatures rise from circa 400℃ in the pelitic and psammitic Precambrian metasediments of the Lesser Himalayan Tumlingtar Unit, to 550～620℃ in the overlying LHC, to over 700℃ in the muscovite\|free Barun Gneiss, the lowermost HHC unit in the Arun valley.展开更多
Eclogite was firstly discovered at the Da Qaidam region (Yang,et al., 1998), and then in the Xitieshan and Dulan regions in 1999, constituting an over 350km long high\|pressure metamorphic belt in the northeastern Qin...Eclogite was firstly discovered at the Da Qaidam region (Yang,et al., 1998), and then in the Xitieshan and Dulan regions in 1999, constituting an over 350km long high\|pressure metamorphic belt in the northeastern Qinghai—Tibet plateau. Eclogites occur as pods in the garnet\|muscovite gneiss of the Dakendaban Group (or called Shaliuhe Group in Dulan) of Upper Proterozoic age. In general, the pods of eclogite vary in size; most of them are less than 20m×10m, some large ones up to about 100m×50m. The eclogite\|hosted gneiss is pale\|gray in color, consisting mainly plagioclase and quartz, and minor muscovite (5%～10% in vol.) and garnet (1%～2%). Some of the country rocks of eclogite are mica\|quartz\|(feldspar) schist, quartzite, and ultramafic rocks, the latter also occur in blocks.Over 50 pods were found in a belt of 10km×3km in the Da Qaidam region (No.1 location). Only a few pods of eclogite were found in the Xitieshan region in 1999 field expedition (No.2 location). Eclogite in Dulan occurs in the Proterozoic strata of Shaliuhe Group (same as the Dakendaban Group but with a different name). The eclogites in the Dulan region (No.3 location) expose about 10km wide in SN and an unknown length in EW, and can be subdivided into two belts, the North Eclogite Belt of Dulan (NEBD) and the South Eclogite Belt of Dulan (SEBD).展开更多
The shallow Biella and Traversella late-orogenic plutons are intruded in the Sesia Lanzo Zone(SLZ) the innermost structural element of the Western Alpine arc,a continental unit that records a pervasive metamorphic imp...The shallow Biella and Traversella late-orogenic plutons are intruded in the Sesia Lanzo Zone(SLZ) the innermost structural element of the Western Alpine arc,a continental unit that records a pervasive metamorphic imprint related to the Alpine subduction. The country rocks consist of metapelites with minor metagranitoids,meta-aplites,metabasites and marbles. The pre-intrusive pervasive metamorphic imprint developed under eclogite facies conditions. The ductile syn-metamorphic deformation展开更多
North of the study area in lower Swat, the rocks have been found to have undergone multiple deformations with at least four periods of folding during a single Paleogene metamorphism (DiPietro and Lawrence, 1991). The ...North of the study area in lower Swat, the rocks have been found to have undergone multiple deformations with at least four periods of folding during a single Paleogene metamorphism (DiPietro and Lawrence, 1991). The earliest folds are composite W—SW vergent, syn\|metamorphic F 1/F 2 folds associated with the formation of the regional foliation. Late\|metamorphic, N—S trending open upright F 3 folds are associated with local foliation development, and E—W trending open F 4 folds are associated with retrograde metamorphism. These interfere with each other to produce dome/basin structures.展开更多
文摘The Lesser Himalaya in central Nepal consists of greenschist\|facies metasedimentary rocks, which are overthrust by the amphibolite\|facies rocks of the Higher Himalaya along the Upper Main Central Thrust (UMCT). Despite a number of works on metamorphism of the MCT zone and the Higher Himalaya, the low\|grade metamorphic rocks to the south of the MCT zone have not been studied yet.In the present study, an attempt was made to constrain the metamorphic events and thermal structure of the whole Lesser Himalaya by means of white mica (Ms) compositions. About 600Ms grains in 48 metapelitic samples from the Lesser Himalaya were analysed by the EPMA. Compositional zoning in individual Ms grains was checked by means of X\|ray compositional mapping. There exist wide intersample, intrasample and within grain compositional variations in Ms in the samples from the Lesser Himalaya. Sheared Ms phenocrysts in pegmatites and gneisses have compositions very close to that of the ideal muscovite. Detrital Ms show wide variation in phengite content, most of which are poor in phengite content, and are most probably derived from older higher\|grade metamorphic rocks.
文摘New monazite U\|Pb geochronological data from the Everest region suggest that 20～25Ma elapsed between the initial India—Asia collision and kyanite\|sillimanite grade metamorphism. Our results indicate a two\|phase metamorphic history, with peak Barrovian metamorphism at (32 2±0 4)Ma and a later high\|temperature, low\|pressure event (620℃, 400MPa) at (22 7±0 2)Ma.. Emplacement and crystallization of the Everest granite subsequently occurred at 20 5～21 3Ma. The monazite crystallization ages that differ by 10Ma are recorded in two structurally adjacent rocks of different lithology, which have the same post collisional p—T history.. Scanning electron microscopy reveals that the younger monazite is elaborately shaped and grew in close association with apatite at grain boundaries and triple junctions, suggesting that growth was stimulated by a change in the fluid regime. The older monazite is euhedral, is not associated with apatite, and is commonly armoured within silicate minerals. During the low\|pressure metamorphic event, the armouring protected the older monazites, and a lack of excess apatite in this sample prevented new growth. Textural relationships suggest that apatite is one of the necessary monazite\|producing reactants, and spots within monazite that are rich in Ca, Fe, Al and Si suggest that allanite acted as a preexisting rare earth element host. We propose a simplified reaction for monazite crystallization based on this evidence.
文摘The oxidative desulphurization process of coal with different metamorphism degrees treated by an air-steam mixture has been studied.It has been shown that the pyrite present in black coal and anthracite is oxidized with the sulphur dioxide formation,and the process chemical mechanism does not depend on the quality of organic matter.The medium-metamorphized coal,capable of turning into a plastic state and cake in the range of investigated temperatures(350～450 ℃),is desulphurized with the greatest difficulty.The chemical mechanism dealing with the transformations of pyritic sulphur present in brown coal differs from similar processes taking place in black coal and anthracite,because FeS2 is converted with hydrogen sulphide formation at desulphurization.
文摘The Arun mega\|antiform, a large N—S structure transversal to the tectonic trend of the E Nepal Himalaya, is a tectonic window offering a complete section of the Himalayan nappe pile, from the Lesser Himalayan zone to the Tethyan Himalaya. At the northern end of the Arun tectonic window (ATW), the Ama Drime—Nyonno Ri range of south Tibet exposes a section of that portion of the Main Central Thrust (MCT) zone and Lesser Himalayan Crystallines (LHC) which elsewhere in Nepal is concealed below the overlying Higher Himalayan Crystalline (HHC) nappe (Fig. 1). As throughout the Himalaya at the structural level of the MCT, the ATW is characterized by an inverted metamorphic field gradient characterized by a progression from chlorite to sillimanite grade from low to high structural levels of the nappe pile. Metamorphic peak temperatures rise from circa 400℃ in the pelitic and psammitic Precambrian metasediments of the Lesser Himalayan Tumlingtar Unit, to 550～620℃ in the overlying LHC, to over 700℃ in the muscovite\|free Barun Gneiss, the lowermost HHC unit in the Arun valley.
文摘Eclogite was firstly discovered at the Da Qaidam region (Yang,et al., 1998), and then in the Xitieshan and Dulan regions in 1999, constituting an over 350km long high\|pressure metamorphic belt in the northeastern Qinghai—Tibet plateau. Eclogites occur as pods in the garnet\|muscovite gneiss of the Dakendaban Group (or called Shaliuhe Group in Dulan) of Upper Proterozoic age. In general, the pods of eclogite vary in size; most of them are less than 20m×10m, some large ones up to about 100m×50m. The eclogite\|hosted gneiss is pale\|gray in color, consisting mainly plagioclase and quartz, and minor muscovite (5%～10% in vol.) and garnet (1%～2%). Some of the country rocks of eclogite are mica\|quartz\|(feldspar) schist, quartzite, and ultramafic rocks, the latter also occur in blocks.Over 50 pods were found in a belt of 10km×3km in the Da Qaidam region (No.1 location). Only a few pods of eclogite were found in the Xitieshan region in 1999 field expedition (No.2 location). Eclogite in Dulan occurs in the Proterozoic strata of Shaliuhe Group (same as the Dakendaban Group but with a different name). The eclogites in the Dulan region (No.3 location) expose about 10km wide in SN and an unknown length in EW, and can be subdivided into two belts, the North Eclogite Belt of Dulan (NEBD) and the South Eclogite Belt of Dulan (SEBD).
文摘The shallow Biella and Traversella late-orogenic plutons are intruded in the Sesia Lanzo Zone(SLZ) the innermost structural element of the Western Alpine arc,a continental unit that records a pervasive metamorphic imprint related to the Alpine subduction. The country rocks consist of metapelites with minor metagranitoids,meta-aplites,metabasites and marbles. The pre-intrusive pervasive metamorphic imprint developed under eclogite facies conditions. The ductile syn-metamorphic deformation
文摘North of the study area in lower Swat, the rocks have been found to have undergone multiple deformations with at least four periods of folding during a single Paleogene metamorphism (DiPietro and Lawrence, 1991). The earliest folds are composite W—SW vergent, syn\|metamorphic F 1/F 2 folds associated with the formation of the regional foliation. Late\|metamorphic, N—S trending open upright F 3 folds are associated with local foliation development, and E—W trending open F 4 folds are associated with retrograde metamorphism. These interfere with each other to produce dome/basin structures.
