In the Northern Himalayan region of Southern Xizang (Tibet),from the Lower Triassic to Upper Eocene 73 Sequences have been identified, with an average duration of 2.9 Ma;these can in turn be grouped into 24 super-Sequ...In the Northern Himalayan region of Southern Xizang (Tibet),from the Lower Triassic to Upper Eocene 73 Sequences have been identified, with an average duration of 2.9 Ma;these can in turn be grouped into 24 super-Sequences and 6 super-sequence sets. During Mesozoic and Paleogene, several large sea - level falls occurred in the Eastern Neo-Tethys. Among the recognized sea- level falls, the important ones include those at the ages of 255 Ma, 215 Ma,177 Ma, 138 Ma, 103 Ma and 68 Ma .Those at 239 Ma, 215 Ma, 157 Ma,80 Ma, 50Ma and 36 Ma are also significant. The third-order Sequences and sea-level cycles Probably reflect mainly global sea - level fluctuations, while the higher rank cycles seem more closely related to the basin evolution of the Neo-Tethys. Based on the study, six major periods have been suggested for ths tectonic evolution of the Eastern Neo-Tethys and the plates, i. e. the Pangea Period (Pre-Triassic), continental rifting Period (Triassic to Early Jurassic ), inter-continental sea Period (Middle Jurassic ), continental divergence period (late Middle Jurassic to Early Cretaceous ), continental convergence period (Late Cretaceous ) and the continental collision Period (Paleogene ). These major Periods can be further subdivided into eight stages according to the basin evolution. In each of the periods and Stages, Sequences and their boundaries show clear characters related to the tectonic background. The study indicater that the initial breakup of the Pangea along the Indus- Yarlung may have taken Place around 239 Ma. The Late Bathonian to Early Callovian seems to have been a critical time in the evolution of the Neo-Tethys, with the turning Point around 158 Ma. The blocks split from the northern margin of the Gondwana continual did not obviously drift away from the Indian Plate until Callovian .The oceanic crust subduction in the Neo- Tethys may have Started at 113Ma, while the contraction of the ocean probably began at 107- 103 Ma. The initial contact of the Indian Plate with the Eurasian plate may have taken Place around 80 Ma, with strong uplifting and thrushng in Late Paleocene.展开更多
The Himalayan leucogranites provide insights into the partial melting behavior of relatively deeper crustal rocks and tectono-magmatic history of the Himalayan Orogen. The Paiku leucogranites of northern Himalaya can ...The Himalayan leucogranites provide insights into the partial melting behavior of relatively deeper crustal rocks and tectono-magmatic history of the Himalayan Orogen. The Paiku leucogranites of northern Himalaya can be subdivided into two-mica leucogranite(TML), garnet-bearing leucogranite(GL), cordierite-bearing leucogranite(CL), and tourmaline-bearing leucogranite(TL). All of them are high-K, peraluminous, calc-alkalic to alkali-calcic rocks. They are enriched in light rare earth elements(LREE) and large ion lithophile elements(LILE), and show pronounced negative anomalies of Sr, Ba, K and Ti, but positive anomalies of Nb and Rb. LA-ICP-MS U-Pb zircon dating of one TML, one GL, and two CL samples yielded variable 206Pb/238U ages ranging from 23.6 to 16.1 Ma, indicating the Paiku leucogranites underwent a low degree of partial melting process. Combining with previous studies, we suggest the Paiku leucogranites were derived from partial melting of metasedimentary rocks of the Higher Himalayan Sequence(HHS). The GL and TL mainly resulted from the muscovite-dehydration melting, whereas the TML and CL were mainly derived from the biotite-dehydration melting. Finally, it is concluded that the Paiku leucogranites were probably formed during the subduction of the Indian crust.展开更多
The northern Himalayas was situated on the north margin of the Indian plate and was part of the Gondwana. During Mesozoic and Cenozoic, the geological development of the region was mainly controlled by the evolution o...The northern Himalayas was situated on the north margin of the Indian plate and was part of the Gondwana. During Mesozoic and Cenozoic, the geological development of the region was mainly controlled by the evolution of the Neotethyan ocean as well as the movement of the plates (or blocks) on its two sides, showing as a typical passive continental margin [1] . The Mesozoic and Cenozoic sedimentation forms a giant transgression\|regression cycle in this region [2] . The strata have clearly recorded the processes that the Gondwana continent broke up, the Indian plate drifted northward, and consequently collided with the Eurasia, suggesting a Wilson cycle. They also reveals the evolution of the Neotethyan ocean from breakup to expanding, contracting and finally to closing. 1\ The major sedimentary cycles\;The marine Mesozoic and Cenozoic developed continuously in the northern Himalayas, south Tibet, with a total thickness of about 8000m. From the Triassic to Eocene, 70 third\|order sequences have been recognized [2] . Among them 12 are in the Triassic, 22 in the Jurassic, 27 in the Cretaceous and 9 in the Paleogene, with an average duration of 3m.y for each. These can in turn be grouped as 21 sequence sets and 6 mesosequences (2nd order). All of the mesosequences are bounded by prominent discontinuity at bottom, either with subaerial erosion or submarine truncation [2] , suggesting abrupt falls of sea\|level in long\|term changes. The approximate ages for the basal boundaries of these mesosequences are respectively at ca. 257Ma (latest Capitanian), 215Ma (latest Norian), 177Ma (early Aalenian), 138Ma (mid Tithonian), 103Ma (mid Albian) and 68Ma (late Maastrichtian). Each of mesosequences forms a major sedimentary cycles in the region and may result from the joint effects of global sea\|level changes and regional tectonic\|basin evolution.展开更多
文摘In the Northern Himalayan region of Southern Xizang (Tibet),from the Lower Triassic to Upper Eocene 73 Sequences have been identified, with an average duration of 2.9 Ma;these can in turn be grouped into 24 super-Sequences and 6 super-sequence sets. During Mesozoic and Paleogene, several large sea - level falls occurred in the Eastern Neo-Tethys. Among the recognized sea- level falls, the important ones include those at the ages of 255 Ma, 215 Ma,177 Ma, 138 Ma, 103 Ma and 68 Ma .Those at 239 Ma, 215 Ma, 157 Ma,80 Ma, 50Ma and 36 Ma are also significant. The third-order Sequences and sea-level cycles Probably reflect mainly global sea - level fluctuations, while the higher rank cycles seem more closely related to the basin evolution of the Neo-Tethys. Based on the study, six major periods have been suggested for ths tectonic evolution of the Eastern Neo-Tethys and the plates, i. e. the Pangea Period (Pre-Triassic), continental rifting Period (Triassic to Early Jurassic ), inter-continental sea Period (Middle Jurassic ), continental divergence period (late Middle Jurassic to Early Cretaceous ), continental convergence period (Late Cretaceous ) and the continental collision Period (Paleogene ). These major Periods can be further subdivided into eight stages according to the basin evolution. In each of the periods and Stages, Sequences and their boundaries show clear characters related to the tectonic background. The study indicater that the initial breakup of the Pangea along the Indus- Yarlung may have taken Place around 239 Ma. The Late Bathonian to Early Callovian seems to have been a critical time in the evolution of the Neo-Tethys, with the turning Point around 158 Ma. The blocks split from the northern margin of the Gondwana continual did not obviously drift away from the Indian Plate until Callovian .The oceanic crust subduction in the Neo- Tethys may have Started at 113Ma, while the contraction of the ocean probably began at 107- 103 Ma. The initial contact of the Indian Plate with the Eurasian plate may have taken Place around 80 Ma, with strong uplifting and thrushng in Late Paleocene.
基金supported by the National Natural Science Foundation of China (Nos. 41872070, 41802071, 41773026 and 41303028)the China Geological Survey (No. DD20190053)
文摘The Himalayan leucogranites provide insights into the partial melting behavior of relatively deeper crustal rocks and tectono-magmatic history of the Himalayan Orogen. The Paiku leucogranites of northern Himalaya can be subdivided into two-mica leucogranite(TML), garnet-bearing leucogranite(GL), cordierite-bearing leucogranite(CL), and tourmaline-bearing leucogranite(TL). All of them are high-K, peraluminous, calc-alkalic to alkali-calcic rocks. They are enriched in light rare earth elements(LREE) and large ion lithophile elements(LILE), and show pronounced negative anomalies of Sr, Ba, K and Ti, but positive anomalies of Nb and Rb. LA-ICP-MS U-Pb zircon dating of one TML, one GL, and two CL samples yielded variable 206Pb/238U ages ranging from 23.6 to 16.1 Ma, indicating the Paiku leucogranites underwent a low degree of partial melting process. Combining with previous studies, we suggest the Paiku leucogranites were derived from partial melting of metasedimentary rocks of the Higher Himalayan Sequence(HHS). The GL and TL mainly resulted from the muscovite-dehydration melting, whereas the TML and CL were mainly derived from the biotite-dehydration melting. Finally, it is concluded that the Paiku leucogranites were probably formed during the subduction of the Indian crust.
基金theNationalNaturalScienceFoundationofChina (No .4982 5 10 2 )
文摘The northern Himalayas was situated on the north margin of the Indian plate and was part of the Gondwana. During Mesozoic and Cenozoic, the geological development of the region was mainly controlled by the evolution of the Neotethyan ocean as well as the movement of the plates (or blocks) on its two sides, showing as a typical passive continental margin [1] . The Mesozoic and Cenozoic sedimentation forms a giant transgression\|regression cycle in this region [2] . The strata have clearly recorded the processes that the Gondwana continent broke up, the Indian plate drifted northward, and consequently collided with the Eurasia, suggesting a Wilson cycle. They also reveals the evolution of the Neotethyan ocean from breakup to expanding, contracting and finally to closing. 1\ The major sedimentary cycles\;The marine Mesozoic and Cenozoic developed continuously in the northern Himalayas, south Tibet, with a total thickness of about 8000m. From the Triassic to Eocene, 70 third\|order sequences have been recognized [2] . Among them 12 are in the Triassic, 22 in the Jurassic, 27 in the Cretaceous and 9 in the Paleogene, with an average duration of 3m.y for each. These can in turn be grouped as 21 sequence sets and 6 mesosequences (2nd order). All of the mesosequences are bounded by prominent discontinuity at bottom, either with subaerial erosion or submarine truncation [2] , suggesting abrupt falls of sea\|level in long\|term changes. The approximate ages for the basal boundaries of these mesosequences are respectively at ca. 257Ma (latest Capitanian), 215Ma (latest Norian), 177Ma (early Aalenian), 138Ma (mid Tithonian), 103Ma (mid Albian) and 68Ma (late Maastrichtian). Each of mesosequences forms a major sedimentary cycles in the region and may result from the joint effects of global sea\|level changes and regional tectonic\|basin evolution.
