The team established the chemical stratigraphy, biostratigraphy and geochronology (framework) in the strata crossing the Ediacaran-Cambrian boundary in Sonora, Mexico. In La Ciénega Formation, hematite-rich sandy dolomite 20m above carbonate rocks with the lowest carbon isotope drift in Cambrian basement was recorded, and the angular volcanic zircon crystals in it were analyzed by U-Pb chemical denudation-isotope dilution-thermal ionization mass spectrometry, and the maximum sedimentary age was 539.40±0.23Ma. The strata containing reconstructed tuff are located above the last occurrence point of macro fossils in the late Ediacaran period and below the first occurrence point of the Cambrian trace fossil Treptichnus pedum, so this age corrected the marker layer of the Ediacaran-Cambrian boundary. The volcanic activity of overflow basalt, the drift of negative carbon isotope and the time consistency of biological transition related to the southern Lauren continental rift all conform to the mechanism of extinction caused by the eruption of igneous provinces at the end of Ediacaran period.
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Literature sources &; Original link
Geology, (202 1)49(2),115-19.
https://doi.org/ 10. 1 130/G47972. 1
translator
Nanjing University @ Shen Boheng
02
The composition of he isotope (He/ 3 4 HeHe) in geothermal fluid or gas samples from Cumbre Vieja (Cumbre Vieja volcano) in La Palma Island and Teide peak in Tenerife Island has been studied for more than 25 years (He/ 34Hehe value of Cumbre Vieja sample is 9.4 0.1R A, and He/ 3 4 HeHe of Teide sample). These samples have similar CO 2/3 He ratio (2 109-4 109). The δ 13 C composition close to the mantle value (-3.3‰~ 4.4‰) is different from the similar CO emission flux (0.1-0.21010 mol/yr), but the he isotopic composition of these samples is different. The results show that the different helium isotopic compositions of these samples are not caused by the time difference or the increase of 2 4 He in the source region. However, because they come from different He reservoirs (La plama sample comes from HIMU mantle source area, Tenerife sample comes from enriched mantle source area influenced by lithospheric mantle). The geothermal samples in the Canary Islands recorded the he composition of the present source area, and the he/ 3 4 HeHe value recorded in the olivine of the older lava in the east was higher than the He/ 3 4 HeHe value measured in the present geothermal samples, indicating that the He reservoir in the mantle source area of the Canary Islands evolved with time. In this paper, the helium isotope data of geothermal samples from Canary Islands, Azores Islands, Cape Verde Islands, Hawaii Islands and Iceland are compared with those of olivine phenocrysts, pyroxene phenocrysts and glasses. The results show that even in the years above1m y, there are heterogeneous he isotopic compositions among Hawaiian Islands, Azores Islands and Iceland Islands except the Canary Islands, and these heterogeneous information are stored in their hydrothermal samples, minerals and glasses. Especially in the northwest of Iceland, the He/ 3 4 HeHe value in olivine of the older lava in this area is higher than that of the current geothermal samples. This difference may reflect the decrease of mantle-derived 3 He input in Icelandic magmatism since Miocene. The method of evaluating the variation of HeHe value with time by using geothermal and geological samples provides a powerful tool for studying the heterogeneity of volcanic source areas in the plate and the evolution of source areas with time.
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Literature sources &; Original link
Geology, (202 1)49(2), 120- 124.
https://doi.org/ 10. 1 130/G47676. 1
translator
NJU@ haha Yu
03
Quantifying the time scale of volatilization loss of siliceous rock slurry during fusion eruption by lithium isotope
Most explosive siliceous volcanoes have a quiet period of thousands of years between two eruptions. The timing of transition from quiet period to re-eruption is the key to interpret monitoring signals and improve the safety of residents near active volcanoes. In order to solve this problem, the researchers studied the lithium isotope (δ7li) and element concentration distribution in the tuff plagioclase crystal of Mesa Falls in Yellowstone volcanic system in Idaho and Wyoming. Using this new method, the minimum time scale of volatile degassing before explosion is limited to a few minutes. In this short time, the concentration of Li decreased by 4 to 10 times from the core to the crystal edge, while the increase of δ7li was as high as 10‰, reflecting the diffusion-driven balance between plagioclase core and degassed lithium-poor melt. The new time scale obtained in this study shows that the total amount of magma volatiles may change rapidly during the same eruption period.
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Literature sources &; Original link
Geology, (202 1) 49 (2), 125- 129.
https://doi.org/ 10. 1 130/G47764. 1
translator
CUGB@ Tang Yan
Passive continental margin magmatism caused by increased plate tension in central Tibet.
This paper reports the mafic dike swarms of about 239Ma in the South Qiangtang terrane in central Tibet, which were formed on the passive continental margin of subduction plate. The dyke is tholeiite, which is characterized by the enrichment of light rare earth elements, moderate negative anomalies in Nb and Ta and isotope enrichment. The rock wall is contemporary with the back-arc basin formed by the rotation of the Paleo-Tethys ocean plate and the overlying plate. Therefore, after the subduction of the ocean ridge, the plate tension caused by plate rotation on one side of the ocean increased, and the passive continental margin on the other side extended and magmatized. This study holds that the enhanced plate tension is the formation mechanism of passive continental margin magmatism of subduction plate, which was not recognized before.
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Literature sources &; Original link
Geology, (202 1) 49 (2),130–134.
https://doi.org/ 10. 1 130/G47957. 1
translator
6 1
05
It is difficult to investigate the seismic activity below the standard earthquake-producing area, because the geological records of such earthquakes have usually been reacted or distorted. This paper describes the abnormal primitive pseudo-basalt glass in granulite in the lower crust of Lofoton Islands in northern Norway. The mineral composition of pseudo-basaltic glass is basically the same as that of host rock (mainly plagioclase, alkali feldspar and orthopyroxene), and it contains microstructure indicating rapid cooling, namely feldspar microcrystal, spherulite and cauliflower garnet. There is no mylonite and basaltic pseudocrystalline debris in the surrounding rock. There is no record about the characteristics of precursor ductile deformation, which excludes several common mechanisms that cause earthquakes in the lower crust, including heat transfer, plastic instability and earthquake propagation along the brittle part of the fault to the ductile part. Dehydrated minerals and pseudo-basaltic glass in the host rocks exclude embrittlement caused by dehydration. Without this weakening mechanism, the stress level of the lower crust must be very high.
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Literature sources &; Original link
Geology, (202 1) 49 (2),135–139.
https://doi.org/ 10. 1 130/G48002. 1
translator
Frame young Xiao Muchun @ Yu
Similar glacial activities in South America and tropical Africa during Holocene.
Under the trend of global warming, glaciers in tropical areas are shrinking with the increase of temperature. However, in the geological history with a relatively long time scale, the changing trend of glacier activity in these tropical areas is still unknown. Recently, Anthony C. Vickers of Boston College and his collaborators have reconstructed the Holocene glacial activity history of Quelccaya Ice Cap in South America and Rwenzori Mountains in Africa by in-situ 14 C and 10 Be isotopic dating of newly exposed bedrock. The results show that the Holocene glacial activity history in the two areas is similar. In the early Holocene (about 5 ka ago), the glacier area was smaller than today; In the late Holocene (about 5 ka later), most glaciers were larger than today. The similarity of Holocene glacial activity in tropical areas of two continents shows that the wider temperature change is driven by glacial activity in tropical areas, rather than regional precipitation. The results of this paper also show that under the background of glacier expansion in tropical areas in the late Holocene, compared with the trend of glacier activity in the past thousand years, the phenomenon of tropical glacier retreat caused by the current climate intensification and warming is abnormal.
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Literature sources &; Original link
Geology, (202 1) 48 (2), 140- 144.
https://doi.org/ 10. 1 130/g 48059. 1。
translator
Three-mouth knife
07
The melting of ice and snow in Cape Eliza, Ross Sea, Antarctica exposed the settlement of ancient Adelie penguins.
Recently, Steven Emslie, an American biologist who specializes in penguins, accidentally discovered several newly exposed survival sites and some seemingly "fresh" ancient Adelie penguins' remains in Cape Iriza, Antarctica.
The Ross Sea, located in Antarctica, is one of the most productive marine ecosystems in the Southern Ocean, providing living conditions for nearly 654.38 million+00,000 pairs of Adelaide sea squirts every year. Here, there is a well-preserved penguin habitat site from the last ice peak (14 C analysis results show that it was 45,000 years ago) to the Holocene.
Cape Iriza is a rocky headland, located south of Drygalski glacier tongue on the coast of Scott. 20 16, 1 June, due to the melting of snow, several ancient survival sites of Adelie penguins and a large number of penguin bones, feathers and fresh-looking corpses were exposed here. The researchers sampled it and conducted a radiocarbon analysis. The analysis results show that these seemingly "fresh" relics are actually long ago. Adelie penguins occupied this area for three times, which began about 5,000 years ago, and the last occupation ended about 800 years ago.
These seemingly "fresh" penguin remains are actually ancient, which shows that until recently, the melting of ice and snow made the previously frozen penguin corpses and other remains exposed for the first time after about 800 years, and made them rot and look fresh. The recent trend of climate warming and snow reduction in headlands since 20 13, as shown in Landsat images, supports this hypothesis.
The increase of penguin collagen δ13 c further shows that the period when the living conditions of ancient penguins reached the "mildest" was the period when the marine productivity was greatly improved, that is, the warm period from 4,000 years ago to 2,000 years ago, which may be related to the expansion of polynyas in Terranova Bay and the ice-breaking event of Drygalski glacier tongue.
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Literature sources &; Original link
Geology, (202 1) 49 (2), 145- 149.
https://doi.org/ 10. 1 130/G48230. 1
translator
Tianjin Normal University @ Liao Cifei
Redefining kinematics of rift system in East Africa
The geometry and surface motion of the East African Rift Valley system are the least constrained parts in the global plate motion model. The team used GPS data to control the rotation of the Somali plate and proposed a new tectonic plate geometry for the region. In addition, the team also tested the geological data of the southwest Indian ridge and the new GPS data of Madagascar to determine the redefined Irish microplate kinematics. A large deformation zone was found, extending from the eastern boundary of the Ruwuma microplate to the Comoros Islands, including parts of central and northern Madagascar. Madagascar plate is splitting, southern Madagascar rotates with Irish microplate, and a plate in eastern and south-central Madagascar moves with Somali plate. The divergence of Nubian-Somali plate system across the East African Rift Valley system includes diffusion deformation and strain adjustment along the narrow rift valley section that constrains rigid blocks.
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Literature sources &; Original link
Geology, (202 1)49(2),150–155.
https://doi.org/ 10. 1 130/G47985. 1
translator
China Geo University @ Huang Yonghui
Enlightenment of 09 Giant Oolitic Particles on Early Triassic Seawater Carbonate System
The lower Triassic limestone contains more typical oolites and other carbonate sedimentary structures than Precambrian strata. These characteristics may be caused by the hydrochemical changes of seawater during the late Permian extinction, but it is still full of challenges to quantitatively restore the carbonate system of seawater in the early Triassic. According to the grain size data of the Lower Triassic oolitic grains in southern China, the author restricted the formation process of oolitic grains through physical and chemical models, and restricted the carbonate saturation index, dissolved inorganic carbon content, alkalinity and pH value of seawater during the formation period of oolitic grains. Based on the above methods, the author found that Jurassic giant oolitic particles were formed in seawater with high carbonate saturation index, which is similar to the environment in which modern oolitic particles were formed. The calculation results show that the saturation indexes of aragonite and calcite in early Triassic seawater are both greater than 7. Combined with the reconstruction results of atmospheric carbon dioxide and seawater calcium ion concentration, the author found that the concentration and alkalinity of dissolved inorganic carbon in the early Triassic ocean were twice as high as today, and its pH value was about 7.6. Therefore, the early Triassic seawater carbonate system hindered the recovery of calcareous organisms.
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Literature sources &; Original link
Geology, (202 1)48(2), 156- 16 1.
https://doi.org/ 10. 1 130/G47655. 1。
translator
Small claw claw
10
In the late Holocene, the lack of sediment supply led to the temporary degradation of the barrier island chain in Walden, Denmark.
Understanding the direct coupling relationship between sediment supply and sea level change is very important for predicting the response of barrier coasts (barrier island and Barrier Sand Mouth) to future sea level rise. A large number of cores, seismic profiles and high-resolution dating data in the Wadden Sea in the southeast of the North Sea show that the progradation of barrier island chain stopped and degenerated during 3.5~2.0 ka. The decline of barrier island is caused by the weakening of coastal drift caused by regional coastal reorganization. The large-scale forward movement of the triangular promontory leads to the deposition trajectory away from the barrier coast, which leads to the decrease of the supply of marine sediments and the stability of the barrier chain, thus leading to the reduction of the regional sea level rise threshold from 2~9mm/yr to about 0.9mm/yr lower than the modern sea level rise rate. Therefore, to predict the response of barrier coast to sea level rise, it is necessary to consider the changes of sediment supply and the feedback of large-scale landforms that may be caused by human and natural reasons.
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Literature sources &; Original link
Geology, (202 1) 49 (2),162–167.
https://doi.org/ 10. 1 130/G47978. 1
translator
CDUT @ ether
1 1 the roots of deep magma accumulation in the Acadia orogenic belt in eastern North America
For the model that the redistribution of mass and energy in the crust is the cause of neutral to acidic magmatism in the crust, the loss of the foundation of accumulated magmatic rocks in accretionary orogenic belts is its cornerstone. Similarly, the origin of the Acadia rock mass in Appalachia, New England (northeastern United States), has long been interpreted as closed system crustal melting due to the lack of relevant contemporary deep mafic counterparts. The researchers reported the newly discovered Acadia water-bearing ultramafic deposit (southern New England, Connecticut, USA), which was formed by the separation and crystallization of mantle-derived melt. These rocks were first discovered in the Appalachian orogenic belt, and they are also the only well-preserved deep arc water-bearing reactor crystals in the world. The researchers believe that these accumulations are related to syngenetic rocks in south-central New England, in which the former represents deep accumulation roots lacking the same magmatic arc. The researchers' findings support the hypothesis that the deep separation, crystallization and contamination of the crust lead to the differentiation of mantle-derived water-bearing magma, which is the basic process of intermediate-acid magmatism and continental crust geochemical evolution.
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Literature sources &; Original link
Geology, (202 1)49(2), 168- 173.
https://doi.org/ 10. 1 130/G47887. 1
translator
CUGB@ Qiningyuan
12
Paleomagnetic basis for the core connection time between Australia and Lauren continent, namely Nuna supercontinent.
The combination time of Australia and Laurentian in Nuna supercontinent began from Proterozoic to Mesoproterozoic at 1.6Ga, and both landmasses were located in the original SWEAT (Southwest America-East Antarctica) combination landmass. However, there is little research on the duration of this combination. This study reports the latest high-quality paleomagnetic polarity data obtained in Derim Derim bedrock at 1.3Ga in northern Australia. Evidence shows that Australia and Laurenson are in the same united continent at 1.3Ga, and this new paleomagnetic constraint also supports the connection between Australia and China North China Plate. Combined with the paleomagnetic data of various continents reported by predecessors, it shows that the division of Nuna supercontinent probably occurred in the period of1.3-1.2ga.
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Literature sources &; Original link
Geology, (202 1) 49 (2),174–179.
https://doi.org/ 10. 1 130/G47823. 1
translator
CUGB/MQ@SH
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