Table of contents for this issue
01
Combined seismic surface rupture zone of the San Andrés Fault and San Jacinto Fault in California, USA
Large earthquakes associated with multiple fault zones can trigger stronger shaking on the surface and can also change the rate of future earthquakes in that fault zone. The connecting belt of the fault acts as a barrier to certain conditions, or as an earthquake gate, and the connection belt can block most earthquakes, but when the stress conditions are favorable, an earthquake across the connection zone occurs. To study the physical conditions conducive to the occurrence of large earthquakes in multiple fault zones, it is necessary to grasp the frequency information of local earthquakes and multi-fault zone earthquakes. Because the uncertainty of the age interferes with the matching of different faults and paleoseismic, it becomes difficult to measure the seismic frequency information, and it is necessary to directly measure the rupture zone through the seismic gate. The team's research using literature and finite element models of secondary fault staggering shows that over the past 2000 years, the San Andreas and San Jacinto faults in California have ruptured at the same time at the seismic gates of the Cajon Pass, most recently caused by an earthquake in 1812 AD. The model shows that when interstitial displacement is staggered, seismic gate rupture events decrease sharply and stop abruptly. Independent chronological data support the same view: 20 to 23 percent of earthquakes at the San Andrés and San Jacinto faults occurred at the Cajon Pass.
Source:
Geology (2022) 50 (4): 387–391
Original link:
https://doi.org/10.1130/G49415.1
translator
University of Jena @ Zhang Yiqiong
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CUGB@ sea breeze
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02
The importance of storing pollutants in oxbow lakes in river floodplains
Oxbow lakes are important reservoirs of fine-grained sediments, and this property may make them a key sinkhole for sediment-related contaminants. Using detailed core records to aid the data collected, the team quantitatively assessed the use of Oxbow Lake as an out-of-river pool. Located in western Massachusetts, the Housatonic River is an active meandering river. The team sampled its oxbow lake to study the loading trends of polychlorinated biphenyls (PCBs) adsorbed by sediments in the oxbow lake. The results showed that the average concentration of THE PCB when the oxbow lake was used as a sink was 14.8 ppm, while the average concentration of the surrounding river floodplain was 7.56 ppm, which was almost twice that of the latter. Although the 5.83km2 river floodplain is the largest pool of PCB content, with PCBs stored as much as 14.1t or 2.42g/m2, the area of Oxbow Lake only accounts for more than 5% of the floodplain area, but it stores more than 20% of the PCBs (PCBs can reach 3.63t or 11.2gm-2). Nearly 85% of the oxbow lakes where PCBs are stored occur in the river floodplain range of nearly 50m, which confirms the significance of the occurrence of oxbow phenomenon under normal circumstances for the storage of sediment-related pollutants outside the river.
Source:
Geology (2022) 50 (4): 392–396
Original link:
https://doi.org/10.1130/G49427.1
translator
Guangdong Petrochemical @ Cai Huina
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University of Jena @ Zhang Yiqiong
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03
Neutron-X-ray associated tomography reveals unusually well-preserved Jurassic ammonites using a funnel swim propulsion mechanism
Among the fossils of ammonites, it is extremely rare that soft tissues can be preserved, so this also means that there is still a gap in the basic research on the physiological habits of ammonites. In response to this problem, the team used neutron-X-ray associated tomography to study a very well-preserved middle Jurassic ammonite fossil to interpret the soft tissue information contained in it. The first three-dimensional imaging of muscles and organs of this class of iconic fossil taxa has laid an important foundation for subsequent morphological function research. The team found that its pairs of back muscles allowed its body to retract into its shell, rather than controlling propulsion through a funnel like the Nautilus. This suggests that ammonites rely on a movable and free body and a unique swimming propulsion mechanism to protect themselves. The team speculates that the trait may have evolved early in the ammonite-suborder pseudophylla lineage.
Source:
Geology (2022) 50 (4): 397–401
Original link:
https://doi.org/10.1130/G49551.1
translator
University of Otago@ Wu Yutong
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Nanjing University @ Jim Renault
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04
The thickness of the crust of the Glenville Orogenic Belt: A Medieval "Tibet"?
One of the cores of the Rhodinia supercontinent is a medieval Lauren continent orogenic plateau, and Glenville is a remnant of this plateau on the eastern edge of the continent Lauren. As a long-standing Himalayan orogenic belt, Glenville's orogeny is crucial to elucidating the tectonics and paleoenvironmental evolution of the Middle Proterozoic. In the study, the team compared two geochemical indicators of crustal thickness: the whole rock [La/Yb]N (lanthanum/ybthromum) ratio of neutral to long-term ytterbium rocks and the osmium anomaly [Eu/Eu*] in clastic zircon. The team collected all-rock geochemical data from 124 deep diagenetic masses in Lauren-Glenville and trace element and geochronology data from clastic zircons in the Ottawa and St. Lawrence river basins in Canada. The above two indicators reveal several stages of crustal thickening and thinning events during the Glenville orogeny. During the Ottawa period (about 1080Ma to 1045Ma), the thickness of the earth's crust reached its thickest, about 60 kilometers, but it was still nearly 20 kilometers thinner than the current Tibetan crust. The team speculates that the hot crust and several crustal thinning events prevented Glenville from forming a plateau similar to present-day Tibet, most likely due to the asthenosphere-lithosphere responding to warm mantle action under the ancient Nuna-Rodinian supercontinent, thus enhancing the interaction between the two.
Source:
Geology (2022) 50 (4): 402–406
Original link:
https://doi.org/10.1130/G49591.1
translator
Institute of Geology and Earth Sciences, Chinese Academy of Sciences @ Liu Tanjie
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Nanjing University @ Jim Renault
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05
Formation of rock beds during the expansion of rock walls
At present, there is still debate about the genesis of horizontal rock beds, especially in the context of tension, and the expansion of vertical rock walls in this background is a possible way for magma to intrude. The team used a two-dimensional viscoelastic medium instead of the expansion center of the plate, simulating the short-term expansion of the rock wall after experiencing long-term elongation. The results show that when the lithosphere is stretched, the expansion of the rock wall can reduce the vertical stress of the lower part of the lithosphere in order to form a horizontal rock bed, provided that the following three conditions are met: (1) The Maxwell time of the asthenosphere is less than 5 times the intrusion period of the rock wall; (2) the average density of the lithosphere cannot be much greater than the density of the magma; (3) The depth of the rift valley along the ocean ridge is generally less than a few hundred meters. This mechanism may explain why the rockbeds mostly arise along the axis of rapidly expanding ocean ridges, but do not develop in thick, dense lithospheres and/or slowly expanding centers with large rift valleys.
Source:
Geology (2022) 50 (4): 407-411
Original link:
https://doi.org/10.1130/G49400.1
translator
CUGB@ Wang Wenbo
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Northwestern University @ Ren Xiang
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06
Full lithosphere shear phenomenon during oblique rifts
Although the formation mechanism of the continental all-lithosphere shear zone has been controversial, this process undoubtedly requires mechanical coupling of the entire lithosphere from bottom to top. The study reported the formation of a full-lithospheric-scale right-way shear zone in Death Valley in the southwestern United States. The perpendicular change in the lithosphere-asthenosphere boundary and the rightward deformation within the Moho face defines a shear zone located 20–50 km wide and about 60 km shear in the lower part of the lithosphere. These deformations lie below an upper crustal fault zone. The upper crustal fault zone has been slipping on the right for about 60 km since 8-7 Ma. The team speculates that this period was the beginning of the formation of this all-lithosphere-scale shear zone. It is found that the displacement of the shear zone at the bottom of the lithosphere is smaller than the net right-handed displacement of the upper crustal fault zone (about 90 km displacement occurs at about 13-0Ma) and its total stretch (about 16-0 Ma occurs about 250 km). The study notes that prior to 8-7 Ma, the presence of a weak middle crust decoupled the deformation of the upper crust with the deformation between the lower crust and the mantle lithosphere. The detachment slip between 16-7 Ma thins, lifts, cools and strengthens the middle crust, and finally exposes it in the metamorphic nuclear hybrid rocks associated with the all-lithosphere-scale shear zone. The strengthened middle crust couples the deformation of the vertical upper lithosphere layers and allows for right-way shear at the all-lithosphere scale. In thick crusts like Death Valley before 16Ma, the strength of the middle crust may be necessary for all-lithosphere shear to occur.
Source:
Geology (2022) 50 (4): 412–416
Original link:
https://doi.org/10.1130/G49603.1
translator
@Chai Mu Lan
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Chengdu University of Technology @ Huatian
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07
Rapid regression at the southwest edge of the Lauren Ice Sheet during B lling-Aller d
The retreat time of the southwestern rim of the Lauren Ice Sheet controls the evolution of large glacial lakes and helps to understand the process of human migration to the Americas. The process of accurately reconstructing the retreat of the ice sheet not only provides constraints for the glacier equilibrium adjustment model, but is also critical to understanding the sensitivity of the ice sheet to climate forcing. Nonetheless, only a small number of 14C age constrains the regression of the southwestern rim of the Lauren Ice Sheet (SWLIS). The study reported 26 new 10Be exposure ages across Canada's western inland plains and corrected the region's chronology using Bayesian simulation-based methods combined with geomorphology, 10Be and high-precision 14C ages. The dataset showed good internal consistency in the fading records of the ice sheet and showed that before 15.0ka, SWLIS began to undergo initial regression from its intersection with the Cordilleran ice sheet. Its regression coincided with or earlier the start of B lling-Aller d (14.7–12.9ka) and over a period of about 2500 years, retreated more than 1200 km and reached its position in the Neo-Nymph Period (YD). Due to the stability of the ice sheet in the CreeLake Moraine region, a glacial river flowing from Agassiz glacial lake to the Arctic was formed during the YD period, but this glacial river did not necessarily form at the beginning of the YD period. The study's new constraints on glacier retreat records and YD events suggest that glaciers in inland plains regress 60 percent faster than presumed by the minimum age of 14C. Numerical simulations have shown that the rapid fading of SWLIS during B lling-Aller d leads to sea level rise of about 3.7 m.
Source:
Geology (2022) 50 (4): 417–421
Original link:
https://doi.org/10.1130/G49493.1
translator
China University of Geosciences (Beijing) @ Zhu Yimin
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Small claw claws
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08
Isotopic and volatile trace element composition of galena silver in the Iberian Peninsula and its implications for the source of silver in Roman currency
Silver played an important role in the monetization of early Mediterranean civilizations. The research team combined the isotopes of lead (Pb) and silver (Ag) with the volatile trace elements bismuth (Bi), antimony (Sb) and arsenic (As) to explore whether galena was the main source of silver during the Roman Occupation of the Iberian Peninsula. They found no correlation between Pb and Ag isotopic compositions of 47 galena samples from 8 different mineralization provinces in Iberia, suggesting that their isotopic variation depends on different diagenetic processes. Moreover, compared to global silver coins and Roman silver coins, the Ag isotope composition of these galena varies six times as much as they do. Although the castor ore from the Betix Mountains most closely matches the Pb isotope of Roman silver coins, their Ag isotope composition is different. Combined with the evidence from Bi, Sb, and As, the researchers believe that Ag comes from vaporized and separated fluids in the divergent mantle source magma, which in turn reacts with pre-existing galena, and that galena acts as a fixation of Ag. The significant deviation of ε109Ag from 0 reflects the fractionation process of low-temperature isotopes in the upper crust, while lead sulfides with ε109Ag~0 and abnormal enrichment of Ag, Bi, Sb and As are are the most likely source of silver for ancient silver coins.
Source:
Geology (2022) 50 (4): 422–426
Original link:
https://doi.org/10.1130/G49690.1
translator
Nanjing University @ People on the Moon
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Small claw claws
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09
The role of sediments in the generation of contemporaneous, "types" of granitic magma
Granite taxonomy divides granites according to magma sources, spawning conditions, and indicated tectonic environment. However, the complexity of elemental and isotopic geochemistry makes granite far from being a simple classification scheme, and the academic community has proposed a more complex rock genesis classification of granite. The granites located in the Songpan-Ganzi plateau in the eastern Part of the Qinghai-Tibet Plateau of China were in place in a very short time (~15m.y.). The mineralogical and geochemical characteristics they show are consistent with the various granite division schemes proposed by previous scholars (e.g., type I, S, and type A; high Ba-Sr granite and Edak mass variants). Although they are closely related in space and time, these granites exhibit diversity in geochemical signatures, suggesting a wide range of sources of diagenetic material contribution. Radioisotope data reveal a uniform continuum from the original crustal composition to the evolutionary crust composition; i.e., 87Sr/86Sr(t)= 0.704 to 0.715 and εNd(t)= +2 to -11. All granite "types" have variable but generally higher zircon δ18O (+4.1‰~+11.6‰) and lower whole-rock Li-B-Mg isotopic ratios (δ7Li=+5.1‰~-3.2‰; δ11B=-10.7‰~-16.5‰; δ26Mg=-0.23‰~-0.59‰). These stable isotopic compositions suggest that all "types" of Granite magmas of Songpan-Ganzi have sediment contributions, ranging from small to large sediment contribution weights. The highly variable isotopic composition of granites precludes the possibility that these variable but contemporaneous granites originate from a single homogeneous source region. Their compositional variability may be significantly influenced by sediment contributions, so the findings suggest that traditional taxonomic schemes do not directly explain the genesis of granite.
Source:
Geology (2022) 50 (4): 427-431
Original link:
https://doi.org/10.1130/G49509.1
translator
Chinese Academy of Geological Sciences @ Guo Donghai
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Nanjing University @ Jim Renault
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10
When did the North Anatolian Fault extend to southern Marmara, Turkey?
The team conducted a chronology study of the U-Th chronology of the Tectonic Calcite U-Th fault in the western section of the North Anatolian fault (NAF) in northern Turkey. In this study, the gyration faults associated with the present regional stress field in kinematics were used for dating, and the age range of tomographic activity was obtained from 700 ka onwards. Among them, the most prominent age peak is 510.5±9.5ka (1σ), which is consistent with the maximum cumulative slip distance and the plate tectonic movement observed by GPS, indicating that the tectonic pattern of the present-day North Anatolian Fault Zone was formed at about 500ka or earlier. Combined with the study of pre-human regional tectonics, the new isotopic age data in this paper reveal that the fault activity of the western section of the NAF fault zone mainly began in southern Marmara, at least hundreds of thousands of years earlier than the onset activity time of the northern branch of the western section of the fault zone. The study proposes a new way to constrain the onset time of the current active break. Therefore, the use of calcite in the fault zone U-Th chronology to determine the fault activity period of the wider shear zone of the plate boundary has a wide application value.
Source:
Geology (2022) 50 (4): 432–436
Original link:
https://doi.org/10.1130/G49726.1
translator
University of Jena @ Zhang Yiqiong
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Chengdu University of Technology @ Tong Kui
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11
Early Earth zircon crystallized in residual granite melts produced by an inflection diorite magma
The earliest recorded rocks on Earth belong to the clastic zircon (>4Ga) of the Hades. However, the geochemical properties of these Plutocrypian clastic zircons, as well as the significantly lower magmatic temperatures (≤700°C) obtained by the Zircon Ti thermometer, are very different from the magmatic properties of the main Archean magne magnesites, Inglain-Oligo granite-granite-granite-diorite (TTG, 4.0-2.5Ga). The study explored these questions using trace element and thermodynamic simulation methods of zircon from the Barbarton TTG of the Archean Archean TTG in South Africa. The results show that these zircons are granite melts that crystallize in a homogeneous composition under near-solid phase conditions, which correspond to the residues after the crystallization of the inland diorite parent magma, so the whole rock composition is different from TTG in terms of main quantities and trace elements. Through the statistics of global data, it is found that most of the Plutocrypian clastic zircons and Zircons in the Archean TTG have unique trace element characteristics, which are different from the geochemical trends of Proteozoic zircons. The new model simulated the activity of TiO2 in the melt, and the results were lower than previous estimates, so the low Ti content in Earth's early zircon actually reflected the relatively high magma temperature (720–800°C). Therefore, the research team proposes that The zircon of the early Earth mainly crystallized in more evolved evergreen melts similar to the TTG magmatic environment.
Source:
Geology (2022) 50 (4): 437–441
Original link:
https://doi.org/10.1130/G49232.1
translator
Northwestern University @ Ren Xiang
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CUGB@ sea breeze
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12
Cold springs became biological refuges during ash settlement in the western inland seaways of Late Cretaceous North America
Cold springs host rich biomes, which are sporadically distributed around the world but highly productive. Continuous hydrocarbon emissions maintain a food web in cold springs that can be synthesized. The inland waterways of western North America during the Late Cretaceous period had a large number of cold springs. The area has also experienced intermittent ash depositions, which can have a negative impact on marine life. The study suggests that during this period of environmental disturbance, cold springs became biological refuges. The team reported on transverse continuous porphyry in the Baculites compressus belt of the upper Campan Steps in southwestern South Dakota, which cut through a cold spring deposit. The team compared the fossil records of macro-bodied invertebrate organisms above and below the porphyry in cold and non-cold spring areas. The study showed that paleontological communities (measured by abundance and diversity) were largely unaffected by ash deposition in cold springs, while there were significant changes in non-cold spring areas. As a result, cold springs in the Western Inland Seaway, after severe environmental disturbances, may become sanctuaries or biological oases for living things.
Source:
Geology (2022) 50 (4): 442-447
Original link:
https://doi.org/10.1130/G49372.1
translator
Central South University @ Du Minghao
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13
The mechanism of double destruction of the mass extinction at the end of the Triassic
Combining the isotopic distribution of high-resolution biomarker compounds and specific compounds with degradation of calcareous fossil remains, the researchers found that volcanic activity in the Central Atlantic magmatic province (CAMP) drives intense vulcanization and decalcification (acidification) in the oceans, which together form the dual extinction mechanism of the end-Triassic mass extinction. In the newly discovered mass extinction strata at the bottom of the Blue Lias formation in the Bristol Strait Basin, the distribution of biomarkers reflects a long period of marine translucent zone vulcanized hypoxia (PZE), which extends upward to surface waters. In the same layer, the shells disappeared almost completely. Starting with the thin-layered shale at the bottom of the Blue Lias Formation, the formation preserves a "miniaturized ( Lilliput ) biological combination containing small amounts of calcareous oysters (Liostrea) and calciumized paleontine bivalves fossil remains. The ecological pressures caused by PZE and decalcification succinctly explain the causes of the mass extinction event, while revealing that when A global-scale PZE occurs, other biological crisis events may also be related to multiple consequences of infestation in igneous provinces, particularly at the end of the Permian.
Source:
Geology (2022) 50 (4): 448–453
Original link:
https://doi.org/10.1130/G49560.1
translator
ITPCAS@ Tethys Surf
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Nanjing University @ Jim Renault
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14
Are gypsum fluid inclusions reliable paleoenvironmental indicators? Assessment of the evidence from evaporative rocks in Messina
The palear salinity of brine deposited during the Salinity Crisis in Messina is controversial. Recent microthermal studies of native gypsum fluid inclusions have shown that their salinity values are very low, lower than the salinity that seawater sediments should have, and may precipitate in well-mixed water bodies of seawater and non-marine water bodies rich in calcium sulfate. The team used a new microscopic temperature measurement method to stretch gypsum crystals from nine profiles in the Mediterranean to measure more fluid inclusions. The results show that the salinity range (NaCl equivalent) is 9~238wt‰, and most of it belongs to the evaporation path of normal seawater. The data from previous studies came mainly from fluid inclusions that generate stable bubbles after slight stretching, which may be formed by a post-deposition rupture and sealing process with low salinity. Instead, the data suggests that the native gypsum is precipitated from marine brine and modified by the construction and stripping process after capture.
Source:
Geology (2022) 50 (4): 454-459
Original link:
https://doi.org/10.1130/G49475.1
translator
ZYU@CAGS
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Nanjing University @ People on the Moon
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15
Red Bole Zircon records mysterious siliceous volcanic action in the Indian Deccan Igneous Province
Both ferrous and siliceous magmas are prevalent in the Igneous Provinces (LIPs), but siliceous magmas have not been adequately studied relative to the predominantly mafic magmas by volume, although they may play a role in the environmental degradation caused by LIP. Records of evolutionary magma have been found in the 66-Ma Indian Deccan Igneous Province, but little is known about its geographical distribution, duration and significance. Zircon in sediments at the top of the Deccan lava flows, known as red boles, is thought to be related to volcanic dust from siliceous volcanic action. This siliceous, explosive volcanic action may be widely distributed throughout the eruption period of overflow basalt. These zircons provide indirect methods for studying such volcanic effects. The results show that zircon in monolayer red boles has different volcanic source regions. These volcanic source areas may have formed in the intra-plate environment of the Craton Lithosphere in India. However, the red bole zircon geochemical and isotopic characteristics obtained by the study do not match the siliceous magma centers studied by previous generations, suggesting that they must come from undeveloped or unprovoked volcanic centers associated with Deccan LIP.
Source:
Geology (2022) 50 (4): 460-464
Original link:
https://doi.org/10.1130/G49613.1
translator
Great 61
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CUGB@ sea breeze
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16
Multi-indicator evidence of Neogene Caribbean invasions in the western Amazon of Brazil
Academic questions about the timing of the initiation of transgressions within the western continent of the Brazilian Amazon in the Neogene Period remain to be resolved. Although many indicators of Neogene transgressions have been found in the academic community, there are still controversies about the path and duration of transgressions in the late Miocene. In response to this problem, the team conducted a collaborative study of calcareous and organic matter micro-fossils and geochemistry in the Neogene strata of 6 perforational cores in the Solim es Basin in Brazil. The results showed that several small seawater invasion events occurred in the early Miocene, mid-Miocene and early Pliocene, respectively, at the time of 23.0, 21.1, 18.6, 16.3Ma, 14.9, 13.7, 12.9Ma and 4.7, 4.2–4.1 and 3.8Ma, respectively. At the same time, salinity indicators such as microemicrosite and geochemical data jointly revealed that significant transgressions occurred in the study area in the late Miocene (11.1–8.8Ma). The study's findings challenged the traditional view of large-scale transgressions in the early and mid-Miocene in the region, identifying for the first time a late Miocene incursion (LMI) as the main transgression experienced in the Neogene period in western Amazon. The study compared the geological records in 6 inshore cores with 3 offshore cores in the Atlantic and Pacific Oceans and found that the similarity of the fossil mix between the Solim es Basin and the Caribbean Sea, as well as evidence of increased runoff from the Orinoco River system, suggested that the main source of coastal intrusion was the Caribbean Sea, which formed the Venezuelan SeaWay at the same time as the invasion. The study also discusses for the first time the relationship between Neogene transgressions (mainly LMI) in the Solim es Basin and several major disturbances in the global carbon cycle.
Source:
Geology (2022) 50 (4): 465-469
Original link:
https://doi.org/10.1130/G49544.1
translator
Soochow University @ Yang Hanfei
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Nanjing University @ Jim Renault
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17
Portable light-emitting age map of ancient earthquake outcrops
The quality and quantity of geochronological data can constrain the history of major earthquakes that occur in an area, and also play a major control role in the accurate assessment of the risk of earthquakes that affect millions of people. However, the assessment of geochronological data is often limited by the uncertainty of the factors associated with the original complex sedimentary processes, which may vary both spatially and temporally. To improve the credibility of the seismic time model, the study used a set of high-density radiocarbon and photoreflective (OSL) dating and 342 portable OSL sample fills to explore the spatio-temporal trends of geochronological data revealed by typical positive fault avalanche wedges. These data show a two-dimensional age map of paleo-seismic outcrops and show trends in age in vertical and horizontal directions and their correlation to the main sedimentary facies and soil characteristics at the site. Portable OSL data provide key information for explaining the ages of 14C and OSL, and the study shows that the geological age limit between pre-earthquake and post-earthquake sediments does not match stratigraphic contact, providing a theoretical basis for the selection of seismic time alternative Bayesian models. The results show that the use of emerging, portable OSL methods can significantly improve the study of paleoseismic seismic time limits.
Source:
Geology (2022) 50 (4): 470–475
Original link:
https://doi.org/10.1130/G49472.1
translator
Northeastern University @ Wentian Zhao
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Nanjing University @ Jim Renault
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18
Experimental evidence of sedimentary limestone interacting with mantle-source super-based magma to form calcium-rich carbonate melts
Through experimental studies, the team found that the reaction of yellow long-matter and basalt melts with calcite can produce ultra-calcium super-base melts. The study mixed three SiO2 strong-moderately unsaturated volcanic rocks from the Bohemian plot in Central Europe with 10, 30, and 50wt% CaCO3 and performed melting experiments at three temperatures of 100°C, 1200°C and 1300°C at pressures of 2kbar to assess how much carbonate natural superbasitious melt could absorb under shallow conditions. Experimental results show that all the caCO3s added can fully enter the silicate melt and are not easy to achieve carbonate saturation, and the typical liquid phase line mineral phases are olivine, spinel, yellow feldspar and monoclinic pyroxene. Only in sio2's most unsaturated melt experiments did a large amount of calcium-magnesium olivine appear. All initial substances produced super-base (SiO2 content as low as 15.6wt%), CaO-rich (CaO content up to 43.6%) and ultracalcium (CaO/Al2O3 up to about 27% higher) melt composition at 1200 °C and 1300 °C, and dissolved CO2 in the melt up to 25wt%. At the same time, the olivine (Fo95–97) in this experiment has a significantly higher Fo value relative to the natural olivine (Fo79–85). The study had two implications: (1) the silicate-carbonate melt composition can also be produced during limestone assimilation, which does not necessarily mean that carbonate components are present in the mantle; (2) the high Fo value of peridot cannot be used to infer any of the original characteristics of the melt and crystallize at higher ambient temperatures.
Source:
Geology (2022) 50 (4): 476–480
Original link:
https://doi.org/10.1130/G49621.1
translator
China University of Petroleum (Beijing) @ Century
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Hahayu
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19
Black mica records the lithium-rich volatile phase dissolved in the siliceous magma reservoir on the Earth's crust
When melts coexist with fluids, the distribution behavior of many elements changes, so the magma-hydrothermal transition zone is key to controlling many economically important elements. Despite the increasing economic value of lithium (Li), little is currently known about li's behavior in the magma-hydrothermal transition zone. The team studied black mica minerals in the heliary tuff of California and the tuff of the Kos Plateau in Greece, and found that these black mica have an unusual chemical composition and contain volatile phases in magma between the layers of black mica. Although these specially composed black mica are produced in native deposits and have an XRD spectrum similar to that of normal black mica, the electron probe test results show that the total number of elements is less than 95 wt%, indicating that there are a large number of lighter elements in these black mica that cannot be detected by electronic probes. These black mica are enriched with Li elements (>2300 ppm) and have a very light Li isotopic composition (δ7Li as low as -27.6‰), and there is a large Li isotope fractionation between the black mica single mineral and the whole rock, with a maximum fractionation of -36.5 ‰. Since none of the other mineral phases, matrices, and melt inclusions in this sample have high Li levels, this indicates that the magma itself is not rich in Li. However, the black mica in the Ringite samples from the Tenerife Island of the Canary Islands and the Campi Flegrei region of Italy did not have significant composition differences, and its Li content was balanced with the melt, and the maximum fractionation of the Li isotope between the black mica and the whole rock did not exceed -10.9 ‰. The team attributed the differences in the behavior of black mica in different magmas to the crystallization of black mica in alkaline magma near the liquid phase line before the rich volatile phase dissolution, while the black mica in rhyolite magma crystallized at low temperatures, capturing the dissolved fluid phase components.
Source:
Geology (2022) 50 (4): 481-485
Original link:
https://doi.org/10.1130/G49484.1
translator
NJU@Hahayu
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Northwestern University @ Ren Xiang
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20
A large amount of CO2 emitted by Mount Etna in Italy comes from carbon-rich lithosphere mantles
Italy's Mount Etna emits a large amount of CO2 (9083 tons / day), contributing 10% to global volcanic gas emissions, but the reason for such a large amount of CO2 emissions is not clear. The team conducted high-precision tests on the concentration of high field strength elements (HFSE) in the volcanic magma of southern Italy, and the analysis results showed that Mount Etna had a high Nb/Ta (up to 26) value, indicating that its source area of the mantle had undergone carbonate melt accounting, resulting in a large amount of CO2 in its source region. Observations of Mount Etna show that carbon-rich mantle source regions affect volcanic CO2 degassing fluxes other than continental rifts, a finding that is important for explaining volcanic CO2 fluxes in different geodynamic environments. In addition, the study suggests that the HFSE ratio of magmatic rocks can trace the degassing effects of volcanic carbon and can be used to study volcanic carbon emissions in different geodynamic environments today and in the past.
Source:
Geology (2022) 50 (4): 486–490
Original link:
https://doi.org/10.1130/G49510.1
translator
CUGB@ Zhang Lei
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Hahayu
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21
January 2020 Taal Volcano eruption in the Philippines – a powered eruption that triggered a volcanic thunderstorm
Advances in global lightning detection have provided new ways to characterize volcanic eruptions. However, scholars' understanding of how volcanic plumes of smoke are charged on different spatio-temporal scales is still in its infancy. The team analyzed the steam magma eruption of The Taal Volcano in the Philippines in January 2020 to understand the causes of its intense volcanic thunderstorm activity. Satellite analysis showed that before lightning was produced, water-rich ash columns rose to an altitude of more than 10 km. Over time, the lightning frequency increases with the height of the ash column and the expansion of the ash cloud, reaching a lightning frequency of >70 times per minute. The photo shows a highly electrified area at the base of the umbrella cloud, where the team speculates that the collision of upwelling and cold air by strong convection enhances conductive activity. The discovery provides a conceptual model of the charge generated during the eruption of vapor magma: initially due to the collision of ash particles near the crater, and then thunderstorm-like electrification in the icy region above the ash column. Although the Taal ash cloud spreads far, most lightning occurs in areas within 20-30 km around the volcano and produces thousands of dangerous cloud-to-ground lightning in densely populated areas. The eruption showed that cities close to volcanoes, in addition to being threatened by previously recognized explosive volcanic activity, could also cause disasters independently of volcanic lightning.
Source:
Geology (2022) 50 (4): 491–495
Original link:
https://doi.org/10.1130/G49490.1
translator
SCSIO@ Zhao Tao
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CUGB@ sea breeze
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22
Narrowness is the norm: the width of the continental shelf and its significance in different climatic conditions
Continental shelves are ubiquitous on modern Earth and have developed extensively in many sedimentary basins, with landforms manifesting as submerged slopes at the edges of the basins. The team studied 10 basins and 80 slope build-ups spanning different climatic conditions in the Cenozoic and Mesozoic eras, with different climatic conditions including ice chamber, transition and greenhouse periods. The results show that after the data are uniformly standardized mean treatment, the width of the continental shelf in the greenhouse period is 33% of the width of the slope accumulation caestum, while the width equivalent value of the transition period is 43%, and the width of the continental shelf in the ice chamber period is 72%. This suggests that the continental shelf in the greenhouse period is much narrower than the continental shelf in the corresponding icy chamber climate period. The narrower continental shelf and the delta at the edge of the persistent continental shelf are the result of the low rate of spatial variation in the greenhouse period, due to the lack of large ice sheets required to cause high amplitude, high-frequency sea level rise and fall during the greenhouse period. Since greenhouse climate has been the dominant pattern in Earth's history, and narrow continental shelves may also be dominant forms, conceptual models based on the modern relatively broad continental shelf may not be applicable to paleogeographic predictions, sediment paths, and sediment demarcation studies for much of Earth's history.
Source:
Geology (2022) 50 (4): 496-499
Original link:
https://doi.org/10.1130/G49468.1
translator
Wuhan University @ Chen Yiwei
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University of Jena @ Zhang Yiqiong
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23
Responses to carbon cycle fluctuations in the Smackover group in the Gulf of Mexico
During the Mid-Late Jurassic Period, the central Atlantic Ocean and the former Caribbean SeaWay, which connects the Pacific Ocean to the Tethys Ocean, gradually opened and sea levels gradually rose. These changes have led to significant marine environment and climate change, contributing to the formation of widespread carbonate terraces and diverse biological reefs. Changes in carbonate productivity and the timing of the opening of the Tethys Ocean have been well constrained in the outcrops of Europe and western Asia, marked by the pronounced positive drift of carbon isotopes (delta 13C) in the gregoryceras transversarium ammonite belt in the middle of the Oxford order, known as "MOxE". However, in the west wing of the Global Seaway, located in the former Caribbean and Gulf of Mexico, the timing of this transition has not yet been determined. The study published for the first time isotopic records of organic matter and carbonates from the Smackover Formation in the Gulf of Mexico. This set of strata records δ13C positive drift and is istho-time with the transversarium belt in the middle of the Oxford order. This data is the record for the first MOxE in the Western Hemisphere and provides constraints on the opening time of the Gulf of Mexico. In addition, its carbon isotope variation profile similar to that of the European basin strongly indicates the synergistic response of the carbon cycle to the opening of the central Atlantic and the former Caribbean Sea Road.
Source:
Geology (2022) 50 (4): 500–505
Original link:
https://doi.org/10.1130/G49662.1
translator
CUGB/MQ@SH
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Small claw claws
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24
Dating study of russ ya carbon isotope negative drift in Svalbard region of Norway and its implications for neoproterochronology
The Hecla Hoek sediment of the Stretch-Ediacaran period in Svalbard, Norway, is one of the most complete and best-preserved Neoproterozoic sedimentary sequences in the world. This set of formations contains a diverse combination of fossils, rich carbonate isotope records, and sedimentary records of two neoproterozoic ice ages, so studying this set of formations will help the academic community to further improve the understanding of the evolution of the neoproterozoic Earth system. However, the current strata lack a direct radioisotope age-constrained stratigraphic time frame. In response to this problem, the study reported two new Re-Os ages and the initial Os isotopic composition, thereby constraining the neoproteroic glacial initiation time in the Svalbard region, further supporting the global isochronicity of the two neoproterozoic glacial periods, and also constraining the global weathering state before and after the "Snowball Earth". The dating results show that the negative drift of carbon isotopes recorded in the Elbobreen Formation Russ ya segment in this set of formations is isochronic with the negative drift of "Islay" carbon isotopes recorded by the Didikama and Matheos formations in Ethiopia and the Callsion Lake formation in northwestern Canada. In addition, starting with geochronology, the study proposes to name the global isotope negative drift event that occurred before about 735 Ma as the Russ ya event. This new isotopic age also provides an opportunity to calibrate the chronological stratigraphic framework of the Svalbard region and to assess the correlation between biogeochemical cycles and eukaryote evolution and climate change, the most extreme in geological history.
Source:
Geology (2022) 50 (4):506-510
Original link:
https://doi.org/10.1130/G49593.1
translator
Small claw claws
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Nanjing University @ Jim Renault
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25
Quantitative study of volcanic action and organic carbon deposition of OAE2
OAE2 (oceanic Anoxic Event 2) is one of the largest carbon cycle disturbance events in the Mesozoic, but current studies still lack constraints on carbon emissions from the Caribbean igneous provinces during OIE2 and marine carbon buried fluxes. In this regard, the team used the carbon cycle black box model LOSCAR-P to constrain the amplitude and morphology of the positive drift of carbon isotopes (δ13C) in the surface carbon pool to reconstruct atmospheric pCO2, so as to quantitatively study the effects of volcanic activity in igneous provinces and the enhancement of marine organic carbon burial on OASE2. To best simulate the changes in δ13C and pCO2 observed in the geological record, the team used the following parameters: carbon input rates of 0.065Pg C yr–1 (continuous input 170,000 years) and 0.075Pg C yr–1 (continuous input 40,000 years) for both volcanic activities, respectively; 80,000 years apart for two volcanic activities, and 0.02 Pg C yr–1 for the interval period. At the time of the cessation of carbon input from two volcanic reactions, igneous provincial activity and the weakening of organic carbon deposits led to a significant decrease in pCO2, consistent with evidence of climate cooling and the negative trend recorded in geological time by the global surface carbon pool δ13C. The team notes that the time lag between these features observed in the geological record and computer simulations may be due to differences in the response times of different carbon cycle components to the volcano drive.
Source:
Geology (2022) 50 (4): 511-515
Original link:
https://doi.org/10.1130/G49649.1
translator
Nanjing University @ Jim Renault
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NJU@Hahayu
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26
A study of the historical earthquakes of the Peristome of the San Andrés Fault in California, USA
It is difficult to assess the seismic hazard of creepy faults because they may be involved in rupture, even if they do not have the nucleation conditions for large earthquakes. So far, the San Andrés Fault in California, USA, has not been involved in the major earthquakes in history. However, seismic rupture nucleation on the northern and southern segments of the latched fault may be propagated through the creep segment. The study looked for evidence of earthquakes in samples from the San Andrés Fault Deep Observatory by using methods of biomarker compound thermal maturity and K/Ar dating. Biomarker compounds indicate that there are a large number of earthquakes with displacements greater than 1.5 meters in and around the 3.5-meter-wide fault. K/Ar age decreases with increasing thermal maturity, and local reset occurs when heated by co-vibration. Thus, the test age provides the maximum constraint on the age at which the earthquake occurred, and the youngest earthquake at that location occurred within 3 million years. The study suggests that creepy faults may trigger large earthquakes on longer timescales.
Source:
Geology (2022) 50 (4): 516-521
Original link:
https://doi.org/10.1130/G49451.1
translator
Chengdu University of Technology @ Huatian
proofread
University of Jena @ Zhang Yiqiong
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27
Comparative geomorphological analysis suggests that Ceres has ice core mounds
NASA's Dawn mission suggests that the base of Occator Crater on Ceres (the main asteroid belt between Mars and Jupiter) is covered with small quasi-cone-shaped hills. Many of these landforms have the morphological characteristics of the ice-edged hills (ice core mounds) with ice cores. In addition, some of the mounds within these Occattors are also thought to be of icy volcanic origin. If these hills are similar to ice core mounds, then they represent an ice-rich environment, which will be an area worth exploring in the future. The team reported morphological characteristics of mounds within the Occator, which helped determine their causes. At the same time, through comparative statistical analysis, the morphological similarities between the hills of Occator Crater and the ice core mounds and volcanic cones on Earth were also studied. In addition, based on nuclear density estimation and markov chain Monte Carlo method, the study demonstrated that ice core mounds and volcanic cones on Earth are morphologically distinct, while the hills within Cerean Crater have significant morphological similarities with ice core mounds on Earth. The results suggest that the statistical treatment of morphology itself can be a powerful tool for classifying and comparing planetary surface features, and that most of the hills within Cerean Crater that have been identified are more morphologically similar to ice core mounds than small terrestrial volcanic cones.
Source:
Geology (2022) 50 (4): 522-527
Original link:
https://doi.org/10.1130/G49321.1
translator
Dai Yunlong
proofread
Small claw claws
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Editor: Qin Huaqing
Proofreaders: Liu Qijun, Zhu Jianning
Past period review
Frontiers in geoscience || Introduction to Geology's 2021 No. 6 paper
Frontiers in geoscience || Introduction to Geology's 2021 No. 7 paper
Frontiers in geoscience || Introduction to Geology's 8th issue of 2021
Frontiers in geoscience || Introduction to Geology's 9th issue of 2021
Frontiers in geoscience || Introduction to Geology's 10th issue of 2021
Frontiers in geoscience || Geology, No. 11, 2021
Frontiers in geoscience || Introduction to Geology's 12th issue of 2021
Frontiers in geoscience || Introduction to Geology's 2022 No. 1 paper
Frontiers in geoscience || Introduction to Geology's 2022 No. 2 paper
Frontiers in geoscience || Introduction to Geology's 2022 No. 3 paper