Loess deposits are widespread in the Quaternary, but relatively rare in older geological records. This disparity is commonly linked to the unique climate conditions of the Quaternary, but those cannot fully explain the scarcity of loess in older records. Instead, we propose that the poor preservation of loess also plays an essential role. To test this hypothesis, we assess the preservation potential of loess by quantifying its modern‐day distribution in active sedimentary basins. This analysis shows that on the global scale only 20% of loess occurs in basins of which the majority is in a foreland setting. This could be due to nearby silt‐producing mountains and the effects of rain shadow aridity. The other 80% is ultimately either eroded or reworked and therefore poorly preserved in the long term. This conclusion implies that loess deposits may have been more common in pre‐Quaternary periods, despite being less abundant in the geological record.
{"title":"Loss of loess in the geological record due to poor preservation","authors":"N. Meijer, B. van der Meulen","doi":"10.1111/ter.12642","DOIUrl":"https://doi.org/10.1111/ter.12642","url":null,"abstract":"Loess deposits are widespread in the Quaternary, but relatively rare in older geological records. This disparity is commonly linked to the unique climate conditions of the Quaternary, but those cannot fully explain the scarcity of loess in older records. Instead, we propose that the poor preservation of loess also plays an essential role. To test this hypothesis, we assess the preservation potential of loess by quantifying its modern‐day distribution in active sedimentary basins. This analysis shows that on the global scale only 20% of loess occurs in basins of which the majority is in a foreland setting. This could be due to nearby silt‐producing mountains and the effects of rain shadow aridity. The other 80% is ultimately either eroded or reworked and therefore poorly preserved in the long term. This conclusion implies that loess deposits may have been more common in pre‐Quaternary periods, despite being less abundant in the geological record.","PeriodicalId":22260,"journal":{"name":"Terra Nova","volume":"35 1","pages":"185 - 192"},"PeriodicalIF":2.4,"publicationDate":"2022-12-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43979007","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
S. Zerathe, L. Audin, X. Robert, S. Schwartz, J. Carcaillet
The western flank of the Central Andes offers a unique geomorphological record of large paleolandslides that are well preserved on long time‐scales (i.e. ≥Pleistocene) due to the long‐lasting aridity of this region. However, the lack of chronological constraints on those landslides limits our understanding of the respective role of tectonics and climate on their triggering. Here, we report new 10Be surface exposure dating obtained on one of those giant slope‐failures: the Limaxina landslide (northern Chile, 19°S). Five tightly grouped exposure‐ages (one outlier discarded) point to a single landslide failure at 80 ± 4 ka. This timing being consistent with others local records of a wet episode in the Atacama Desert, it suggests a primary role of climate‐forcing on landslide activity in this region, calling to further slope failures dating in the arid Central western Andes to explore landscapes responses to Quaternary climate oscillations and extreme events.
{"title":"Large landslide of the hyperarid Central Western Andes triggered during a humid period of the Late Pleistocene (ca. 19°S; northern Chile)","authors":"S. Zerathe, L. Audin, X. Robert, S. Schwartz, J. Carcaillet","doi":"10.1111/ter.12641","DOIUrl":"https://doi.org/10.1111/ter.12641","url":null,"abstract":"The western flank of the Central Andes offers a unique geomorphological record of large paleolandslides that are well preserved on long time‐scales (i.e. ≥Pleistocene) due to the long‐lasting aridity of this region. However, the lack of chronological constraints on those landslides limits our understanding of the respective role of tectonics and climate on their triggering. Here, we report new 10Be surface exposure dating obtained on one of those giant slope‐failures: the Limaxina landslide (northern Chile, 19°S). Five tightly grouped exposure‐ages (one outlier discarded) point to a single landslide failure at 80 ± 4 ka. This timing being consistent with others local records of a wet episode in the Atacama Desert, it suggests a primary role of climate‐forcing on landslide activity in this region, calling to further slope failures dating in the arid Central western Andes to explore landscapes responses to Quaternary climate oscillations and extreme events.","PeriodicalId":22260,"journal":{"name":"Terra Nova","volume":"35 1","pages":"174 - 184"},"PeriodicalIF":2.4,"publicationDate":"2022-12-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45309959","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
T. Slagstad, E. Kulakov, M. Anderson, K. Saalmann, C. Kirkland, I. Henderson, M. Ganerød
Late Ediacaran opening of the Iapetus Ocean is typically considered to reflect separation of Baltica and Laurentia during final breakup of the Rodinia supercontinent, with subsequent closure during the Caledonian Orogeny. However, evidence of the pre‐opening juxtaposition of Baltica and Laurentia is limited to purportedly similar apparent polar wander paths and correlation of Rodinia‐forming orogenic events. We show that a range of existing data do not unequivocally support correlation of these orogens, and that geologic and palaeomagnetic data instead favour separation of Baltica and Laurentia as early as 1.1–1.2 Ga. Furthermore, new detrital zircon U–Pb age and Ar–Ar thermochronological data from Norway point towards an active western Baltican margin throughout most of the Neoproterozoic and early Palaeozoic. These findings are inconsistent with the majority of palaeogeographic reconstructions that place Baltica near the core of the Rodinia supercontinent.
{"title":"Was Baltica part of Rodinia?","authors":"T. Slagstad, E. Kulakov, M. Anderson, K. Saalmann, C. Kirkland, I. Henderson, M. Ganerød","doi":"10.1111/ter.12640","DOIUrl":"https://doi.org/10.1111/ter.12640","url":null,"abstract":"Late Ediacaran opening of the Iapetus Ocean is typically considered to reflect separation of Baltica and Laurentia during final breakup of the Rodinia supercontinent, with subsequent closure during the Caledonian Orogeny. However, evidence of the pre‐opening juxtaposition of Baltica and Laurentia is limited to purportedly similar apparent polar wander paths and correlation of Rodinia‐forming orogenic events. We show that a range of existing data do not unequivocally support correlation of these orogens, and that geologic and palaeomagnetic data instead favour separation of Baltica and Laurentia as early as 1.1–1.2 Ga. Furthermore, new detrital zircon U–Pb age and Ar–Ar thermochronological data from Norway point towards an active western Baltican margin throughout most of the Neoproterozoic and early Palaeozoic. These findings are inconsistent with the majority of palaeogeographic reconstructions that place Baltica near the core of the Rodinia supercontinent.","PeriodicalId":22260,"journal":{"name":"Terra Nova","volume":"35 1","pages":"167 - 173"},"PeriodicalIF":2.4,"publicationDate":"2022-12-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44234812","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Early Toarcian (~183 Ma) was marked by a global warming event which accelerated continental chemical weathering. To constrain the early Toarcian weathering intensity of a Cleveland Basin (Yorkshire, UK) region, this study employed its sediment chemical weathering proxies (potassium/aluminium (K/Al) and K/rubidium (K/Rb)). The K/Al and K/Rb exhibit an anomalous chemical weathering intensity signal from the contemporaneous warm, moist world. Variations in weathering intensity for the Yorkshire section inversely comply with detrital grain size changes (indicated by Al/silicon (Al/Si)). This finding implies that continental chemical weathering did not play a major role in changing detrital grain sizes in the Yorkshire sediments. Instead, short‐term sea‐level changes in the Cleveland Basin can explain the stratigraphic variations in detrital grain sizes. Anomalies of geochemical proxies for chemical weathering and eustatic sea‐level changes do exist at local scales possibly driven by Milankovitch cycle, which reminds us to be more careful when reconstructing palaeoclimate states.
{"title":"Anomalous weathering records in the Cleveland Basin (Yorkshire, UK) during the T‐OAE global warming","authors":"Yunfeng Wang","doi":"10.1111/ter.12639","DOIUrl":"https://doi.org/10.1111/ter.12639","url":null,"abstract":"Early Toarcian (~183 Ma) was marked by a global warming event which accelerated continental chemical weathering. To constrain the early Toarcian weathering intensity of a Cleveland Basin (Yorkshire, UK) region, this study employed its sediment chemical weathering proxies (potassium/aluminium (K/Al) and K/rubidium (K/Rb)). The K/Al and K/Rb exhibit an anomalous chemical weathering intensity signal from the contemporaneous warm, moist world. Variations in weathering intensity for the Yorkshire section inversely comply with detrital grain size changes (indicated by Al/silicon (Al/Si)). This finding implies that continental chemical weathering did not play a major role in changing detrital grain sizes in the Yorkshire sediments. Instead, short‐term sea‐level changes in the Cleveland Basin can explain the stratigraphic variations in detrital grain sizes. Anomalies of geochemical proxies for chemical weathering and eustatic sea‐level changes do exist at local scales possibly driven by Milankovitch cycle, which reminds us to be more careful when reconstructing palaeoclimate states.","PeriodicalId":22260,"journal":{"name":"Terra Nova","volume":"35 1","pages":"153 - 166"},"PeriodicalIF":2.4,"publicationDate":"2022-12-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49505602","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Broadly similar Early to Middle Jurassic stratigraphic sequences including bimodal igneous rocks of the Sanandaj–Sirjan Zone of Iran and the Sakarya Zone of Turkey suggest that these formed in a common tectonic setting in an extensional basin that evolved from a terrestrial magmatic rift to a marine shelf and passive continental margin. Whole‐rock chemistry and Sr–Nd isotope signatures indicate derivation of mafic melts from partial melting of the subcontinental lithosphere. Decompression associated with extension led to 5%–30% partial melting of spinel–garnet lherzolite with minor involvement of continental crust, producing tholeiitic to transitional basaltic magma. Extensional basins inverted during the Mid‐Late Jurassic. These relationships suggest the Early to Middle Jurassic formation of a volcanic rifted margin on the SW Eurasian margin, similar to that of offshore Norway.
{"title":"A Jurassic volcanic passive margin in Iran and Turkey","authors":"H. Azizi, R. Stern, Raif Kandemir, O. Karslı","doi":"10.1111/ter.12638","DOIUrl":"https://doi.org/10.1111/ter.12638","url":null,"abstract":"Broadly similar Early to Middle Jurassic stratigraphic sequences including bimodal igneous rocks of the Sanandaj–Sirjan Zone of Iran and the Sakarya Zone of Turkey suggest that these formed in a common tectonic setting in an extensional basin that evolved from a terrestrial magmatic rift to a marine shelf and passive continental margin. Whole‐rock chemistry and Sr–Nd isotope signatures indicate derivation of mafic melts from partial melting of the subcontinental lithosphere. Decompression associated with extension led to 5%–30% partial melting of spinel–garnet lherzolite with minor involvement of continental crust, producing tholeiitic to transitional basaltic magma. Extensional basins inverted during the Mid‐Late Jurassic. These relationships suggest the Early to Middle Jurassic formation of a volcanic rifted margin on the SW Eurasian margin, similar to that of offshore Norway.","PeriodicalId":22260,"journal":{"name":"Terra Nova","volume":"35 1","pages":"141 - 152"},"PeriodicalIF":2.4,"publicationDate":"2022-12-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47524493","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Dynamic subsidence and uplift of plates are often explained by the vertical motion of density anomalies in the mantle. Such models predict surface vertical motion rates of less than 100 m Myr−1 at long‐wavelengths with a timespan of tens of Myr. However, during periods of relative sea‐level stability, some of the phases of vertical motion on stable portions of plates have occurred at rates greater than 100 m Myr−1 during episodes that may last only a few Myr. Here, we show that vertical surface motions, with rates greater than 100 m Myr−1 and durations less than a few Myr, can be explained by changes in basal shear stress caused by variation in horizontal motion of a viscous plate relative to the asthenosphere. We apply our physical model to the short‐lived mid‐Eocene immersion of the southern margin of Australia.
板块的动态沉降和隆升通常用地幔中密度异常的垂直运动来解释。这种模式预测地表垂直运动速率在长波长下小于100 m Myr−1，时间跨度为几十Myr。然而，在海平面相对稳定的时期，板块稳定部分的某些垂直运动阶段发生的速率大于100米迈r−1，而这些阶段可能只持续几个迈r。在这里，我们表明，垂直表面运动的速率大于100 m Myr−1，持续时间小于几个Myr，可以用相对于软流层的粘性板块的水平运动变化引起的基底剪切应力的变化来解释。我们将我们的物理模型应用于澳大利亚南缘短暂的中始新世浸没。
{"title":"Brief immersion of southern Australia by change in relative plate speed","authors":"Ömer F. Bodur, G. Houseman, P. Rey","doi":"10.1111/ter.12637","DOIUrl":"https://doi.org/10.1111/ter.12637","url":null,"abstract":"Dynamic subsidence and uplift of plates are often explained by the vertical motion of density anomalies in the mantle. Such models predict surface vertical motion rates of less than 100 m Myr−1 at long‐wavelengths with a timespan of tens of Myr. However, during periods of relative sea‐level stability, some of the phases of vertical motion on stable portions of plates have occurred at rates greater than 100 m Myr−1 during episodes that may last only a few Myr. Here, we show that vertical surface motions, with rates greater than 100 m Myr−1 and durations less than a few Myr, can be explained by changes in basal shear stress caused by variation in horizontal motion of a viscous plate relative to the asthenosphere. We apply our physical model to the short‐lived mid‐Eocene immersion of the southern margin of Australia.","PeriodicalId":22260,"journal":{"name":"Terra Nova","volume":"35 1","pages":"134 - 140"},"PeriodicalIF":2.4,"publicationDate":"2022-11-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42714201","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Megan E. Flansburg, Eirini M. Poulaki, D. Stockli, K. Soukis
Miocene extension in the back arc of the retreating Hellenic subduction zone resulted in metamorphic core complex formation and exhumation of the Cycladic HP‐LT rocks. The extension was accommodated by bivergent detachment systems, generally occupying the interface between the Cycladic Blueschist Unit (CBU) and overlying Pelagonian units. However, the nature and kinematic history of the contact between the CBU and underlying Cycladic Basement (CB) in the southern Cyclades remains debated due to the presence of both top‐to‐the‐N and top‐to‐the‐S kinematics and ambiguities dating the final exhumation stages. Zircon and apatite (U‐Th)/He data and thermal modelling for the CB and CBU on Ios and Sikinos show that both units were likely exhumed as a coherent footwall block in response to rapid slip along the bivergent Miocene Santorini and Naxos‐Paros detachment systems.
{"title":"Coeval Miocene exhumation of the Cycladic Blueschist Unit and the Cycladic Basement in the southern Cyclades, Ios and Sikinos, Greece","authors":"Megan E. Flansburg, Eirini M. Poulaki, D. Stockli, K. Soukis","doi":"10.1111/ter.12636","DOIUrl":"https://doi.org/10.1111/ter.12636","url":null,"abstract":"Miocene extension in the back arc of the retreating Hellenic subduction zone resulted in metamorphic core complex formation and exhumation of the Cycladic HP‐LT rocks. The extension was accommodated by bivergent detachment systems, generally occupying the interface between the Cycladic Blueschist Unit (CBU) and overlying Pelagonian units. However, the nature and kinematic history of the contact between the CBU and underlying Cycladic Basement (CB) in the southern Cyclades remains debated due to the presence of both top‐to‐the‐N and top‐to‐the‐S kinematics and ambiguities dating the final exhumation stages. Zircon and apatite (U‐Th)/He data and thermal modelling for the CB and CBU on Ios and Sikinos show that both units were likely exhumed as a coherent footwall block in response to rapid slip along the bivergent Miocene Santorini and Naxos‐Paros detachment systems.","PeriodicalId":22260,"journal":{"name":"Terra Nova","volume":"35 1","pages":"124 - 133"},"PeriodicalIF":2.4,"publicationDate":"2022-11-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46200518","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A. Petroccia, R. Carosi, C. Montomoli, S. Iaccarino, A. Vitale Brovarone
Unravelling the architecture and evolution of orogenic wedges are often hampered by the presence of strongly deformed large‐scale nappes made by homogeneous metasedimentary rocks lacking diagnostic metamorphic phases. Involving nappes or tectonic units which occupy most of the chain, reconstructing the thermal architecture of the hinterland–foreland transition zone of collisional belts represents a key point to comprehend the orogenic wedge tectonics. This work provides new thermal data from Raman Spectroscopy on Carbonaceous Material (RSCM) carried out in the low‐grade metamorphic rocks of the hinterland–foreland transition zone in the Variscan belt of Sardinia. The obtained TRSCM highlighted a temperature difference, from ~470–440°C down to ~440–380°C, for the internal and external nappes, respectively. We propose that both nappes experienced syn‐nappe greenschist‐facies metamorphism with different TRSCM, further heating localized along the tectonic boundary in between, that is the Barbagia Thrust (BT), and finally, post‐nappe stacking regional‐scale folding, that deformed the TRSCM spatial distribution and drove the present‐day thermal architecture.
{"title":"Thermal variation across collisional orogens: Insights from the hinterland–foreland transition zone of the Sardinian Variscan belt","authors":"A. Petroccia, R. Carosi, C. Montomoli, S. Iaccarino, A. Vitale Brovarone","doi":"10.1111/ter.12635","DOIUrl":"https://doi.org/10.1111/ter.12635","url":null,"abstract":"Unravelling the architecture and evolution of orogenic wedges are often hampered by the presence of strongly deformed large‐scale nappes made by homogeneous metasedimentary rocks lacking diagnostic metamorphic phases. Involving nappes or tectonic units which occupy most of the chain, reconstructing the thermal architecture of the hinterland–foreland transition zone of collisional belts represents a key point to comprehend the orogenic wedge tectonics. This work provides new thermal data from Raman Spectroscopy on Carbonaceous Material (RSCM) carried out in the low‐grade metamorphic rocks of the hinterland–foreland transition zone in the Variscan belt of Sardinia. The obtained TRSCM highlighted a temperature difference, from ~470–440°C down to ~440–380°C, for the internal and external nappes, respectively. We propose that both nappes experienced syn‐nappe greenschist‐facies metamorphism with different TRSCM, further heating localized along the tectonic boundary in between, that is the Barbagia Thrust (BT), and finally, post‐nappe stacking regional‐scale folding, that deformed the TRSCM spatial distribution and drove the present‐day thermal architecture.","PeriodicalId":22260,"journal":{"name":"Terra Nova","volume":"35 1","pages":"113 - 123"},"PeriodicalIF":2.4,"publicationDate":"2022-11-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42574324","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Thomas Gyomlai, P. Agard, H. Marschall, L. Jolivet
The spatiotemporal scales at which fluid flow events occur along the subduction interface remain poorly constrained. This study illustrates the benefit of using in‐situ Rb/Sr dating on metasomatic white mica to constrain the timing of metasomatic events, taking advantage of the well‐studied reaction zones of the Kampos‐Lia unit of Syros, Greece. This unit is a subducted block‐in‐matrix structure corresponding to a preserved fragment of a discontinuous, slow‐spreading oceanic domain. Results reveal that the main metasomatic event took place at ~36 Ma, coincident with the transition from blueschist to greenschist facies and syn‐ to post‐orogenic exhumation in the Cyclades marking the end of a first exhumation stage along the subduction interface. Results highlight that fluid–rock interaction along the subduction interface cannot be treated as the result of continuous fluid influx, but rather reflect punctuated, heterogeneously distributed events (both in time and space) tied to specific tectonometamorphic episodes.
{"title":"Hygrochronometry of punctuated metasomatic events during exhumation of the Cycladic blueschist unit (Syros, Greece)","authors":"Thomas Gyomlai, P. Agard, H. Marschall, L. Jolivet","doi":"10.1111/ter.12634","DOIUrl":"https://doi.org/10.1111/ter.12634","url":null,"abstract":"The spatiotemporal scales at which fluid flow events occur along the subduction interface remain poorly constrained. This study illustrates the benefit of using in‐situ Rb/Sr dating on metasomatic white mica to constrain the timing of metasomatic events, taking advantage of the well‐studied reaction zones of the Kampos‐Lia unit of Syros, Greece. This unit is a subducted block‐in‐matrix structure corresponding to a preserved fragment of a discontinuous, slow‐spreading oceanic domain. Results reveal that the main metasomatic event took place at ~36 Ma, coincident with the transition from blueschist to greenschist facies and syn‐ to post‐orogenic exhumation in the Cyclades marking the end of a first exhumation stage along the subduction interface. Results highlight that fluid–rock interaction along the subduction interface cannot be treated as the result of continuous fluid influx, but rather reflect punctuated, heterogeneously distributed events (both in time and space) tied to specific tectonometamorphic episodes.","PeriodicalId":22260,"journal":{"name":"Terra Nova","volume":"35 1","pages":"101 - 112"},"PeriodicalIF":2.4,"publicationDate":"2022-11-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45737296","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Natural fault gouges reactivated by the 2008 Wenchuan earthquake are typically rich in carbon in shallow parts of the seismogenic fault zone. Although experimental evidence indicates that amorphous carbon can be changed to graphite during seismic slips, this transformation has not yet been observed in nature. We conducted a nanoscale investigation of a carbon‐rich co‐seismic gouge from a surface rupture related to the Wenchuan earthquake using high‐resolution transmission electron microscopy. We found that all mineral grains were wrapped in amorphous carbonaceous materials with sinuate and straight graphene layer stacks. The sinuate layer was the transient material (~0.3456 nm) formed by amorphous carbon transforming to graphite; the graphene layer was graphite flakes (0.3354 nm). This means that graphitization occurred on the mineral grain surfaces (asperities) in the shallow slip zones during previous earthquake cycles, which could decrease the friction strength of the co‐seismic fault gouge and explain the dynamic weakness of the shallow parts of the Longmenshan seismogenic fault zone.
{"title":"Structural fabrics of carbon grains in a natural fault gouge reactivated by the 2008 Wenchuan earthquake","authors":"Jiaxiang Dang, Yongsheng Zhou","doi":"10.1111/ter.12633","DOIUrl":"https://doi.org/10.1111/ter.12633","url":null,"abstract":"Natural fault gouges reactivated by the 2008 Wenchuan earthquake are typically rich in carbon in shallow parts of the seismogenic fault zone. Although experimental evidence indicates that amorphous carbon can be changed to graphite during seismic slips, this transformation has not yet been observed in nature. We conducted a nanoscale investigation of a carbon‐rich co‐seismic gouge from a surface rupture related to the Wenchuan earthquake using high‐resolution transmission electron microscopy. We found that all mineral grains were wrapped in amorphous carbonaceous materials with sinuate and straight graphene layer stacks. The sinuate layer was the transient material (~0.3456 nm) formed by amorphous carbon transforming to graphite; the graphene layer was graphite flakes (0.3354 nm). This means that graphitization occurred on the mineral grain surfaces (asperities) in the shallow slip zones during previous earthquake cycles, which could decrease the friction strength of the co‐seismic fault gouge and explain the dynamic weakness of the shallow parts of the Longmenshan seismogenic fault zone.","PeriodicalId":22260,"journal":{"name":"Terra Nova","volume":"35 1","pages":"100 - 91"},"PeriodicalIF":2.4,"publicationDate":"2022-11-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47377059","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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