<strong>Abstract.</strong> The Koyna-Warna Seismogenic Region of western India has been recognized as one of the hotspots for reservoir-triggered seismicity (RTS) since 1967. The current study investigates the fluid's interaction with the severely fractured granitoid basement of this area and its potential contribution to the recurring seismicity. The presence of several secondary minerals, such as chlorite, epidote, calcite, illite, etc., along the pre-existing faults and fractures, is revealed by detailed petrologic investigation at mesoscopic and microscopic scales along with XRD analysis. This indicates the fluid-rock interaction along these mechanically weak planes and subsequent propylitic grade of hydrothermal alteration under acidic to neutral conditions (pH 5.5–7) and the temperature of above 200–220 °C up to about 350 °C. Additionally, the transformation of biotite into chlorite due to fluid interaction has been inferred from the microscopic appearance of biotitic remnant within neoformed chlorite which is further supported by the mass loss of K<sub>2</sub>O and concurrent gain of MgO and FeO, demonstrating the replacement of potassium (K) interlayer sheet by brucite-like [Mg (OH)<sub>2</sub>] layer during biotite chloritization. However, this released K<sub>2</sub>O further assists in the formation of illite resulting in the mass gain of K<sub>2</sub>O at a few certain depths, whereas the dissolution of plagioclase justifies the formation of albite and calcite as evidenced by the gain of Na<sub>2</sub>O and CaO. The present study also highlights that the recurring nature of the seismicity in this area may be related to clay mineralization along the faults and fractures due to fluid-rock interaction, such as chlorite, illite, etc., in addition to the existing fault geometry and stress build-up due to reservoir impoundment. At increasing stress condition, the anisotropic and weakly bonded, layered crystal structure of chlorite forming ripplocations may develop kink bands and increases the yield strength proportionally with rising pressure up to dehydration temperature. Such visco-elastic behaviour of chlorite may promote aseismic creep in the faults. On the other hand, epidote noticed at certain depths has a contrasting behaviour; it tends to wear at the micron or submicron‐scale asperity contacts and produce fine particles which generate unstable sliding. However, the relatively higher abundance of chlorite in the faults and fractures disrupts the epidote‐epidote contact asperities and prevents such wearing of epidote grains into fine particles. Thus, biotite chloritization in conjunction with relatively less production of epidote along pre-existing faults and fractures helps to release the accumulated stress through a series of small-scale earthquakes and results in the steady fault creep observed in this region during the past 50 years. In this context, fluid-rock interaction along the pre-existing faults and fractures at shallow dept
摘要自 1967 年以来，印度西部的科伊纳-瓦尔纳成震区一直被认为是储层触发地震（RTS）的热点地区之一。目前的研究调查了流体与该地区严重断裂的花岗岩基底之间的相互作用及其对反复发生的地震的潜在影响。通过中观和微观尺度的详细岩石学调查以及 XRD 分析，揭示了在已有的断层和裂缝中存在多种次生矿物，如绿泥石、绿帘石、方解石、伊利石等。这表明在酸性至中性条件（pH 值 5.5-7）和高于 200-220 °C 至约 350 °C 的温度下，流体与岩石沿着这些机械性较弱的平面相互作用，随后发生了丙基热液蚀变。此外，从新形成的绿泥石中的生物残留物的微观外观可以推断出流体相互作用导致了生物橄榄石向绿泥石的转化，而 K2O 的大量流失以及 MgO 和 FeO 的同时增加进一步证实了这一点，表明在生物橄榄石绿泥石化过程中，钾（K）层间薄片被青金石类[Mg (OH)2]层所取代。然而，释放出的 K2O 进一步促进了伊利石的形成，导致在几个特定深度 K2O 的质量增加，而斜长石的溶解则证明了白云石和方解石的形成，Na2O 和 CaO 的增加证明了这一点。本研究还强调，该地区地震的反复发生可能与沿断层和裂缝的粘土矿化有关，这些粘土矿化是流体与岩石相互作用的结果，如绿泥石、伊利石等，此外还有现有的断层几何形状和水库蓄水导致的应力增加。在应力不断增加的情况下，形成波纹位点的各向异性弱粘结层状绿泥石晶体结构可能会形成扭结带，并随着压力的上升成比例地增加屈服强度，直至脱水温度。绿泥石的这种粘弹性可能会促进断层的抗震蠕变。另一方面，在某些深度注意到的绿泥石具有相反的行为；它倾向于在微米或亚微米尺度的表面接触处磨损，并产生细小颗粒，从而产生不稳定的滑动。然而，断层和裂缝中相对较多的绿泥石破坏了闪长岩与闪长岩的接触面，阻止了闪长岩晶粒磨损成细颗粒。因此，生物绿泥石化与先前存在的断层和裂缝中相对较少的表土的产生相结合，有助于通过一系列小规模地震释放累积的应力，并导致在过去 50 年中在该地区观察到的稳定的断层蠕变。在这种情况下，浅层原有断层和断裂沿线的流体-岩石相互作用对科伊纳-瓦尔纳成震区起到了保护作用，使其免受相对较大震级地震的影响--这对该地区来说是一大福音。
{"title":"Fluid-rock interaction in the intraplate active seismic zone: Boon or bane?","authors":"Piyal Halder, Matsyendra Kumar Shukla, Kamlesh Kumar, Anupam Sharma","doi":"10.5194/egusphere-2023-2553","DOIUrl":"https://doi.org/10.5194/egusphere-2023-2553","url":null,"abstract":"<strong>Abstract.</strong> The Koyna-Warna Seismogenic Region of western India has been recognized as one of the hotspots for reservoir-triggered seismicity (RTS) since 1967. The current study investigates the fluid's interaction with the severely fractured granitoid basement of this area and its potential contribution to the recurring seismicity. The presence of several secondary minerals, such as chlorite, epidote, calcite, illite, etc., along the pre-existing faults and fractures, is revealed by detailed petrologic investigation at mesoscopic and microscopic scales along with XRD analysis. This indicates the fluid-rock interaction along these mechanically weak planes and subsequent propylitic grade of hydrothermal alteration under acidic to neutral conditions (pH 5.5–7) and the temperature of above 200–220 °C up to about 350 °C. Additionally, the transformation of biotite into chlorite due to fluid interaction has been inferred from the microscopic appearance of biotitic remnant within neoformed chlorite which is further supported by the mass loss of K<sub>2</sub>O and concurrent gain of MgO and FeO, demonstrating the replacement of potassium (K) interlayer sheet by brucite-like [Mg (OH)<sub>2</sub>] layer during biotite chloritization. However, this released K<sub>2</sub>O further assists in the formation of illite resulting in the mass gain of K<sub>2</sub>O at a few certain depths, whereas the dissolution of plagioclase justifies the formation of albite and calcite as evidenced by the gain of Na<sub>2</sub>O and CaO. The present study also highlights that the recurring nature of the seismicity in this area may be related to clay mineralization along the faults and fractures due to fluid-rock interaction, such as chlorite, illite, etc., in addition to the existing fault geometry and stress build-up due to reservoir impoundment. At increasing stress condition, the anisotropic and weakly bonded, layered crystal structure of chlorite forming ripplocations may develop kink bands and increases the yield strength proportionally with rising pressure up to dehydration temperature. Such visco-elastic behaviour of chlorite may promote aseismic creep in the faults. On the other hand, epidote noticed at certain depths has a contrasting behaviour; it tends to wear at the micron or submicron‐scale asperity contacts and produce fine particles which generate unstable sliding. However, the relatively higher abundance of chlorite in the faults and fractures disrupts the epidote‐epidote contact asperities and prevents such wearing of epidote grains into fine particles. Thus, biotite chloritization in conjunction with relatively less production of epidote along pre-existing faults and fractures helps to release the accumulated stress through a series of small-scale earthquakes and results in the steady fault creep observed in this region during the past 50 years. In this context, fluid-rock interaction along the pre-existing faults and fractures at shallow dept","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"81 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-03-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140055749","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-03-01DOI: 10.5194/egusphere-2024-586
Peter Achtziger-Zupančič, Alberto Ceccato, Alba Simona Zappone, Giacomo Pozzi, Alexis Shakas, Florian Amann, Whitney Maria Behr, Daniel Escallon Botero, Domenico Giardini, Marian Hertrich, Mohammadreza Jalali, Xiaodong Ma, Men-Andrin Meier, Julian Osten, Stefan Wiemer, Massimo Cocco
Abstract. Performing stimulation experiments at approximately 1 km depth in the Bedretto Underground Laboratory for Geosciences and Geoenergies necessitates identifying and characterizing the target fault zone for on-fault monitoring of induced fault-slip and seismicity, a current challenge in understanding seismogenic processes. We discuss the multidisciplinary approach for selecting the target fault zone for the experiments planned within the Fault Activation and Earthquake Ruptures (FEAR) project, aiming to induce fault-slip and seismicity up to a magnitude 1.0 earthquake while enhancing monitoring and control of fluid-injection experiments. Structural geological mapping, remote sensing, exploration drilling and borehole logging, ground-penetration radar, and laboratory investigations were employed to identify and characterize the target fault – a ductile-brittle shear zone several meters wide with intensely fractured volume persisting over 100 m. Its orientation in the in-situ stress field favors reactivation in normal to strike-slip regimes. Laboratory tests showed slight velocity strengthening of the fault gouge. The fault's architecture, typical for crystalline environments, poses challenges for fluid flow, necessitating detailed hydraulic and stress characterization before each of the FEAR experiments. This multidisciplinary approach was crucial for managing rock volume heterogeneity and understand implications for the dense monitoring network. Successfully identifying the fault sets the stage for seismic activation experiments commencing in spring 2024.
{"title":"Selection and Characterisation of the Target Fault for Fluid-Induced Activation and Earthquake Rupture Experiments","authors":"Peter Achtziger-Zupančič, Alberto Ceccato, Alba Simona Zappone, Giacomo Pozzi, Alexis Shakas, Florian Amann, Whitney Maria Behr, Daniel Escallon Botero, Domenico Giardini, Marian Hertrich, Mohammadreza Jalali, Xiaodong Ma, Men-Andrin Meier, Julian Osten, Stefan Wiemer, Massimo Cocco","doi":"10.5194/egusphere-2024-586","DOIUrl":"https://doi.org/10.5194/egusphere-2024-586","url":null,"abstract":"<strong>Abstract.</strong> Performing stimulation experiments at approximately 1 km depth in the Bedretto Underground Laboratory for Geosciences and Geoenergies necessitates identifying and characterizing the target fault zone for on-fault monitoring of induced fault-slip and seismicity, a current challenge in understanding seismogenic processes. We discuss the multidisciplinary approach for selecting the target fault zone for the experiments planned within the Fault Activation and Earthquake Ruptures (FEAR) project, aiming to induce fault-slip and seismicity up to a magnitude 1.0 earthquake while enhancing monitoring and control of fluid-injection experiments. Structural geological mapping, remote sensing, exploration drilling and borehole logging, ground-penetration radar, and laboratory investigations were employed to identify and characterize the target fault – a ductile-brittle shear zone several meters wide with intensely fractured volume persisting over 100 m. Its orientation in the in-situ stress field favors reactivation in normal to strike-slip regimes. Laboratory tests showed slight velocity strengthening of the fault gouge. The fault's architecture, typical for crystalline environments, poses challenges for fluid flow, necessitating detailed hydraulic and stress characterization before each of the FEAR experiments. This multidisciplinary approach was crucial for managing rock volume heterogeneity and understand implications for the dense monitoring network. Successfully identifying the fault sets the stage for seismic activation experiments commencing in spring 2024.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"16 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140005484","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ana Fonseca, Simon Nachtergaele, Amed Bonilla, Stijn Dewaele, Johan De Grave
Abstract. This study presents results from apatite fission track (AFT) thermochronology to investigate the thermal history and exhumation dynamics of the Rio Negro–Juruena basement, situated within the western Guiana Shield of the Amazonian Craton. AFT dating and associated thermal history modeling in South America has largely been restricted to the plate's margins (e.g., Andean active margin, Brazilian passive margin, and others). Our paper reports on low-temperature thermochronological data from the internal part of the western Guiana Shield for the first time. This area is part of a vast cratonic lithosphere that is generally thought to be stable and little influenced by Mesozoic and Cenozoic tectonics. Our data, however, show AFT central ages ranging from 79.1 ± 3.2 to 177.1 ± 14.8 Ma, with mean confined track lengths of ca. 12 µm. Contrary to what might be expected of stable cratonic shields, inverse thermal history modeling indicates a rapid basement cooling event in the early Cretaceous. This cooling is interpreted as a significant exhumation event of the basement that was likely driven by the coeval extensional tectonics associated with back-arc rifts in the Llanos and Putumayo–Oriente–Maranon basins. The extensional tectonics facilitated both basement uplift and subsidence of the adjoining basins, increasing erosional dynamics and consequent exhumation of the basement rocks. The tectonic setting shifted in the late Cretaceous from extensional to contractional, resulting in reduced subsidence of the basins and consequential diminishing cooling rates of the Guiana Shield basement. Throughout the Cenozoic, only gradual, slow subsidence occurred in the study area due to regional flexure linked to the Andean orogeny. Comparative analysis with low-temperature thermochronology data from other west Gondwana cratonic segments highlights that exhumation episodes are highly controlled by tectonic inheritance, lithospheric strength, and proximity to rift zones. This study underscores the complex interplay between tectonic events and the response of cratonic lithosphere over geological timescales and highlights extensional settings as an important geological context for craton exhumation.
{"title":"Extensional exhumation of cratons: insights from the Early Cretaceous Rio Negro–Juruena belt (Amazonian Craton, Colombia)","authors":"Ana Fonseca, Simon Nachtergaele, Amed Bonilla, Stijn Dewaele, Johan De Grave","doi":"10.5194/se-15-329-2024","DOIUrl":"https://doi.org/10.5194/se-15-329-2024","url":null,"abstract":"Abstract. This study presents results from apatite fission track (AFT) thermochronology to investigate the thermal history and exhumation dynamics of the Rio Negro–Juruena basement, situated within the western Guiana Shield of the Amazonian Craton. AFT dating and associated thermal history modeling in South America has largely been restricted to the plate's margins (e.g., Andean active margin, Brazilian passive margin, and others). Our paper reports on low-temperature thermochronological data from the internal part of the western Guiana Shield for the first time. This area is part of a vast cratonic lithosphere that is generally thought to be stable and little influenced by Mesozoic and Cenozoic tectonics. Our data, however, show AFT central ages ranging from 79.1 ± 3.2 to 177.1 ± 14.8 Ma, with mean confined track lengths of ca. 12 µm. Contrary to what might be expected of stable cratonic shields, inverse thermal history modeling indicates a rapid basement cooling event in the early Cretaceous. This cooling is interpreted as a significant exhumation event of the basement that was likely driven by the coeval extensional tectonics associated with back-arc rifts in the Llanos and Putumayo–Oriente–Maranon basins. The extensional tectonics facilitated both basement uplift and subsidence of the adjoining basins, increasing erosional dynamics and consequent exhumation of the basement rocks. The tectonic setting shifted in the late Cretaceous from extensional to contractional, resulting in reduced subsidence of the basins and consequential diminishing cooling rates of the Guiana Shield basement. Throughout the Cenozoic, only gradual, slow subsidence occurred in the study area due to regional flexure linked to the Andean orogeny. Comparative analysis with low-temperature thermochronology data from other west Gondwana cratonic segments highlights that exhumation episodes are highly controlled by tectonic inheritance, lithospheric strength, and proximity to rift zones. This study underscores the complex interplay between tectonic events and the response of cratonic lithosphere over geological timescales and highlights extensional settings as an important geological context for craton exhumation.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"13 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140019317","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-02-29DOI: 10.5194/egusphere-2024-569
Agathe Faucher, Frédéric Gueydan, Jeroen van Hunen
Abstract. During gravitational collapse of orogenic systems or in hot extending back-arc systems, normal faulting is often associated with strike slip faulting whose origin remains enigmatic. The formation of major strike slip fault zones during subduction upper plate extension driven by slab-roll back can be related to slab tearing at depth. In the Aegean, where back-arc extension driven by southwest-ward migration of the Hellenic trench (slab rollback) has occurred since at least 30 Ma, the co-existence of normal faulting and a multiple strike-slip fault zones is observed since the onset of the westward extrusion of Anatolia, but before the onset of slab tearing that occurs in the Pliocene. Here we show how strike slip faults and normal faults can coexist in a hot deforming continental lithosphere. Our 3D numerical models with two deformation stages (initial pure extension followed by combined shortening and extension) can explain the Aegean tectonics. Several rifts form during the purely extensional stage that, during the second deformation stage, are either fully reactivated as strike-slip faults, or remain active but rimmed by dextral and sinistral strike-slip faults. This suggests that the extension driven by slab rollback and shortening driven by westward extrusion of Anatolia interact in space and time in the Aegean domain to create a complex tectonic pattern with coeval active normal faulting (e.g. Corinth and Evvia rifts) and dextral strike-slip faulting (e.g. the North Anatolian and Myrthes-Ikaria faults). These results show that strike slip faults in extending domain can be a sign of shortening at high angle to the extension direction.
摘要。在造山系统的重力塌陷过程中或在热延伸的后弧系统中，正断层往往与走向滑动断层相关联，而走向滑动断层的成因至今仍是个谜。在板块回滚驱动的俯冲上板块延伸过程中，主要走向滑动断层带的形成可能与深部板块撕裂有关。在爱琴海，希腊海沟的西南迁移（板块回滚）驱动的弧后延伸至少从 30 Ma 开始，自安纳托利亚开始向西挤压以来，在上新世板块撕裂开始之前，就观察到了正常断层和多个走向滑动断层带的共存。在这里，我们展示了在热变形大陆岩石圈中，走向滑动断层和正断层是如何共存的。我们的三维数值模型包含两个变形阶段（最初的纯伸展阶段，随后是缩短和伸展的结合阶段），可以解释爱琴海构造。在纯伸展阶段形成的几条断裂，在第二个变形阶段，要么作为走向滑动断层被完全重新激活，要么保持活跃但被右旋和正弦走向滑动断层环绕。这表明，在爱琴海海域，板块滚回所驱动的延伸和安纳托利亚向西挤压所驱动的缩短在空间和时间上相互作用，形成了一种复杂的构造模式，其中既有共时活动的正断层（如科林斯断裂和埃维亚断裂），也有右旋的走向滑动断层（如北安纳托利亚断层和马尔他-伊卡里亚断层）。这些结果表明，延伸域中的走向滑动断层可能是与延伸方向呈大角度缩短的标志。
{"title":"Strike-slip faulting in extending upper plates: insight from the Aegean","authors":"Agathe Faucher, Frédéric Gueydan, Jeroen van Hunen","doi":"10.5194/egusphere-2024-569","DOIUrl":"https://doi.org/10.5194/egusphere-2024-569","url":null,"abstract":"<strong>Abstract.</strong> During gravitational collapse of orogenic systems or in hot extending back-arc systems, normal faulting is often associated with strike slip faulting whose origin remains enigmatic. The formation of major strike slip fault zones during subduction upper plate extension driven by slab-roll back can be related to slab tearing at depth. In the Aegean, where back-arc extension driven by southwest-ward migration of the Hellenic trench (slab rollback) has occurred since at least 30 Ma, the co-existence of normal faulting and a multiple strike-slip fault zones is observed since the onset of the westward extrusion of Anatolia, but before the onset of slab tearing that occurs in the Pliocene. Here we show how strike slip faults and normal faults can coexist in a hot deforming continental lithosphere. Our 3D numerical models with two deformation stages (initial pure extension followed by combined shortening and extension) can explain the Aegean tectonics. Several rifts form during the purely extensional stage that, during the second deformation stage, are either fully reactivated as strike-slip faults, or remain active but rimmed by dextral and sinistral strike-slip faults. This suggests that the extension driven by slab rollback and shortening driven by westward extrusion of Anatolia interact in space and time in the Aegean domain to create a complex tectonic pattern with coeval active normal faulting (e.g. Corinth and Evvia rifts) and dextral strike-slip faulting (e.g. the North Anatolian and Myrthes-Ikaria faults). These results show that strike slip faults in extending domain can be a sign of shortening at high angle to the extension direction.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"14 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-02-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140019328","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-02-28DOI: 10.5194/egusphere-2024-183
Marc Campeny, Inmaculada Menéndez, Luis Quevedo, Jorge Yepes, Ramón Casillas, Agustina Ahijado, Jorge Méndez-Ramos, José Mangas
Abstract. Rare earth elements (REEs) play a pivotal role in the ongoing energy and mobility transition challenges. Given their critical importance, governments worldwide and especially from the European Union, are actively promoting the exploration of REE resources. In this context, alkaline magmatic rocks (including trachytes, phonolites, syenites, melteigites and ijolites), carbonatites and their associated weathering products were subjected to a preliminary evaluation as potential targets for REE exploration on Fuerteventura Island (Canary Archipelago, Spain) based on mineralogical and geochemical studies. These lithologies show significant REE concentrations. However, only carbonatites exhibit the potential to host economically viable REE mineral deposits. REE concentrations in carbonatites of up to 10,301.83 ppm REY (REEs plus yttrium) have been detected, comparable to other locations hosting significant deposits of these critical elements worldwide. Conversely, alkaline magmatic rocks and the resulting weathering products display limited REE enrichment. Notably, REEs in carbonatites are associated with primary accessory phases such as REE-bearing pyrochlore and britholite, and secondary monazite. The carbonatites of Fuerteventura hold promise as prospective REE deposits within a non-conventional geological setting (oceanic island). However, due to intricate structural attributes and possible land use constraints, additional future detailed investigations are imperative to ascertain their genuine economic viability as substantial REE resources.
{"title":"Rare earth element resources on Fuerteventura, Canary Islands, Spain: a geochemical and mineralogical approach","authors":"Marc Campeny, Inmaculada Menéndez, Luis Quevedo, Jorge Yepes, Ramón Casillas, Agustina Ahijado, Jorge Méndez-Ramos, José Mangas","doi":"10.5194/egusphere-2024-183","DOIUrl":"https://doi.org/10.5194/egusphere-2024-183","url":null,"abstract":"<strong>Abstract.</strong> Rare earth elements (REEs) play a pivotal role in the ongoing energy and mobility transition challenges. Given their critical importance, governments worldwide and especially from the European Union, are actively promoting the exploration of REE resources. In this context, alkaline magmatic rocks (including trachytes, phonolites, syenites, melteigites and ijolites), carbonatites and their associated weathering products were subjected to a preliminary evaluation as potential targets for REE exploration on Fuerteventura Island (Canary Archipelago, Spain) based on mineralogical and geochemical studies. These lithologies show significant REE concentrations. However, only carbonatites exhibit the potential to host economically viable REE mineral deposits. REE concentrations in carbonatites of up to 10,301.83 ppm REY (REEs plus yttrium) have been detected, comparable to other locations hosting significant deposits of these critical elements worldwide. Conversely, alkaline magmatic rocks and the resulting weathering products display limited REE enrichment. Notably, REEs in carbonatites are associated with primary accessory phases such as REE-bearing pyrochlore and britholite, and secondary monazite. The carbonatites of Fuerteventura hold promise as prospective REE deposits within a non-conventional geological setting (oceanic island). However, due to intricate structural attributes and possible land use constraints, additional future detailed investigations are imperative to ascertain their genuine economic viability as substantial REE resources.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"15 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-02-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140005498","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-02-27DOI: 10.5194/egusphere-2024-166
Haris Raza, George Sand França, Eveline Sayão, Victor Vilarrasa
Abstract. The necessity to reduce carbon emissions to mitigate climate change is accelerating the transition from fossil fuels to renewable energy sources. Specifically, hydropower, in particular, has emerged as a prominent and safe renewable energy source but entails reservoir-triggered seismicity (RTS). This phenomenon causes significant challenges for safe reservoir management. Irapé, in Brazil, is a prominent RTS site where seismicity surged after reservoir filling, with a maximum event of magnitude 3.0 in May 2006, just six months after the start of reservoir impoundment. Despite more than a decade has passed since the seismicity occurred, the factors governing these earthquakes and their connection to subsurface rock properties remain poorly understood. Here, we attempt to understand the potential causes of RTS at Irapé dam, which is the highest dam in Brazil with 208 m, and the second highest in South America. Permeability and porosity measurements of cylindrical cores from hard and intact rock samples, which have been extracted near the RTS zone, by pitting 10 cm from the surface, reveal a low-permeability rock. Porosity values range from 6.340 to 14.734 %. Only 3 out of the 11 tested samples present permeability higher than the lowest measurable value of the apparatus (0.002 mD), with the highest permeability being 0.0098 mD. The undrained response of the low-permeability rock placed below the reservoir results in an instantaneous increase in pore pressure and poroelastic stress changes due to elastic compression, which brings potential faults located below the reservoir closer to failure conditions. According to our analytical calculations, the increase in 136 m of the reservoir-water level caused a 0.54 MPa pore pressure buildup at the depth of the Magnitude 3.0 earthquake, i.e., 3.88 km, resulting in an increase of 0.82 MPa in the vertical effective stress and a decrease of 0.34 MPa in the horizontal effective stress. These changes resulted in an increase in the deviatoric stress that led to fault destabilization, causing the RTS. The laboratory measurements and analytical calculations corroborate the hypothesis that the initial seismic activity was induced by the undrained subsurface response to the reservoir loading at Irapé.
{"title":"Earthquakes triggered by the subsurface undrained response to reservoir-impoundment at Irapé, Brazil","authors":"Haris Raza, George Sand França, Eveline Sayão, Victor Vilarrasa","doi":"10.5194/egusphere-2024-166","DOIUrl":"https://doi.org/10.5194/egusphere-2024-166","url":null,"abstract":"<strong>Abstract.</strong> The necessity to reduce carbon emissions to mitigate climate change is accelerating the transition from fossil fuels to renewable energy sources. Specifically, hydropower, in particular, has emerged as a prominent and safe renewable energy source but entails reservoir-triggered seismicity (RTS). This phenomenon causes significant challenges for safe reservoir management. Irapé, in Brazil, is a prominent RTS site where seismicity surged after reservoir filling, with a maximum event of magnitude 3.0 in May 2006, just six months after the start of reservoir impoundment. Despite more than a decade has passed since the seismicity occurred, the factors governing these earthquakes and their connection to subsurface rock properties remain poorly understood. Here, we attempt to understand the potential causes of RTS at Irapé dam, which is the highest dam in Brazil with 208 m, and the second highest in South America. Permeability and porosity measurements of cylindrical cores from hard and intact rock samples, which have been extracted near the RTS zone, by pitting 10 cm from the surface, reveal a low-permeability rock. Porosity values range from 6.340 to 14.734 %. Only 3 out of the 11 tested samples present permeability higher than the lowest measurable value of the apparatus (0.002 mD), with the highest permeability being 0.0098 mD. The undrained response of the low-permeability rock placed below the reservoir results in an instantaneous increase in pore pressure and poroelastic stress changes due to elastic compression, which brings potential faults located below the reservoir closer to failure conditions. According to our analytical calculations, the increase in 136 m of the reservoir-water level caused a 0.54 MPa pore pressure buildup at the depth of the Magnitude 3.0 earthquake, i.e., 3.88 km, resulting in an increase of 0.82 MPa in the vertical effective stress and a decrease of 0.34 MPa in the horizontal effective stress. These changes resulted in an increase in the deviatoric stress that led to fault destabilization, causing the RTS. The laboratory measurements and analytical calculations corroborate the hypothesis that the initial seismic activity was induced by the undrained subsurface response to the reservoir loading at Irapé.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"36 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-02-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140005482","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-02-27DOI: 10.5194/egusphere-2024-425
Peter Haas, Myron F. H. Thomas, Christian Heine, Jörg Ebbing, Andrey Seregin, Jimmy van Itterbeeck
Abstract. Oceanic transform faults connect the segments of active spreading ridges that slide past each other. In a classical view, transform faults are considered as conservative, where no material is added or destroyed. Recent studies, however, suggest that the crust in the transform fault region is deformed during different episodes. We combine high resolution 3D broadband seismic data with shipborne potential field data to study ancient fault zones in Albian-Aptian aged oceanic crust in the eastern Gulf of Guinea offshore São Tomé and Príncipe. The crust in this region is characterized by a thin, high-reflective upper crust, which is underlain by a thick, almost seismically transparent unit that comprises localized dipping reflectors, previously interpreted as extrusive lava flows. This layer defines the target area for inversion and forward modelling of the potential field data. The picked seismic horizons are used as geometrical boundaries of the crustal model. First, we perform a lateral parameter inversion for the lower crust, which provides vertical columns of density and magnetic susceptibility. Second, we sort the estimated values using a clustering approach and identify five groups with common parameter relationships. Third, we use the clustered lower crustal domains to define a consistent 3D model of the study area that aligns with the seismic structure and geological concepts, preferred to the simple inversion of the first step. The final model shows anomalous low susceptibility and medium to high density close to the buried fracture zones, which reflects increasing pressure and temperature conditions accompanied by a change of metamorphic facies. Our model indicates enhanced tectonic activity with an extensional component during the formation of oceanic crust that culminates in the transform region. These results are in line with recent studies and strengthen the impressions of a non-conservative character of ridge-transform intersections.
{"title":"Increased metamorphic conditions in the lower crust during oceanic transform fault evolution","authors":"Peter Haas, Myron F. H. Thomas, Christian Heine, Jörg Ebbing, Andrey Seregin, Jimmy van Itterbeeck","doi":"10.5194/egusphere-2024-425","DOIUrl":"https://doi.org/10.5194/egusphere-2024-425","url":null,"abstract":"<strong>Abstract.</strong> Oceanic transform faults connect the segments of active spreading ridges that slide past each other. In a classical view, transform faults are considered as conservative, where no material is added or destroyed. Recent studies, however, suggest that the crust in the transform fault region is deformed during different episodes. We combine high resolution 3D broadband seismic data with shipborne potential field data to study ancient fault zones in Albian-Aptian aged oceanic crust in the eastern Gulf of Guinea offshore S<span>ã</span>o Tomé and Príncipe. The crust in this region is characterized by a thin, high-reflective upper crust, which is underlain by a thick, almost seismically transparent unit that comprises localized dipping reflectors, previously interpreted as extrusive lava flows. This layer defines the target area for inversion and forward modelling of the potential field data. The picked seismic horizons are used as geometrical boundaries of the crustal model. First, we perform a lateral parameter inversion for the lower crust, which provides vertical columns of density and magnetic susceptibility. Second, we sort the estimated values using a clustering approach and identify five groups with common parameter relationships. Third, we use the clustered lower crustal domains to define a consistent 3D model of the study area that aligns with the seismic structure and geological concepts, preferred to the simple inversion of the first step. The final model shows anomalous low susceptibility and medium to high density close to the buried fracture zones, which reflects increasing pressure and temperature conditions accompanied by a change of metamorphic facies. Our model indicates enhanced tectonic activity with an extensional component during the formation of oceanic crust that culminates in the transform region. These results are in line with recent studies and strengthen the impressions of a non-conservative character of ridge-transform intersections.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"29 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-02-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139980781","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-02-26DOI: 10.5194/egusphere-2024-257
Peter Jung, Götz Hornbruch, Andreas Dahmke, Peter Dietrich, Ulrike Werban
Abstract. During test operation of a geological latent heat storage system as a potential option in the context of heat supply for heating and cooling demands a part of a shallow quaternary glacial aquifer at the “TestUM” test site is frozen. To evaluate the current thermal state in the subsurface the dimension of the frozen volume has to be known. With the target being too deep for high resolution imaging from the surface, the use of borehole Ground-Penetrating-Radar (GPR) is assessed. For imaging and monitoring of a vertical freeze-thaw boundary, crosshole zero-offset and reflection measurements are applied. The freezing can be imaged in ZOP, but determination of ice body size is ambiguous, because of lacking velocity information in the frozen sediment. Reflection measurements are able to image the position of the freezing boundary with an accuracy determined through repeated measurements of ±0.1 m, relying on the velocity information from ZOP. We found, that the complementary use of ZOP and reflection measurements make for a fast and simple method, to image freezing in geological latent heat storage systems. Problematic is the presence of superimposed reflections from other observation wells and low signal-to-noise ratio. The use in multiple observation wells allows for an estimation of ice body size. A velocity model derived from zero-offset profiles (ZOP) enabled to extrapolate geological information from direct-push based logging and sediment cores to a 3D-subsurface model.
{"title":"Combining crosshole and reflection borehole-GPR for imaging controlled freezing in shallow aquifers","authors":"Peter Jung, Götz Hornbruch, Andreas Dahmke, Peter Dietrich, Ulrike Werban","doi":"10.5194/egusphere-2024-257","DOIUrl":"https://doi.org/10.5194/egusphere-2024-257","url":null,"abstract":"<strong>Abstract.</strong> During test operation of a geological latent heat storage system as a potential option in the context of heat supply for heating and cooling demands a part of a shallow quaternary glacial aquifer at the “TestUM” test site is frozen. To evaluate the current thermal state in the subsurface the dimension of the frozen volume has to be known. With the target being too deep for high resolution imaging from the surface, the use of borehole Ground-Penetrating-Radar (GPR) is assessed. For imaging and monitoring of a vertical freeze-thaw boundary, crosshole zero-offset and reflection measurements are applied. The freezing can be imaged in ZOP, but determination of ice body size is ambiguous, because of lacking velocity information in the frozen sediment. Reflection measurements are able to image the position of the freezing boundary with an accuracy determined through repeated measurements of ±0.1 <em>m</em>, relying on the velocity information from ZOP. We found, that the complementary use of ZOP and reflection measurements make for a fast and simple method, to image freezing in geological latent heat storage systems. Problematic is the presence of superimposed reflections from other observation wells and low signal-to-noise ratio. The use in multiple observation wells allows for an estimation of ice body size. A velocity model derived from zero-offset profiles (ZOP) enabled to extrapolate geological information from direct-push based logging and sediment cores to a 3D-subsurface model.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"42 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-02-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139980630","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-02-22DOI: 10.5194/egusphere-2024-468
Silvia Pondrelli, Simone Salimbeni, Judith M. Confal, Marco Malusà, Anne Paul, Stephane Guillot, Stefano Solarino, Elena Eva, Coralie Aubert, Liang Zhao
Abstract. There are still open questions about the deep structure beneath the Western Alps. Seismic velocity tomographies show the European slab subducting beneath the Adria plate, but all these images did not clarify completely about the possible presence of tears, slab windows or detachments. Seismic anisotropy, addressed as an indicator of mantle deformation and studied using data recorded by dense networks, may shed some light about the location and orientation of mantle flow at depth. Using the large amount of shear wave splitting and splitting intensity measurements available in the Western Alps, collected through the CIFALPS2 temporary seismic network, together with already available data, highlight some new patterns, filling the gaps left by previous studies. Instead of the typical seismic anisotropy pattern parallel to the entire arc of the Western Alps, this study supports the presence of a differential contribution along the belt, only partly related to the European slab retreat. A nearly NS anisotropy pattern beneath the external Alps, direction that cuts the morphological features of the belt, is clearly found with the new CIFALPS2 measurements. It is however confirmed that the asthenospheric flow from Central France toward the Tyrrhenian Sea, is turning around the southern tip of the European slab.
{"title":"Highlights on mantle deformation beneath the Western Alps with seismic anisotropy using CIFALPS2 data","authors":"Silvia Pondrelli, Simone Salimbeni, Judith M. Confal, Marco Malusà, Anne Paul, Stephane Guillot, Stefano Solarino, Elena Eva, Coralie Aubert, Liang Zhao","doi":"10.5194/egusphere-2024-468","DOIUrl":"https://doi.org/10.5194/egusphere-2024-468","url":null,"abstract":"<strong>Abstract.</strong> There are still open questions about the deep structure beneath the Western Alps. Seismic velocity tomographies show the European slab subducting beneath the Adria plate, but all these images did not clarify completely about the possible presence of tears, slab windows or detachments. Seismic anisotropy, addressed as an indicator of mantle deformation and studied using data recorded by dense networks, may shed some light about the location and orientation of mantle flow at depth. Using the large amount of shear wave splitting and splitting intensity measurements available in the Western Alps, collected through the CIFALPS2 temporary seismic network, together with already available data, highlight some new patterns, filling the gaps left by previous studies. Instead of the typical seismic anisotropy pattern parallel to the entire arc of the Western Alps, this study supports the presence of a differential contribution along the belt, only partly related to the European slab retreat. A nearly NS anisotropy pattern beneath the external Alps, direction that cuts the morphological features of the belt, is clearly found with the new CIFALPS2 measurements. It is however confirmed that the asthenospheric flow from Central France toward the Tyrrhenian Sea, is turning around the southern tip of the European slab.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"31 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-02-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139921242","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Karsten Reiter, Oliver Heidbach, Moritz O. Ziegler
Abstract. The impact of faults on the contemporary stress field in the upper crust has been discussed in various studies. Data and models clearly show that there is an effect, but so far, a systematic study quantifying the impact as a function of distance from the fault is lacking. In the absence of data, here we use a series of generic 3-D models to investigate which component of the stress tensor is affected at which distance from the fault. Our study concentrates on the far field, located hundreds of metres from the fault zone. The models assess various techniques to represent faults, different material properties, different boundary conditions, variable orientation, and the fault's size. The study findings indicate that most of the factors tested do not have an influence on either the stress tensor orientation or principal stress magnitudes in the far field beyond 1000 m from the fault. Only in the case of oblique faults with a low static friction coefficient of μ=0.1 can noteworthy stress perturbations be seen up to 2000 m from the fault. However, the changes that we detected are generally small and of the order of lateral stress variability due to rock property variability. Furthermore, only in the first hundreds of metres to the fault are variations large enough to be theoretically detected by borehole-based stress data when considering their inherent uncertainties. This finding agrees with robust stress magnitude measurements and stress orientation data. Thus, in areas where high-quality and high-resolution data show gradual and continuous stress tensor rotations of >20∘ observed over lateral spatial scales of 10 km or more, we infer that these rotations cannot be attributed to faults. We hypothesize that most stress orientation changes attributed to faults may originate from different sources such as density and strength contrasts.
{"title":"Impact of faults on the remote stress state","authors":"Karsten Reiter, Oliver Heidbach, Moritz O. Ziegler","doi":"10.5194/se-15-305-2024","DOIUrl":"https://doi.org/10.5194/se-15-305-2024","url":null,"abstract":"Abstract. The impact of faults on the contemporary stress field in the upper crust has been discussed in various studies. Data and models clearly show that there is an effect, but so far, a systematic study quantifying the impact as a function of distance from the fault is lacking. In the absence of data, here we use a series of generic 3-D models to investigate which component of the stress tensor is affected at which distance from the fault. Our study concentrates on the far field, located hundreds of metres from the fault zone. The models assess various techniques to represent faults, different material properties, different boundary conditions, variable orientation, and the fault's size. The study findings indicate that most of the factors tested do not have an influence on either the stress tensor orientation or principal stress magnitudes in the far field beyond 1000 m from the fault. Only in the case of oblique faults with a low static friction coefficient of μ=0.1 can noteworthy stress perturbations be seen up to 2000 m from the fault. However, the changes that we detected are generally small and of the order of lateral stress variability due to rock property variability. Furthermore, only in the first hundreds of metres to the fault are variations large enough to be theoretically detected by borehole-based stress data when considering their inherent uncertainties. This finding agrees with robust stress magnitude measurements and stress orientation data. Thus, in areas where high-quality and high-resolution data show gradual and continuous stress tensor rotations of >20∘ observed over lateral spatial scales of 10 km or more, we infer that these rotations cannot be attributed to faults. We hypothesize that most stress orientation changes attributed to faults may originate from different sources such as density and strength contrasts.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"6 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-02-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139945535","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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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