Pub Date : 2024-10-02DOI: 10.1016/j.pepi.2024.107268
Tom A. Jordan, Teal R. Riley
The Dufek layered mafic intrusion represents the only exposed, deep-seated, part of the Ferrar Large Igneous Province, which extends >3500 km across Antarctica and into parts of Tasmania and New Zealand. The Dufek Intrusion is in a key position at the boundary between the Jurassic Weddell Sea Rift System and the East Antarctic Craton. It may have been a conduit for some of the Ferrar magmas, or a deep-seated equivalent to the shallower sills seen in other sectors of Antarctica. Although a significant intrusion, equivalent at least to the Stillwater complex in the USA, its true scale and geometry, along with the relative timing of emplacement is disputed. We present new 3D models of gravity and magnetic data which constrain the geometry of the intrusion, show how separate lobes of the intrusion are linked and identify a possible extension of the intrusion to the east. We also discuss the implications for how the intrusion may have been emplaced.
{"title":"Reinvestigating the Dufek Intrusion, through joint gravity and magnetic models","authors":"Tom A. Jordan, Teal R. Riley","doi":"10.1016/j.pepi.2024.107268","DOIUrl":"10.1016/j.pepi.2024.107268","url":null,"abstract":"<div><div>The Dufek layered mafic intrusion represents the only exposed, deep-seated, part of the Ferrar Large Igneous Province, which extends >3500 km across Antarctica and into parts of Tasmania and New Zealand. The Dufek Intrusion is in a key position at the boundary between the Jurassic Weddell Sea Rift System and the East Antarctic Craton. It may have been a conduit for some of the Ferrar magmas, or a deep-seated equivalent to the shallower sills seen in other sectors of Antarctica. Although a significant intrusion, equivalent at least to the Stillwater complex in the USA, its true scale and geometry, along with the relative timing of emplacement is disputed. We present new 3D models of gravity and magnetic data which constrain the geometry of the intrusion, show how separate lobes of the intrusion are linked and identify a possible extension of the intrusion to the east. We also discuss the implications for how the intrusion may have been emplaced.</div></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"356 ","pages":"Article 107268"},"PeriodicalIF":2.4,"publicationDate":"2024-10-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142428239","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-24DOI: 10.1016/j.pepi.2024.107264
Jamie Ward , Andrew M. Walker , Andy Nowacki , James Panton , J Huw Davies
It is widely believed that seismic anisotropy in the lowermost mantle is caused by the flow-induced alignment of anisotropic crystals such as post-perovskite. What is unclear, however, is whether the anisotropy observations in the lowermost mantle hold information about past mantle flow, or if they only inform us about the present-day flow field. To investigate this, we compare the general and seismic anisotropy calculated using Earth-like mantle convection models where one has a time-varying flow, and another where the present-day flow is constant throughout time. To do this, we track a post-perovskite polycrystal through the flow fields and calculate texture development using the sampled strain rate and the visco-plastic self-consistent approach. We assume dominant slip on (001) and test the effect of the relative importance of this glide plane over others by using three different plasticity models with different efficiencies at developing texture. We compare the radial anisotropy parameters and the anisotropic components of the elastic tensors produced by the flow field test cases at the same location. We find, under all ease-of-texturing cases, the radial anisotropy is very similar (difference ) in the majority of locations and in some regions, the difference can be very large (). The same is true when comparing the elastic tensors directly. Varying the ease-of-texture development in the crystal aggregate suggests that easier-to-texture material may hold a stronger signal from past flow than harder-to-texture material. Our results imply that broad-scale observations of seismic anisotropy such as those from seismic tomography, 1-D estimates and normal mode observations, will be mainly sensitive to present-day flow. Shear-wave splitting measurements, however, could hold information about past mantle flow. In general, mantle memory expressed in anisotropy may be dependent on path length in the post-perovskite stability field. Our work implies that, as knowledge of the exact causative mechanism of lowermost mantle anisotropy develops, we may be able to constrain both present-day and past mantle convection.
{"title":"The sensitivity of lowermost mantle anisotropy to past mantle convection","authors":"Jamie Ward , Andrew M. Walker , Andy Nowacki , James Panton , J Huw Davies","doi":"10.1016/j.pepi.2024.107264","DOIUrl":"10.1016/j.pepi.2024.107264","url":null,"abstract":"<div><div>It is widely believed that seismic anisotropy in the lowermost mantle is caused by the flow-induced alignment of anisotropic crystals such as post-perovskite. What is unclear, however, is whether the anisotropy observations in the lowermost mantle hold information about past mantle flow, or if they only inform us about the present-day flow field. To investigate this, we compare the general and seismic anisotropy calculated using Earth-like mantle convection models where one has a time-varying flow, and another where the present-day flow is constant throughout time. To do this, we track a post-perovskite polycrystal through the flow fields and calculate texture development using the sampled strain rate and the visco-plastic self-consistent approach. We assume dominant slip on (001) and test the effect of the relative importance of this glide plane over others by using three different plasticity models with different efficiencies at developing texture. We compare the radial anisotropy parameters and the anisotropic components of the elastic tensors produced by the flow field test cases at the same location. We find, under all ease-of-texturing cases, the radial anisotropy is very similar (difference <span><math><mo><</mo><mn>2</mn><mo>%</mo></math></span>) in the majority of locations and in some regions, the difference can be very large (<span><math><mo>></mo><mn>10</mn><mo>%</mo></math></span>). The same is true when comparing the elastic tensors directly. Varying the ease-of-texture development in the crystal aggregate suggests that easier-to-texture material may hold a stronger signal from past flow than harder-to-texture material. Our results imply that broad-scale observations of seismic anisotropy such as those from seismic tomography, 1-D estimates and normal mode observations, will be mainly sensitive to present-day flow. Shear-wave splitting measurements, however, could hold information about past mantle flow. In general, mantle memory expressed in anisotropy may be dependent on path length in the post-perovskite stability field. Our work implies that, as knowledge of the exact causative mechanism of lowermost mantle anisotropy develops, we may be able to constrain both present-day and past mantle convection.</div></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"356 ","pages":"Article 107264"},"PeriodicalIF":2.4,"publicationDate":"2024-09-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142328310","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-21DOI: 10.1016/j.pepi.2024.107265
Yishi Wang , Yu Hu , Gang Yang , Zehui Li , Xun Liu , Haijun Huang , Toshimori Sekine
The phase stability of carbonates under mantle conditions is important for understanding the global carbon cycle. In this study, the Hugoniot data of a natural siderite (FeCO3) were measured up to 90 GPa using the plane-plate impact method. Two successive phase transitions were observed at 38–40 GPa and 65–69 GPa, respectively. In comparison with the static compression results, the first phase transition was identified as a spin transition, and the second is attributed to the self-redox reaction. The volume change during the self-redox transition is consistent with the reaction products of tetrairon orthocarbonate Fe4C3O12 and diamond. Using the measured Hugoniot data, we estimated the density of Fe4C3O12 along the lower mantle conditions and found it to be higher than the seismic values. Our results suggest siderite plays an important role in the deep carbon cycle.
{"title":"Shock-induced phase transitions in siderite up to 90 GPa and implications for deep carbon cycle","authors":"Yishi Wang , Yu Hu , Gang Yang , Zehui Li , Xun Liu , Haijun Huang , Toshimori Sekine","doi":"10.1016/j.pepi.2024.107265","DOIUrl":"10.1016/j.pepi.2024.107265","url":null,"abstract":"<div><div>The phase stability of carbonates under mantle conditions is important for understanding the global carbon cycle. In this study, the Hugoniot data of a natural siderite (FeCO<sub>3</sub>) were measured up to 90 GPa using the plane-plate impact method. Two successive phase transitions were observed at 38–40 GPa and 65–69 GPa, respectively. In comparison with the static compression results, the first phase transition was identified as a spin transition, and the second is attributed to the self-redox reaction. The volume change during the self-redox transition is consistent with the reaction products of tetrairon orthocarbonate Fe<sub>4</sub>C<sub>3</sub>O<sub>12</sub> and diamond. Using the measured Hugoniot data, we estimated the density of Fe<sub>4</sub>C<sub>3</sub>O<sub>12</sub> along the lower mantle conditions and found it to be higher than the seismic values. Our results suggest siderite plays an important role in the deep carbon cycle.</div></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"356 ","pages":"Article 107265"},"PeriodicalIF":2.4,"publicationDate":"2024-09-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142323620","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}
Pub Date : 2024-09-20DOI: 10.1016/j.pepi.2024.107263
G. Pavankumar, A. Manglik, M. Demudu Babu, Raj Sunil Kandregula, Akashdeep Barman
The Ladakh Himalaya is a repository of the evolutionary history of the India-Eurasia convergent plate margin. We present the results of a magnetotelluric (MT) study carried out in Eastern Ladakh along a 40-km-long profile traversing across various tectonic domains of this plate margin. We modeled the MT dataset by two-dimensional (2-D) and three-dimensional (3-D) inversion algorithms. The upper crustal geoelectric model obtained by 2-D inversion of distortion corrected and decomposed data of 18 sites shows an excellent match with the surface geology. In this model, the Indus Suture Zone (ISZ) appears as a steeply dipping contact and the Ladakh batholith is about 10 to 12 km thick. The model yields a prominent electrical conductor of ∼6 km diameter at 4 km depth beneath the Tso Morari Crystallines with an offshoot of a small conductor that rises upward along the ISZ. The geoelectrical model obtained by 3-D inversion is broadly consistent with the 2-D model but also reveals off-profile features and a connectivity of the shallow conductors with a widespread conductive zone at deeper level of the upper crust. In view of the presence of Puga and Chumathang hot springs towards west and Demchok hot springs towards east of our study region, we infer these conductors to be representing a potential major geothermal reservoir system connected to the widespread deeper conductive zone of partial melts, which extends from the southern Tibet to the eastern Ladakh region.
{"title":"A potential deep geothermal reservoir in eastern Ladakh as inferred from the upper crustal geoelectric structure of the region","authors":"G. Pavankumar, A. Manglik, M. Demudu Babu, Raj Sunil Kandregula, Akashdeep Barman","doi":"10.1016/j.pepi.2024.107263","DOIUrl":"10.1016/j.pepi.2024.107263","url":null,"abstract":"<div><div>The Ladakh Himalaya is a repository of the evolutionary history of the India-Eurasia convergent plate margin. We present the results of a magnetotelluric (MT) study carried out in Eastern Ladakh along a 40-km-long profile traversing across various tectonic domains of this plate margin. We modeled the MT dataset by two-dimensional (2-D) and three-dimensional (3-D) inversion algorithms. The upper crustal geoelectric model obtained by 2-D inversion of distortion corrected and decomposed data of 18 sites shows an excellent match with the surface geology. In this model, the Indus Suture Zone (ISZ) appears as a steeply dipping contact and the Ladakh batholith is about 10 to 12 km thick. The model yields a prominent electrical conductor of ∼6 km diameter at 4 km depth beneath the Tso Morari Crystallines with an offshoot of a small conductor that rises upward along the ISZ. The geoelectrical model obtained by 3-D inversion is broadly consistent with the 2-D model but also reveals off-profile features and a connectivity of the shallow conductors with a widespread conductive zone at deeper level of the upper crust. In view of the presence of Puga and Chumathang hot springs towards west and Demchok hot springs towards east of our study region, we infer these conductors to be representing a potential major geothermal reservoir system connected to the widespread deeper conductive zone of partial melts, which extends from the southern Tibet to the eastern Ladakh region.</div></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"356 ","pages":"Article 107263"},"PeriodicalIF":2.4,"publicationDate":"2024-09-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142323619","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}
Pub Date : 2024-09-18DOI: 10.1016/j.pepi.2024.107249
Steve Lund , Gary Acton , Brad Clement , Makoto Okada , Lloyd Keigwin
This study has developed paleomagnetic secular variation (PSV) records from Sites 1060, 1061, 1062, and 1063 (ODP Leg 172) from the western North Atlantic Ocean during MIS 11–12 (374–478 ka). We have identified 46 inclination features and 49 declination features that can be correlated among the records. We have also developed relative paleointensity records and identified 13 paleointensity features that can be correlated among them. These features can also be dated using the oxygen-isotope dated Global relative-paleointensity record PISO-1500 of Channell et al. (2009). There is one excursion located in these four records. We use the name Levantine/Bermuda Excursion developed elsewhere by Ryan (1972) and Channell et al. (2017). The Excursion occurred at 408 ± 4 ka. The excursion is recorded at Sites 1061, 1062, and 1063. The most detailed excursion records occur at Site 1062 where we have both shipboard PSV records and one u-channel PSV record of the excursion. The excursion has two intervals of excursional directions, one short interval (∼I ky) followed by a long interval (∼5 ky). Both intervals have counter-clockwise looping of the excursional directions and the excursion is considered to be a Class I Excursion (Lund et al., 2005). Statistical study of the PSV records after removal of the excursion directions has identified two characteristics of the ‘normal’ PSV. The first feature is a long-term (>104 yrs) deviation in inclination and declination averages from the overall site averages. These deviations suggest some type on long-term memory in the regional dynamo process. The second feature is the variation in PSV angular dispersion (a measure of directional variability). The angular dispersion is quite low (∼12°) for most of the 374–478 ka interval. But, there is a short (∼8 ky) interval with angular dispersion more than double the amplitude (∼25°-30°). This interval has a sharp (<3 ky) onset and termination, This interval contains the Levantine/Bermuda Excursion. Such high-angular dispersion intervals with associated excursions and low paleointensity appear to be regular distinctive features of the Brunhes Chron PSV.
{"title":"On the relationship between paleomagnetic secular variation and excursions – Records from MIS 11 and 12 – ODP Leg 172, western North Atlantic Ocean","authors":"Steve Lund , Gary Acton , Brad Clement , Makoto Okada , Lloyd Keigwin","doi":"10.1016/j.pepi.2024.107249","DOIUrl":"10.1016/j.pepi.2024.107249","url":null,"abstract":"<div><p>This study has developed paleomagnetic secular variation (PSV) records from Sites 1060, 1061, 1062, and 1063 (ODP Leg 172) from the western North Atlantic Ocean during MIS 11–12 (374–478 ka). We have identified 46 inclination features and 49 declination features that can be correlated among the records. We have also developed relative paleointensity records and identified 13 paleointensity features that can be correlated among them. These features can also be dated using the oxygen-isotope dated Global relative-paleointensity record PISO-1500 of Channell et al. (2009). There is one excursion located in these four records. We use the name Levantine/Bermuda Excursion developed elsewhere by Ryan (1972) and Channell et al. (2017). The Excursion occurred at 408 ± 4 ka. The excursion is recorded at Sites 1061, 1062, and 1063. The most detailed excursion records occur at Site 1062 where we have both shipboard PSV records and one u-channel PSV record of the excursion. The excursion has two intervals of excursional directions, one short interval (∼I ky) followed by a long interval (∼5 ky). Both intervals have counter-clockwise looping of the excursional directions and the excursion is considered to be a Class I Excursion (Lund et al., 2005). Statistical study of the PSV records after removal of the excursion directions has identified two characteristics of the ‘normal’ PSV. The first feature is a long-term (>10<sup>4</sup> yrs) deviation in inclination and declination averages from the overall site averages. These deviations suggest some type on long-term memory in the regional dynamo process. The second feature is the variation in PSV angular dispersion (a measure of directional variability). The angular dispersion is quite low (∼12°) for most of the 374–478 ka interval. But, there is a short (∼8 ky) interval with angular dispersion more than double the amplitude (∼25°-30°). This interval has a sharp (<3 ky) onset and termination, This interval contains the Levantine/Bermuda Excursion. Such high-angular dispersion intervals with associated excursions and low paleointensity appear to be regular distinctive features of the Brunhes Chron PSV.</p></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"356 ","pages":"Article 107249"},"PeriodicalIF":2.4,"publicationDate":"2024-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142272088","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}
Pub Date : 2024-09-18DOI: 10.1016/j.pepi.2024.107260
Mofei Du , Jianshe Lei , Dapeng Zhao , Yinshuang Ai , Hongbin Lu , Changqing Sun
We determine new tomographic models of Pn anisotropic velocity and Sn isotropic velocity in and around the Wudalianchi volcanic area by inverting high-quality Pn and Sn arrival times manually picked from waveforms recorded at the newly deployed high-dense WAVESArray portable seismic stations. Our high-resolution Pn and Sn velocity models reveal strong lateral heterogeneities in the uppermost mantle under the study region. The average Pn and Sn velocities in the uppermost mantle are 8.2 and 4.5 km/s, respectively. Both Pn and Sn velocity models exhibit obvious low-velocity (low-V) anomalies under the Wudalianchi and Keluo volcanoes, whereas under the Songliao basin distinct high-velocity (high-V) zones are revealed. In particular, our Pn model reveals two separate low-V anomalies under the Nuominhe and Halaha volcanic groups, suggesting that they have different deep origins. A large-scale L-shaped low-V zone exists under the Keluo, Wudalianchi, Erkeshan, and Xunke volcanoes, characterized by Pn-wave fast propagation directions (FPDs) parallel with the low-V zone, suggesting that these volcanoes may have the same deep origin. Furthermore, southeast-opened U-shaped Pn FPDs exist around the Wudalianchi volcano, whereas NE-SW FPDs appear under the Great Xing'an range, which are generally consistent with SKS splitting measurements. This feature may reflect lithosphere-asthenosphere coupling beneath the Wudalianchi volcano associated with horizontal flows in the big mantle wedge and compressional tectonics under the Great Xing'an range. These results shed new lights on the Wudalianchi volcanism and mantle dynamics beneath Northeast China.
我们通过反演从新部署的高密度 WAVESArray 便携式地震台站记录的波形中人工选取的高质量 Pn 和 Sn 到达时间，确定了五大连池火山区及其周边地区 Pn 各向异性速度和 Sn 各向同性速度的新层析模型。我们的高分辨率 Pn 和 Sn 速度模型揭示了研究区域下最上层地幔强烈的横向异质性。最上地幔的平均 Pn 和 Sn 速度分别为每秒 8.2 公里和 4.5 公里。Pn和Sn速度模型在五大连池和开鲁火山下都显示出明显的低速（低V）异常，而在松辽盆地下则显示出明显的高速（高V）带。特别是，我们的Pn模型在诺敏河火山群和哈拉哈火山群下发现了两个独立的低V异常，这表明它们具有不同的深部起源。在凯洛火山群、五大连池火山群、额尔齐斯火山群和寻克火山群下存在一个大尺度的 L 型低 V 值区，其特征是 Pn 波快速传播方向（FPD）与低 V 值区平行，表明这些火山可能具有相同的深部起源。此外，五大连池火山周围存在东南向开口的U形Pn波快速传播方向（FPD），而大兴安岭下则出现东北-西南向的FPD，这与SKS劈裂测量结果基本一致。这一特征可能反映了五大连池火山下岩石圈-岩石圈耦合，与大地幔楔的水平流动和大兴安岭下的压缩构造有关。这些结果为五大连池火山活动和中国东北地下地幔动力学提供了新的线索。
{"title":"Wudalianchi volcanism and mantle dynamics in Northeast China: New insight from Pn and Sn tomography","authors":"Mofei Du , Jianshe Lei , Dapeng Zhao , Yinshuang Ai , Hongbin Lu , Changqing Sun","doi":"10.1016/j.pepi.2024.107260","DOIUrl":"10.1016/j.pepi.2024.107260","url":null,"abstract":"<div><div>We determine new tomographic models of Pn anisotropic velocity and Sn isotropic velocity in and around the Wudalianchi volcanic area by inverting high-quality Pn and Sn arrival times manually picked from waveforms recorded at the newly deployed high-dense WAVESArray portable seismic stations. Our high-resolution Pn and Sn velocity models reveal strong lateral heterogeneities in the uppermost mantle under the study region. The average Pn and Sn velocities in the uppermost mantle are 8.2 and 4.5 km/s, respectively. Both Pn and Sn velocity models exhibit obvious low-velocity (low-V) anomalies under the Wudalianchi and Keluo volcanoes, whereas under the Songliao basin distinct high-velocity (high-V) zones are revealed. In particular, our Pn model reveals two separate low-V anomalies under the Nuominhe and Halaha volcanic groups, suggesting that they have different deep origins. A large-scale L-shaped low-V zone exists under the Keluo, Wudalianchi, Erkeshan, and Xunke volcanoes, characterized by Pn-wave fast propagation directions (FPDs) parallel with the low-V zone, suggesting that these volcanoes may have the same deep origin. Furthermore, southeast-opened U-shaped Pn FPDs exist around the Wudalianchi volcano, whereas NE-SW FPDs appear under the Great Xing'an range, which are generally consistent with SKS splitting measurements. This feature may reflect lithosphere-asthenosphere coupling beneath the Wudalianchi volcano associated with horizontal flows in the big mantle wedge and compressional tectonics under the Great Xing'an range. These results shed new lights on the Wudalianchi volcanism and mantle dynamics beneath Northeast China.</div></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"356 ","pages":"Article 107260"},"PeriodicalIF":2.4,"publicationDate":"2024-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142310256","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}
Pub Date : 2024-09-18DOI: 10.1016/j.pepi.2024.107250
Alexander Bershadskii
It is shown, using results of numerical simulations and geomagnetic observations, that the spatial and temporal randomization of the Earth's global and local magnetic fields is driven by magnetic helicity (an ideal magnetohydrodynamic invariant). In the frames of the distributed chaos notion, the magnetic helicity determines the degree of magnetic field randomization and the results of numerical simulations are in quantitative agreement with the geophysical observations despite the considerable differences in the scales and physical parameters.
{"title":"Randomization of the Earth's magnetic field driven by magnetic helicity","authors":"Alexander Bershadskii","doi":"10.1016/j.pepi.2024.107250","DOIUrl":"10.1016/j.pepi.2024.107250","url":null,"abstract":"<div><p>It is shown, using results of numerical simulations and geomagnetic observations, that the spatial and temporal randomization of the Earth's global and local magnetic fields is driven by magnetic helicity (an ideal magnetohydrodynamic invariant). In the frames of the distributed chaos notion, the magnetic helicity determines the degree of magnetic field randomization and the results of numerical simulations are in quantitative agreement with the geophysical observations despite the considerable differences in the scales and physical parameters.</p></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"356 ","pages":"Article 107250"},"PeriodicalIF":2.4,"publicationDate":"2024-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142272015","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}
Pub Date : 2024-09-17DOI: 10.1016/j.pepi.2024.107258
Edoardo Del Pezzo , Francesca Bianco
<div><p>We describe the space-time pattern of seismicity occurring on Campi Flegrei Caldera (CFC), Italy, where ground deformations and seismicity represent the drivers of its current bradyseismic crisis, well known and extensively studied at an international level. In detail we consider the seismicity in the time interval starting on 1.1.2000 and ending on 31.12.2023. We revise the statistics of the earthquake occurrence, focusing at possible precursory time changes of the b-parameter of the Gutenberg and Richter (G&R <span><math><mi>b</mi><mo>−</mo><mi>value</mi></math></span>) distribution and at the time distribution of the total seismic moment inside any swarm. To estimate the G&R <span><math><mi>b</mi><mo>−</mo><mi>value</mi></math></span> we use a Monte Carlo method instead of the ordinary Least Squares or Maximum likelihood methods, to easily measure the uncertainty on the <span><math><mi>b</mi><mo>−</mo><mi>value</mi></math></span> taking into account uncertainties on the magnitude estimates. Results show that G&R <span><math><mi>a</mi><mo>−</mo><mi>value</mi></math></span> and <span><math><mi>b</mi><mo>−</mo><mi>value</mi></math></span> calculated for cumulative and discrete distributions of <span><math><msub><mi>M</mi><mi>w</mi></msub></math></span>, the moment-magnitude, and <span><math><msub><mi>M</mi><mi>d</mi></msub></math></span>, the so-called duration-magnitude, are the same inside the uncertainties; <span><math><mi>a</mi><mo>−</mo><mi>value</mi></math></span> and <span><math><mi>b</mi><mo>−</mo><mi>value</mi></math></span> for <span><math><msub><mi>M</mi><mi>d</mi></msub></math></span> are significantly different from the same parameters estimated for <span><math><msub><mi>M</mi><mi>w</mi></msub></math></span>, being <span><math><mi>b</mi><mo>−</mo><mi>value</mi></math></span> for <span><math><msub><mi>M</mi><mi>w</mi></msub></math></span> close to the value of 1.0 and <span><math><mi>b</mi><mo>−</mo><mi>value</mi></math></span> for <span><math><msub><mi>M</mi><mi>d</mi></msub></math></span> close to 0.8. The “bounded” G&R distribution fits the data yielding <span><math><mi>a</mi><mo>−</mo><mi>value</mi></math></span> and <span><math><mi>b</mi><mo>−</mo><mi>value</mi></math></span> close to those for the unbounded distribution. The mean annual rate of exceedance, calculated for the entire catalogue, results to be 0.033<span><math><mo>±</mo><mn>0.015</mn></math></span> (years<sup>−1</sup>) corresponding to a return period of <span><math><mn>30</mn><mo>±</mo><mn>14</mn></math></span> years for <span><math><msub><mi>M</mi><mi>w</mi></msub><mo>=</mo><mn>4.5</mn></math></span>. The time dependence of G&R b-parameter show a <span><math><mi>b</mi><mo>−</mo><mi>value</mi></math></span> time pattern characterized by variations slightly outside 1-<span><math><mi>σ</mi></math></span> uncertainty bar, tending to the value of 1 approaching present. As evidenced by several past studies, earthquakes in CFC occur in space-t
我们描述了发生在意大利坎皮弗莱格雷火山口（Campi Flegrei Caldera，CFC）的地震时空模式，地面变形和地震是该火山口当前缓震危机的驱动因素。我们详细考虑了从 2000 年 1 月 1 日到 2023 年 12 月 31 日这段时间内的地震情况。我们修订了地震发生的统计数据，重点关注古腾堡和里氏（G&R b 值）分布的 b 参数可能发生的前兆时间变化，以及任何震群内部总地震力矩的时间分布。为了估算 G&R b 值，我们使用蒙特卡罗方法而不是普通的最小二乘法或最大似然法，以便在考虑震级估算的不确定性的同时，轻松测量 b 值的不确定性。结果表明，在不确定性范围内，为时刻幅度 Mw 和持续时间幅度 Md 的累积分布和离散分布计算出的 G&R a 值和 b 值是相同的；Md 的 a 值和 b 值与 Mw 的相同参数估计值有显著差异，Mw 的 b 值接近 1.0，Md 的 b 值接近 0.8。有界 "G&R 分布与数据拟合，得出的 a 值和 b 值与无界分布接近。计算整个目录的年平均超标率为 0.033±0.015（年-1），对应于 Mw=4.5 时 30±14 年的回归期。G&R b参数的时间依赖性显示了一个b值时间模式，其特点是变化略微超出1-σ的不确定性条，趋向于接近1的值。过去的一些研究表明，CFC 地震发生在时空群中，平均持续时间为 1 天。我们根据对连续事件偶的到达时间和事件间距离的联合估计，用选择算法选出了地震群。每个群中的事件数与发生时间的对比图清楚地表明，在 CFC 中，从 2010 年开始，群发生的次数和每个群中的事件数都在加速增长。每个震群的总地震力矩的时间模式表明，与事件数相反，震群总地震力矩并没有随着时间的推移而明显增加。这一数据显示，在过去的 15 个月中，断裂岩石体积明显向西扩大，深度在海平面以下 3000 米左右。本研究证实，当前的动荡阶段仍在持续，与 22 个月前相比，岩石断裂带向南、向西扩展。
{"title":"Space and time distribution of seismic source energy at Campi Flegrei, Italy through the last unrest phase (1.1.2000–31.12.2023)","authors":"Edoardo Del Pezzo , Francesca Bianco","doi":"10.1016/j.pepi.2024.107258","DOIUrl":"10.1016/j.pepi.2024.107258","url":null,"abstract":"<div><p>We describe the space-time pattern of seismicity occurring on Campi Flegrei Caldera (CFC), Italy, where ground deformations and seismicity represent the drivers of its current bradyseismic crisis, well known and extensively studied at an international level. In detail we consider the seismicity in the time interval starting on 1.1.2000 and ending on 31.12.2023. We revise the statistics of the earthquake occurrence, focusing at possible precursory time changes of the b-parameter of the Gutenberg and Richter (G&R <span><math><mi>b</mi><mo>−</mo><mi>value</mi></math></span>) distribution and at the time distribution of the total seismic moment inside any swarm. To estimate the G&R <span><math><mi>b</mi><mo>−</mo><mi>value</mi></math></span> we use a Monte Carlo method instead of the ordinary Least Squares or Maximum likelihood methods, to easily measure the uncertainty on the <span><math><mi>b</mi><mo>−</mo><mi>value</mi></math></span> taking into account uncertainties on the magnitude estimates. Results show that G&R <span><math><mi>a</mi><mo>−</mo><mi>value</mi></math></span> and <span><math><mi>b</mi><mo>−</mo><mi>value</mi></math></span> calculated for cumulative and discrete distributions of <span><math><msub><mi>M</mi><mi>w</mi></msub></math></span>, the moment-magnitude, and <span><math><msub><mi>M</mi><mi>d</mi></msub></math></span>, the so-called duration-magnitude, are the same inside the uncertainties; <span><math><mi>a</mi><mo>−</mo><mi>value</mi></math></span> and <span><math><mi>b</mi><mo>−</mo><mi>value</mi></math></span> for <span><math><msub><mi>M</mi><mi>d</mi></msub></math></span> are significantly different from the same parameters estimated for <span><math><msub><mi>M</mi><mi>w</mi></msub></math></span>, being <span><math><mi>b</mi><mo>−</mo><mi>value</mi></math></span> for <span><math><msub><mi>M</mi><mi>w</mi></msub></math></span> close to the value of 1.0 and <span><math><mi>b</mi><mo>−</mo><mi>value</mi></math></span> for <span><math><msub><mi>M</mi><mi>d</mi></msub></math></span> close to 0.8. The “bounded” G&R distribution fits the data yielding <span><math><mi>a</mi><mo>−</mo><mi>value</mi></math></span> and <span><math><mi>b</mi><mo>−</mo><mi>value</mi></math></span> close to those for the unbounded distribution. The mean annual rate of exceedance, calculated for the entire catalogue, results to be 0.033<span><math><mo>±</mo><mn>0.015</mn></math></span> (years<sup>−1</sup>) corresponding to a return period of <span><math><mn>30</mn><mo>±</mo><mn>14</mn></math></span> years for <span><math><msub><mi>M</mi><mi>w</mi></msub><mo>=</mo><mn>4.5</mn></math></span>. The time dependence of G&R b-parameter show a <span><math><mi>b</mi><mo>−</mo><mi>value</mi></math></span> time pattern characterized by variations slightly outside 1-<span><math><mi>σ</mi></math></span> uncertainty bar, tending to the value of 1 approaching present. As evidenced by several past studies, earthquakes in CFC occur in space-t","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"356 ","pages":"Article 107258"},"PeriodicalIF":2.4,"publicationDate":"2024-09-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S003192012400116X/pdfft?md5=a859af686a6ea4310c7c90813110214b&pid=1-s2.0-S003192012400116X-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142272089","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-12DOI: 10.1016/j.pepi.2024.107259
Sambit Sahoo , Batakrushna Senapati , Dibyashakti Panda , Shuanggen Jin , Bhaskar Kundu
Seismicity associated with hydrothermal systems (e.g., submarine volcanoes, mid-oceanic ridges, oceanic transform faults, etc.) share a complex relationship with the tidal forcing and induced fluid flow process under different tectonic settings. The hydrothermal circulation drives the deformation at the brittle-ductile transition zone within a permeable brittle crust. Although the tidal loading amplitudes are too small to generate a brittle deformation, the incremental pressure exerted by the tidal loading can modulate the flow of hydrothermal fluid circulation and trigger the critically stressed faults or fracture zones. We present a compelling case of tidal modulation in seismicity along the Blanco Ridge Transform Fault Zone (BRTFZ), in the northeast Pacific. The strong diurnal and fortnightly periodicity has been observed in the deeper seismic swarm (7–15 km), whereas the shallow seismic swarm (0–7 km) does not exhibit any such tidal periodicity. The dominance of diurnal and fortnightly periodicity in the deeper seismic swarm is explained by the high amplitude tidal cycles providing additional stress on the fluid circulation at the crust-mantle boundary. Moreover, our robust statistical correlation of seismicity with tidal stress and resonance destabilization model under rate-and-state friction formalism suggests that the fault segments are conditionally unstable and more sensitive to periodic tidal stress perturbation.
{"title":"Tidal triggering of seismic swarm associated with hydrothermal circulation at Blanco ridge transform fault zone, Northeast Pacific","authors":"Sambit Sahoo , Batakrushna Senapati , Dibyashakti Panda , Shuanggen Jin , Bhaskar Kundu","doi":"10.1016/j.pepi.2024.107259","DOIUrl":"10.1016/j.pepi.2024.107259","url":null,"abstract":"<div><p>Seismicity associated with hydrothermal systems (e.g., submarine volcanoes, mid-oceanic ridges, oceanic transform faults, etc.) share a complex relationship with the tidal forcing and induced fluid flow process under different tectonic settings. The hydrothermal circulation drives the deformation at the brittle-ductile transition zone within a permeable brittle crust. Although the tidal loading amplitudes are too small to generate a brittle deformation, the incremental pressure exerted by the tidal loading can modulate the flow of hydrothermal fluid circulation and trigger the critically stressed faults or fracture zones. We present a compelling case of tidal modulation in seismicity along the Blanco Ridge Transform Fault Zone (BRTFZ), in the northeast Pacific. The strong diurnal and fortnightly periodicity has been observed in the deeper seismic swarm (7–15 km), whereas the shallow seismic swarm (0–7 km) does not exhibit any such tidal periodicity. The dominance of diurnal and fortnightly periodicity in the deeper seismic swarm is explained by the high amplitude tidal cycles providing additional stress on the fluid circulation at the crust-mantle boundary. Moreover, our robust statistical correlation of seismicity with tidal stress and resonance destabilization model under rate-and-state friction formalism suggests that the fault segments are conditionally unstable and more sensitive to periodic tidal stress perturbation.</p></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"356 ","pages":"Article 107259"},"PeriodicalIF":2.4,"publicationDate":"2024-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142238660","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}
Pub Date : 2024-08-21DOI: 10.1016/j.pepi.2024.107247
Xin Yang , Shan Xu , Xiangyun Hu , Zuzhi Hu , Weiyang Liao , Wenlong Zhou
The Xuefeng Orogenic Belt (XFOB), located in the central part of the South China Block, is a typical Mesozoic intracontinental orogen in the central Jiangnan Orogenic Belt. By collecting magnetotelluric (MT) data across the XFOB, we obtained the resistivity structure of the lithosphere, which sheds light on the Mesozoic intracontinental orogenic processes in the XFOB. The resistivity structure reveals a low-resistivity body (<10 Ω∙m), beneath the XFOB, dipping southeast wards from a depth of 10 km to the bottom of the crust. This conductor is interpreted as a relic of the lower detachment zone, which coincides with low-density areas obtained from joint inversion of seismic models. It is believed to result from mineral fluids migrating along the thrust fault and squeezing sulfides into folds. Four low-resistivity bodies were identified at three extensional locations along the Jiangshan-Shaoxing Fault and at the Cili-Baojing Fault. The low-resistivity body (<10 Ω∙m) at the junction of the Shaoyang and the Hengyang Basin is located at the point where the Moho depth thins. The variation trend of the terrestrial heat flow values, with this low-resistivity body as the plate boundary, is consistent with the average variation of the terrestrial heat flow values within the block. We propose that the low-resistivity body under the Qidong-Yongzhou-Guilin fault conforms to the characteristics of the suture zone in the resistivity structure. Its existence indicates that the missing location of the Jiangshan-Shaoxing suture zone of the Yangtze and Cathaysia Block in the middle-southwest section of the South China Block is the Qidong-Yongzhou-Guilin fault. The Yangtze Block and the Hengyang Basin show high resistivity, the depth of which reaches 100 km and 40 km, respectively. Based on the resistivity model and geological data, the XFOB experienced Triassic compression, leading to basement decollement, thrusting, and nappe structures due to low-angle Paleo-Pacific Plate subduction. This compression also led to the uplift of the orogenic belt. Moreover, under the tension caused by the high-angle retreat of the Paleo-Pacific Plate, the Cretaceous extensional tectonics led to detachment along the thrust faults, forming half-graben and basin structures along the margins.
{"title":"Lithospheric resistivity structure of the Xuefeng Orogenic Belt and its implications for intracontinental deformation in South China","authors":"Xin Yang , Shan Xu , Xiangyun Hu , Zuzhi Hu , Weiyang Liao , Wenlong Zhou","doi":"10.1016/j.pepi.2024.107247","DOIUrl":"10.1016/j.pepi.2024.107247","url":null,"abstract":"<div><p>The Xuefeng Orogenic Belt (XFOB), located in the central part of the South China Block, is a typical Mesozoic intracontinental orogen in the central Jiangnan Orogenic Belt. By collecting magnetotelluric (MT) data across the XFOB, we obtained the resistivity structure of the lithosphere, which sheds light on the Mesozoic intracontinental orogenic processes in the XFOB. The resistivity structure reveals a low-resistivity body (<10 Ω∙m), beneath the XFOB, dipping southeast wards from a depth of 10 km to the bottom of the crust. This conductor is interpreted as a relic of the lower detachment zone, which coincides with low-density areas obtained from joint inversion of seismic models. It is believed to result from mineral fluids migrating along the thrust fault and squeezing sulfides into folds. Four low-resistivity bodies were identified at three extensional locations along the Jiangshan-Shaoxing Fault and at the Cili-Baojing Fault. The low-resistivity body (<10 Ω∙m) at the junction of the Shaoyang and the Hengyang Basin is located at the point where the Moho depth thins. The variation trend of the terrestrial heat flow values, with this low-resistivity body as the plate boundary, is consistent with the average variation of the terrestrial heat flow values within the block. We propose that the low-resistivity body under the Qidong-Yongzhou-Guilin fault conforms to the characteristics of the suture zone in the resistivity structure. Its existence indicates that the missing location of the Jiangshan-Shaoxing suture zone of the Yangtze and Cathaysia Block in the middle-southwest section of the South China Block is the Qidong-Yongzhou-Guilin fault. The Yangtze Block and the Hengyang Basin show high resistivity, the depth of which reaches 100 km and 40 km, respectively. Based on the resistivity model and geological data, the XFOB experienced Triassic compression, leading to basement decollement, thrusting, and nappe structures due to low-angle Paleo-Pacific Plate subduction. This compression also led to the uplift of the orogenic belt. Moreover, under the tension caused by the high-angle retreat of the Paleo-Pacific Plate, the Cretaceous extensional tectonics led to detachment along the thrust faults, forming half-graben and basin structures along the margins.</p></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"355 ","pages":"Article 107247"},"PeriodicalIF":2.4,"publicationDate":"2024-08-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142050258","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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