Pub Date : 2024-10-25DOI: 10.1016/j.epsl.2024.119092
Fan Yang , Juan Li , Chunquan Yu , Sidan Chen , Yang Li , Zhigang Zhang , Wei Wang
The Philippine Sea Plate (PSP), a region renowned for its intricate history of multi-stage subduction and back-arc extension, encounters difficulties in elucidating its deep seismic structure, primarily due to the sparse distribution of seismic stations. This study uses over 44,086 traces of SS precursors collected from >1,000 seismic stations over 10–20 years period, to image the mantle transition zone (MTZ) beneath the PSP. With the curvelet denoising technique, we provide high-resolution maps of the depths of the 410 km (D410) and 660 km (D660) discontinuities and the thickness of the MTZ. Notably, we demonstrate a 10–35 km MTZ thickening extending from the West Philippine Basin to the Shikoku Basin, which may be associated with the thermal effect and dehydration of stagnated slabs in the MTZ. Furthermore, the reflection gap and multiple reflectors were both observed in D410 and D660 beneath the Mariana Trench, which suggests that the vertically subducted Pacific plate transports substantial water and non-olivine components into the MTZ in this area. Additionally, a ∼10–25 km MTZ thinning with an abnormally shallow D660 has been observed beneath the Parece Vela Basin and Caroline Plate in the southern PSP, suggesting the potential existence of thermal upwelling from a secondary plume, which may be possibly the tree branch of the Caroline mantle plume in MTZ. Our results provide new seismological constraints on present and past mantle dynamics in and around the PSP.
{"title":"Complicated thermo-chemical heterogeneity of the mantle transition zone beneath the Philippine Sea Plate revealed by SS precursors investigation","authors":"Fan Yang , Juan Li , Chunquan Yu , Sidan Chen , Yang Li , Zhigang Zhang , Wei Wang","doi":"10.1016/j.epsl.2024.119092","DOIUrl":"10.1016/j.epsl.2024.119092","url":null,"abstract":"<div><div>The Philippine Sea Plate (PSP), a region renowned for its intricate history of multi-stage subduction and back-arc extension, encounters difficulties in elucidating its deep seismic structure, primarily due to the sparse distribution of seismic stations. This study uses over 44,086 traces of SS precursors collected from >1,000 seismic stations over 10–20 years period, to image the mantle transition zone (MTZ) beneath the PSP. With the curvelet denoising technique, we provide high-resolution maps of the depths of the 410 km (D410) and 660 km (D660) discontinuities and the thickness of the MTZ. Notably, we demonstrate a 10–35 km MTZ thickening extending from the West Philippine Basin to the Shikoku Basin, which may be associated with the thermal effect and dehydration of stagnated slabs in the MTZ. Furthermore, the reflection gap and multiple reflectors were both observed in D410 and D660 beneath the Mariana Trench, which suggests that the vertically subducted Pacific plate transports substantial water and non-olivine components into the MTZ in this area. Additionally, a ∼10–25 km MTZ thinning with an abnormally shallow D660 has been observed beneath the Parece Vela Basin and Caroline Plate in the southern PSP, suggesting the potential existence of thermal upwelling from a secondary plume, which may be possibly the tree branch of the Caroline mantle plume in MTZ. Our results provide new seismological constraints on present and past mantle dynamics in and around the PSP.</div></div>","PeriodicalId":11481,"journal":{"name":"Earth and Planetary Science Letters","volume":"648 ","pages":"Article 119092"},"PeriodicalIF":4.8,"publicationDate":"2024-10-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142534642","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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 : 2024-10-24DOI: 10.1016/j.epsl.2024.119070
Ziyi Zhu , Zefeng Li , Ian H. Campbell , Peter A. Cawood , Neng Lu , Oliver Nebel
Reworking and recycling of continental crust, through processes such as erosion and delamination, are essential geological mechanisms that not only shape the topography of continents but also influence the composition of the continental crust and mantle. Continent-continent collisions are crucial settings to study these processes, as they primarily involve the thickening and uplift of the existing crust, with little new crustal addition compared with ocean-continent convergent plate boundaries. In this study, we investigate the three modern collisional systems that formed the Himalaya-Tibetan Plateau, the European Alps, and Zagros in central Asia, and quantify the amount of crust lost into the mantle by comparing the shortened crustal volume with the present-day preserved thickened crust, laterally extruded crust and surficial eroded crust. We find that crustal loss into the mantle accounts for at least 30% of the shortened crust, which exceeds the crust lost by surficial erosion by at least a factor of 2 in the Himalaya-Tibetan Plateau and Zagros. The volume of crust lost into the mantle during the formation of the Alps lies between 15% and 50%, depending on the values assumed for the pre-collisional crustal thickness and the volume of eroded crust.
For the Himalaya-Tibetan Plateau, our calculated crustal loss corresponds to an elevation increase of ∼ 2 km, which can be explained by delamination of thick, eclogitised lower crustal roots in the late Oligocene, consistent with the distribution of shoshonitic-adakitic magmatism in southern Lhasa. This phase of rapid uplift, which followed the removal of dense lower lithosphere, corresponds with monsoon intensification in southern Asia. Furthermore, extending the concept of crustal loss to ancient mountain belts that occurred during the past cycles of supermountain formation, we propose that detachment of lower crustal roots can explain the trace element and isotopic characteristics of exotic crustal components in some plume-related mantle melts, ultimately linking mountain-building and mantle heterogeneity on a multi-million-year timescale.
{"title":"Quantifying the loss of continental crust into the mantle from volume/mass balance calculations in modern collisional mountains","authors":"Ziyi Zhu , Zefeng Li , Ian H. Campbell , Peter A. Cawood , Neng Lu , Oliver Nebel","doi":"10.1016/j.epsl.2024.119070","DOIUrl":"10.1016/j.epsl.2024.119070","url":null,"abstract":"<div><div>Reworking and recycling of continental crust, through processes such as erosion and delamination, are essential geological mechanisms that not only shape the topography of continents but also influence the composition of the continental crust and mantle. Continent-continent collisions are crucial settings to study these processes, as they primarily involve the thickening and uplift of the existing crust, with little new crustal addition compared with ocean-continent convergent plate boundaries. In this study, we investigate the three modern collisional systems that formed the Himalaya-Tibetan Plateau, the European Alps, and Zagros in central Asia, and quantify the amount of crust lost into the mantle by comparing the shortened crustal volume with the present-day preserved thickened crust, laterally extruded crust and surficial eroded crust. We find that crustal loss into the mantle accounts for at least 30% of the shortened crust, which exceeds the crust lost by surficial erosion by at least a factor of 2 in the Himalaya-Tibetan Plateau and Zagros. The volume of crust lost into the mantle during the formation of the Alps lies between 15% and 50%, depending on the values assumed for the pre-collisional crustal thickness and the volume of eroded crust.</div><div>For the Himalaya-Tibetan Plateau, our calculated crustal loss corresponds to an elevation increase of ∼ 2 km, which can be explained by delamination of thick, eclogitised lower crustal roots in the late Oligocene, consistent with the distribution of shoshonitic-adakitic magmatism in southern Lhasa. This phase of rapid uplift, which followed the removal of dense lower lithosphere, corresponds with monsoon intensification in southern Asia. Furthermore, extending the concept of crustal loss to ancient mountain belts that occurred during the past cycles of supermountain formation, we propose that detachment of lower crustal roots can explain the trace element and isotopic characteristics of exotic crustal components in some plume-related mantle melts, ultimately linking mountain-building and mantle heterogeneity on a multi-million-year timescale.</div></div>","PeriodicalId":11481,"journal":{"name":"Earth and Planetary Science Letters","volume":"648 ","pages":"Article 119070"},"PeriodicalIF":4.8,"publicationDate":"2024-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142533949","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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 : 2024-10-24DOI: 10.1016/j.epsl.2024.119085
Kristijan Rajič , Hugues Raimbourg , Vincent Famin , Benjamin Moris-Muttoni
Mélanges, intriguing rock units often found in accretionary complexes, consist of basalt lenses embedded in a highly sheared sedimentary matrix. The origin of mélanges remains a subject of vigorous debate, with consequences on our understanding of subduction processes. A first line of thought interprets mélanges as mixed lithologies intertwined by convergent tectonics. Supporters of this interpretation regard mélanges as fossilized witnesses of the lower- and upper-plate interface, with their rheological properties reflecting seismogenic subduction zones. However, a second line of thought is to consider that basalts and sediments were mixed prior to subduction by sedimentary and/or magmatic processes, this mix being only later incorporated into the accretionary wedge.
In this study, we present evidence supporting the pre-subduction mixing interpretation for mélanges from two paleo-accretionary complexes: the Kodiak complex in Alaska and the Shimanto Belt in Japan. In modern seafloor sediments in contact with basaltic submarine magmas, we show that the crystallinity of carbonaceous particles in sediments increases toward basalts, indicating a ∼1 cm-thick aureole of contact metamorphism. Intriguingly, a comparable aureole of increased crystallinity is observed in four mélanges from the two paleo-accretionary complexes. Basalts were thus emplaced onto and into sediments by magmatism rather than by tectonics, challenging the notion of mélanges explored in this study as formed along the plate boundary interface. Moreover, the studied mélanges are made of mid-ocean ridge basalts, and deposition ages of mélange sediments coincide with proposed ridge subductions. This implies that the mid-ocean ridges at the trench were the source of the magmas that intruded into and extruded onto the clastic sediments and contributed to form the multilayered basalt-sediments architecture.
{"title":"The origin of tectonic mélanges from the Kodiak complex and Shimanto Belt and its implication for subduction interface processes","authors":"Kristijan Rajič , Hugues Raimbourg , Vincent Famin , Benjamin Moris-Muttoni","doi":"10.1016/j.epsl.2024.119085","DOIUrl":"10.1016/j.epsl.2024.119085","url":null,"abstract":"<div><div>Mélanges, intriguing rock units often found in accretionary complexes, consist of basalt lenses embedded in a highly sheared sedimentary matrix. The origin of mélanges remains a subject of vigorous debate, with consequences on our understanding of subduction processes. A first line of thought interprets mélanges as mixed lithologies intertwined by convergent tectonics. Supporters of this interpretation regard mélanges as fossilized witnesses of the lower- and upper-plate interface, with their rheological properties reflecting seismogenic subduction zones. However, a second line of thought is to consider that basalts and sediments were mixed prior to subduction by sedimentary and/or magmatic processes, this mix being only later incorporated into the accretionary wedge.</div><div>In this study, we present evidence supporting the pre-subduction mixing interpretation for mélanges from two paleo-accretionary complexes: the Kodiak complex in Alaska and the Shimanto Belt in Japan. In modern seafloor sediments in contact with basaltic submarine magmas, we show that the crystallinity of carbonaceous particles in sediments increases toward basalts, indicating a ∼1 cm-thick aureole of contact metamorphism. Intriguingly, a comparable aureole of increased crystallinity is observed in four mélanges from the two paleo-accretionary complexes. Basalts were thus emplaced onto and into sediments by magmatism rather than by tectonics, challenging the notion of mélanges explored in this study as formed along the plate boundary interface. Moreover, the studied mélanges are made of mid-ocean ridge basalts, and deposition ages of mélange sediments coincide with proposed ridge subductions. This implies that the mid-ocean ridges at the trench were the source of the magmas that intruded into and extruded onto the clastic sediments and contributed to form the multilayered basalt-sediments architecture.</div></div>","PeriodicalId":11481,"journal":{"name":"Earth and Planetary Science Letters","volume":"648 ","pages":"Article 119085"},"PeriodicalIF":4.8,"publicationDate":"2024-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142534643","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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 : 2024-10-23DOI: 10.1016/j.epsl.2024.119089
Debasis D. Mohanty , Satyapriya Biswal , Kazunori Yoshizawa
Ongoing oblique convergence at the eastern margin of the Indo-Eurasian collision zone provides a natural laboratory for studying the deformation and dynamics of subduction beneath the Indo-Burmese Wedge (IBW). Here, we conduct the first comprehensive seismological investigations to understand the mechanical coupling between the crust and mantle beneath IBW using shear-wave splitting analysis and stress modeling. The deformation patterns in the crust signify a strong E-W compressional stress regime throughout IBW, with negligible influence from the major geological structures. These observations derived from local seismicity strongly support that the eastward active subduction of the Indian plate beneath the Burmese sliver is responsible for the crustal-scale deformation. Contrary to the crust, our splitting measurements from the mantle are in line with the major N-S trending arcs created by slip-partitioning due to transpressional oblique subduction. The splitting measurements with an N-S orientated fast axes and the estimated depth of the anisotropy source obtained from the spatial coherency of splitting parameters strongly suggest the presence of trench-parallel sub-slab flow system driven by slab retreat with westward trench migration, which can be the major controlling mechanism of the mantle deformation beneath IBW. Throughout the IBW, a significant change in the orientations of stress and splitting parameters between the crust and mantle supports a decoupled deformation scenario, implying the necessity of a new seismotectonic model. Our integrative study on the present stress patterns and decoupled deformation mechanism between crust and mantle combined with anisotropy measurements beneath the IBW suggests active subduction in the present scenario.
{"title":"Decoupled deformation between crust and mantle beneath Indo-Burmese Wedge: A new seismotectonic model","authors":"Debasis D. Mohanty , Satyapriya Biswal , Kazunori Yoshizawa","doi":"10.1016/j.epsl.2024.119089","DOIUrl":"10.1016/j.epsl.2024.119089","url":null,"abstract":"<div><div>Ongoing oblique convergence at the eastern margin of the Indo-Eurasian collision zone provides a natural laboratory for studying the deformation and dynamics of subduction beneath the Indo-Burmese Wedge (IBW). Here, we conduct the first comprehensive seismological investigations to understand the mechanical coupling between the crust and mantle beneath IBW using shear-wave splitting analysis and stress modeling. The deformation patterns in the crust signify a strong E-W compressional stress regime throughout IBW, with negligible influence from the major geological structures. These observations derived from local seismicity strongly support that the eastward active subduction of the Indian plate beneath the Burmese sliver is responsible for the crustal-scale deformation. Contrary to the crust, our splitting measurements from the mantle are in line with the major N-S trending arcs created by slip-partitioning due to transpressional oblique subduction. The splitting measurements with an N-S orientated fast axes and the estimated depth of the anisotropy source obtained from the spatial coherency of splitting parameters strongly suggest the presence of trench-parallel sub-slab flow system driven by slab retreat with westward trench migration, which can be the major controlling mechanism of the mantle deformation beneath IBW. Throughout the IBW, a significant change in the orientations of stress and splitting parameters between the crust and mantle supports a decoupled deformation scenario, implying the necessity of a new seismotectonic model. Our integrative study on the present stress patterns and decoupled deformation mechanism between crust and mantle combined with anisotropy measurements beneath the IBW suggests active subduction in the present scenario.</div></div>","PeriodicalId":11481,"journal":{"name":"Earth and Planetary Science Letters","volume":"648 ","pages":"Article 119089"},"PeriodicalIF":4.8,"publicationDate":"2024-10-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142534640","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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 : 2024-10-22DOI: 10.1016/j.epsl.2024.119069
Shunjie Han , Tao Yuan , Wei Mao , Shijie Zhong
Mantle viscosity exerts important controls on the long-term (i.e., >106 years) dynamics of the mantle and lithosphere and the short-term (i.e., 10 to 104 years) crustal motion induced by loading forces including ice melting, sea-level changes, and earthquakes. However, mantle viscosity structures inferred from modeling observations associated with mantle dynamic and loading processes may differ significantly and remain a hotly debated topic over recent decades. In this study, we investigate the effects of mantle viscosity structures on observations of the geoid, mantle structures, and present-day crustal motions and time-varying gravity by considering five representative mantle viscosity structures in models of mantle convection and glacial isostatic adjustment (GIA). These five viscosity models fall into two categories: 1) two viscosity models derived from modeling the geoid in mantle convection models with ∼100 times more viscous lower mantle than the upper mantle, and 2) the other three with less viscosity increase from the upper to lower mantles that are derived from modeling the late Pleistocene and Holocene relative sea level changes and other observations in GIA models. Our convection models use the plate motion history for the last 130 Myrs as the surface boundary conditions and depth- and temperature-dependent viscosity to predict the present-day convective mantle structure of subducted slabs and the intermediate wavelength (degrees 4–12) geoid. Our GIA models using different ice history models (e.g., ICE-6 G and ANU) compute the GIA-induced present-day crustal motions and time-varying gravity. Our calculations demonstrate that while the viscosity models with a higher viscosity in the lower mantle (∼2 × 1022 Pa.s) reproduce the degrees 4–12 geoid and seismic slab structures, they significantly over-predict the geodetic (i.e., GPS and GRACE) observations of crustal motions and time varying gravity. Our calculations also show that while two viscosity models derived from fitting the RSL data with averaged mantle viscosity of ∼1021 Pa.s for the top 1200 km of the mantle reproduce well the geodetic observations independent of ice models, they fail to explain the geoid and seismic slab structures. Therefore, our study highlights the persisting conundrum of mantle viscosity structures derived from different observations. We also discuss a number of possible ways including transient, stress-dependent and 3-D viscosity to resolve this important issue in Geodynamics.
地幔粘度对地幔和岩石圈的长期（即106年）动力学以及由冰融化、海平面变化和地震等加载力引起的短期（即10至104年）地壳运动具有重要的控制作用。然而，从与地幔动力学和加载过程相关的模拟观测中推断出的地幔粘度结构可能存在很大差异，这也是近几十年来一直争论不休的话题。在本研究中，我们通过考虑地幔对流和冰川等静力调整（GIA）模型中五个具有代表性的地幔粘度结构，研究地幔粘度结构对大地水准面、地幔结构以及当今地壳运动和时变重力观测的影响。这五个粘性模型分为两类：1）地幔对流模型中的大地水准面建模得到的两个粘度模型，其下地幔粘度是上地幔的100倍；2）其他三个模型，其上地幔到下地幔的粘度增加较少，这些模型是在冰川等静力调整模型中模拟晚更新世和全新世相对海平面变化和其他观测结果得到的。我们的对流模型利用过去 130 Myrs 的板块运动历史作为地表边界条件，并利用与深度和温度相关的粘度来预测俯冲板块和中间波长（4-12 度）大地水准面的现今对流地幔结构。我们的 GIA 模型使用不同的冰历史模型（如 ICE-6 G 和 ANU）计算 GIA 引起的当今地壳运动和时变重力。我们的计算表明，虽然下地幔粘度较高的粘度模型（∼2 × 1022 Pa.s）重现了 4-12 度大地水准面和地震板块结构，但它们对地壳运动和时变重力的大地测量（即 GPS 和 GRACE）观测结果的预测明显偏高。我们的计算还表明，虽然用平均地幔粘度 ∼1021 Pa.s（地幔顶部 1200 公里）拟合 RSL 数据得到的两个粘度模型很好地再现了大地测量观测结果，而与冰模型无关，但它们无法解释大地水准面和地震板块结构。因此，我们的研究凸显了从不同观测数据中得出的地幔粘度结构这一长期存在的难题。我们还讨论了一些可能的方法，包括瞬态粘度、应力依赖粘度和三维粘度，以解决地球动力学中的这一重要问题。
{"title":"The persisting conundrum of mantle viscosity inferred from mantle convection and glacial isostatic adjustment processes","authors":"Shunjie Han , Tao Yuan , Wei Mao , Shijie Zhong","doi":"10.1016/j.epsl.2024.119069","DOIUrl":"10.1016/j.epsl.2024.119069","url":null,"abstract":"<div><div>Mantle viscosity exerts important controls on the long-term (i.e., >10<sup>6</sup> years) dynamics of the mantle and lithosphere and the short-term (i.e., 10 to 10<sup>4</sup> years) crustal motion induced by loading forces including ice melting, sea-level changes, and earthquakes. However, mantle viscosity structures inferred from modeling observations associated with mantle dynamic and loading processes may differ significantly and remain a hotly debated topic over recent decades. In this study, we investigate the effects of mantle viscosity structures on observations of the geoid, mantle structures, and present-day crustal motions and time-varying gravity by considering five representative mantle viscosity structures in models of mantle convection and glacial isostatic adjustment (GIA). These five viscosity models fall into two categories: 1) two viscosity models derived from modeling the geoid in mantle convection models with ∼100 times more viscous lower mantle than the upper mantle, and 2) the other three with less viscosity increase from the upper to lower mantles that are derived from modeling the late Pleistocene and Holocene relative sea level changes and other observations in GIA models. Our convection models use the plate motion history for the last 130 Myrs as the surface boundary conditions and depth- and temperature-dependent viscosity to predict the present-day convective mantle structure of subducted slabs and the intermediate wavelength (degrees 4–12) geoid. Our GIA models using different ice history models (e.g., ICE-6 G and ANU) compute the GIA-induced present-day crustal motions and time-varying gravity. Our calculations demonstrate that while the viscosity models with a higher viscosity in the lower mantle (∼2 × 10<sup>22</sup> Pa<sup>.</sup>s) reproduce the degrees 4–12 geoid and seismic slab structures, they significantly over-predict the geodetic (i.e., GPS and GRACE) observations of crustal motions and time varying gravity. Our calculations also show that while two viscosity models derived from fitting the RSL data with averaged mantle viscosity of ∼10<sup>21</sup> Pa<sup>.</sup>s for the top 1200 km of the mantle reproduce well the geodetic observations independent of ice models, they fail to explain the geoid and seismic slab structures. Therefore, our study highlights the persisting conundrum of mantle viscosity structures derived from different observations. We also discuss a number of possible ways including transient, stress-dependent and 3-D viscosity to resolve this important issue in Geodynamics.</div></div>","PeriodicalId":11481,"journal":{"name":"Earth and Planetary Science Letters","volume":"648 ","pages":"Article 119069"},"PeriodicalIF":4.8,"publicationDate":"2024-10-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142533833","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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 : 2024-10-22DOI: 10.1016/j.epsl.2024.119083
Hannah R. Sanderson, James F.J. Bryson, Claire I.O. Nichols
Accreting in the first few million years (Ma) of the Solar System, planetesimals record conditions in the protoplanetary disc and are the remnants of planetary formation processes. The meteorite paleomagnetic record carries key insights into the thermal history of planetesimals and their extent of differentiation. The current paradigm splits the meteorite paleomagnetic record into three magnetic field generation epochs: an early nebula field (≲5 Ma after CAI formation), followed by thermal dynamos (∼5–34 Ma after CAI formation), then a gap in dynamo generation, before the onset of core solidification and compositional dynamos. These epochs have been defined using current thermal evolution and dynamo generation models of planetesimals. Here, we demonstrate these epochs are not as distinct as previously thought based on refined thermal evolution models that include more realistic parametrisations for mantle convection, non-eutectic core solidification, and radiogenic 60Fe in the core. We find thermal dynamos can start earlier and last longer. Inclusion of appreciable 60Fe in the core brings forward the onset of dynamo generation to ∼1–2 Ma after CAI formation, which overlaps with the existence of the nebula field. The second epoch of dynamo generation begins prior to the onset of core solidification this epoch is not purely compositionally driven. Planetesimal radius is the dominant control on the strength and duration of dynamo generation, and the choice of reference viscosity can widen the gap between epochs of dynamo generation from 0–200 Ma. Overall, variations in planetesimal properties lead to more variable timings of different planetesimal magnetic field generation mechanisms than previously thought. This alters the information we can glean from the meteorite paleomagnetic record about the early Solar System. Evidence for the nebula field requires more careful interpretation, and late paleomagnetic remanences, for example in the pallasites, may not be evidence for planetesimal core solidification.
{"title":"Early and elongated epochs of planetesimal dynamo generation","authors":"Hannah R. Sanderson, James F.J. Bryson, Claire I.O. Nichols","doi":"10.1016/j.epsl.2024.119083","DOIUrl":"10.1016/j.epsl.2024.119083","url":null,"abstract":"<div><div>Accreting in the first few million years (Ma) of the Solar System, planetesimals record conditions in the protoplanetary disc and are the remnants of planetary formation processes. The meteorite paleomagnetic record carries key insights into the thermal history of planetesimals and their extent of differentiation. The current paradigm splits the meteorite paleomagnetic record into three magnetic field generation epochs: an early nebula field (≲5<!--> <!-->Ma after CAI formation), followed by thermal dynamos (∼5–34<!--> <!-->Ma after CAI formation), then a gap in dynamo generation, before the onset of core solidification and compositional dynamos. These epochs have been defined using current thermal evolution and dynamo generation models of planetesimals. Here, we demonstrate these epochs are not as distinct as previously thought based on refined thermal evolution models that include more realistic parametrisations for mantle convection, non-eutectic core solidification, and radiogenic <sup>60</sup>Fe in the core. We find thermal dynamos can start earlier and last longer. Inclusion of appreciable <sup>60</sup>Fe in the core brings forward the onset of dynamo generation to ∼1–2<!--> <!-->Ma after CAI formation, which overlaps with the existence of the nebula field. The second epoch of dynamo generation begins prior to the onset of core solidification this epoch is not purely compositionally driven. Planetesimal radius is the dominant control on the strength and duration of dynamo generation, and the choice of reference viscosity can widen the gap between epochs of dynamo generation from 0–200<!--> <!-->Ma. Overall, variations in planetesimal properties lead to more variable timings of different planetesimal magnetic field generation mechanisms than previously thought. This alters the information we can glean from the meteorite paleomagnetic record about the early Solar System. Evidence for the nebula field requires more careful interpretation, and late paleomagnetic remanences, for example in the pallasites, may not be evidence for planetesimal core solidification.</div></div>","PeriodicalId":11481,"journal":{"name":"Earth and Planetary Science Letters","volume":"648 ","pages":"Article 119083"},"PeriodicalIF":4.8,"publicationDate":"2024-10-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142534515","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Significant increases in methane discharge from gas hydrate systems into the global ocean can influence oceanic carbon dynamics and potentially present significant challenges to ocean biogeochemistry, marine ecosystems, and broader climate. Gas hydrate/cold seep systems are highly dynamic and susceptible to environmental perturbations and processes active in the subsurface. This complexity poses significant challenges in identifying their driving forces and evolution. Through quantitative time-lapse seismic monitoring, we characterized the subsurface fluid dynamics at Woolsey Mound, a gas hydrate/cold seep system in the Gulf of Mexico. Using information from five reflection seismic surveys, we quantified the fluid volumes within the subsurface and reconstructed their migration process from key permeable sedimentary units at different depths up to the seafloor over a time span of 23 years (1991–2014). Our results reveal that fluid discharge is governed by overpressure build-up and subsequent release, enabled by a network of faults and fractures providing connectivity between deep sedimentary units and the seafloor, crossing through the gas hydrate stability zone. Despite gas hydrates reducing the permeability of these faults, overpressure within shallow sedimentary units can induce transient fault permeability and effective fluid migration, thus enhancing fluid discharge at the seafloor. Our analysis identifies the critical role of shallow permeable layers acting as buffers between deep fluid reservoirs and surface discharge points. This buffering mechanism significantly modulates the frequency and intensity of fluid discharge episodes over decadal timescales. Similar processes observed at Woolsey Mound have been hypothesized at cold seep/hydrate systems along active continental margins, suggesting a common model for deep-sourced fluid discharge across environments in different geological and geodynamic contexts. This research advances our understanding of the mechanisms controlling fluid discharge in cold seep/hydrate systems, providing insights into the complex interplay of geological and environmental factors that drive these profoundly dynamic systems.
{"title":"Controls on fluid discharge at cold seep-hydrate systems: 4D seismic monitoring of Woolsey Mound, Gulf of Mexico","authors":"Ferdinando Cilenti , Davide Oppo , Leonardo Macelloni","doi":"10.1016/j.epsl.2024.119087","DOIUrl":"10.1016/j.epsl.2024.119087","url":null,"abstract":"<div><div>Significant increases in methane discharge from gas hydrate systems into the global ocean can influence oceanic carbon dynamics and potentially present significant challenges to ocean biogeochemistry, marine ecosystems, and broader climate. Gas hydrate/cold seep systems are highly dynamic and susceptible to environmental perturbations and processes active in the subsurface. This complexity poses significant challenges in identifying their driving forces and evolution. Through quantitative time-lapse seismic monitoring, we characterized the subsurface fluid dynamics at Woolsey Mound, a gas hydrate/cold seep system in the Gulf of Mexico. Using information from five reflection seismic surveys, we quantified the fluid volumes within the subsurface and reconstructed their migration process from key permeable sedimentary units at different depths up to the seafloor over a time span of 23 years (1991–2014). Our results reveal that fluid discharge is governed by overpressure build-up and subsequent release, enabled by a network of faults and fractures providing connectivity between deep sedimentary units and the seafloor, crossing through the gas hydrate stability zone. Despite gas hydrates reducing the permeability of these faults, overpressure within shallow sedimentary units can induce transient fault permeability and effective fluid migration, thus enhancing fluid discharge at the seafloor. Our analysis identifies the critical role of shallow permeable layers acting as buffers between deep fluid reservoirs and surface discharge points. This buffering mechanism significantly modulates the frequency and intensity of fluid discharge episodes over decadal timescales. Similar processes observed at Woolsey Mound have been hypothesized at cold seep/hydrate systems along active continental margins, suggesting a common model for deep-sourced fluid discharge across environments in different geological and geodynamic contexts. This research advances our understanding of the mechanisms controlling fluid discharge in cold seep/hydrate systems, providing insights into the complex interplay of geological and environmental factors that drive these profoundly dynamic systems.</div></div>","PeriodicalId":11481,"journal":{"name":"Earth and Planetary Science Letters","volume":"648 ","pages":"Article 119087"},"PeriodicalIF":4.8,"publicationDate":"2024-10-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142534639","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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 : 2024-10-21DOI: 10.1016/j.epsl.2024.119050
Emma S. Sosa , Claire E. Bucholz , Juan David Hernández-Montenegro , Andrés Rodríguez-Vargas , Michael A. Kipp , François L.H. Tissot
Lower-crustal garnet clinopyroxenite (sometimes termed “arclogite”) fractionation in thick-crustal (>35 km) arc settings presents a compelling model to explain Fe-depletion trends, high oxygen fugacity, and evidence of recent delamination observed in many continental arcs. However, the origin of the garnet clinopyroxenites via igneous or metamorphic processes remains unclear. Due to the preferential incorporation of light Fe isotopes in garnet relative to clinopyroxene or amphibole, Fe isotopes are ideally suited for studying the effects of garnet fractionation on magmatic systems. Here, we present whole-rock and mineral Fe isotope data from a suite of lower to mid/upper-crustal Andean xenoliths from Mercaderes, Colombia. This data is combined with petrography, major and trace element mineral and whole-rock chemistry, geothermobarometry, and thermodynamic modeling to explore the xenoliths' petrogenesis and the Northern Andes' crustal structure. Whole-rock samples display a narrow range of Fe isotope compositions (δ56Fe = –0.02 to +0.11 ‰), which do not correlate with lithology, chemistry, or pressure-temperature conditions. This result is inconsistent with previous studies predicting the existence of an isotopically light Fe reservoir in the garnet-rich lower Andean crust. Through thermodynamic modeling, we show that the lack of isotopic fractionation in the Mercaderes xenoliths is more consistent with the suite representing a prograde metamorphic sequence, in which amphibole dehydration reactions drive metamorphism of mid/upper-crustal diorite protoliths. While our data do not preclude the presence of garnet clinopyroxenite cumulates at the base of the Andean crust, or that the delamination of such cumulates played an important role in the evolution of the Andes, they do indicate that not all garnet clinopyroxenites are cumulate in origin. Instead, the lower Andean crust represents an amalgamation of igneous and metamorphic rock, with metamorphism of mid-crustal lithologies and partial melting of mafic cumulate roots acting in tandem to drive densification and delamination of the lower crust in a self-feeding mechanism.
{"title":"Garnet clinopyroxenite formation via amphibole-dehydration in continental arcs: Evidence from Fe isotopes","authors":"Emma S. Sosa , Claire E. Bucholz , Juan David Hernández-Montenegro , Andrés Rodríguez-Vargas , Michael A. Kipp , François L.H. Tissot","doi":"10.1016/j.epsl.2024.119050","DOIUrl":"10.1016/j.epsl.2024.119050","url":null,"abstract":"<div><div>Lower-crustal garnet clinopyroxenite (sometimes termed “arclogite”) fractionation in thick-crustal (>35 km) arc settings presents a compelling model to explain Fe-depletion trends, high oxygen fugacity, and evidence of recent delamination observed in many continental arcs. However, the origin of the garnet clinopyroxenites via igneous or metamorphic processes remains unclear. Due to the preferential incorporation of light Fe isotopes in garnet relative to clinopyroxene or amphibole, Fe isotopes are ideally suited for studying the effects of garnet fractionation on magmatic systems. Here, we present whole-rock and mineral Fe isotope data from a suite of lower to mid/upper-crustal Andean xenoliths from Mercaderes, Colombia. This data is combined with petrography, major and trace element mineral and whole-rock chemistry, geothermobarometry, and thermodynamic modeling to explore the xenoliths' petrogenesis and the Northern Andes' crustal structure. Whole-rock samples display a narrow range of Fe isotope compositions (δ<sup>56</sup>Fe = –0.02 to +0.11 ‰), which do not correlate with lithology, chemistry, or pressure-temperature conditions. This result is inconsistent with previous studies predicting the existence of an isotopically light Fe reservoir in the garnet-rich lower Andean crust. Through thermodynamic modeling, we show that the lack of isotopic fractionation in the Mercaderes xenoliths is more consistent with the suite representing a prograde metamorphic sequence, in which amphibole dehydration reactions drive metamorphism of mid/upper-crustal diorite protoliths. While our data do not preclude the presence of garnet clinopyroxenite cumulates at the base of the Andean crust, or that the delamination of such cumulates played an important role in the evolution of the Andes, they do indicate that not all garnet clinopyroxenites are cumulate in origin. Instead, the lower Andean crust represents an amalgamation of igneous and metamorphic rock, with metamorphism of mid-crustal lithologies and partial melting of mafic cumulate roots acting in tandem to drive densification and delamination of the lower crust in a self-feeding mechanism.</div></div>","PeriodicalId":11481,"journal":{"name":"Earth and Planetary Science Letters","volume":"648 ","pages":"Article 119050"},"PeriodicalIF":4.8,"publicationDate":"2024-10-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142534638","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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 : 2024-10-21DOI: 10.1016/j.epsl.2024.119071
V.K. Pedersen , N. Gomez , J.X. Mitrovica , G. Jungdal-Olesen , J.L. Andersen , J. Garbe , A. Aschwanden , R. Winkelmann
Over geological time scales, the combination of solid-Earth deformation and climate-dependent surface processes have resulted in a distinct hypsometry (distribution of surface area with elevation) on Earth, with the highest concentration of surface area focused near the present-day sea surface. However, in addition to a single, well-defined maximum at the present-day sea surface, Earth's hypsometry is also characterized by a prominent maximum ∼2–5 m above this level, with the range accounting for uncertainties in recent digital elevation models. Here we explore the nature of this enigmatic maximum and examine, using a gravitationally self-consistent model of ice-age sea-level change, how it evolved over the last glacial cycle and may evolve moving towards a near-ice-free future. We argue that the hypsometric maximum captures topographic conditions at the end of the last deglaciation phase and subsequent glacial isostatic adjustment (GIA) raised it from the sea surface to its present-day elevation. Moreover, ongoing GIA will raise the maximum a further ∼2 m in the absence of future ice mass loss. If a portion of the hypsometric maximum has persisted for longer than Holocene time scales, the resulting GIA-converged elevation of the hypsometric maximum at +4–7 m above the sea surface implies a longer-term mean state of the Earth that may reflect lower ice volumes, trends in erosion, dynamic topography, or a combination of these. The signature of these various contributions on present-day hypsometry is intimately connected to the time scale of erosional and depositional processes near shorelines.
{"title":"Earth's hypsometry and what it tells us about global sea level","authors":"V.K. Pedersen , N. Gomez , J.X. Mitrovica , G. Jungdal-Olesen , J.L. Andersen , J. Garbe , A. Aschwanden , R. Winkelmann","doi":"10.1016/j.epsl.2024.119071","DOIUrl":"10.1016/j.epsl.2024.119071","url":null,"abstract":"<div><div>Over geological time scales, the combination of solid-Earth deformation and climate-dependent surface processes have resulted in a distinct hypsometry (distribution of surface area with elevation) on Earth, with the highest concentration of surface area focused near the present-day sea surface. However, in addition to a single, well-defined maximum at the present-day sea surface, Earth's hypsometry is also characterized by a prominent maximum ∼2–5 m above this level, with the range accounting for uncertainties in recent digital elevation models. Here we explore the nature of this enigmatic maximum and examine, using a gravitationally self-consistent model of ice-age sea-level change, how it evolved over the last glacial cycle and may evolve moving towards a near-ice-free future. We argue that the hypsometric maximum captures topographic conditions at the end of the last deglaciation phase and subsequent glacial isostatic adjustment (GIA) raised it from the sea surface to its present-day elevation. Moreover, ongoing GIA will raise the maximum a further ∼2 m in the absence of future ice mass loss. If a portion of the hypsometric maximum has persisted for longer than Holocene time scales, the resulting GIA-converged elevation of the hypsometric maximum at +4–7 m above the sea surface implies a longer-term mean state of the Earth that may reflect lower ice volumes, trends in erosion, dynamic topography, or a combination of these. The signature of these various contributions on present-day hypsometry is intimately connected to the time scale of erosional and depositional processes near shorelines.</div></div>","PeriodicalId":11481,"journal":{"name":"Earth and Planetary Science Letters","volume":"648 ","pages":"Article 119071"},"PeriodicalIF":4.8,"publicationDate":"2024-10-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142534121","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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 : 2024-10-19DOI: 10.1016/j.epsl.2024.119082
Marie Kepp , Lu Pan , Jens Frydenvang , Martin Bizzarro
The Mars Science Laboratory has been investigating the central mound of Gale crater since 2012 and revealed evidence of silica enrichment in several locations, suggesting that the geologic processes related to the formation of hydrated silica could be widespread. A reanalysis of orbital data over Aeolis Mons indicates the existence of an extensive unit rich in hydrated silica. These silica-enriched deposits, found at the base of Aeolis Mons, span elevations from -4513 m to -3351 m. The mapped hydrated silica deposits are spatially adjacent to an erosion-resistant capping unit, previously mapped as the mound skirting unit, which lies beneath the terminal deposits from local canyons and valleys. We hypothesize that the hydrated silica-bearing unit precipitated from groundwater which migrated upwards or deposited as a volcaniclastic silica-rich layer which was rehydrated during the late-stage canyon and valley forming events. The silica-bearing unit beneath the capping unit is protected against erosion by younger fan-shaped deposits and became exposed only recently. The mineralogy and stratigraphic relations with Mount Sharp units imply that the aqueous activities leading to silica diagenesis were likely a basin-wide process that occurred long after the formation of lakes in Gale crater's geological history and experienced limited water-rock interaction since then.
{"title":"Orbital identification of widespread hydrated silica deposits in Gale crater","authors":"Marie Kepp , Lu Pan , Jens Frydenvang , Martin Bizzarro","doi":"10.1016/j.epsl.2024.119082","DOIUrl":"10.1016/j.epsl.2024.119082","url":null,"abstract":"<div><div>The Mars Science Laboratory has been investigating the central mound of Gale crater since 2012 and revealed evidence of silica enrichment in several locations, suggesting that the geologic processes related to the formation of hydrated silica could be widespread. A reanalysis of orbital data over Aeolis Mons indicates the existence of an extensive unit rich in hydrated silica. These silica-enriched deposits, found at the base of Aeolis Mons, span elevations from -4513 m to -3351 m. The mapped hydrated silica deposits are spatially adjacent to an erosion-resistant capping unit, previously mapped as the mound skirting unit, which lies beneath the terminal deposits from local canyons and valleys. We hypothesize that the hydrated silica-bearing unit precipitated from groundwater which migrated upwards or deposited as a volcaniclastic silica-rich layer which was rehydrated during the late-stage canyon and valley forming events. The silica-bearing unit beneath the capping unit is protected against erosion by younger fan-shaped deposits and became exposed only recently. The mineralogy and stratigraphic relations with Mount Sharp units imply that the aqueous activities leading to silica diagenesis were likely a basin-wide process that occurred long after the formation of lakes in Gale crater's geological history and experienced limited water-rock interaction since then.</div></div>","PeriodicalId":11481,"journal":{"name":"Earth and Planetary Science Letters","volume":"648 ","pages":"Article 119082"},"PeriodicalIF":4.8,"publicationDate":"2024-10-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142534637","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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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