地球的水从何而来?这个看似简单的问题,实际上牵涉到行星科学中最基本也最复杂的谜题之一。地球的水可追溯至地球形成初期,源于含水星子的吸积或对太阳星云气体的捕获(Young et al.,2023)。然而,早期地球经历了剧烈的撞击事件,整个地幔...地球的水从何而来?这个看似简单的问题,实际上牵涉到行星科学中最基本也最复杂的谜题之一。地球的水可追溯至地球形成初期,源于含水星子的吸积或对太阳星云气体的捕获(Young et al.,2023)。然而,早期地球经历了剧烈的撞击事件,整个地幔可能处于熔融状态,形成深达核幔边界的岩浆洋。地幔从早期的广泛熔融到现今固态为主的转变过程中,水这种高度不相容的挥发分组分究竟如何留存,并最终演化为今天地球内部的水储库(Peslier et al.,2017)?这一问题长期缺乏直接的实验约束。展开更多
断裂带尾端扩展变形与连接方式是认识断裂带生长和连接机制的关键。大凉山断裂从北向南由雁列状排列的公益海断层等6条断层组成,构成鲜水河与小江左行走滑断裂间的转换连接断裂。因此,位于最北端的公益海断层是理解鲜水河断裂尾端扩展变...断裂带尾端扩展变形与连接方式是认识断裂带生长和连接机制的关键。大凉山断裂从北向南由雁列状排列的公益海断层等6条断层组成,构成鲜水河与小江左行走滑断裂间的转换连接断裂。因此,位于最北端的公益海断层是理解鲜水河断裂尾端扩展变形,并进而分析大凉山连接断裂形成的关键。然而,由于对公益海断层的应变性质和强度缺少有效约束,导致对断裂扩展和连接机制认识的分歧。我们对公益海断层进行了详细的地质调查和构造解析,并对变形岩石的磁化率各向异性(anisotropy of magnetic susceptibility,AMS)进行了分析。结果表明:1)公益海断层的活动分为两阶段:D_(1)阶段以逆冲作用为主,兼具右行走滑分量,D_(2)阶段以左行走滑作用为主,兼具逆冲分量;2)磁化率各向异性分析显示,公益海断层两盘岩石以顺磁性矿物为主导(K_(m)=36~1330μSI);磁化率椭球呈现两期变形特征:D_(1)期为NNE—NE向缩短,特征值(P_(j)—T)显示应变强度自断层北、中和南段中部向两端递增;D_(2)期为NW向缩短,指示应变集中分布于断层尾端;3)基于前人年代学研究成果,本文提出新的构造演化模型:在鲜水河和小江断裂尾端共同作用下,D_(1)期形成多个具有逆冲性质的韧-脆性剪切带,以左列或者右列形式组合并沿剪切带向两端扩展;D_(2)期各韧-脆性剪切带以左行走滑作用为主并逐渐完成连接形成大凉山断裂,进一步则向鲜水河—大凉山—小江断裂系的完全贯通发展。展开更多
The Almus Fault Zone(AFZ)is one of the major splay faults of the North Anatolian Fault Zone(NAFZ)and is important for understanding its tectonic features and assessing regional seismic hazards.This research presents t...The Almus Fault Zone(AFZ)is one of the major splay faults of the North Anatolian Fault Zone(NAFZ)and is important for understanding its tectonic features and assessing regional seismic hazards.This research presents the integration of morphometric indices to quantitatively assess the spatial variation of tectonic activity along the AFZ.The AFZ is an active fault with both strike-slip and normal fault components and consists of two main branches,Mercimekdağı-Çamdere Fault(MÇF)and Tokat Fault(TF)segments.This study aims to assess the relative tectonic activity of the AFZ using various morphometric indices,based on a 10 m resolution DEM,with the aid of ArcGIS and MATLAB software.For this purpose,morphometric indices such as hypsometric integral(HI:0.35-0.65),mountain front sinuosity(Smf:1.3-1.44),valley floor width-height ratio(Vf:0.15-2.28),asymmetry factor(AF:23-77),drainage basin shape(Bs:1.13-6.10)and normalized steepness index(ksn:1-498)were applied to 53 drainage basins.When the Smf and mean Vf indices results were evaluated,it was calculated that the uplift ratio of the region was more than 0.5 mm/yr.The spatial distribution of the relative tectonic activity(Iat)of the area was revealed by combining the obtained morphometric indices analysis results.According to the Iat result,it was concluded that the MercimekdağıÇamdere Fault and Tokat Fault segments have high tectonic activity,but the Mercimekdağı-Çamdere Fault segment has higher tectonic activity.The results obtained were also confirmed by field observations.This research provides valuable information for the evaluation of tectonic activity in drainage systems controlled by splay faults.展开更多
Supercritical fluids play a crucial role in material transport within Earth's deep interior.Investigating the pressure-dependent atomic structures and transport properties of such fluids is essential for understan...Supercritical fluids play a crucial role in material transport within Earth's deep interior.Investigating the pressure-dependent atomic structures and transport properties of such fluids is essential for understanding their petrological,chemical,and geophysical behaviors.In this study,we employed first-principles molecular dynamics simulations to explore the structures,self-diffusion coefficients(D),and viscosities(η)of supercritical NaAlSi_(3)O_(8)-H_(2)O fluids under conditions of 2000 K and 3-10 GPa,with water contents of 30 wt% and 50 wt%.Our calculations indicate that at a water content of 30 wt%,Q^(2) and Q^(3) exhibit a certain degree of positive and negative pressure dependence,respectively,while other Q^(n) species(n represents the number of bridging oxygens connected to Si/Al)show minimal changes.At a water content of 50 wt%,Q^(2) and Q^(0) exhibit a certain degree of positive and negative pressure dependence,respectively,while other Q^(n) species show minimal changes.At both water contents,Si-O-H and molecular water in the system exhibit negative pressure dependence,suggesting that the migration of supercritical fluids from deep to shallow regions is accompanied by the release of water.The self-diffusion coefficients in the supercritical NaAlSi_(3)O_(8)-H_(2)O fluid follow the order D_(Na)≈D_(H)>D_(O)>D_(Al)≈D_(Si),with an overall weak negative pressure dependence.By comparing the viscosities of anhydrous and hydrous silicate melts from previous studies,we found that the addition of water caused a transition from negative to positive pressure dependence of viscosity,corresponding to a structural change from polymerization to depolymerization.Additionally,we calculated the fluid mobility Δp/η of supercritical NaAlSi_(3)O_(8)-H_(2)O fluids and found that their mobility is several orders of magnitude higher than that of basalt melt and is also significantly greater than that of carbonate melt.As supercritical fluids ascend from deeper to shallower regions,their mobility is further enhanced,significantly contributing to the transport of elements from subducting slabs to the overlying mantle wedge.展开更多
近20多年来,以南阿尔金为代表的多个典型超高压变质带中陆续发现了陆壳超深俯冲到或接近于斯石英稳定域地幔深度(>250~300km)并折返回地表的岩石学证据,代表了国际上大陆深俯冲与超高压作用研究领域的突破性新进展,并由此催生出了“...近20多年来,以南阿尔金为代表的多个典型超高压变质带中陆续发现了陆壳超深俯冲到或接近于斯石英稳定域地幔深度(>250~300km)并折返回地表的岩石学证据,代表了国际上大陆深俯冲与超高压作用研究领域的突破性新进展,并由此催生出了“陆壳超深俯冲作用”和“极超高压变质作用”的新概念。然而,由于以下两个方面的原因致使这些研究和认识还没有得到地学界的广泛认可。其一,这些岩石学证据主要是来自一些具有溶解度实验资料支撑的特殊矿物的显微出溶结构等,但由于矿物出溶结构成因的复杂性或多解性,尤其是矿物出溶结构的高温高压实验(或矿物溶解度实验的反向实验)研究鲜有报道,使得对矿物显微出溶结构成因的解释及其指示的地质意义存在较大争议,甚至怀疑其是否是“出溶结构”。其二,实验岩石学资料表明,大陆地壳物质俯冲到>250km的地幔深度时会发生一系列矿物相变,最终成为以高密度斯石英、K-锰钡矿、石榴子石等为主要组成矿物的岩石,并导致其密度高于围岩地幔岩而失去浮力,因此250km的地幔深度被前人定义为陆壳岩石“永不回返的深度”(Depth of no return)。那么,超深俯冲到斯石英稳定域地幔深度(>250km)的陆壳岩石是如何折返到地表的?这既是困惑国际地球科学界的一道难题,也是陆壳岩石超深俯冲到斯石英稳定域地幔深度后折返回地表的认识未被广泛接受的另一重要理由。本文重点针对这两个关键科学问题,并围绕极超高压变质作用及其构造地质意义等衍生科学问题,概述了近年来我们和其他研究团队取得的一些重要新进展,主要包括:(1)陆壳超深俯冲到斯石英或相当于斯石英稳定域的地幔深度(>250~300km)形成极超高压变质岩石,然后再折返回地表的地质现象在全球可能具有一定的普遍性,极超高压变质岩石类型具有多样性;(2)有溶解度实验和出溶实验数据支撑的矿物显微出溶结构与指示压力的特征矿物(如柯石英、金刚石、斯石英等)一样,可作为超-极超高压变质条件的识别标志,南阿尔金先期依据先存斯石英出溶蓝晶石+尖晶石等证据获得的关于陆壳岩石可俯冲到斯石英稳定域地幔深度并折返回地表的结论是可靠的;(3)俯冲陆壳与洋壳板片在>250km的地幔深度仍未断离,是控制陆壳超深俯冲与引发极超高压变质的必要条件之一;(4)加热使斯石英相变为柯石英导致岩石密度的减小,是超深俯冲到斯石英稳定域地幔深度(>250~300km)长英质陆壳岩石折返的主要驱动力,合理地解释了超深俯冲到斯石英稳定域地幔深度陆壳岩石的折返机制;(5)大陆板片超深俯冲过程中发生的4次矿物相变使其密度逐渐增大,尤其是柯石英相转变为斯石英(>250km的地幔深度)后俯冲板片的密度会显著大于围岩地幔,从而引发超深俯冲陆壳板片的后撤或回卷(rollback),进而导致俯冲带上盘出现伸展以及软流圈地幔的上涌,而上涌的软流圈地幔又可能为超深俯冲到斯石英稳定域地幔深度的大陆板片的加热提供了热源,致使其中斯石英转变为柯石英而获得自折返的浮力;(6)以大陆深-超深俯冲与折返过程及其地质响应为主线,以陆壳成因超-极超高压岩石的峰期变质、退变质和深熔-岩浆作用的演化序列为时间坐标,可用来约束大陆深-超深俯冲作用形成的碰撞造山带演化过程中洋盆关闭、大陆俯冲-碰撞、造山带伸展垮塌并抬升剥蚀等关键事件的时间节点。另外,本文还提出了关于陆壳超深俯冲与极超高压变质作用深入研究面临挑战的一些科学问题及其思考。展开更多
文摘地球的水从何而来?这个看似简单的问题,实际上牵涉到行星科学中最基本也最复杂的谜题之一。地球的水可追溯至地球形成初期,源于含水星子的吸积或对太阳星云气体的捕获(Young et al.,2023)。然而,早期地球经历了剧烈的撞击事件,整个地幔可能处于熔融状态,形成深达核幔边界的岩浆洋。地幔从早期的广泛熔融到现今固态为主的转变过程中,水这种高度不相容的挥发分组分究竟如何留存,并最终演化为今天地球内部的水储库(Peslier et al.,2017)?这一问题长期缺乏直接的实验约束。
文摘断裂带尾端扩展变形与连接方式是认识断裂带生长和连接机制的关键。大凉山断裂从北向南由雁列状排列的公益海断层等6条断层组成,构成鲜水河与小江左行走滑断裂间的转换连接断裂。因此,位于最北端的公益海断层是理解鲜水河断裂尾端扩展变形,并进而分析大凉山连接断裂形成的关键。然而,由于对公益海断层的应变性质和强度缺少有效约束,导致对断裂扩展和连接机制认识的分歧。我们对公益海断层进行了详细的地质调查和构造解析,并对变形岩石的磁化率各向异性(anisotropy of magnetic susceptibility,AMS)进行了分析。结果表明:1)公益海断层的活动分为两阶段:D_(1)阶段以逆冲作用为主,兼具右行走滑分量,D_(2)阶段以左行走滑作用为主,兼具逆冲分量;2)磁化率各向异性分析显示,公益海断层两盘岩石以顺磁性矿物为主导(K_(m)=36~1330μSI);磁化率椭球呈现两期变形特征:D_(1)期为NNE—NE向缩短,特征值(P_(j)—T)显示应变强度自断层北、中和南段中部向两端递增;D_(2)期为NW向缩短,指示应变集中分布于断层尾端;3)基于前人年代学研究成果,本文提出新的构造演化模型:在鲜水河和小江断裂尾端共同作用下,D_(1)期形成多个具有逆冲性质的韧-脆性剪切带,以左列或者右列形式组合并沿剪切带向两端扩展;D_(2)期各韧-脆性剪切带以左行走滑作用为主并逐渐完成连接形成大凉山断裂,进一步则向鲜水河—大凉山—小江断裂系的完全贯通发展。
文摘The Almus Fault Zone(AFZ)is one of the major splay faults of the North Anatolian Fault Zone(NAFZ)and is important for understanding its tectonic features and assessing regional seismic hazards.This research presents the integration of morphometric indices to quantitatively assess the spatial variation of tectonic activity along the AFZ.The AFZ is an active fault with both strike-slip and normal fault components and consists of two main branches,Mercimekdağı-Çamdere Fault(MÇF)and Tokat Fault(TF)segments.This study aims to assess the relative tectonic activity of the AFZ using various morphometric indices,based on a 10 m resolution DEM,with the aid of ArcGIS and MATLAB software.For this purpose,morphometric indices such as hypsometric integral(HI:0.35-0.65),mountain front sinuosity(Smf:1.3-1.44),valley floor width-height ratio(Vf:0.15-2.28),asymmetry factor(AF:23-77),drainage basin shape(Bs:1.13-6.10)and normalized steepness index(ksn:1-498)were applied to 53 drainage basins.When the Smf and mean Vf indices results were evaluated,it was calculated that the uplift ratio of the region was more than 0.5 mm/yr.The spatial distribution of the relative tectonic activity(Iat)of the area was revealed by combining the obtained morphometric indices analysis results.According to the Iat result,it was concluded that the MercimekdağıÇamdere Fault and Tokat Fault segments have high tectonic activity,but the Mercimekdağı-Çamdere Fault segment has higher tectonic activity.The results obtained were also confirmed by field observations.This research provides valuable information for the evaluation of tectonic activity in drainage systems controlled by splay faults.
基金funded by National Natural Science Foundation of China(42373033,Yicheng Sun)Fundamental Research Funds for the Central Universities(B240201111,Yicheng Sun)。
文摘Supercritical fluids play a crucial role in material transport within Earth's deep interior.Investigating the pressure-dependent atomic structures and transport properties of such fluids is essential for understanding their petrological,chemical,and geophysical behaviors.In this study,we employed first-principles molecular dynamics simulations to explore the structures,self-diffusion coefficients(D),and viscosities(η)of supercritical NaAlSi_(3)O_(8)-H_(2)O fluids under conditions of 2000 K and 3-10 GPa,with water contents of 30 wt% and 50 wt%.Our calculations indicate that at a water content of 30 wt%,Q^(2) and Q^(3) exhibit a certain degree of positive and negative pressure dependence,respectively,while other Q^(n) species(n represents the number of bridging oxygens connected to Si/Al)show minimal changes.At a water content of 50 wt%,Q^(2) and Q^(0) exhibit a certain degree of positive and negative pressure dependence,respectively,while other Q^(n) species show minimal changes.At both water contents,Si-O-H and molecular water in the system exhibit negative pressure dependence,suggesting that the migration of supercritical fluids from deep to shallow regions is accompanied by the release of water.The self-diffusion coefficients in the supercritical NaAlSi_(3)O_(8)-H_(2)O fluid follow the order D_(Na)≈D_(H)>D_(O)>D_(Al)≈D_(Si),with an overall weak negative pressure dependence.By comparing the viscosities of anhydrous and hydrous silicate melts from previous studies,we found that the addition of water caused a transition from negative to positive pressure dependence of viscosity,corresponding to a structural change from polymerization to depolymerization.Additionally,we calculated the fluid mobility Δp/η of supercritical NaAlSi_(3)O_(8)-H_(2)O fluids and found that their mobility is several orders of magnitude higher than that of basalt melt and is also significantly greater than that of carbonate melt.As supercritical fluids ascend from deeper to shallower regions,their mobility is further enhanced,significantly contributing to the transport of elements from subducting slabs to the overlying mantle wedge.
文摘近20多年来,以南阿尔金为代表的多个典型超高压变质带中陆续发现了陆壳超深俯冲到或接近于斯石英稳定域地幔深度(>250~300km)并折返回地表的岩石学证据,代表了国际上大陆深俯冲与超高压作用研究领域的突破性新进展,并由此催生出了“陆壳超深俯冲作用”和“极超高压变质作用”的新概念。然而,由于以下两个方面的原因致使这些研究和认识还没有得到地学界的广泛认可。其一,这些岩石学证据主要是来自一些具有溶解度实验资料支撑的特殊矿物的显微出溶结构等,但由于矿物出溶结构成因的复杂性或多解性,尤其是矿物出溶结构的高温高压实验(或矿物溶解度实验的反向实验)研究鲜有报道,使得对矿物显微出溶结构成因的解释及其指示的地质意义存在较大争议,甚至怀疑其是否是“出溶结构”。其二,实验岩石学资料表明,大陆地壳物质俯冲到>250km的地幔深度时会发生一系列矿物相变,最终成为以高密度斯石英、K-锰钡矿、石榴子石等为主要组成矿物的岩石,并导致其密度高于围岩地幔岩而失去浮力,因此250km的地幔深度被前人定义为陆壳岩石“永不回返的深度”(Depth of no return)。那么,超深俯冲到斯石英稳定域地幔深度(>250km)的陆壳岩石是如何折返到地表的?这既是困惑国际地球科学界的一道难题,也是陆壳岩石超深俯冲到斯石英稳定域地幔深度后折返回地表的认识未被广泛接受的另一重要理由。本文重点针对这两个关键科学问题,并围绕极超高压变质作用及其构造地质意义等衍生科学问题,概述了近年来我们和其他研究团队取得的一些重要新进展,主要包括:(1)陆壳超深俯冲到斯石英或相当于斯石英稳定域的地幔深度(>250~300km)形成极超高压变质岩石,然后再折返回地表的地质现象在全球可能具有一定的普遍性,极超高压变质岩石类型具有多样性;(2)有溶解度实验和出溶实验数据支撑的矿物显微出溶结构与指示压力的特征矿物(如柯石英、金刚石、斯石英等)一样,可作为超-极超高压变质条件的识别标志,南阿尔金先期依据先存斯石英出溶蓝晶石+尖晶石等证据获得的关于陆壳岩石可俯冲到斯石英稳定域地幔深度并折返回地表的结论是可靠的;(3)俯冲陆壳与洋壳板片在>250km的地幔深度仍未断离,是控制陆壳超深俯冲与引发极超高压变质的必要条件之一;(4)加热使斯石英相变为柯石英导致岩石密度的减小,是超深俯冲到斯石英稳定域地幔深度(>250~300km)长英质陆壳岩石折返的主要驱动力,合理地解释了超深俯冲到斯石英稳定域地幔深度陆壳岩石的折返机制;(5)大陆板片超深俯冲过程中发生的4次矿物相变使其密度逐渐增大,尤其是柯石英相转变为斯石英(>250km的地幔深度)后俯冲板片的密度会显著大于围岩地幔,从而引发超深俯冲陆壳板片的后撤或回卷(rollback),进而导致俯冲带上盘出现伸展以及软流圈地幔的上涌,而上涌的软流圈地幔又可能为超深俯冲到斯石英稳定域地幔深度的大陆板片的加热提供了热源,致使其中斯石英转变为柯石英而获得自折返的浮力;(6)以大陆深-超深俯冲与折返过程及其地质响应为主线,以陆壳成因超-极超高压岩石的峰期变质、退变质和深熔-岩浆作用的演化序列为时间坐标,可用来约束大陆深-超深俯冲作用形成的碰撞造山带演化过程中洋盆关闭、大陆俯冲-碰撞、造山带伸展垮塌并抬升剥蚀等关键事件的时间节点。另外,本文还提出了关于陆壳超深俯冲与极超高压变质作用深入研究面临挑战的一些科学问题及其思考。
