三江南段景洪大勐龙地区基性高压变质岩岩石地球化学特征及其大地构造意义

本文以三江南段景洪大勐龙地区新发现的退变榴辉岩和蓝片岩为研究对象,对其进行了系统的地球化学、原岩性质及锆石U-Pb定年的综合研究。大勐龙地区退变榴辉岩呈透镜状产于白云钠长石英片岩、白云母片岩和斜长角闪（片）岩中,其原岩为亚碱性拉斑玄武岩,球粒陨石标准化稀土元素配分曲线呈轻稀土弱亏损、重稀土平坦型的分布特征,不具有Nb、Ta、Ti的亏损,与典型的N-MORB（正常型洋中脊玄武岩）地球化学特征一致,表明其原岩可能来源于亏损的地幔区,形成于洋中脊环境;变质锆石SHRIMP U-Pb年龄为230.3±1.7Ma,可能代表榴辉岩峰期的变质时代。蓝片岩的原岩为亚碱性拉斑玄武岩,具有较高Ti玄武岩的特征（TiO₂含量2.55%~2.88%,均大于2%）,稀土元素总量变化范围小,比典型的N-MORB稀土总量偏高,轻稀土元素（LREE）亏损,无明显负Eu异常,地球化学性质与N-MORB类似。结合以往区域研究成果,进一步确定研究区退变榴辉岩和蓝片岩的原岩属于典型N-MORB型,该项研究不仅在昌宁-孟连缝合带的南段发现典型的特提斯洋壳残片,而且为进一步深入探讨滇西地区特提斯洋消减-闭合的动力学背景及其复杂的构造演化过程提供了重要的科学依据。

     

Neoproterozoic high-pressure/low-temperature metamorphic rocks in the Avalon terrane, southern New Brunswick, Canada

High‐P/low‐T metamorphic rocks of the Hammondvale metamorphic suite (HMS) are exposed in an area of 10 km² on the NW margin of the Caledonian (Avalon) terrane in southern New Brunswick, Canada. The HMS is in faulted contact on the SE with c. 560–550 Ma volcanic and sedimentary rocks and co‐magmatic plutonic units of the Caledonian terrane. The HMS consists of albite‐ and garnet‐porphyroblastic mica schist, with minor marble, calc‐silicate rocks and quartzite. Pressure and temperature estimates from metamorphic assemblages in the mica schist and calc‐silicate rocks using TWQ indicate that peak pressure conditions were 12.4 kbar at 430 °C. Peak temperature conditions were 580 °C at 9.0 kbar. ⁴⁰Ar/³⁹Ar muscovite ages from three samples range up to 618–615 Ma, a minimum age for high‐P/low‐T metamorphism in this unit. These ages indicate that the HMS is related to the c. 625–600 Ma subduction‐generated volcanic and plutonic units exposed to the SE in the Caledonian terrane. The ages are also similar to those obtained from detrital muscovite in a Neoproterozoic‐Cambrian sedimentary sequence in the Caledonian terrane, suggesting that the HMS was exposed by latest Neoproterozoic time and supplied detritus to the sedimentary units. The HMS is interpreted to represent a fragment of an accretionary complex, similar to the Sanbagawa Belt in Japan. It confirms the presence of a major cryptic suture between the Avalon terrane sensu stricto and the now‐adjacent Brookville terrane.     

The Kamuikotan zone in Hokkaido, Japan: tectonic mixing of high-pressure and low-pressure metamorphic rocks

Abstract. In the Kamuikotan zone, central Hokkaido, Japan, two distinct types of metamorphic rocks are tectonically mixed up, along with a great quantity of ultramafic rocks; one type consists of high-pressure metamorphic rocks, and the other of low-pressure ones. The high-pressure metamorphic rocks are divided into two categories. (1) Prograde greenschist to glaucophaneschist facies rocks derived from mudstone, sandstone, limestone, a variety of basic rocks such as pillow and massive lavas, hyaloclastite and tuff, and radiolarian (Valanginian to Hauterivian) chert, among which the basic rocks and the chert, and occasionally the sandstone, occur as incoherent blocks (or inclusions) enveloped by mudstone. (2) Retrograde amphibolites with minor metachert and glaucophane-calcite rock, which are tectonic (or exotic) blocks enclosed within prograde mudstone or serpentinite, or separated from these prograde rocks by faults. The K-Ar ages of the prograde metamorphic rocks (72, 107 and 116 Ma on phengitic muscovites) are younger than those of the retrograde rocks (109, 132, 135 and 145 Ma on muscovites, and 120 Ma on hornblende). The low-pressure metamorphic rocks consist of the mafic members of an ophiolite sequence with a capping of radiolarian (Tithonian) chert with the metamorphic grade ranging from the zeolite facies, through the greenschist (partly, actinolite-calcic plagioclase) facies to the amphibolite (partly, hornblende-granulite) facies. The low-pressure metamorphism has a number of similarities with that described for'ocean-floor'metamorphism. The tectonic evolution of such a mixed-up zone is discussed in relation to Mesozoic plate motion.     

西藏羌塘中部亚丹高压变质岩年代学、地球化学特征及其构造意义

羌南和羌北地块沿龙木错-双湖缝合带碰撞对接,标志着古特提斯洋的最终闭合,然而古特提斯洋的构造演化,尤其它的打开时限一直争议不断。本文对龙木错-双湖缝合带以南荣玛地区的变质杂岩进行了岩相学、年代学和地球化学特征研究,进而约束古特提斯洋的开、合时限及其关闭后的构造演化特征。通过LA-ICP-MS锆石U-Pb定年,本文首次报道了1件新元古代斜长角闪岩,其加权平均年龄为717±7Ma(n=61,MSWD=1. 9),表明原岩形成于新元古代中期,反映羌南地区存在前寒武基底;另获得1件中侏罗世斜长角闪岩的锆石加权平均年龄为163±2Ma(n=26,MSWD=1. 9),表明其原岩形成于中侏罗世;获得2件石榴石多硅白云母石英片岩锆石边部谐和年龄范围分别为267～1349Ma和214～2050Ma;另对片岩中2组多硅白云母样品进行~(40)Ar/~(39)Ar定年,分别获得224. 2±1. 5Ma和223. 9±1. 5Ma的一致坪年龄,暗示区域变质作用可能从～224Ma持续到214Ma之后,且～214Ma的岩浆事件可能形成于碰撞过程中。新元古代和中侏罗世斜长角闪岩的岩石地球化学特征显示,前者原岩具E-MORB特征,后者原岩趋向于OIB特征。基于区域岩石组合与地球化学特征,推断二者均形成于伸展环境,前者可能形成于陆内伸展背景,响应Rodinia超大陆的裂解,后者可能形成于大陆裂谷环境,响应羌南、羌北地块碰撞结束后的裂解。综合前人与本文研究成果,认为新元古代中期(～717Ma),某未知陆块可能就已逐渐开始从羌南-印度大陆裂解,导致"古特提斯洋"在ca. 717～517Ma之间的某个时间点就已打开;古特提斯洋可能在～224Ma才完成闭合,羌南、羌北陆陆碰撞挤压持续到214Ma之后;中侏罗世区域为裂谷伸展环境,并发育OIB特征的碱性玄武岩和双峰式火成岩。     

Structural studies and their bearing on the Early Precambrian history of the Dharwar tectonic province,southern India

In the Dharwar tectonic province, the Peninsular Gneiss was considered to mark an event separating the deposition of the older supracrustal Sargur Group and the younger supracrustal Dharwar Supergroup. Compelling evidence for the evolution of the Peninsular Gneiss, a polyphase migmatite, spanning over almost a billion years from 3500 Ma to 2500 Ma negates a stratigraphic status for this complex, so that the decisive argument for separating the older and younger supracrustal groups loses its basis. Correlatable sequence of superposed folding in all the supracrustal rocks, the Peninsular Gneiss and the banded granulites, indicate that the gneiss ‘basement’ deformed in a ductile manner along with the cover rocks. An angular unconformity between the Sargur Group and the Dharwar Super-group, suggested from some areas in recent years, has been shown to be untenable on the basis of detailed studies, A number of small enclaves distributed throughout the gneissic terrane, with an earlier deformational, metamorphic and migmatitic history, provide the only clue to the oldest component which has now been extensively reworked.     

澜沧江构造带南段变质岩系锆石U-Pb年代学及构造涵义

澜沧江构造带南段的古老变质岩系因临沧花岗岩基的大面积出露而呈零星分散状出露,该地区是否存在前寒武纪结晶基底和变质岩系的精确时代以及澜沧江构造带变质岩系的变质时限等问题还不是很清楚。本文以变质岩系为研究对象,挑选出锆石颗粒进行U-Pb SHRIMP定年,获得锆石核部U-Pb年龄是1802Ma、1404Ma、1092Ma、906~961Ma、812Ma和727~623Ma,时代为古元古代、中元古代和新元古代,揭示研究区存在前寒武纪的结晶基底,三叠纪(~230Ma)发育区域性岩浆作用事件,破坏改造了其结晶基底;昌宁-耈街剖面近澜沧江岸边花岗质片麻岩的锆石U-Pb谐和年龄为73.9±1.8Ma(MSWD=1.3,N=6),记录澜沧江构造带变质岩经历了晚白垩世变质事件。综合研究认为澜沧江构造带南段存在区域性前寒武纪结晶基底,构造带中昌宁段之变质岩系的变质时间为晚白垩世(85~74Ma),并一直持续到36Ma,约32Ma之后构造带发生走滑运动,变质事件明显早于走滑运动事件。     

大别地块超高压变质省的构造变形研究

构造解析的基本目的是建立构造事件造成的地质体几何学、运动学、动力学和流变学。大陆碰撞造山带内含柯石英及微粒金刚石等矿物组合的超高压（ＵＨＰ） 变质岩的形成和折返,是极为复杂的地球动力学过程。与世界上已知大多数超高压变质带相似,中国大别地块内超高压变质省现今观察到的主体构造形式,主要是在碰撞或超高压变质峰期后伸展体制下形成的。通过对大别超高压变质省内伸展组构及挤压（ 碰撞） 组构的鉴别、分析,结合有关超高压变质带构造学研究领域的简略综述指出,在揭示超高压变质带的形成及折返动力学过程中,构造解析的思维和工作方法是行之有效的     

佳木斯地块中部岩浆岩锆石U-Pb年代学、地球化学及其大地构造意义

佳木斯地块中部桦南隆起区广泛发育古生代-中生代岩浆岩,这些岩石的成因对深入探讨中亚造山带的形成演化具有重要的指示意义。LA-ICP-MS U-Pb定年和地球化学测试分析结果表明,研究区广泛分布的片麻状花岗闪长岩形成于中二叠世(267±2Ma),具有I型花岗岩的地球化学特征,表明其岩浆起源可能和俯冲板片产生的熔体有关,形成于岛弧构造环境。而正长花岗岩形成于中三叠世(244±2Ma),地球化学揭示其岩浆起源于下部陆壳物质的部分熔融,具有同碰撞花岗岩的地球化学特点。上述特征表明,研究区在中二叠世处于大陆边缘的构造背景,与古亚洲洋板块俯冲于佳木斯板块之下的构造作用相关,而中三叠世处于同碰撞的构造环境,俯冲此时已经消失,古亚洲洋已经最终闭合,因此三叠纪应该为中亚造山带重要的地质转折期。     

Very fast exhumation of high-pressure metamorphic rocks with excess Ar and inherited Sr, Betic Cordilleras, southern Spain

In order to attempt to further constrain the age of the early Alpine tectonic evolution of the Mulhacén Complex and to explore the influence of inherited isotopes, micas from a small number of well-characterised rocks from the Sierra de los Filábres, with a penetrative tectonic fabric related to the exhumation of eclogite-facies metamorphic rocks, were selected for ⁴⁰Ar/³⁹Ar and Rb–Sr dating.

A single phengite grain from an amphibolite yielded an ⁴⁰Ar/³⁹Ar laser step heating plateau age of 86.9±1.2 Ma (2σ; 70% ³⁹Ar released) and an inverse isochron age of 86.2±2.4 Ma with an ³⁶Ar/⁴⁰Ar intercept within error of the atmospheric value. Induction furnace step heating of a biotite separate from a gabbro relic in an eclogite yielded a weighted mean age of 173.2±6.3 Ma (2σ; 95% ³⁹Ar released). These ages are diagnostic of excess argon (⁴⁰Ar_XS) incorporation, as they are older than independent age estimates for the timing of eclogite-facies metamorphism and intrusion of the gabbros. ⁴⁰Ar_XS incorporation probably resulted from restricted fluid mobility in the magmatic rocks during their metamorphic recrystallisation.

Rb–Sr whole-rock–phengite ages of graphite-bearing mica schists from Paleozoic rocks (Secano unit) show a dramatic variation (66.1±3.2, 40.6±2.6 and 14.1±2.2 Ma). An albite chlorite mica schist from the Mesozoic series of the Nevado–Lubrín unit has a whole-rock–mica–albite age of 17.2±1.9 Ma, which is within error of an ⁴⁰Ar/³⁹Ar plateau age published previously and of the youngest Rb–Sr age of the Paleozoic series obtained in this study. The significant spread in Rb–Sr ages implies that progressive partial resetting of an older isotopic system has occurred. The microstructure of the samples with pre-Miocene Rb–Sr ages reveals incomplete recrystallisation of white mica and inhibited grain growth due to the presence of graphite particles. This interpretation agrees with previously published, disturbed and slightly dome-shaped ⁴⁰Ar/³⁹Ar age spectra that may point similarly to the presence of an older isotope component. The progressively reset Rb–Sr system is a relic of Variscan metamorphism of the Paleozoic series of the Mulhacén Complex. In contrast, the origin of the ca. 17.2 Ma old sample from the Mesozoic series precludes any isotopic inheritance, in agreement with its pervasive tectono-metamorphic recrystallisation during the Miocene.

Exhumation of the eclogite-facies Mulhacén Complex occurred in two stages with contrasting rates of about 22.5 mm/year during the early phase and 9–10 mm/year during the late phase; the latter with a cooling rate in the order of 330 °C/Ma.     

Partitioning and budget of Li, Be and B in high-pressure metamorphic rocks

Partitioning and budget of Li, Be and B in high-pressure metamorphic rocks from the island of Syros (Greece) were studied, using secondary ion mass spectrometry, inductively coupled plasma optical emission spectrometry and prompt gamma neutron activation analysis. Partitioning between coexisting mineral phases was found to be rather constant and independent of element concentrations. For several mineral pairs, apparent partition coefficients vary in a narrow range, while concentrations vary by more than an order of magnitude. Hence, it was possible to establish sets of inter-mineral partition coefficients for Li, Be and B among 15 different high-pressure minerals. This data set provides important information on the behaviour of the light elements in different lithologies within subducting slabs from the onset of metamorphism to the eclogite stage. It is essential for modelling trace-element and isotope fractionation during subduction and dehydration of oceanic crust.     

Exhumation of high-pressure rocks of the Kokchetav massif: facts and models

The exhumation of ultrahigh-pressure (UHP) metamorphic units from depths more than 100-120 km is one of the most intriguing questions in modern petrology and geodynamics. We use the diamondiferous Kumdy-Kol domain in the Kokchetav Massif to show that exhumation models should take into consideration initially high uplift velocities (from 20 down to 6 cm/year) and the absence of the deformation of UHP assemblages. The high rate of exhumation are indicated by ion microprobe (SHRIMP) dating of zircons from diamondiferous rocks and supported by the low degree of nitrogen aggregation in metamorphic diamonds.Diamondiferous rocks in the Kumdy-Kol domain occur as steeply dipping (60°-80°) thin slices (few hundred metres) within granite-gneiss. Using geological, petrological and isotopic-geochemical data, we show that partial melting of diamondiferous metamorphic rocks occurred; a very important factor which has not been taken into account in previous models.Deformation of diamondiferous rocks at Kumdy-Kol is insignificant; diamond inclusions in garnet are often intergrown with mica crystals carrying no traces of deformation. All these facts could be explained by partial melting of metapelites and granitic rocks in the Kumdy-Kol domain. The presence of melt is responsible for an essential reduction of viscosity and a density difference (Δρ) between crustal rocks and mantle material and reduced friction between the upwelling crustal block, the subducting and overriding plates. Besides Δρ, the exhumation rate seems to depend on internal pressure in the subducting continental crustal block which can be regarded as a viscous layer between subducting continental lithosphere and surrounding mantle.We construct different models for the three stages of exhumation: a model similar to “corner flow” for the first superfast exhumation stage, an intermediate stage of extension (most important from structural point of view) and a very low rate of exhumation in final diapir+erosional uplift.     

浙江龙泉地区变质基性岩年代学、地球化学特征及构造意义

浙西南龙泉地区集中出露一套中深变质岩系,是华夏地块的重要组成部分,对其形成时代和成岩构造属性等问题历来存在争议。本文通过对龙泉变质岩中变质基性岩的地球化学研究,认为这些岩石的原岩成岩环境至少有两类:Ⅰ类岩石稀土配分曲线、微量元素蛛网图特征均显示与IAB的相似性,微量元素比值和图解判别均指示这套岩石形成于与俯冲有关的岛弧构造环境;Ⅱ类岩石稀土配分曲线和微量元素蛛网图均与OIB有相似性,微量元素比值和图解判别也指示这套岩石形成于与俯冲无关的OIB构造环境。多种不同构造属性的岩石共生,佐证了原龙泉岩群变质岩系为一形成于早古生代的俯冲增生杂岩。变质基性岩锆石U-Pb测年获得其峰期变质时间为404～402Ma。龙泉俯冲增生杂岩的厘定对重新认识丽水-余姚断裂带构造属性、区域构造格架的建立以及进一步分析华夏造山系物质组成与结构提供了新资料。     

赣北星子群变质岩的原岩恢复及其形成构造环境判别

对星子群变质岩的原岩性质及其形成的构造环境研究表明，星子群变质岩中的片岩和变粒岩的原岩是沉积岩，其中云母片岩的原岩为粘土岩，石英片岩和变粒岩的原岩是杂砂岩或亚杂砂岩。斜长角闪岩、角闪片岩和榴闪岩的原岩为基性火山岩。变质沉积岩的形成构造环境判别结果表明，它们形成于活动大陆边缘环境。而变质基性火山岩属于岛弧拉斑玄武岩与大洋拉斑玄武岩的过渡类型，它们形成于拉张盆地。     

New insights into the history and origin of the southern Maya block,SE México: U–Pb–SHRIMP zircon geochronology from metamorphic rocks of the Chiapas massif

The histories of the pre-Mesozoic landmasses in southern México and their connections with Laurentia, Gondwana, and among themselves are crucial for the understanding of the Late Paleozoic assembly of Pangea. The Permian igneous and metamorphic rocks from the Chiapas massif as part of the southern Maya block, México, were dated by U–Pb zircon geochronology employing the SHRIMP (sensitive high resolution ion microprobe) facility at Stanford University. The Chiapas massif is composed of deformed granitoids and orthogneisses with inliers of metasedimentary rocks. SHRIMP data from an anatectic orthogneiss demonstrate that the Chiapas massif was part of a Permian (∼ 272 Ma) active continental margin established on the Pacific margin of Gondwana after the Ouachita orogeny. Latest Permian (252–254 Ma) medium- to high-grade metamorphism and deformation affected the entire Chiapas massif, resulting in anatexis and intrusion of syntectonic granitoids. This unique orogenic event is interpreted as the result of compression due to flat subduction and accretionary tectonics. SHRIMP data of zircon cores from a metapelite from the NE Chiapas massif yielded a single Grenvillian source for sediments. The majority of the zircon cores from a para-amphibolite from the SE part of the massif yielded either 1.0–1.2 or 1.4–1.5 Ga sources, indicating provenance from South American Sunsás and Rondonian-San Ignacio provinces.     

桐柏-大别山区高压变质相的构造配置

作为华北和扬子陆块间的碰撞造山带桐柏大别山区以发育高压、超高压变质带为特征,从南到北变质相从低级到高级,代表俯冲带深度不同的变质产物,整体形成高压变质相系列。不过现今各变质相岩石的分布极受后期地壳规模的伸展构造控制,大别杂岩的穹隆作用更使高压变质相带的空间分布复杂化。超高压变质岩今日多呈大小不等的块体嵌布于相对低压的大别杂岩之内,造山带根部物质的热软化,使许多深层地幔物质得以像挤牙膏一样挤出于大别杂岩内。它们之中广泛发育着减压退变质的显微结构,与大别杂岩内一些麻粒岩相表壳岩所保存的减压退变质证迹一样,同是挤出作用和碰撞后隆升的构造证迹。高压相系的发育使南桐柏山和大别山迥然不同于桐商（ 商丹） 断裂以北的北秦岭北淮阳变质带。新近发表的同位素年代学（４０Ａｒ ３９ Ａｒ） 资料：３１６ ～４３４ Ｍａ ,已证明北秦岭是古生代变质带,它与桐柏－ 大别印支期碰撞造山带差异甚大。这两个变质地温梯度差异甚大的变质地体的拼合,说明华北和扬子陆块碰撞的主缝合带是商丹－ 桐商断裂带     

东昆仑前寒武纪基底变质岩系的锆石SHRIMP年龄及其构造意义

东昆仑地区有一系列前寒武纪变质基底岩系出露 ,这些基底岩块可以划分为两类 :北部基底以太古宙—古元古代的白沙河岩群和中元古代的小庙岩群为代表 ,南部基底以古、中元古代苦海杂岩为代表。对北部基底岩系小庙岩群变质碎屑岩系的锆石U PbSHRIMP年龄分析结果显示小庙岩群(Pt2 x)碎屑物源区是年龄大于 2 4亿年的岩石 ,2 4～ 2 5亿年的碎屑锆石的群组年龄很可能反映了小庙岩群源区的一期变质作用时间。个别 32亿年的碎屑锆石年龄指示源区存在古太古代的陆核。变质锆石及深熔成因的锆石给出的 10 35～ 10 74Ma群组年龄是小庙岩群的主期构造热事件时间 ,反映以清水泉蛇绿岩为代表的中元古代洋盆的闭合和南北不同基底块体的愈合 ,是Rodinia大陆聚合事件在东昆仑地区的表现。     

西藏南部南迦巴瓦地区变泥质岩和含石榴子石淡色花岗岩及其对构造事件的约束

西藏南部南迦巴瓦地区位于喜马拉雅造山带的东端,该区保留了大量新生代变质和深熔作用记录,是研究喜马拉雅碰撞造山带演化过程的关键地区。本文在野外地质调查和室内显微岩石学观察基础上,通过锆石 U-Pb 年代学和全岩地球化学研究,分析南迦巴瓦地区变质岩和淡色花岗岩的年代学意义和地球化学特征。研究区露头可见含石榴子石淡色花岗岩平行片麻理侵入到变泥质岩中,该变泥质岩为含石榴子石的黑云斜长片麻岩,其继承锆石年龄为1617.0~565.5 Ma,还记录了28.1~16.4 Ma的新生代变质作用。含石榴子石淡色花岗岩形成于23.3±0.4 Ma,经历了18.4~8.6 Ma的岩浆事件,是南迦巴瓦地区构造减压过程中变质岩多次部分熔融的产物。该淡色花岗岩具有较高的SiO2、K2O、FeOT和铝饱和指数A/CNK,较低的Al2O3、CaO、Na2O和Na2O/K2O,为过铝质富钾花岗岩。其富集Rb、K、Pb,亏损Ba、Sr、Nb、Ta、Nd、Zr、Ti,具有强烈的Eu负异常和海鸥状稀土分布模式,较高的Rb/Sr、Nb/Ta和较低的Zr/Hf,可能与发育大量的石榴子石并经历了较高程度的斜长石、独居石分离结晶作用和熔体结构改变有关。     

大别山造山带高压-超高压变质岩的折返过程

高压-超高压变质岩的形成与折返是地球动力学过程,虽人眼不能见及,但在岩石中留下种种记录。本文以大别山为例对高压-超高压变质岩的折返过程进行了探讨。文中(1) 综合构造地质学和地球物理学观测资料,剖析了大别山造山带的结构构造,指出了作为高压-超高压变质岩折返通道的莫霍面断口和折返形成的挤压穹隆地壳结构;(2) 综合变质岩石学P-T-t轨迹研究资料,追踪高压-超高压变质岩在地下的运动轨迹,揭示了其在俯冲-折返过程不同时段经过的深度和运动速率,并指出其向南的折返极性;(3) 结合沉积岩石学研究资料,利用合肥盆地中砾岩成分和碎屑白云母Si含量记录,限定了高压-超高压变质岩折返至地表的时间为中侏罗世前。基于上述资料,本文重建了大别山高压-超高压变质岩的三阶段折返过程,指出大别山包含三个岩片,于230Ma左右分别从不同深度快速折返,折返速率为3~10km/Ma,于210Ma左右进入中地壳,并于180Ma左右快速折返(折返速率为3km/Ma左右) 至上地壳,白垩纪折返速率极慢(0.1km/Ma左右)。