东海到南海晚中生代岩浆弧及陆缘汇聚体制综述

晚中生代是古太平洋板块俯冲汇聚东亚大陆的重要时期,这一构造期促发了华南强烈的岩浆活动和陆内变形,相关俯冲杂岩残留在日本西南、中国台湾到婆罗洲一线。华南大陆特别是岩浆岩研究已取得了丰富的成果认识,但缺乏与典型岩浆弧相关的中性岩浆岩发现。位于海陆结合部的东海到南海区域,将是开展晚中生代岩浆弧和弧前盆地等研究的优选地区,目前已陆续发现了相关岩浆岩和沉积记录。开展东海到南海这一区域性的岩浆弧和弧前盆地等研究,同时结合东部俯冲杂岩和华南大陆岩浆岩等成果资料,将有助于形成和完善晚中生代古太平洋俯冲体制和东亚活动大陆边缘的演变模式,也是深化认识我国海域中生界沉积盆地性质及其油气潜力的重要环节。     

中国东南大陆边缘中新生代地幔柱活动的岩石学记录

东南大陆边缘华北陆块与扬子陆块的碰撞造山以及华夏陆块西南部离散块体拼合（230 ～150 Ma） ,是受中特提斯消减作用的影响,其后叠加了古太平洋对古欧亚大陆的伸展—走滑—扩张（145 ～70Ma） ,新生代后研究区进入了大陆裂谷期。从晚中生代—新生代,岩浆来源由上地壳源—中下地壳源—大陆岩石圈地幔源—软流圈地幔源,构成了一个漫长而巨大的构造岩浆旋回。145±5Ma和20±5Ma两次重要的地质转换是联系板块构造和幔柱构造的纽带。     

古林省中—新生代火山岩及其构造环境初析

吉林省地处欧亚大陆板块的东部边缘地带,中生代以来,先后喷发了在岩浆活动性质和构造环境方面都有继承和发展特点的两套火山岩组合。中生代为大陆边缘断陷盆地一山脉构造环境的玄武岩-安山岩-流纹岩组合,新生代为大陆边缘裂谷一断裂构造环境的碱性橄榄玄武岩-拉斑玄武岩-石英粗面岩组合。一、火山岩分区及火山活动时代中生代火山岩可分为三个呈北东向平行分布的火山岩带,西火山岩带分布在白城、洮南以西一带,研究区分布很少,中火山岩带在白城、洮南以东、沈(阳)—哈(尔滨)铁     

松辽盆地形成与演化的深部作用过程--中生代火山岩探针

松辽盆地中生代火山作用从一个侧面揭示了松辽盆地形成与演化历史。松辽盆地中生代火山岩的岩石地球化学研究表明，中生代火山作用的深部过程表现为岩浆源区从逐渐上升到下降的过程。晚侏罗世到早白垩世早期为降温降压过程，表现为等温面逐渐升高，岩石圈伸展速度增大，岩浆源区变浅，盆地演化由断焰向坳陷转化。从早白垩世早期到晚白垩世，则为升温升压过程，等温面下降，岩石圈伸展速度变小，岩浆源区加深，盆地演化进入坳陷期。     

岛弧橄榄岩包体从地幔楔到地壳的旅行

岛弧岩浆作为俯冲作用的产物不仅可以理解大陆地壳的形成,而且对指示大陆地壳的循环作用具有重要的意义。目前关于岛弧岩浆的源区交代作用和分异深度等相关问题一直存在争议。其中,弧岩浆的结晶分异究竟发生在莫霍面附近并伴随着堆晶岩的拆沉,还是发生在更浅的地壳深度?     

莫霍面,下地壳与岩浆作用

美国地质学会近期在意大利北部阿尔卑斯山区召开的关于地壳分异作用的Ｐｅｎｒｏｓｅ会议,以Ｉｖｒｅａ带大陆地壳剖面为样板,讨论了与大陆生长和演化有关的主要过程。文中结合会议情况,评述了岩浆作用与大陆生长、莫霍面演化和地壳动力学的关系。大陆壳特有的成分和大的花岗岩基的形成,要求下地壳有大体积的基性超镁铁质岩存在。这样的基性超镁铁质岩,既可能代表囤积在下地壳的幔源岩浆,也可能是幔源岩浆分异的堆积岩,或是在壳内分异作用过程中产生出花岗质熔体后的残余体。在伸展构造区,幔源岩浆的底侵作用强烈地影响了大陆壳的结构、组成和热状态,而在陆陆碰撞带,由于地壳加厚,下地壳的基性超镁铁质岩石会转变为“榴辉岩”,促进地壳沉没作用和下地壳拆沉作用。由于地壳岩石的榴辉岩相变质作用,地球物理莫霍面与壳幔边界可能并不对应。莫霍面和地壳对岩浆的密度过滤作用,又控制了大陆壳中岩浆的侵位和演化。     

华南构造演化的基本特征

华南至少经历了4期区域规模的大陆动力学过程,除新元古代和晚中生代具有活动陆缘背景外,均在板块内部发生并完成。华夏块体是一个以新元古代岩石为主体构成的前南华纪基底,不是稳定的克拉通古陆,经历了聚合-裂解-再聚合的复杂构造演化。志留纪发生的板内碰撞-拼合事件使华夏块体与扬子块体再次缝合,形成真正统一的中国南方大陆。在震旦纪—早侏罗世期间,整个华南基本处于陆内滨海-浅海-斜坡环境,内部没有切穿岩石圈的断层,没有大规模幔源岩浆和火山喷发的记录,多次构造变形与岩浆活动均在统一的华南岩石圈之上进行。经过早—中侏罗世的构造体制转换,才演化成为晚中生代西太平洋活动大陆边缘的一部分。从早到晚,华南岩石圈经历了多期、幕式的生长,以侧向增生为主(块体拼合),垂向生长为辅(岩浆上侵)。到晚中生代,在古太平洋板块俯冲和陆内伸展的背景下,形成了独特的华南盆岭构造。长期的板内构造演化和多期的花岗岩浆活动使华南具有很好的成矿条件,成为各种矿产与资源的富集区。新元古代南华纪和晚中生代晚侏罗世—早白垩世是华南最有利的成矿期,尤以后者矿种最多、储量最大。     

中国东南部中生代大陆边缘成矿体系和成矿模式

依据成矿作用与板块构造－岩浆的时空演化关系，研究了不同构造－岩浆带内的矿床类型有其组合与矿床的稳定同位素组成特征，将中国东南部中生代大陆边缘的主要矿床分成陆缘火山热液，陆缘弧后火山－沉积与热液，亲弧张裂构造内的岩浆－热液，陆内裂陷火山热液和古地热水环流热液五个成矿系列；并建立了俯冲体制下的大陆边缘成矿体系和成矿模式。     

东南沿海成矿带矿床形成的时间演化规律研究

东南沿海成矿带成矿作用时代与华夏古陆的形成演化 ,特提斯向环太平洋构造成矿域的转换及中新生代中国东部大陆边缘构造活动关系密切。东南沿海成矿作用时代主要与该区中—新元古代古裂谷环境、晚古生代局部裂陷环境、中生代以来的伸展构造环境等拉张构造应力场相对应。中生代以来的成矿作用强度大、持续时间长 ,在东南沿海成矿史占主导地位。根据同位素测年成果厘定出特提斯向环太平洋构造成矿域转换的早期 ,即早侏罗世也存在一期重要的锡、金成矿作用。福建中部地区存在早期成矿被晚中生代构造岩浆热液作用强烈叠加的特征。文中在此基础上归纳了东南沿海成矿区不同时代区域成矿系列演化特征 ,为进一步找矿提供科学依据     

中国东北及邻区大陆边缘构造

中国东北及邻区大陆边缘包括两个构造带。内带由裂解的古陆碎块组成，其北部与古亚洲洋的演化有关，南部与古太平洋演化有关。外带由中生代地体组成。它们是晚古生代到早中生代的洋壳碎块与晚中生代的深海沟堆积组成的混杂体带。古亚洲洋封闭后到现代太平洋板块活动前，即由泥盆纪到侏罗纪曾存在过另一个大洋－古太平洋，其洋底扩张活动形成了上述的构造带。晚侏罗世后本区发育左旋平移断裂系，晚白垩世一早第三纪形成了大陆缘火山－     

Crustal structure of the continental margin of Korea in the East Sea (Japan Sea) from deep seismic sounding data: evidence for rifting affected by the hotter than normal mantle

Despite the various opening models of the southwestern part of the East Sea (Japan Sea) between the Korean Peninsula and the Japan Arc, the continental margin of the Korean Peninsula remains unknown in crustal structure. As a result, continental rifting and subsequent seafloor spreading processes to explain the opening of the East Sea have not been adequately addressed. We investigated crustal and sedimentary velocity structures across the Korean margin into the adjacent Ulleung Basin from multichannel seismic (MCS) reflection and ocean bottom seismometer (OBS) data. The Ulleung Basin shows crustal velocity structure typical of oceanic although its crustal thickness of about 10 km is greater than normal. The continental margin documents rapid transition from continental to oceanic crust, exhibiting a remarkable decrease in crustal thickness accompanied by shallowing of Moho over a distance of about 50 km. The crustal model of the margin is characterized by a high-velocity (up to 7.4 km/s) lower crustal (HVLC) layer that is thicker than 10 km under the slope base and pinches out seawards. The HVLC layer is interpreted as magmatic underplating emplaced during continental rifting in response to high upper mantle temperature. The acoustic basement of the slope base shows an igneous stratigraphy developed by massive volcanic eruption. These features suggest that the evolution of the Korean margin can be explained by the processes occurring at volcanic rifted margins. Global earthquake tomography supports our interpretation by defining the abnormally hot upper mantle across the Korean margin and in the Ulleung Basin.     

Crustal structure of the Levant Basin, eastern Mediterranean

A seismic refraction/wide-angle reflection experiment was undertaken in the Levant Basin, eastern Mediterranean. Two roughly east–west profiles extend from the continental shelf of Israel toward the Levant Basin. The northern profile crosses the Eratosthenes Seamount and the southern profile crosses several distinct magnetic anomalies. The marine operation used 16 ocean bottom seismometers deployed along the profiles with an air gun array and explosive charges as energy sources. The results of this study strongly suggest the existence of oceanic crust under portions of the Levant Basin and continental crust under the Eratosthenes Seamount. The seismic refraction data also indicate a large sedimentary sequence, 10–14 km thick, in the Levant Basin and below the Levant continental margin. Assuming the crust is of Cretaceous age, this gives a fairly high sedimentation rate. The sequence can be divided into several units. A prominent unit is the 4.2 km/s layer, which is probably composed of the Messinian evaporites. Overlying the evaporitic layer are layers composed of Plio–Pleistocene sediments, whose velocity is 2.0 km/s. The refraction profiles and gravity and magnetic models indicate that a transition from a two layer continental to a single-layer oceanic crust takes place along the Levant margin. The transition in the structure along the southern profile is located beyond the continental margin and it is quite gradual. The northern profile, north of the Carmel structure, presents a different structure. The continental crust is much thinner there and the transition in the crustal structure is more rapid. The crustal thinning begins under western Galilee and terminates at the continental slope. The results of the present study indicate that the Levant Basin is composed of distinct crustal units and that the Levant continental margin is divided into at least two provinces of different crustal structure.     

被动大陆边缘张-破裂过程与岩浆活动:南海的归属

岩浆在被动大陆边缘的张-破裂过程中起到决定性作用.南海东北部陆缘发育厚度达10 km的下地壳高速体,其成因机制长期存在争议,影响了对南海东北部陆缘构造归属的界定.为了分析南海共轭陆缘的张破裂机制,本文调研了国内外最新研究进展,系统分析了南海南北陆缘的地壳结构和岩浆活动特点,提出:南海陆缘和海盆中发育有大量岩浆活动,但东西陆缘存在较大差异,底侵高速体东厚西薄,推测为同张裂成因.根据地壳结构与底侵岩浆的量,将被动陆缘划分为5个子类,南海陆缘东侧为多岩浆型,向西变为少岩浆型.东西差异除与伸展速率有关,可能还与东侧陆缘发生了板缘破裂,而西侧陆缘发生了板内破裂有关.      

华北北部古生代大陆地壳增生过程中的岩浆作用与成矿效应

包括前寒武纪克拉通与显生宙造山带两大构造单元的华北北部,古生代时期板块构造体制下古亚洲洋的裂解-扩展-消亡与汇聚大陆边缘的俯冲-碰撞-伸展循环构成了其大陆地壳增生与再造演化的基本图景,并形成了一系列记录这些因果演变连续过程的岩浆侵入与喷发事件。这些物质记录无疑是研究汇聚大陆边缘壳-幔作用和物质交换、大陆地壳演化与大规模成矿作用耦合关系的绝佳窗口。本文在系统总结最近几年积累的年代学和岩石地球化学资料的基础上,以一些带有特定过程印记的标志性岩浆事件为纲领,表征这些古生代岩浆作用形成过程中的地球动力学演变,揭示其所记录的华北北部大陆地壳的多阶段增生与再造演化机制,并初步探讨了有利地球动力学过程制约下的岩浆行为引起的成矿物质聚集效应。     

华北古大陆西南边缘构造格架与成矿系统

根据本区地层、构造、岩浆作用特点,在“系统论”、“活动论”思想指导下,厘定华北古大陆西南边缘的构造格局如下：龙首山陆缘带、河西走廊弧后盆地、北祁连缝合带、中祁连离散型岛弧地体、南祁连弧后盆地、柴达木地块。根据构造发展阶段和成矿作用特点,确定本区成矿系统及组合如下：（１）华北板块西南边缘太古宙—中元古代裂解期前成矿系统：东大山铁成矿组合,金川镍铜成矿组合;（２）柴达木板块北缘中、新元古代裂解成矿系统：桦树沟—柳沟峡铁成矿组合;（３）加里东期活动大陆边缘成矿系统：早期岛弧裂谷成矿组合（白银厂—清水沟铜及多金属成矿组合）,中、晚期岛弧成矿组合（红沟—蛟龙掌铜及多金属成矿组合）,弧后扩张盆地成矿组合（猪咀哑巴—九个泉—石居里铜及多金属成矿组合）,与俯冲作用有关的岩浆热液成矿组合（塔尔沟—小柳沟钨成矿组合,桦树沟—柳沟峡铜成矿组合,大东沟—吊大坂铅锌成矿组合）,洋壳残片成矿组合（大道尔吉铬成矿组合,玉石沟铬成矿组合）;（４）碰撞造山成矿系统：前陆盆地成矿组合（天鹿铜成矿组合）,陆内造山韧性剪切成矿组合（寒山—鹰咀山金成矿组合）。     

Crustal Structure across the Northwestern Margin of South China Sea: Evidence for Magma‐poor Rifting from a Wide‐angle Seismic Profile

We present results from a 484 km wide-angle seismic profile acquired in the northwest part of the South China Sea (SCS) during OBS2006 cruise. The line that runs along a previously acquired multi-channel seismic line (SO49-18) crosses the continental slope of the northern margin, the Northwest Subbasin (NWSB) of the South China Sea, the Zhongsha Massif and partly the oceanic basin of the South China Sea. Seismic sections recorded on 13 ocean-bottom seismometers were used to identify refracted phases from the crustal layer and also reflected phases from the crust-mantle boundary (Moho). Inversion of the traveltimes using a simple start model reveals crustal images in the study area. The velocity model shows that crustal thickness below the continental slope is between 14 and 23 km. The continental part of the line is characterized by gentle landward mantle uplift and an abrupt oceanward one. The velocities in the lower crust do not exceed 6.9 km/s. With the new data we can exclude a high-velocity lower crustal body (velocities above 7.0 km/s) at the location of the line. We conclude that this part of the South China Sea margin developed by a magma-poor rifting. Both, the NWSB and the Southwest Sub-basin (SWSB) reveal velocities typical for oceanic crust with crustal thickness between 5 and 7 km. The Zhongsha Massif in between is extremely stretched with only 6–10 km continental crust left. Crustal velocity is below 6.5 km/s; possibly indicating the absence of the lower crust. Multi-channel seismic profile shows that the Yitongansha Uplift in the slope area and the Zhongsha Massif are only mildly deformed. We considered them as rigid continent blocks which acted as rift shoulders of the main rift subsequently resulting in the formation of the Northwest Sub-basin. The extension was mainly accommodated by a ductile lower crustal flows, which might have been extremely attenuated and flow into the oceanic basin during the spreading stage. We compared the crustal structures along the northern margin and found an east-west thicken trend of the crust below the continent slope. This might be contributed by the east-west sea-floor spreading along the continental margin.     

Observations on the processes of sedimentary basin formation at the margins of Southern Africa

Three variants of Atlantic-type continental margin border Southern Africa. On the west is a rifted margin with a rift phase no more than 50 m.y. in length (180–130 m.y. ago). Sedimentary basin formation was by upbuilding of a sediment terrace during the rift phase and the 30 m.y. following, with outbuilding of the terrace dominant during the Cainozoic. Little downwarping of the oceanic crust occurred but the continent—ocean transition zone appears to be wide.To the south of South Africa is an extensive sheared margin. Basin formation began here in mid-Triassic times with intermontane deposition. Local increase in lower crustal density appears to have accompanied subsidence. Truncation of the basins occurred 130–2100 m.y. ago and in places detrital influx was trapped behind a marginal fracture ridge. No continental rise sedimentary apron and characteristic deep structure were formed in these places. A ‘welding’ of the continental edge appears to have taken place.East of 30° E a complex continental margin with a protracted rift phase exists. From Triassic to Cretaceous times sedimentary basin formation was controlled by an E-W tensional stress regime resulting in N-S horsts and grabens. This was accompanied by vol-canicity and crustal thinning. Other stress systems may have prevailed during continental break-up in the Cretaceous while today the region is seismically active and the tensional stress assumed to be E-W. Following break-up sedimentary basins in Natal Valley and Mozambique Channel encroached southwards.     

Towards an understanding of the southern Appalachian Piedmont crustal transition—A multidisciplinary approach

The Piedmont of the southern Appalachians is characterized by significant geophysical and geological anomalies which indicate there is a major crustal transition. Multiple hypotheses, including a suture zone and a subducted continental margin, have been presented to explain the variations. Although crustal seismic reflection data have provided significant constraints, there are ambiguities inherent in the interpretation of such data. The ambiguities can be reduced by careful consideration of related geophysical and geological observations. Although the importance of correlating crustal reflection data with known geologic features by tracing reflections to drill holes or to the surface cannot be overestimated, only rarely are such correlations possible. In almost all interpretations of crustal reflection structure it is necessary to constrain the model with methods such as seismic refraction, gravity, magnetics, conductivity, and surface geology (including palinspastic reconstructions). When information from these techniques is incorporated into interpretations of the Piedmont crustal structure, the model which appears to be most consistent with the observations is one in which the upper crust of the Piedmont is decoupled from the lower crust, and in which the lower crust thins eastward. The lower crust may be a subducted Precambrian continental margin and its associated transition toward thinner, basinal crust.     

Tectonothermal history of the Hercynian continental crust of the Serre (southern Calabria, Italy) monitored by Rb–Sr biotite resetting

In the Serre mountains of Calabria, Italy, an exposed section of the continental crust, as left by the Hercynian orogeny, consists of intermediate-lower to upper crustal units. Huge masses of granitoids separate the lower from the upper crustal units. Many mica ages have been obtained from metamorphic and plutonic rocks, which have been interpreted as reflecting continuous cooling or discrete Mesozoic events. A reappraisal of previously determined isotopic data integrated with new Rb–Sr biotite ages is presented and assessed at regional scale to better constrain the post-Hercynian geological evolution of the continental crust of the Serre. The ages cover a wide span of time and form clusters which fit a model involving magmatic, hydrothermal and tectonic events preceding and accompanying the opening and closure of the Tethyan ocean.     

从岩石Sm—Nd同位素模式年龄论北秦岭地壳增生和地壳深部性质

北秦岭各岩类１１６个样品Ｓｍ－Ｎｄ同位素模式年龄（ｔＤＭ）变化于０．９～２．４Ｇａ之间，反映北秦岭地壳主要形成于元古代，０．９Ｇａ之后没有明显大规模新生地壳的形成。在Ｎｄ模式年龄分布图上出现２．０５Ｇａ、１．４０Ｇａ和１．０５Ｇａ三个明显的峰值，它们相应地代表北秦岭地壳的三个增生期。与华北克拉通南缘地壳存在２．６５Ｇａ、２．１０Ｇａ和１．４０Ｇａ三个增生期相对比，表明从华北克拉通南缘到北秦岭，地壳侧向增生是逐渐发展的，这是一个统一典型陆块的地壳增长过程，而北秦岭原来应属于华北的一部分。另外，从北秦岭花岗岩揭示的北秦岭地壳深部性质看，北秦岭地壳深部在１．０Ｇａ～１．２Ｇａ左右的板底垫托作用是相当明显的，而在晚古生代后可能又受到区域折离层作用的影响。