极地峡湾有机碳来源和埋藏研究进展

万霞, 张海龙, 肖晓彤

万霞,张海龙,肖晓彤. 极地峡湾有机碳来源和埋藏研究进展[J]. 海洋地质与第四纪地质,2022,42(4): 73-83. DOI: 10.16562/j.cnki.0256-1492.2022021401
引用本文: 万霞,张海龙,肖晓彤. 极地峡湾有机碳来源和埋藏研究进展[J]. 海洋地质与第四纪地质,2022,42(4): 73-83. DOI: 10.16562/j.cnki.0256-1492.2022021401
WAN Xia,ZHANG Hailong,XIAO Xiaotong. Review of organic carbon source and burial in polar fjords[J]. Marine Geology & Quaternary Geology,2022,42(4):73-83. DOI: 10.16562/j.cnki.0256-1492.2022021401
Citation: WAN Xia,ZHANG Hailong,XIAO Xiaotong. Review of organic carbon source and burial in polar fjords[J]. Marine Geology & Quaternary Geology,2022,42(4):73-83. DOI: 10.16562/j.cnki.0256-1492.2022021401

极地峡湾有机碳来源和埋藏研究进展

基金项目: 国家自然科学基金项目“北冰洋西部过去130 ka海冰演变记录及其对碳循环的影响”(41876214),“极地海洋地球化学:北极海冰演变历史及驱动机制” (42022047);青岛海洋科学与技术试点国家实验室开放基金-青年培育“北冰洋边缘海有机碳来源和埋藏”(LMEES-YTSP-2018-02-05);中央高校基本科研业务费-优青培育计划“极地海洋有机地球化学” (201841009)
详细信息
    作者简介:

    万霞(1997—),女,硕士研究生,主要从事海洋有机地球化学研究,E-mail:wanxiaouc@163.com

    通讯作者:

    张海龙(1981—),男,博士,高级实验师,主要从事海洋有机地球化学研究,E-mail:zhanghailong@ouc.edu.cn

  • 中图分类号: P736.2

Review of organic carbon source and burial in polar fjords

  • 摘要: 峡湾是开阔海洋与陆地生态系统重要的连接区域,在全球气候变化的背景下,峡湾的生物地球化学过程正发生剧烈的变化。峡湾的特殊地形以及生物地球化学特性使其成为有机碳埋藏和储存的重要区域。研究表明,全球峡湾的平均有机碳累积速率高达54 gC·m−2·a−1,有机碳埋藏量为18×1012 gC·a−1,约占全球海洋有机碳埋藏量的11%,有巨大的储碳潜力。极地峡湾由于存在冰川作用,其沉积有机碳的输入、迁移转化和埋藏呈现与温带峡湾不同的特征。极地峡湾湾内以及各峡湾之间的沉积有机碳来源、组成和累积、埋藏速率均存在空间差异,湾内表现为由峡湾前端向湾口方向的梯度变化;各峡湾之间表现为有冰川的峡湾比无冰川的峡湾有更高的碳累积速率;沉积有机碳组成差异受到淡水和海水输入的影响。厘清峡湾沉积有机碳的来源对认识峡湾有机碳埋藏至关重要,通过测定总有机碳及单体化合物放射性碳同位素可实现对不同来源有机碳的定量估算。全球变暖使冰川快速消融,导致极地峡湾表现出不同的有机碳累积或埋藏特征,而在全球碳循环中,极地峡湾捕获和埋藏有机碳的能力是否能适应全球气候变化变得愈发重要。
    Abstract: Fjords are an important interface between the open ocean and terrestrial ecosystems. In the context of global climate change, the biogeochemical processes in fjords are undergoing dramatic changes. The special topography and biogeochemical properties of fjord make it an important ecosystem for organic carbon (OC) burial and storage. Studies have shown that the average OC accumulation rate in the global fjords is as high as 54 gC·m−2·a−1, and the OC burial amount is 18×1012 gC·a−1, taking about 11% of the annual global marine OC burial and showing a great carbon storage potential. The input, composition, and accumulation or burial of sedimentary OC in polar fjords are different from those in temperate fjords due to glaciation. There are spatial differences in the source, composition, accumulation, and burial rate of sedimentary OC within and between polar fjords. Within a fjord, there is a gradient change from the front of the fjord to the mouth of the fjord; and between fjords, those with glaciers have higher carbon accumulation rates than those without glaciers. In addition, the composition of sedimentary OC varies due to the influence of different freshwater and seawater inputs. Clarifying the sources of fjord sediment OC is crucial to understanding fjord OC burial. Quantitative estimation of OC from different sources can be achieved by measuring total OC and radiocarbon isotopes of bulk organic matter and the technology of Compound - Specific Radiocarbon Analysis (CSRA). The accumulation or burial of OC in polar fjords shows different characteristics due to the rapid retreating of glaciers by global warming. Global warming is causing rapid glaciers to melt, causing polar fjords to exhibit different organic carbon accumulation or burial characteristics. In the global carbon cycle, it is increasingly important to study whether the ability of polar fjords to capture and bury OC can adapt to global climate change.
  • 南黄海盆地位于扬子板块的东缘,被认为是下扬子块体的主体部分(陈建文等,2018)。由南往北划分为青岛坳陷、崂山隆起和烟台坳陷3个二级构造单元。南黄海盆地作为扬子板块的一部分,经历了多期构造演化过程(图1)。欧亚大陆东部由多个块体拼合而成[1-2],其中华北板块与扬子板块的碰撞拼合过程是地质演化过程中最重要的构造事件之一[3],控制着秦岭-大别-苏鲁造山带的形成,也影响着华北与扬子板块周边盆地的形成、发育以及演化[4]

    图  1  华北-扬子板块碰撞区域大地构造图(a)及南黄海盆地构造单元和本研究中二维地震剖面位置图(b)(修改自文献[5])
    F1. 古洛南-栾川缝合带,F2. 商丹缝合带,F3. 勉略缝合带及其延伸部分,F4. 五莲-烟台断裂带,F5. 江绍断裂带,F6. 郯庐断裂带。
    Figure  1.  Tectonic map of North China and Yangtze collision zone (a), and tectonic unit map of South Yellow Sea and location map of 2D seismic profiles (b)
    From reference [5]. F1. Paleo-Luonan-Luanchuan suture, F2. Shangdan suture, F3. Mianlue suture and its extension, F4. Gulian-Yantai Fault zone, F5. Jiangshao Fault zone, F6. Tanlu Fault zone.

    扬子板块位于华北板块和华夏古陆之间(如图1),由多个小型板块群组成[6-7],发育太古代—元古代结晶基底[8-9],上覆7~10 km厚新元古代—中三叠世海相地层,中生代印支运动强烈变形使海相地层之上被陆相地层不整合覆盖;扬子板块晚三叠世—中侏罗世地层记录了大别-苏鲁造山带形成时期的前陆盆地沉积,而之后早白垩世—古近纪局部地区发育裂谷盆地沉积。

    华北板块位于扬子板块北侧(图1),为中国最古老的构造单元,保存世界上最古老的岩石[10-12]。华北板块太古代—早元古代强烈变质结晶基底被中元古代—早二叠世海相地层广泛覆盖,其上中—新生代陆相沉积位于华北板块内部多个盆地之中。在北部,华北板块与西伯利亚-蒙古板块在晚二叠世发生碰撞,形成了中亚造山带[13-15],而在其西南部以秦岭-大别-苏鲁造山带为界[15-16]

    大别-苏鲁造山带的形成受控于华北-扬子板块碰撞,为世界最大的连续超高压变质带[3, 17]。大别造山带呈北西西向分布[18],自南向北包括高压绿片岩相单元、高压角闪岩相单元、高压榴辉岩相单元、超高压榴辉岩相单元、北大别单元以及北淮阳单元[19]。苏鲁造山带呈北东向展布,其南界为嘉山-响水断裂,北界为五莲-烟台缝合带,苏鲁造山带包含南部的高压绿片岩相单元和北部的超高压榴辉岩单元,可以与大别造山带相关联。

    前人针对华北板块和扬子板块的碰撞过程做了大量的研究工作,提出了多种碰撞模型(图2[5, 20-26],针对华北-扬子板块的俯冲极性和方式、高压/超高压岩石变质作用和折返过程以及郯庐断裂形成等关键问题提出多种观点,然而大多数的研究工作主要集中于陆地,在华北-扬子板块碰撞作用影响的海域开展的工作仍相对匮乏。

    图  2  前人对于华北-扬子板块碰撞模型总结 (据文献[5, 20-26]修改)
    Figure  2.  Previous models for North China-Yangtze collision (from references[5, 20-26])

    关于华北板块与扬子板块的碰撞时间,不同学者在不同研究区域得到了不同的结论[27-32],其中确定大别-苏鲁超高压变质作用发生的时间,是认识大陆碰撞及高压变质岩折返过程的关键。关于该问题,超高压变质作用的时间存在新元古代、早古生代和早中生代三种观点,现如今主流观点认为碰撞发生于晚三叠世,Li et al.(1993)通过Sm-Nd同位素确定超高压变质岩年龄为三叠纪[27],同时Ames et al.(1993)通过U-Pb定年方法得出变质年龄在晚三叠世,认为晚三叠世是扬子-华北板块碰撞的上限时间[31]。作为一个横跨中国东部的巨型造山带,华北-扬子板块在不同时期的碰撞时间具有穿时性,而黄海海域作为造山过程在海域中延伸的位置所在,在不同学者提出的不同碰撞造山模式中,海域中碰撞活动发生的位置及时间均有一定的差异。

    在陆域的研究中,从以郯庐断裂作为转换断层的双向俯冲、扬子板块向北楔入到华北板块之中,到华北板块向南俯冲于华南板块之下,多种不同的大陆拼合模式对于如何整合亚洲大陆东部沉积、深部构造、古地磁等资料提出了挑战(图2)。

    现阶段,主要观点认为苏鲁造山带在海域内对应于千里岩隆起带,而造山带向朝鲜半岛的延伸情况仍然具有一定的争议;除此之外,陆域连云港断裂、嘉山响水等主要断裂与千里岩隆起带各边界断裂的对应关系仍欠缺,哪一条断裂作为华北-扬子板块的主要缝合线尚具有争议[33-36],不同地球物理方法所获得的边界特征具有一定的差异,阻碍了对于海域碰撞缝合带的认识。

    关于华北-扬子板块碰撞在黄海海域的地壳形态,前人地震层析成像结果揭示,苏鲁造山带之下P波速度结构具有复杂的“鳄鱼嘴式”形态,扬子板块上、下地壳拆离,华北板块速度异常体楔入其中,在苏鲁造山带东侧过黄海海域地震层析成像剖面中,华北板块为高速异常体,其上部和下部为扬子板块低速体[36-37],扬子板块上地壳向华北板块仰冲,而俯冲扬子岩石圈部分留存于华北板块之下(图3),该碰撞形态在后续的研究中也得到了其他部分学者的支持[38-39]

    图  3  过苏鲁造山带地震层析成像剖面 (引自文献[37])
    SK-C:华北板块地壳,YZ-UC:扬子板块上地壳,YZ-S:扬子板块下地壳,图中扬子板块呈“鳄鱼嘴”形态,华北板块楔入其中。
    Figure  3.  Tomography profile across Sulu orogeny (from reference[37])
    SK-C. North China crust, YZ-UC. Yangtze upper curust, YZ-S. Yangtze lower crust. The North China block wedged into the crocodile-like Yangtze Block.

    由于不同学者运用不同地质证据来提出自身的模型,并且绝大多数研究主要集中于扬子板块陆域地区,缺乏对于华北-扬子板块拼合带在海域内的延伸情况研究,拼合造山带在海域的深部构造形态仍然没有明确资料进行约束。

    本文对华北-扬子板块碰撞在南黄海海域重力、磁性、地震速度等前人资料进行分析总结,依据项目组近年来在南黄海海域所进行的调查研究工作,通过分析二维地震反射剖面中深部构造信息,对华北-扬子板块碰撞位置以及深部构造格架提供约束。

    下扬子区域构造十分复杂,主要发育近东西—北东、北北东、北西走向构造组成的弧形断裂-褶皱构造系统。西部靠近郯庐断裂带和大别-苏鲁造山带主要以北东走向的褶皱-断裂系统为主,向东构造线逐渐转为北东东—近东西走向[40]

    南黄海海域作为扬子板块和华北板块碰撞带的主要延伸场所具有重要的研究意义。南黄海盆地位于下扬子地块,占据了下扬子地块的主体。根据区域地质特征、重力及磁力异常资料,南黄海盆地在前南华纪结晶基底之上发育,经历了中元古代末四堡运动和新元古代晋宁运动的固结回返后,形成变质岩结晶的基底结构。显生宙以来,南黄海盆地作为扬子地台的一部分,经历了加里东、海西、印支—燕山、喜山等多期构造运动。南黄海盆地根据地层沉积展布特征、构造变形样式、地层保存状况,陆相中—新生代盆地二级构造区可划分为“两坳夹一隆”。由北向南依次为:烟台坳陷、崂山隆起和青岛坳陷(图1)。

    南黄海盆地是由中—古生代海相残留盆地和中—新生代陆相盆地组成的叠合盆地(表1)。震旦纪—志留纪时期南黄海盆地位于扬子板块被动大陆边缘之下,开阔台地相和海陆交互相沉积地层构成了盆地初期发育的基础;自志留纪晚期开始,中国南方发生强烈造山运动,终止了扬子板块自震旦纪以来的海侵旋回历史,扬子板块与华夏古陆碰撞导致江南造山带的形成,区域普遍发生隆升并缺失上志留统和大部分中—下泥盆统,加里东构造期盆地初步形成“两坳夹一隆”的格局;下扬子晚泥盆世开始发生明显海侵,在早二叠世达到顶峰,随后在早二叠世末期转换为挤压汇聚背景,发生大规模区域隆升和海退,南黄海地区由浅海台地变为滨海沼泽环境,沼泽相地层和煤系地层为下扬子地区典型沉积;中三叠世末期发生印支运动,扬子板块-华北板块碰撞拼合形成了大别-苏鲁造山带,强烈的褶皱造山运动导致区域的隆升,形成大量的逆冲推覆构造,南黄海盆地进入前陆盆地演化阶段;从中生代开始,西太平洋构造域逐渐影响盆地演化,至晚侏罗世—早白垩世,下扬子区域广泛发育伸展作用,大范围的陆相断陷盆地沉积叠合于中—古生代海相地层和前陆盆地沉积之上;直至渐新世,南黄海盆地开始坳陷盆地沉积,沉积分布广泛,构造作用减弱,地层平缓且缺乏变形[41]。以华北-扬子板块碰撞为代表的印支构造运动作为南黄海区域最关键的构造活动对海相中—古生界产生了最为强烈的改造,强烈的挤压变形作用影响着区域内地层。

    根据重、磁资料,华北-扬子板块碰撞在下扬子海域具有明显延伸。在区域布格重力异常图中,重力异常具有明显的分带性,南黄海盆地以低异常值为背景,在盆地中部和东部叠加高异常;在盆地北侧千里岩隆起区,主要由一系列高异常连接组成,异常幅值为10~50 mGal,异常带呈北东向展布,其异常特征可以向西追索于苏鲁造山带所在的位置[42]图4)。在重力异常剖面中,千里岩隆起与南北两侧盆地重力异常具有强烈差异,反映了千里岩隆起带位于扬子-华北板块碰撞结合带位置。

    图  4  南黄海海域布格重力异常图及重力异常剖面 (引自文献[42])
    Figure  4.  Bouguer gravity anomaly map with gravity anomaly section of the South Yellow Sea (from reference [42])

    同时,对区域重力异常进行深部的延拓,分别得到向上延拓20 km和50 km的重力异常图,能够反映更大区域尺度上的重力异常特征。在20 km重力异常延拓图中,千里岩隆起区和南黄海盆地东部仍表现为较高重力异常特征;在50 km重力异常延拓图中,千里岩隆起异常区明显减弱,而南黄海盆地东部仍展现为明显的重力高异常带(图5)。

    图  5  南黄海海域布格重力异常上延20 km、50 km延拓图
    Figure  5.  Bouguer 20 km and 50 km prolongation map of South Yellow Sea

    在区域磁异常△T图中,千里岩隆起区为负磁性异常背景下分布着一系列串珠状正异常,异常值为100~250 nT,该异常带将华北与扬子板块分隔开来,此外千里岩隆起带内正异常向西与陆域苏鲁造山带断续连接,推测为苏鲁造山带在海域上的延伸(图6)。

    图  6  南黄海海域磁性异常图及磁性异常剖面 (引自文献[42])
    Figure  6.  Magnetic anomalies map with section of South Yellow Sea (from reference[42])

    据地表露头资料显示,千里岩隆起带高异常值是由变质岩系、火山岩所引起,其中榴辉岩原岩为拉斑玄武岩系列,与大别-苏鲁造山带中榴辉岩相似[43]。崂山隆起东部在重力、磁力异常图上发育有相对高异常值,与千里岩隆起及苏鲁造山带具有一定的相似性。

    为了解华北-扬子板块碰撞在海域内部变形特征,本文选取了南黄海盆地烟台坳陷北缘自西向东三条地震剖面(剖面A-A', B-B', C-C',位置如图1b所示),三条剖面跨过烟台坳陷北部边缘与千里岩隆起的接合部位,能够从地层及构造特征中提取华北-扬子板块碰撞的信息。为反映深部构造特征,本次地震剖面提取了12 s深度的反射信息,能够反映一定深部下地壳和莫霍面的特征。

    在二维反射剖面A-A'中(图7),南黄海盆地基底之上解释出6组反射层,通过区域对比解释,反射层自下而上分别为:南黄海盆地基底顶部反射Tg,Tg反射局部能量较强,大部分能量弱,连续性差,Tg反射层之上为中—古生界海相地层;海相地层之上为印支构造面反射T8,是南黄海盆地内广泛识别的角度不整合界面,代表了下三叠统的顶面,反射多为强振幅、低频,在地震剖面中大部分区域内连续性较好;T8反射层之上为T72反射层,区域对比解释为下白垩统顶界反射,该套地层主要分布于烟台坳陷的北部,反射呈中强振幅、中低频率、连续性较好,为一套互为平行、能量强、连续性较好反射轴;之上T71反射层代表中白垩统赤山组和蒲口组顶界,该波组主要分布于烟台坳陷的东部和中部,为一套平行、能量较强、连续性较好、中低频率的反射;T7反射层被解释为上白垩统或泰州组顶,表现为反射能量中等、连续性较好,在整个烟台坳陷可以追踪对比;解释剖面最上部,T2反射反映了古近系地层的顶面,为整个区域上最大的不整合面,该不整合面为古近系与新近系的分界面,T2反射波组一般由两个相位组成,具有频率高、连续性好、振幅强、波形稳定、相位平行的特征。

    图  7  二维地震剖面A-A'解释图
    Figure  7.  Interpreted section of A-A'

    而在盆地东侧的两条剖面B-B'(图8)及C-C'(图9)中,相比烟台坳陷西侧地震剖面,可以识别出另一套明显的侏罗系顶界反射层T73,位于T8和T72之间,该反射波主要分布于烟台坳陷的东北凹,分布范围很小,表现为中-强振幅、中-低频率、连续性较好。

    图  8  二维地震剖面B-B’解释图
    Figure  8.  Interpreted section of B-B’
    图  9  二维地震剖面C-C’解释图
    Figure  9.  Interpreted section of C-C’

    在西侧地震剖面A-A'中,千里岩隆起与南黄海盆地之间界线明显,地震剖面中接触界线由一系列断续南倾反射组成,推测为断层面的反映,断层向下延伸,并在深度20 km(~6 s)附近断层倾角变缓,向南黄海盆地基底内部延伸,展现出拆离带特征;在千里岩隆起内部,缺乏明显的反射特征,在剖面北侧,千里岩隆起内断续反射发生北倾,呈现一定的背斜形态,自近地表向南延伸进入到盆地中的烟台坳陷基底之中。在剖面A-A'深部,缺乏明显的下地壳反射,在千里岩隆起之下9~10 s深度范围内存在一系列断续反射,为莫霍面反射,莫霍面深度约为30 km;南黄海盆地之下并未识别出莫霍面反射,千里岩隆起之下莫霍面反射并未延伸进入到盆地之下。

    在烟台坳陷东北缘,剖面B-B'及C-C'中可识别出侏罗系,位于边界断裂南侧,侏罗系在横向上厚度变化巨大,在盆地边缘受断裂活动及挤压抬升作用影响,地层厚度明显减薄,而向盆地内部地层厚度显著增大,显示出T8反射层之上的地层为受断层活动影响的生长地层,表明千里岩隆起南缘断裂主要在侏罗纪早期发生一期活动,该时期可以大致约束华北-扬子板块的碰撞时限,碰撞主要发育于不整合界面T8和T73之间。盆地中断裂体系经历了多期活动,主要受新生代伸展活动所影响,在晚三叠世—侏罗纪的华北-扬子板块碰撞时期为挤压逆冲断裂体系,在中生代末期开始发生构造反转,断层受伸展活动影响反转形成正断层。在剖面B-B'和C-C'深部,千里岩隆起和南黄海盆地的边界在深部作为一个拆离带延伸至南黄海盆地之下7~8 s深度范围内。在剖面B-B'中,千里岩隆起之下深度~10 s处具有明显的莫霍面反射,呈断续分布,并且在南黄海盆地之下反射消失,而在剖面C-C'中未识别出莫霍面反射。

    在区域重、磁异常图中(图4, 6),最明显的特征在于存在两个重磁异常高分布区,第一个区域位于南黄海盆地北侧的千里岩隆起带,重力异常呈北东向条带状断续分布,重力异常值为20~40 mGal,该重力异常的分布形态与华北-扬子板块碰撞造山带的分布具有明显的一致性;在重力异常向上延拓20 km及50 km图中(图5),千里岩隆起带所对应的高异常特征仍然存在,表明该异常为相对大尺度区域特征所引起;此外,在重力异常剖面图中,重力异常向深部具有明显的延伸,同样表明该重力异常的形成并不是局部异常所引起。

    在区域磁性异常图中,千里岩隆起地区最明显的特征表现为相对高的磁性异常以串珠状延伸,高异常值为150~200 nT,千里岩隆起与南黄海盆地界线清晰;相比于南黄海区域重力异常特征,千里岩隆起带与陆域地区的连接性更好,具有更明显的从苏鲁造山带延伸至海域地区的特征。

    在南黄海盆地中,崂山隆起区具有明显的高异常,与区域地震剖面对比,可以证实中部崂山隆起具有明显的基底抬升,值得注意的是,崂山隆起重、磁异常值大小与千里岩隆起带异常值大小近似,可能表明千里岩隆起带内物质与扬子板块具有一定相关性。

    南黄海盆地北缘自西向东3条二维地震剖面中,南黄海盆地北部烟台坳陷与千里岩隆起反射特征差异明显,南黄海盆地内浅部地层反射清晰,具有明显沉积盆地特征,与之相比,北侧千里岩隆起带内缺乏清晰反射,但在边界断裂处显示有一系列断续反射,推测为扬子板块深部变质物质折返过程中的痕迹,认为千里岩隆起带内杂乱反射由深部变质岩所引起,而部分空白反射区域则可能由于深部岩浆岩所导致。

    南黄海盆地与千里岩隆起之间的边界断裂在各条地震剖面均为明显的南倾断裂,显示出南黄海盆地在中生代碰撞期间自南向北逆冲的特征,后期在千里岩隆起带内变质物质折返过程中沿前期断裂发生反转。因此,根据前人研究推测,具有3种可能:①扬子板块上地壳与下地壳发生拆离,沿着千里岩隆起仰冲于华北板块(苏鲁造山带)之上,下部岩石圈向下俯冲于华北板块之下,超高压变质岩沿上地壳缝合位置发生折返;②扬子板块整体俯冲于华北板块之下,南倾边界仅仅反映了高压变质岩类似于变质核杂岩的拆离折返过程;③华北板块向南俯冲于扬子板块之下,根据Li et al.的研究结果,其中苏鲁造山带及其延伸千里岩隆起带具有向南北两侧逆冲折返特征[5]

    在本次解释的地震剖面中,千里岩隆起与南黄海盆地以南倾断层接触,在近地表附近为向北仰冲的特征。在地震剖面中千里岩隆起之下具有明显的莫霍面反射,在南黄海盆地之下莫霍面反射消失,而根据陆域地区深反射地震剖面的结果,北侧华北板块的莫霍面反射强度同样比扬子板块内莫霍面反射更强。因此,推测千里岩隆起带深部莫霍面与扬子板块无关,可能为华北板块物质;在千里岩隆起南缘存在一系列南倾反射,并延伸入盆地基底之中,表明千里岩隆起带具有扬子板块亲缘。在以上可能中,本文更倾向于认为至少在碰撞造山带南界处,华北板块向南楔入到南侧扬子板块之中,该“鳄鱼嘴形态”与前人陆域深反射地震剖面、地震层析成像所显示的结果一致[38-39, 44]图10),其中在千里岩隆起之下莫霍面形态平整,并且深度稳定在30 km左右,延伸至南黄海盆地北部莫霍面反射消失,认为南黄海盆地北部莫霍面受到华北-扬子板块碰撞的影响。由于缺乏跨过整个造山带的地震剖面,暂时无法完整约束华北-扬子板块碰撞的完整形态。

    图  10  南黄海海域华北-扬子板块碰撞形态
    Figure  10.  North China-Yangtze collision in the South Yellow Sea

    (1)千里岩隆起带与苏鲁造山带具有相似的重、磁异常特征,华北-扬子板块的碰撞结合位置在黄海海域延伸至千里岩隆起带。

    (2)二维地震剖面中南黄海盆地与千里岩隆起的反射特征具有明显差异,千里岩隆起南界断层作为整个造山带的南界。千里岩隆起带内反射杂乱,南黄海盆地中发育完整中—古生代海相地层以及中—新生代陆相地层,二者之间明显的不整合界线T8代表了强烈的地层缺失,反映了印支运动期间华北与扬子板块的碰撞事件。

    (3)千里岩隆起带南部与南黄海盆地接触界线呈现南倾特征,显示在近地表位置扬子板块呈现向北仰冲的特征,南黄海盆地边界南倾反射在基底深度显示出倾角变缓的趋势,千里岩隆起与南黄海盆地基底岩石具有一定亲缘性。

    (4)千里岩隆起中,约30 km深度附近具有较清晰、平整的莫霍面反射,与前人陆域深反射地震剖面对比,推测千里岩下地壳可能具有华北地壳特征,扬子板块上、下地壳发生拆离,形成“鳄鱼嘴式”结构,华北板块向南楔入到扬子板块之中。

    本研究过程中对于南黄海地区的深部资料有所欠缺,缺乏更为精确的深部资料用以约束扬子板块深部形态。此外,本研究仅涉及南黄海盆地北部边缘二维地震资料,缺乏延伸扬子-苏鲁-华北整个构造域的地震剖面。

  • 图  1   峡湾地形特征示意图[2]

    Figure  1.   Schematic diagram of fjord topographic features [2]

    图  2   南北极峡湾分布图

    蓝色线代表极地气候峡湾,红色线代表亚极地气候峡湾,绿色线代表温带气候峡湾。

    Figure  2.   Distribution of fjords in north and south polar regions

    Polar fjords are shown in blue, subpolar fjords in red, and temperate fjords in green.

    图  3   全球峡湾沉积物有机碳累积速率分布[5, 13-14, 19, 23-25, 27]

    灰色区代表温带峡湾分布区域。

    Figure  3.   Global distribution in accumulation rate of organic carbon in fjords [5, 13-14, 19, 23-25, 27]

    The shaded areas are temperate fjords.

    图  4   弗兰德峡湾和艾蒂安峡湾沉积分布示意图 [30]

    UCDW为深层绕极流上层水体。

    Figure  4.   Illustration of various sediment distribution processes in the Flandres Bay and Etienne [30]

    UCDW: upper circumpolar deep water.

    图  5   影响初级生产力驱动因素的空间示意图[31]

    Figure  5.   Spatial diagram of driving factors affecting primary productivity [31]

    图  6   水文洋流及其对海洋终端冰川和陆地终端冰川峡湾生物地球化学的影响[38]

    Figure  6.   The hydrodynamic circulations and their impact on biogeochemistry of fjords affected by marine-terminating glaciers and by land-terminating glaciers [38]

    图  7   极地峡湾陆源物质运输和生物地球化学过程示意图[22]

    a. 目前的海洋终端冰川,b. 未来的陆地终端冰川。

    Figure  7.   Schematic of material transport and biogeochemical processes by (a) the present marine terminating glaciers and (b) the future land terminating glaciers in polar fjords [22]

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  • 收稿日期:  2022-02-13
  • 修回日期:  2022-03-15
  • 录用日期:  2022-03-19
  • 网络出版日期:  2022-08-08
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