Receiver function study of the crustal structure of Northeast China:Seismic evidence for a mantle upwelling beneath the eastern flank of the Songliao Basin and the Changbaishan region

Northeast China is a unique place to study intra-plate volcanism. We analyzed P-wave receiver function data recorded by 111 permanent broadband seismic stations in Northeast China. The results show that the crustal thickness varies from 27.9 km beneath the eastern flank of the Songliao Basin to 40.7 km beneath the Great Xing＇an Range region. The large depth variations of the Moho can be largely but not completely explained by surface topography. The residual Moho depth calculated based on the Airy＇s isostasy model indicates that the Moho is dynamically uplifted by 〈3 km beneath the eastern flank of the Songliao Basin and the Changbaishan region. We suggest that a mantle upwelling, which has been proposed by several recent seismic studies, might have caused the uplift.

The deep mantle upwelling beneath the northwestern South China Sea:Insights from the time-varying residual subsidence in the Qiongdongnan Basin

Deep hot mantle upwelling is widely revealed around the Qiongdongnan Basin on the northwestern South China Sea margin. However, when and how it influenced the hyper-extended basin is unclear.To resolve these issues, a detailed analysis of the Cenozoic time-varying residual subsidence derived by subtracting the predicted subsidence from the backstripped subsidence was performed along a new seismic reflection line in the western Qiongdongnan Basin. For the first time, a method is proposed to calculate the time-varying strain rates constrained by the faults growth rates, on basis of which, the predicted basement subsidence is obtained with a basin-and lithosphere-scale coupled finite extension model, and the backstripped subsidence is accurately recovered with a modified technique of backstripping to eliminate the effects of later episodes of rifting on earlier sediment thickness. Results show no residual subsidence in 45–28.4 Ma. But after 28.4 Ma, negative residual subsidence occurred, reached and remained ca. -1000 m during 23–11.6 Ma, and reduced dramatically after 11.6 Ma. In the syn-rift period(45–23 Ma), the residual subsidence is ca. -1000 m, however in the post-rift period(23–0 Ma),it is positive of ca. 300 to 1300 m increasing southeastwards. These results suggest that the syn-rift subsidence deficit commenced at 28.4 Ma, while the post-rift excess subsidence occurred after 11.6 Ma.Combined with previous studies, it is inferred that the opposite residual subsidence in the syn-and post-rift periods with similar large wavelengths(>10^(2) km) and km-scale amplitudes are the results of transient dynamic topography induced by deep mantle upwelling beneath the central QDNB, which started to influence the basin at ca. 28.4 Ma, continued into the Middle Miocene, and decayed at ca.11.6 Ma. The initial mantle upwelling with significant dynamic uplift had precipitated considerable continental extension and faulting in the Late Oligocene(28.4–23 Ma). After ca. 11.6 Ma, strong mantle upwelling probably occurred beneath the Leizhou–Hainan area to form vast basaltic lava flow.

Behavior of Siderophile and Chalcophile Elements in the Subcontinental Lithospheric Mantle beneath the Changbaishan Volcano,NE China

The mantle xenoliths in the Quaternary ChangbaishanVolcano in southern Jilin Province contain spinel-facies lherzolites. The equilibration temperatures for these samples range from 902℃ to 1064℃ based on the two-pyroxene thermometer of Brey and Kohler （1990）, and using the oxybarometry of Nell and Wood （1991）, the oxidation state was estimated from FMQ-1.32 to -0.38 with an average value of FMQ-0.81 （n = 8）, which is comparable to that of abyssal peridotites and the asthenospheric mantle. ThefO2 values of peridotites, together with their bulk rock compositions （e.g., Mg#, Al2O3, CaO, Ni, Co, Cr） and mineral compositions （e.g., Mg# of olivine and pyroxene, Cr# [=Cr/ [Cr＋Al]] and Mg# [=Mg/[Mg＋Fe2~] of spinel）, suggest that the present-day subcontinental lithospheric mantle （SCLM） beneath the Changbaishan Volcano most likely formed from an upwelling asthenosphere at some time after the late Mesozoic and has undergone a low degree of partial melting. The studied lherzolite xenoliths show low concentrations of S, Cu, and platinum group elements （PGE）, which plot a flat pattern on primitive-mantle normalized diagram. Very low concentrations in our samples suggest that PGEs occur as alloys or hosted by silicate and oxide minerals. The compositions of the studied samples are similar to those of peridotite xenoliths in the Longgang volcanic field （LVF） in their mineralogy and bulk rock compositions including the abundance of chalcophile and siderophile elements. However, they are distinctly different from those of peridotite xenoliths in other areas of the North China Craton （NCC） in terms of Cu, S and PGE. Our data suggest that the SCLM underlying the northeastern part of the NCC may represent a distinct unit of the newly formed lithospberic mantle.

Seismic evidence for the existence of an entrained mantle flow coupling the northward advancing Indian plate under Tibet

The Tibetan Plateau, known as "the roof of the world" and "the third pole of the earth", is a product of the collision between India and Asia during the last ～50 Ma.The regional tectonics–in particular, growth and expansion of the plateau–has been attributed primarily to deformation within the lithosphere.The role and pattern of the underlying asthenospheric flow, however, remain mostly unaddressed.In light of recent seismic tomographic images and published seismic anisotropic descriptions of the upper mantle, here we propose that an entrained mantle flow is likely to exist under Tibet, induced by the northward advancing Indian plate.The direction of mantle flow is characterized by a gradual rotation from northward in the south to eastward in the north as a result of deflection by the deep root of the Tarim block.The presence of an underlying mantle flow is not only able to account for the west-east oriented fast-axis of seismic anisotropy in northern Tibet, but can also adequately explain the sporadic null splitting in southern Tibet.Specifically, the null splitting results, at least in part, from upwellings of asthenospheric flow through tears of the underthrusting Indian plate that have been revealed by various seismic observations.The mantle flow may in turn promote the block extrusion under Tibet that has been observed in GPS measurements; hot asthenospheric upwellings may also lead to widespread post-collisional magmatism in southern Tibet.

An Asthenospheric Upwelling Beneath Central Mongolia——Implications for Intraplate Surface Uplift and Volcanism

Intraplate processes,such as continental surface uplift and intraplate volcanism,are enigmatic and the underlying mechanisms responsible are not fully understood.Central Mongolia is an ideal natural laboratory for studying such processes because of its location in the continental interior far from tectonic plate boundaries.

Characteristics of mantle degassing and deep-seated geological structures in different typical fault zones of China

In this paper a comprehensive tracing study is conducted on mantle degassing and deep-seated geological structures in different types of fault zones in the continent of China based on the helium isotope data, coupled with some indices such as CO2/3He, CH4/3He and 40Ar/36Ar, and geological tectonics data. There are four representative types of fault zones: (1) Lithospheric fault zones in the extensional tectonic environment are characterized by a small Earth’s crust thickness, a lower CH4/3He-high R and lower CO2/3He-high R system, the strongest mantle de- gassing, and the dominance of mantle fluid, as is represented by the Tancheng-Lujiang fault zone. (2) The lithospheric fault zones or the subduction zone in the strongly compresso-tectonic envi- ronment, for instance, the Bangonghu-Nujiang fault zone, are characterized by a huge thick Earth’s crust, with the R/Ra values within the range of 0.43―1.13, and weak mantle degassing with mantle-source helium accounting for 5%―14% of the total. (3) The deep-seated fault zones at the basinal margins of an orogenic belt are characterized by R values being on order of mag- nitude of 10?7, and the CH4/3He values, 109―1010, CO2/3He values, 106―108; as well as much weak mantle degassing. (4) The crustal fault zones in the orogenic belt, such as the Yaojie fault zone (F19), possess a high CH4/3He-low R (10?8) and high CO2/3He-low R system, with no obvi- ous sign of mantle degassing. Studies have shown that the deep-seated huge fault zones are the major channel ways for mantle degassing, the main factors controlling the intensity of mantle degassing are fault depth, tectonic environment and crust thickness; the intensity of mantle de- gassing can reflect the depth and the status of deep-seated tectonic environment of fault, while the geochemical tracing studies of gases can open up a new research approach; upwelling ac- tivity of hydrothermal fluids from the deep interior of the Earth may be one of the driving forces for the formation and evolution of the huge deep fault zones. Piedmont fault zones are the locations where deep-seated tectonic activity and crust/mantle structure are transformed, which are of great significance in understanding the mechanisms of formation of orogenic belts and basins.

鄂尔多斯及周边地区上地幔三维P波速度结构及其构造意义

利用中国地震科学台阵密集流动地震台站和固定地震台站记录的远震P波资料,采用走时层析成像方法反演获得了鄂尔多斯及周边地区上地幔的精细速度结构。结果显示,鄂尔多斯地块下方存在较厚的高速异常,其中西部深度约为180 km,北部约为150 km,中部的局部地区可达300 km,表明鄂尔多斯地块总体上仍保持克拉通特性。鄂尔多斯地块北部相对较薄的岩石圈可能与地幔物质上涌对岩石圈进行了加热和改造有关,其西部岩石圈的减薄可能与青藏高原东北缘上地幔热物质的横向扩展有关。华北克拉通东部地块、中部地块及鄂尔多斯地块东北部的上地幔表现出大范围的低速异常,推测可能与太平洋板块后撤导致的伸展构造背景、滞留板片脱水以及板片前缘局部对流有关。在该地区的伸展背景下,岩石圈或软流圈的熔融物沿着软弱带上涌并形成了包括大同火山在内的火山群。

广东惠州市黄沙洞地区潜在地幔上涌现象及其对高温地热成因影响

广东惠州市黄沙洞地热田位于中国大热流异常区的东南沿海区。2013年首次在该地区钻探发现广东省内温度最高地热井,地热井井口自流水温98.2℃,井底测得最高水温118.2℃。2018年施工的惠热1#于2900 m测得热水温度为127.7℃,井口最高稳定温度118℃,最大流量137 m^(3)/h。深部热储温度采用无蒸汽损失石英温标计算为142.4℃,指示地热资源成藏潜力巨大。本文为探究该地区高温地热成因,结合区域地质构造特征、地球物理信息、岩石地球化学、气体地球化学、深部钻探信息,提出了高温地热区深部潜在地幔物质上涌现象为主要控制因素。研究区处于高重力异常区的北缘,处在线性重力阶梯带上,航磁异常显示深部存在隐伏岩体。高温地热井周边深部软流圈出现一定面积的垂向带状高导低阻体异常,反映可能有大规模的地幔上涌现象,且存在有较高的壳幔热流值,中下地壳可能存在热扰动的地质结构,紫金—博罗及莲花山深大断裂对软流圈的隆起具有一定的控制作用。研究区花岗岩多数显示为变杂砂岩部分熔融,少数为角闪岩和变安山岩部分熔融,指示研究区花岗岩存在地幔物质的加入。研究区浅层地下冷水稀有气体的比值R/Ra(^(4)He/^(20)Ne)(/^(4)He/^(20)Ne)air均大于1,显示出地幔上涌影响。研究区内存在生热率较高的花岗岩体,但出露规模不大,年龄为150 Ma左右,花岗岩生热率虽然较高,但岩体的生热率不足以形成较高的大地热流背景值。惠热1#深部钻探在2000 m发现基性辉长岩脉,与晚侏罗世二长花岗岩侵入接触关系明显,为深部地壳或上地幔的玄武质岩浆经侵入作用形成。黄沙洞地区高温地热的成因主要是软流圈上侵造成的上地幔的热对流。

A three-dimensional Moho depth model beneath the Yemeni highlands and rifted volcanic margins of the Red Sea and Gulf of Aden, Southwest Arabia

Knowing Moho discontinuity undulation is fundamental to understanding mechanisms of lithosphereasthenosphere interaction, extensional tectonism and crustal deformation in volcanic passive margins such as the study area, which is located in the southwestern corner of the Arabian Peninsula bounded by the Red Sea and the Gulf of Aden. In this work, a 3D Moho depth model of the study area is constructed for the first time by inverting gravity data from the Earth Gravitational Model(EGM2008) using the ParkerOldenburg algorithm. This model indicates the shallow zone is situated at depths of 20 km to 24 km beneath coastal plains, whereas the deep zone is located below the plateau at depths of 30 km to 35 km and its deepest part coincides mainly with the Dhamar-Rada ’a Quaternary volcanic field. The results also indicate two channels of hot magmatic materials joining both the Sana’a-Amran Quaternary volcanic field and the Late Miocene Jabal An Nar volcanic area with the Dhamar-Rada’a volcanic field. This conclusion is supported by the widespread geothermal activity(of mantle origin) distributed along these channels,isotopic data, and the upper mantle low velocity zones indicated by earlier studies.

胶东半岛早白垩世地壳隆升剥蚀及其动力学意义

地壳大规模的隆升剥蚀通常是重大地质事件的响应,是地球动力学研究的重要内容之一。本文总结了胶东半岛中生代燕山期不同阶段的花岗岩侵位和金矿形成深度并以此估算了胶东半岛地壳隆升-剥蚀的厚度。结果表明胶东半岛在中生代早白垩世140～110Ma期间,地壳隆升-剥蚀厚约7km,而从早白垩末期至今的110Ma以来,地壳隆升-剥蚀厚度不足4km这表明胶东半岛早白垩世140～110Ma期间曾发生了一次重大地质事件,从而导致了胶东半岛整体快速隆升和剥蚀。该事件与中国东部岩石圈减薄的峰期时限耦合,应是岩石圈减薄的深部动力学过程的浅部响应。隆升-剥蚀的深部过程可能与该区造山加厚地壳的拆沉有关,同时还伴有因古太平洋斜向加速俯冲所引起的地幔上涌共同作用有关。

桂东南富钾岩浆杂岩的Nd同位素组成:华南中生代地幔物质上涌事件

广西东南部罗容杂岩体由辉长岩 -闪长岩 -二长岩 -正长岩组成 ,马山由碱性辉长岩 -正长岩 -花岗闪长岩 -花岗岩组成。它们富 K、富大离子亲石元素 (L IL ) ,无 Nb、Ta负异常等特征表明它们是形成于板内环境的钾玄质侵入岩。罗容杂岩体的各种岩石和马山的基性岩的εNd(T)高 ,为 +1.5到 +3.3,它们是交代地幔部分熔融产生的岩浆在地壳深部分异的产物。马山的花岗岩的εNd(T)稍低 ,为 - 0 .6 ,此岩石单元是由幔源岩浆加热地壳使之熔融的壳源岩浆形成的 ,并伴有与幔源岩浆的混合或交换。此二杂岩体形成于拉张构造环境。地幔物质上涌导致了中生代华南地壳张裂以及华南大规模花岗岩和相关矿床的形成。

广东三水盆地双峰式火山岩:空间展布、岩石学特征及其盆地动力学意义

广东三水盆地内广泛分布有晚白垩纪-始新世火山岩,在化学成分上他们表现为以玄武岩类(SiO2=44.45%～54.46%;K2O+Na2O=3%～6%)和粗面岩-流纹岩(SiO2=59.23%～73.27%;K2O+Na2O=7.5%～12%)为主的双峰式特征。这些火山岩大致由十三期火山活动所形成,其中,早期形成以粗面岩-流纹岩为主的火山岩分布在盆地的边缘,晚期以玄武岩类为主的火山活动出现在盆地的中部。火山岩的时空分布特征反映了随着盆地断陷程度的不断加深导致岩浆由来自浅部岩浆房向深部岩浆房转化的过程。盆地内岩浆岩主要受区域地幔上涌-部分熔融所控制,盆地的断陷过程诱发了不同深度岩浆房内岩浆的喷发。三水盆地火山岩的不对称分布暗示了盆地的东侧向沿海方向的拉伸更加强烈。

大陆岩石圈伸展与斑岩铜矿成矿作用

华南地区自古生代以来一直属于陆内构造演化环境。华南陆内伸展型斑岩铜矿主要形成于早侏罗世、晚侏罗世和早白垩世3个时期,其中晚侏罗世成矿期与华南中生代大规模钨锡成矿作用的形成基本属于一个时期。这些斑岩型矿床的时空分布与同时期的俯冲带在时间上和空间上具有明显不协调的关系,且与俯冲有关的、后俯冲伸展背景以及陆陆碰撞有关的斑岩铜矿的线性分布特点明显不同,尤其是早白垩世斑岩铜矿的分布明显呈面状分布,与华南中生代地壳明显减薄的区域基本一致。虽然这3个时期的斑岩型铜矿在地球化学上显示出弧岩浆岩的特点,但是地质事实证明在这3个时期,华南岩石圈发生了明显的伸展作用,尽管每个时期华南不同地区岩石圈伸展的程度可能不同。因此,我们把华南这种类型的斑岩铜矿归称之为"陆内伸展型"斑岩铜矿。陆内伸展型斑岩铜矿的成矿机制可能是岩石圈伸展背景下软流圈上涌导致陆下岩石圈地幔或者下地壳被改造有关。

中国东部地区深部结构的层析成像

利用中国国家台网60个宽频带地震台站和国际地震中心(ISC)592个台站分别记录的1996—2007和1990—2004的震相报告,从中提取出可供反演使用的远震事件9806个,共12078个高质量的P波初至走时数据,对中国东部地区进行了远震P波层析成像研究。结果显示,在五大连池火山区和大同火山区有明显的低速异常,大同火山源区较深。另外几个明显的低速区分别分布在广东地区、渤海湾地区和长江中下游地区。四川盆地的高速特征和扬子板块的低速特征在纵剖面图像上也较为明显。中国东南部的软流圈中存在大面积的地幔上涌,认为是由板块之间的碰撞俯冲、引起大尺度地幔横向流动造成的,而太平洋板块的作用局限于其俯冲的"远程效应",为大范围的软流圈物质上涌提供了东侧的深部动力条件。

雅鲁藏布大峡谷地质成因

文中总结了雅鲁藏布大峡谷科学探险考察中获得的岩石学和构造地质学认识与区域上已经取得的多学科成果，论述了雅鲁藏布大峡谷得以形成的根本原因是该地区深部存在着地幔上涌体，雅鲁藏布大峡谷和大拐弯的形成是地幔上涌体作用于岩石圈和地表的效应。地幔上涌体的确认揭开了该地区所特有的生物学、气候特征等方面的奥秘，雅鲁藏布大峡谷及其周缘地区是大陆动力学研究、壳 幔动力学、地球系统中各圈层间耦合作用及大陆块体运动学研究最理想的野外实验室。

吉林南部辉南-靖宇地区岩石圈地幔氧化-还原状态及研究意义

吉林省南部辉南-靖宇地区第四纪碱性玄武岩中的地幔包体主要为尖晶石相二辉橄榄岩和方辉橄榄岩。二辉橄榄岩和方辉橄榄岩的平衡温度分别为770～1000℃和850～1025℃,对应的氧逸度(fO2)值分别为FMQ-0.70至+0.34(均值为FMQ-0.06)和FMQ-0.46至+0.05(均值为FMQ-0.15),它们与深海橄榄岩(abyssal peridotites)以及软流圈地幔的fO2相似。橄榄岩的fO2值,连同其全岩化学成分(如Mg#、Al2O3、CaO、Ni、Co和Cr)和矿物化学成分(如橄榄石的Fo、尖晶石的Cr#和Mg#,以及辉石的Mg#)特征,表明辉南-靖宇地区龙岗火山群下面的岩石圈地幔很可能是在晚中生代以来,伴随着华北克拉通和扬子板块的碰撞以及来自东侧太平洋板块和北侧蒙古-额霍次克(Mongolo-Okhotsk)板块分别向西和向南的俯冲叠加,原来的古老岩石圈失衡、塌陷(拆沉?),取而代之的深部软流圈底辟、上涌,又经历了低度部分熔融的产物。

新疆黄山—镜儿泉铜镍成矿带岩浆作用与区域走滑构造的关系

中国产于造山带的铜镍硫化物矿床占有非常重要的地位,例如中亚造山带南缘的一系列矿床及近年来东昆仑造山带发现的夏日哈木超大型镍钴矿床,其探明的镍金属总储量超过300×104 t,约占中国镍金属总储量的1/3,也是世界上造山带发现这类矿床最多的国家。为什么在造山带也能够形成大型—超大型铜镍硫化物矿床?与其相关的大规模幔源岩浆作用有什么特点,发生在造山带构造演化的哪个阶段?是什么机制导致了这样剧烈的镁铁质岩浆作用?对这些关键问题的认识还很模糊。以大中型铜镍硫化物矿床分布最为集中的新疆北天山黄山—镜儿泉成矿带为例,在对国内外研究成果综合归纳和分析的基础上,对上述问题进行探讨。结果表明:准噶尔—哈萨克斯坦地块与塔里木地块碰撞过程中伴随区域性右行走滑,加剧了俯冲洋壳断离和软流圈上涌,并为源自软流圈及交代地幔部分熔融的镁铁质岩浆上侵提供了良好的通道,这些作用的相互叠加为黄山—镜儿泉成矿带的形成创造了很好的条件。

漳州盆地精细壳、幔异常结构与潜在干热岩探讨

漳州盆地与相邻地带的地质构造复杂,水热活动强烈,且伴随着小地震的频频发生.为厘定该盆地深部是否存在潜在的干热岩体,则必须对其壳、幔精细结构和介质物理属性进行探查、研究与探讨.基于漳州盆地壳幔速度结构的格局发现:(1)"灵霄—漳州—安溪"地带的深处存在一低速层,且在漳浦—长泰之间呈现出一"扁豆状"低速体;(2)该低速体北侧为一伸抵上地幔顶部、且向北倾的深大断裂带,若该"扁豆状"低速体为潜在的干热岩,则该深大断裂带可能为深部热液物质上涌与热源补给的通道.

论多因复成矿床的形成机理

结合现代大陆动力学与地球动力学最新理论与研究和应用进展,以及国内几个典型矿床的成矿实例分析,本文重新审视了地台活化区(即地洼区)多因复成矿床的形成机理。作者认为,陈国达先生所研究的地台活化区应特指中国东部或全球类似地区大地构造发展至中生代时期因发生强烈构造–岩浆活动和相关成矿作用而在大陆地壳的表现。由于成矿作用与大地构造发展和/或地球动力学事件具有密切的成因联系,以及由于地壳演化及其大地构造发展阶段还具有独特性或存在某些差异,成矿作用从而表现出多旋回性、特殊性或叠加改造和富化特点;特别是,地台活化区往往包含多大地构造发展阶段,并发生大规模构造变形、岩浆活动和变质作用等构造–岩浆–热(流体)事件,因而这种活化构造区内的成矿作用往往具有多因复成成矿特征,并形成了具有经济意义的、大而富的矿床。实质上,多因复成矿床是多地质过程包括沉积作用、构造变形、岩浆作用和变质作用及伴生的大规模流体事件等耦合的产物,其动力学机制可能来源于(多期或幕式)地幔(柱)对流和上涌及壳?幔相互作用或地幔柱–岩石圈板块相互作用。作者最后指出,多因复成矿床今后的研究重点仍应关注其成矿动力学机制与过程。

吉林东部汪清新生代玄武岩中地幔包体的矿物化学：对该地区岩石圈地幔形成过程的启示

在对吉林汪清新生代玄武岩中橄榄岩包体进行全岩主、微量元素分析的基础上，重点分析了矿物的主、微量元素含量，讨论了华北克拉通东北缘与兴蒙造山带结合部位陆下岩石圈地幔所经历的部分熔融作用和地幔交代作用。橄榄石的Fo、单斜辉石以及尖晶石的Mg#和Cr#均表明该地区陆下岩石圈地幔相对饱满。对地幔橄榄岩透辉石微量元素模拟计算证实，汪清陆下岩石圈地幔经历了1％～3％的部分熔融作用，并遭受后期硅酸盐熔体交代作用。这些地幔特征与中国东部其他地区新生代主体岩石固相似。研究结果证明，吉林汪清中、新生代以来岩石圈性质的转变是在汇聚板块构造体制下通过“拆沉作用”实现的。