中国东部中新生代火山作用的pTtc模型与岩石圈演化

中国东北和华北地区中新生代火山岩的岩石化学研究表明 ,中新生代火山作用的深部过程均为逆时针的pTt轨迹 ,表现为岩浆源区从逐渐上升到下降的过程。中新生代火山作用的深部过程揭示的岩石圈演化历史为 :早侏罗世至早白垩世早期 ,岩石圈演化主要表现为逐渐减薄的过程 ,直至出现软流圈与地壳直接接触。从早白垩世晚期至中生代末 ,岩石圈演化为一增生过程。第三纪岩石圈演化为减薄过程 ,而到第四纪为岩石圈增生过程。中国东部现代岩石圈地幔是由中生代晚期 (K1末—K3)和第四纪两次增生事件形成的     

http://www.sciencedirect.com/science/article/pii/S1674987112001259

The eastern Pontides orogenic belt provides a window into continental arc magmatism in the Alpine-Himalayan belt.The late Mesozoic-Cenozoic geodynamic evolution of this belt remains controversial.Here we focus on the nature of the transition from the adakitic to non-adakitic magmatism in the Kale area of Gumushane region in NE Turkey where this transition is best preserved.The adakitic lithologies comprise porphyries and hyaloclastites.The porphyries are represented by biotite-rich andesites,hornblende-rich andesite and dacite.The hayaloclastites represent the final stage of adakitic activity and they were generated by eruption/intrusion of adakitic andesitic magma into soft carbonate mud.The non-adakitic lithologies include basaltic-andesitic volcanic and associated pyroclastic rocks. Both rock groups are cutting by basaltic dikes representing the final stage of the Cenozoic magmatism in the study area.We report zircon U-Pb ages of 48.71±0.74 Ma for the adakitic rocks,and 44.68±0.84 Ma for the non-adakitic type,suggesting that there is no significant time gap during the transition from adakitic to non-adakitic magmatism.We evaluate the origin,magma processes and tectonic setting of the magmatism in the southern part of the eastern Pontides orogenic belt.Our results have important bearing on the late Mesozoic-Cenozoic geodynamic evolution of the eastern Mediterranean region.     

西藏冈底斯带石炭纪陆缘裂陷作用：火山岩和地层学证据

冈底斯作为重要的中、新生代岛弧岩浆岩带,历来是青藏高原最热门的地质研究领域,但是对晚古生代火山岩的性质及其形成的构造背景仍缺乏研究。本文在区域地质调查资料的基础上,对冈底斯带石炭纪火山-沉积岩系进行了系统的地层学和岩石地球化学研究,测量了重点剖面,对火山岩进行了常量、微量元素和Sr、Nd、Pb同位素地球化学测试。研究表明,石炭系与下伏泥盆系或前寒武系之间普遍存在不整合或岩性、沉积相的突变面,代表重要的构造转换面。石炭纪的沉积环境大致有两次滨海-深海或深水斜坡-滨海沉积演化旋回,深海-深水斜坡沉积或冰海相含砾板岩与两次火山活动伴生。石炭纪火山岩主要为安山玄武岩和英安岩、流纹岩类,略具双峰式火山岩特点。安山玄武岩类的成分与典型MORB和岛弧玄武岩相比,具有MgO含量低,TiO2、Al2O3、P2O5含量高等特点,稀土和微量元素为LREE和LILE富集型分配模式,与大陆拉斑玄武岩相似。石炭纪酸性火山岩的稀土和微量元素地球化学特征与陆内流纹岩相似。岩石地球化学示踪和地层学研究表明,冈底斯带石炭纪为伸展背景下的冈瓦纳陆缘裂陷环境。火山岩的源区地幔具有典型的Dupal异常,发生过复杂的混合作用,涉及到原始地幔、富集地幔EMII和地壳成分等,说明发生过冈瓦纳古陆壳俯冲、再循环进入古老地幔等过程。玄武岩类成分的某些特殊性,可能与源区混合作用有关。     

中国东南部晚中生代-新生代玄武岩与壳幔作用

中国东南部的火山活动在早中生代时期仅有很小规模,晚中生代最早的、较大规模的岩浆活动始于中侏罗世早期,至早白垩世是火山岩浆活动的鼎盛期,在近100个Ma的时间内形成了大面积分布的晚中生代火山-侵入岩,而在新生代则以面积较小的玄武岩浆喷出活动为主,局限分布于沿海一带。以晚中生代湘南、赣南和闽西南的近EW向火山岩带和浙、闽沿海地区的近NNE向火山岩带,以及新生代近NNE向火山岩带为研究对象,对这些火山岩的地球化学特征对比研究,结合时空分布,讨论了它们的起源及其与壳幔相互作用的关系,以及它们形成的构造环境,其结果显示,EW向晚中生代火山岩带（180～170Ma）的西段玄武岩独立产出,且明显属碱性系列;而中段和东段玄武岩和流纹岩伴生,其中的玄武岩均为亚碱性系列的拉斑玄武岩。它们形成于板内拉张构造环境,是中国东南部特提斯构造域向太平洋构造域转换、晚中生代大规模岩浆作用的序幕。研究表明,该火山岩带自西向东表现出不同程度的壳幔相互作用,玄武岩在成岩过程中有少量陆壳组分加入。NNE向晚中生代火山岩带（130～90Ma）主要为流纹质岩石,安山岩和玄武岩很少。即使是双峰式火山岩也以酸性岩为主,玄武岩仅占全部火山岩体积的30％以下。其中的玄武岩主要属钙碱性系列,少数属拉斑系列。它们形成于火山弧构造环境,是中国东南部受太平洋构造域影响发生大规模火山岩浆作用的主旋律。其中玄武岩岩浆成分受到了较高程度的陆壳物质混染,同时代的中性火山岩是由底侵的玄武岩岩浆和陆壳物质来源的酸性岩浆发生岩浆混合作用而形成的,反映了强烈的壳幔相互作用。NNE向新生代火山岩带,分布在浙闽沿海,以碱性系列玄武岩为主,均含幔源包体,并受NNE向大陆边缘断裂构造的控制。它们形成于板内裂谷环境,是中国东南沿海由晚中生代火山弧构造环境转换为新生代板内裂谷环境的标志,起源于软流圈地幔,并有EMII岩石圈地幔的混合组分,但基本没有受到陆壳物质的混染。     

赤峰地区晚中生代火山岩锆石U-Pb年代学及地球化学特征

内蒙古赤峰地区发育大面积的晚中生代火山岩,是我国东部巨型火山岩带的重要组成部分。锆石U-Pb定年结果显示,火山岩主要形成于晚侏罗世160~147 Ma和早白垩世132~129 Ma两个时期,早期以中酸性火山岩为主,晚期主要为酸性火山岩,局部夹少量的基性火山岩。晚侏罗世早期的安山岩SiO_2含量较低,MgO含量较高,可能是岩石圈地幔部分熔融的产物,流纹岩是安山质熔浆底侵导致下地壳发生部分熔融的产物。晚侏罗世晚期的流纹岩具有与A型花岗岩相似的地球化学特征,表明其形成于伸展构造背景下。早白垩世晚期的流纹岩属于钾玄岩系列,与同时代的玄武岩构成双峰式岩石组合,流纹岩来源于地壳的部分熔融。结合前人研究成果,认为赤峰地区晚中生代的两期火山活动都与蒙古–鄂霍次克缝合带的演化有关,它们分别形成于两次陆壳加厚之后的陆内伸展环境。     

西藏隆巴俄桑地区玄武岩与安山玢岩的地球化学:对班公湖-怒江洋构造演化的启示

狮泉河-永珠-嘉黎蛇绿混杂岩带的构造属性及其与班公湖-怒江缝合带演化的关系,是了解班公湖-怒江洋中生代构造演化的关键.对隆巴俄桑地区的玄武岩和安山玢岩脉开展了岩石地球化学研究.结果表明,玄武岩属拉斑玄武岩系列,富集LREE和大离子亲石元素Rb、Ba、K、Sr、Pb等,亏损高场强元素Nb、Ta、Ti,与岛弧拉斑玄武岩特征一致.安山玢岩脉属拉斑玄武岩系列,有向钙碱系列演化的趋势,富集大离子亲石元素Rb、Ba、K、Sr、Pb、U等,亏损高场强元素Nb、Ta,显示岛弧成因岩浆岩地球化学特征,低ΣREE（11.8×10-6~13.8×10-6）,（La/Yb）_N=0.37~0.43,亏损LREE,与N-MORB相似,具有岛弧岩浆岩（IAB）和正常洋中脊玄武岩（N-MORB）双重特征,与不成熟的弧后盆地玄武岩（BABB）特征一致.综合区域地质资料认为,隆巴俄桑玄武岩和安山玢岩形成的构造环境均与俯冲相关,可能分别形成于班公湖-怒江洋壳南向俯冲消减相关的洋内或者活动大陆边缘的岛弧环境和不成熟的弧后盆地环境,是中侏罗至早白垩世期间班公湖-怒江洋壳南向俯冲消减的再循环的产物.      

Continental margins as global oil and gas accumulation belts: The West Pacific belt

Most present-day oil- and gas-bearing (petroliferous) basins are localized in one of the five global oil and gas accumulation belts confined to continent-ocean transition zones that existed in the Mesozoic and Cenozoic. Two meridional belts are located in the western and eastern peripheral zones of the Pacific Ocean with intense tectonic activity during the major part of the Mesozoic and Cenozoic. The activity was reflected in extension of the continental crust, spreading of the oceanic crust, rapid subsidence of individual crustal blocks, volcanism, and formation of large batholiths and accretionary prisms. In this belt, the fore-arc, back-arc, inter-arc, and marginal riftogenic sedimentary basins are petroliferous.     

浙东早白垩世火山岩组合的地球化学及其成因研究

浙东早白垩世含中性岩的火山岩组合和双峰式火山岩组合的主量元素和微量元素特征对比研究表明，中性火山岩的地球化学特征明显受到伴生的基性和酸性火山岩的影响。它们的微量元素协变关系证实：中性火山岩是由基性岩浆和酸性岩浆混合形成的。双峰式火山岩具有与含中性岩的火山岩组合相类似的主量元素特征，但两者的微量元素特征相差较大。根据东南沿海在早白垩世时期的构造背景是由挤压向伸展拉张转变，以及各种元素具有不同的扩散速度，提出了浙东早白垩世火山岩组合的形成模式：若基性岩浆和酸性岩浆仅进行了部分微量元素的交换，没有来得及发生主量元素的交换，就在伸展拉张的构造背景下喷出地表，则形成双峰式火山岩组合；若基性岩浆与酸性岩浆在地壳深处共存的时间较长，发生一定程度的主量元素交换，则形成偏基性和偏酸性的中性岩浆，若进一步发生化学成分的交换，则可形成典型的安山质岩浆，喷出地表就形成含中性岩的火山岩组合。     

Maestrichtian-Danian andesite series of the Eastern Sikhote Alin: Mineralogy,geochemistry, and petrogenetic aspects

In the stratigraphic sequence of volcanic rocks in the Eastern Sikhote Alin, Maestrichtian-Danian predominantly andesitic volcanics are characterized by a boundary position between the Late Cretaceous subduction, mostly acid volcanic rocks and Cenozoic post-subduction basaltoids. Data on these rocks are important for elucidating the genesis of andesitic magmas, constraining and specifying the geodynamic evolutionary stages in this territory, and revealing the conditions under which the parental melts of these rocks were derived and evolved. Results of detailed mineralogical and geochemical studies, including ICP-MS analysis for trace elements point to a hybrid character of the andesitic volcanic rocks and an important role of fractional crystallization and crustal contamination in their genesis. Although geological evidence (variations in the style of volcanism, the composition of its products, and the character of their distribution) testifies to a change in the geodynamic environment in the Eastern Sikhote Alin in the Maestrichtian-Danian, geochemically the volcanics of this age range are typical subduction-related rocks with anomalously low concentrations of Nb and high contents of K, Ba, Rb, Pb, and U. The volcanic piles contain no adakites, which are indicators of the geodynamic environment in which slab windows are formed. The inconsistency between geological and geochemical indicators of the geodynamic environment suggests certain genetic features of the transitional magmatic series. The parental magmas of the andesitic volcanics were derived from the suprasubduction mantle wedge, which had been metasomatically recycled in the course of the dehydration and melting of the subducted oceanic slab. The increasing extension provided the possibility for the parental basaltic magmas to enter upper crustal levels, where they could interact with the host rocks and form hybrid andesitic melts.     

西藏雄梅地区晚白垩世江巴组火山岩岩石成因及对加厚地壳减薄的指示

江巴组火山岩是西藏雄梅地区近年来发现的火山岩,但其岩石成因尚不明确.通过开展系统的岩相学、地球化学、同位素定年示踪研究,结果表明英安质火山岩锆石U-Pb年龄为85.1±1.0 Ma,为晚白垩世.安山质和英安质火山岩显示出明显的埃达克质岩特征,主量元素显示出较高的SiO₂和Al₂O₃含量及Mg#值;稀土元素整体呈轻稀土元素富集,重稀土元素强烈亏损,轻重稀土元素分异明显,（La/Yb）_N值较高,无明显Eu异常;微量元素具有明显的高Sr,低Y、Yb和高Sr/Y值,相对富集Th、Zr和Hf,亏损Nb、Ta和Ti的特点;英安质火山岩锆石ε_Hf（t）值均为正值,在+2.7~+7.1之间,指示有亏损地幔物质参与成岩作用;以上表明安山质和英安质火山岩可能形成于加厚新生下地壳拆沉的部分熔融并有亏损地幔物质的加入.流纹质火山岩具相对低的MgO、TiO₂含量;LREEs富集、HREEs亏损,但轻重稀土元素分馏明显较安山质和英安质火山岩弱,微量元素富集Rb、Th和K,强烈亏损Eu,Sr,Ba,P和Ti,明显的负Eu异常,表明流纹质火山岩为地壳发生深熔而形成.综合对比江巴组火山岩的地球化学性质,表明班公湖-怒江缝合带中段昂龙岗日-班戈弧地区在晚白垩世期间存在一期板内加厚下地壳拆沉减薄事件.      

青海治多多彩地区火山岩岩石特征

多彩地区处于西金乌兰-义敦晚三叠世岛弧带的东段,成矿区带位于三江成矿带的北西段,区内已发现了尕龙格玛铜多金属矿床和拉迪欧玛铜矿点.重点分析了与该区成矿关系密切的火山岩的岩石特征,初步恢复了该区火山岩的喷发环境和火山机构,并探讨了火山活动与成矿的关系.研究表明,本区火山岩主要为英安岩及英安质火山碎屑岩,其次为安山岩、安山质火山碎屑岩.火山岩微量元素具有富集亲石元素Rb、Sr、Th及亲铁元素Co、Ni,亲Cu元素Zr与参照值相近,V、Ba元素的含量高于地壳的丰度值,Sc、Cr等元素亏损的特征.中-酸性火山岩稀土总量较高,稀土配分曲线上普遍出现Eu负异常,总体特征与造山带火山岩相似,火山岩相为溢流相.本区海相火山喷发发生在浅海地带,火山岩构造环境总体属于岛弧环境.成矿作用主要与古火山机构和后期动力变质作用有关.     

辽河裂谷形成的地史条件

作者获得资料说明,辽河裂谷是以今辽河裂谷中的主断裂为界,辽宁东部和辽宁西部是相互远离的两个地块—辽东地体和辽西地体。在古生代后期或中生代初期它们发生增置作用(或拼合作用)。中生代晚期在拼合的辽东地体和辽西地体接触部位的构造薄弱带上产生了地壳变薄、膨胀上隆,并形成了辽河裂谷。这说明除地幔内部物质所特有的异常活动外,裂谷作用显然与地球历史早期潜伏下来的基底构造格局有关。     

Late Pliocene–recent tectonic setting for the Tianchi volcanic zone, Changbai Mountains, northeast China

Mafic volcanic rocks have erupted in the Tianchi volcanic zone, Changbai Mountains, northeast China, since late Pliocene time. The zone formed in an extensional environment during early-middle Cenozoic time, and in a compressional environment during late Cenozoic. Crustal thickness (about 40 km) in the Changbai Mountains is larger than the regional average of 34–36 km to the northwest and southeast. The conduit for magma upwelling was not coincident with the NE-striking regional faults, but seem to be confined to a deep-seated NW–WNW-striking fault zone. Since the late Pliocene, the Tianchi volcanic zone was subjected to crustal uplift within an intracontinental, weakly compressional environment (with minor WNW–ESE shearing) related to the westward subduction of the West Pacific plate. The nature of this volcanism is not typical of active, subduction-related continental margin volcanism. The magmatic evolutionary process evolved from trachybasalt through basaltic trachyandesite, trachyte, and pantellerite.     

云南腾冲火山岩岩石学特征

腾冲火山岩群是我国著名的新生代火山岩群之一。岩相学特征表明，该火山群为典型的钙碱性系列玄武岩—安山岩—英安岩弧火山岩组合。它喷发于晚上新世—晚更新世，但这一时期腾冲地区已为大陆板内环境，腾冲弧火山岩的形成至少在俯冲作用停止以后60Ma，属于一种滞后型弧火山。     

Ordovician Macquarie Arc and turbidite fan relationships,Lachlan Orogen,southeastern Australia: stratigraphic and tectonic problems

Ordovician rocks of the Lachlan Orogen consist of two major associations, mafic to intermediate volcanic and volcaniclastic rocks (Macquarie Arc), which aerially comprise several north–south-trending belts, and the quartz-rich turbidite succession. Relationships between these associations are integral to resolving their tectonic settings and opinions range between contacts being major thrusts, combinations of various types of faults, and stratigraphic contacts with structural complications. Stratigraphic contacts between these associations are found with volcaniclastic-dominant units overlying quartz-turbidite units along the eastern boundary of the eastern volcanic belt and along the southern boundary of the central volcanic belt. Mixing between these major associations is limited and reflects waning quartzose turbidite deposition along a gently sloping sea floor not penetrating steeper volcaniclastic aprons that were developing around the growing volcanic centres formed during late Middle Ordovician to early Silurian Macquarie Arc igneous activity. An island arc setting has been most widely supported for the Macquarie Arc, but the identification and polarity of the associated subduction zone remain a contentious issue particularly for the Early Ordovician phase of igneous activity. The Macquarie Arc initiated within a Cambrian backarc formed by sea-floor spreading behind a boninitic island arc and presumably reflects a renewed response to regional convergence as subduction ceased along the Ross–Delamerian convergent boundary at the East Gondwana continental margin. An extensional episode accompanied initiation of the late Middle Ordovician expansion in island arc development. A SSE-dipping subduction zone is considered to have formed the Macquarie Arc and underwent anticlockwise rotation about an Euler pole at the western termination of the island arc. This resulted in widespread deformation west of the Macquarie Arc in the Benambran Orogeny and development of subduction along the eastern margin of the orogenic belt.     

Suckling Dome and the Australian–Woodlark plate boundary in eastern Papua: the geology of the Keveri and Ada'u Valleys

The Owen Stanley Fault Zone (OSFZ) is the low-angle thrust boundary between the Australian and Woodlark plates. The eastern extension of the OSFZ links with the Woodlark Basin spreading centre. Recent tectonic models of eastern Papua depict the OSFZ boundary passing through the Mt Suckling district, with the Keveri Fault a key component. Gravity data clearly show that the OSFZ and the Papuan Ultramafic Belt (PUB) pass north of Mt Suckling. Tectonised mafic and ultramafic rocks of the Mt Suckling district, previously referred to the PUB, are reassigned to the Awariobo Range Complex (new name). Extensive pillow basalts previously referred to the middle Eocene part of the Kutu Volcanics at the top of the PUB sequence are, in the map area, reassigned on lithological and biostratigraphic grounds to the late Oligocene–middle Miocene Wavera Volcanics. The detailed work reported here indicates that the Keveri Fault is unrelated to the OSFZ with no evidence for thrusting along the structure. The area's tectonic history has been dominated by large vertical displacements along the Keveri Fault. The commencement of late Miocene buoyant uplift of the Suckling Dome (new name), related to granite intrusion into thick crust of the eastern Papua region, marks the inception of the Keveri Fault and coincides with the initiation of Woodlark rifting. The fault facilitated much of the rapid vertical movement of the dome, with an estimated 8000 m of uplift (2.5 m/10³ a) since the late Miocene. Movement on the Keveri Fault is notably different from structures flanking other metamorphic core complexes in eastern Papua. There is no field evidence for the development of a low-angle, south-dipping detachment fault along the southern margin of the Suckling Dome. The Suckling Dome is the westernmost of the eastern Papua domes, localised within a broad extensional zone that continues to propagate westward along the OSFZ plate boundary.     

中国东部新生代玄武岩记录古太平洋俯冲带壳幔相互作用

大陆玄武岩通常具有与洋岛玄武岩相似的地球化学成分,其中含有显著的壳源组分.对于洋岛玄武岩来说,虽然其中的壳源组分归咎于深俯冲大洋板片的再循环,但是对板片俯冲过程中的壳幔相互作用缺乏研究.对于大陆玄武岩来说,由于其形成与特定大洋板片在大陆边缘之下的俯冲有关,可以用来确定古大洋板片俯冲的地壳物质再循环.本文总结了我们对中国东部新生代玄武岩所进行的一系列地球化学研究,结果记录了古太平洋板片俯冲析出流体对地幔楔的化学交代作用.这些大陆玄武岩普遍具有与洋岛玄武岩类似的地球化学成分,在微量元素组成上表现为富集LILE和LREE、亏损HREE,但是不亏损HFSE的分布特点,在放射成因同位素组成上表现为亏损至弱富集的Sr-Nd同位素组成.在排除地壳混染效应之后,这些玄武岩的地球化学特征可以由其地幔源区中壳源组分的性质来解释.俯冲大洋地壳部分熔融产生的熔体提供了地幔源区中的壳源组分,其中包括洋壳镁铁质火成岩、海底沉积物和大陆下地壳三种组分.华北和华南新生代大陆玄武岩在Pb同位素组成上存在显著差异,反映它们地幔源区中的壳源组分有所区别.中国东部新生代玄武岩的地幔源区是古太平洋板片于中生代俯冲至亚欧大陆东部之下时,在>200 km的俯冲带深度发生壳幔相互作用的产物.在新生代期间,随着俯冲太平洋板片的回卷引起的中国东部大陆岩石圈拉张和软流圈地幔上涌,那些交代成因的地幔源区发生部分熔融,形成了现今所见的新生代玄武岩.      

郯庐断裂带火山活动与深部地质过程的新认识

在郯庐断裂带中生代以来的三期演化中,都伴生了火山活动。早白垩世走滑期的火山活动起源于地幔底侵、壳幔相互作用下的壳幔过渡带,也指示此时的断裂带切入到壳幔边界。断裂带内新生代玄武岩喷发起始于强烈伸展的后期（古新世）,在随后的断裂挤压期达到高温,该玄武岩喷发不但反映了断裂带已深切至上地幔,出现了地幔剪切带,也显示地幔交代,混杂地幔区等重要的深部过程信息。     

青海可可西里地区新生代火山岩的岩石特征与时代

可可西里地区的新生代火山岩属于藏北火山岩带的东段。火山岩主要以熔岩台地、桌状山的形式产出，熔岩厚约４０—１００ｍ。除少量的高钾流纹岩、粗面岩和粗面英安岩外，在数量和分布上以普遍含二辉石斑晶的安粗岩占优势。岩石以富碱（尤其富钾）和富ＬＲＥＥ为特征。火山活动发生在中新世，根据Ｋ／Ａｒ定年结果划分为早、中、晚三期。本区火山岩的特征与西藏境内的同时代岩石完全可以对比。火山活动与高原新生代以来的岩石圈演化有密切的关系     

巴布亚新几内亚铜金矿床大地构造背景、成因类型与成矿特征

巴布亚新几内亚地质构造格架复杂,包括地台、碰撞造山带、外来地体、俯冲带、岛弧和海底扩张中心。巴布亚新几内亚铜金矿床类型主要为斑岩型铜金矿床、浅成低温热液型金银矿床和夕卡岩型铜金矿床（三者之间具有密切的时间、空间和成因关系）,其次为海底块状硫化物矿床。铜金矿床分布比较集中,主要产出于碰撞造山带和岛弧上,其次产出于现代海底扩张中心。铜金矿床大多规模巨大或较大,埋藏较浅,易于勘探和适合露天开采。与铜金矿床有关的岩浆岩大多为钙碱性火山岩和浅成侵入岩,少数与富钾碱性火山岩（橄榄玄粗岩）或侵入岩伴生。铜金矿床蚀变带发育且分带性明显,大多与斑岩体系和／或火山机构有关。虽然许多铜金矿床的矿物成分比较复杂,但是其矿石较易处理和利用。