http://www.sciencedirect.com/science/article/pii/S1674987111001095

During the Late Mesozoic Middle Jurassic-Late Cretaceous,basin and range tectonics and associated magmatism representative of an extensional tectonic setting was widespread in southeastern China as a r...     

黑龙江先锋北山金矿床火山岩地球化学特征、LA-ICP-MS锆石U-Pb定年及地质意义

黑龙江省先锋北山金矿床地处完达山造山带西南段,矿体主要赋存在流纹岩、岩屑晶屑凝灰岩和流纹质角砾岩中。文章系统研究了与成矿密切相关的火山岩的地球化学特征,同时,对其进行了LA-ICP-MS锆石U-Pb测年。与成矿相关的火山岩(流纹岩、岩屑晶屑凝灰岩、流纹质角砾岩)表现出高硅、富碱,贫铝、镁、钙的特征,属碱性系列岩石;具有弱的Eu负异常;富集大离子亲石元素K、Rb、Th等;亏损高场强元素Ta、Nb、P、Ti等。同时,Ba、Sr、Eu等元素亦表现为亏损,具有典型的同碰撞环境的地球化学特征。LA-ICP-MS锆石U-Pb测年显示,流纹岩、流纹质角砾岩和石英闪长玢岩的206Pb/238U谐和年龄分别为(116.98±0.47)Ma、(116.98±0.42)Ma和(108.48±0.99)Ma。结合矿区侵入接触关系,限定先锋北山金矿床的形成时间介于(116.98±0.47)Ma~(108.48±0.99)Ma,即早白垩世晚期。该矿床的形成与太平洋板块的俯冲和佳木斯与完达山地块的拼合有着密切的关系,系古太平洋板块构造体制由挤压变为伸展背景下的产物。     

The Geological Significance of a Tuffite Interlayer in the Cretaceous Port Island Formation in Northeastern Hong Kong

The Port Island Formation(PIF), a typical Cretaceous red bed in Hong Kong, is dominated by non-fossiliferous, reddish clastic rocks, making it difficult to determine the sedimentary age of PIF precisely. Previous studies assigned the PIF to Late Cretaceous provisionally only on the basis of its stratigraphic sequence and lithology. This study identified a tuffite interlayer in the PIF and a zircon UPb age of 128.2±2.7 Ma by LA-ICP-MS method was obtained. It's the first time to date the depositional age of the PIF with a reliable chronological constraint. With the support of stratigraphic evidence, we concluded that the geological age of PIF should be Early Cretaceous rather than Late Cretaceous. Based on the volcanic history of Hong Kong and Southeast China and the distribution of the PIF in Mirs Bay, it is believed that there was no volcanic activity in Hong Kong in ca. 128 Ma. The tuffite interlayer discovered in PIF was formed by the deposition of volcanic ash, which might originate from remote region outside Hong Kong, in an aquatic environment on Port Island. The identification of the tuffite interlayer, as the response to a volcanic event, has great significance not only to the studies of establishment and regional correlation of the strata system and the geological evolution in Hong Kong,but also to the study of volcanic activities in Southeast China.     

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。     

Late Jurassic to Early Cretaceous volcanism of Hong Kong: Insights from the Ping Chau Formation

The vast expanse of Mesozoic igneous rocks in Hong Kong contain important geological records of late Mesozoic magmatic events and tectonic processes from the coastal region of Southeast China. Of these,the Ping Chau Formation in the northwestern New Territories is the youngest known stratum. We perform a detailed study of the volcanic rocks of the Ping Chau Formation utilizing zircon U-Pb dating,with major and trace elements geochemistry. LA-ICP-MS zircon U-Pb data reveal Early Cretaceous age from two volcanic rock samples, with zircon crystallization from magmas at 140.3 ± 0.8 Ma and 139.3 ± 0.9 Ma,respectively. These rocks have high contents of total alkalis(Na_2O + K_2O = 5.58-9.45 wt.%), high-field-strength elements and light rare earth elements, conspicuous negative Eu anomalies, and depletions in Nb, Ta, Ti, Sr, Ba and P. Using this data, in combination with previous studies on the late Mesozoic volcanic belt in Southeast China, we propose that the volcanic rocks of the Ping Chau Formation probably originated from deep melting of the crust in a back-arc extensional setting induced by the subduction of the paleo-Pacific Plate. This formation represents the final stages of Early Cretaceous volcanic activity in Hong Kong, as associated with large-scale lithospheric extension, thinning and magmatism. Our results provide new information that can be used in evaluating the significance of Early Cretaceous volcanism and tectonics in Southeast China.     

吉林延边和龙地区泉水村组火山岩锆石U—Pb定年、地球化学特征及其地质意义

通过对延边地区泉水村组火山岩的岩相学、年代学以及地球化学研究来约束该地区的构造演化。泉水村组火山岩分为两段,上段为流纹岩、流纹质凝灰岩、流纹质角砾岩,下段为安山岩、安山质角砾岩。整体为两个喷发旋回,呈爆发相-喷溢相的持续。锆石U—Pb测年表明流纹质凝灰岩形成年龄为(115. 5±5. 3) Ma,为早白垩世晚期,其地球化学特征表明原始岩浆来源于地壳的部分熔融;安山岩地球化学特征显示其岩浆源区是地幔楔由于遭受俯冲流体交代作用从而发生部分熔融,同时有较多地壳物质的混染,表现出活动大陆边缘构造背景下岩浆岩的特征。结合其他证据推断古太平洋板块至少在早中侏罗世就已经向吉黑东部开始俯冲,晚侏罗世—早白垩世早期俯冲作用消减,早白垩世晚期又发生强烈俯冲。     

Petrogeochemical aspects of the Late Cretaceous and Paleogene ignimbrite volcanism of East Sikhote-Alin

The chemical and trace-element features of the Late Cretaceous and Early Paleogene ignimbrite complexes of East Sikhote Alin are discussed. The Turonian-Campanian volcanic rocks of the Primorsky Complex compose linear structure of the Eastern Sikhote Alin volcanic belt. They are represented by crystalrich rhyolitic, rhyodacitic, and dacitic S-type plateau ignimbrites produced by fissure eruptions of acid magmas. The Maastrichtian-Paleocene volcanic rocks occur as isolated volcanic depression and caldera structures, which have no structural and spatial relations with the volcanic belt. This period is characterized by bimodal volcanism. The Samarginsky, Dorofeevsky, and Severyansky volcanic complexes are made up of basalt-andesite-dacite lavas and pyroclastic rocks, while the Levosobolevsky and Siyanovsky complexes are comprised of rhyolitic and dacitic tuffs and ignimbrites. Petrogeochemically, the felsic volcanic rocks are close to the S-type plateau ignimbrites of the Primorsky Complex. The Paleocene-Early Eocene silicic volcanics of the Bogopolsky Complex are represented by S- and A-type dacitic and rhyolitic tuffs and ignimbrites filling collapsed calderas. The eruption of A-type ferroan hyaloignimbrites occurred at the final stage of the Paleogene volcanism (Bogopolsky Complex). The magmatic rocks show well expressed mineralogical and geochemical evidence for the interaction between the crustal magmas and enriched sublithospheric mantle. It was shown that the revealed differences in the mineralogical and geochemical composition of the ignimbrite complexes are indicative of a change in the geodynamic regime of the Asian active continental margin at the Mesozoic-Cenozoic transition.     

渣尔泰山地区白垩纪酸性火山岩地质特征及成矿作用

渣尔泰山地区位于内蒙古中西部,大地构造位置处于华北地台北缘狼山-渣尔泰山裂陷槽的东段,根据近几年的找矿实践与研究,在白垩纪的酸性火山岩中已发现银金矿床、金银矿床,主要赋存于下白垩统白女羊盘组酸性火山岩中。该套火山岩具富硅富钾、相对贫钙镁的特点,属于铝过饱和的碱性系列;在球粒陨石标准化图解上岩石化学样品均显示为轻稀土(LREE)相对富集、重稀土(HREE)相对亏损的右倾型配分模式,轻重稀土分异较明显,显示较明显的负铕异常;微量元素显示明显的Rb、Pb正异常和Ba、Sr负异常,不相容元素比值Zr/Nb=2.47~4.87,Zr/Y=18.3~103。属大陆碰撞造山期后作用的产物,来源于地壳部分熔融。其岩石类型主要有:流纹质凝灰角砾岩、流纹质角砾凝灰岩、球粒状流纹岩、珍珠岩、显微嵌晶状流纹岩夹流纹斑岩等。银多金属矿的含矿层主要由复碎裂复硅化流纹质凝灰角砾岩、硅化复碎裂流纹岩、多期次硅化黄铁矿化角砾岩化流纹斑岩等组成。成矿元素Ag、Au、Sb、W显著富集于流纹质凝灰角砾岩、多期次硅化碎裂的流纹岩、流纹斑岩中,其平均含量高于中国流纹岩元素丰度10倍以上,说明该套火山岩提供了成矿物质来源;且元素含量的分异程度较大,指示明显受到后期成矿作用的叠加;有一定的找矿潜力。     

中国东南沿海晚白垩世长屿火山的活动过程与古环境意义SCIEI北大核心CSCD

火山是唯一能够直接反映地球深部存在岩浆的地球动力学现象,对于地球气候演变和宜居性具有重要影响。相比年轻火山,古老火山因其活动过程完整、且可能剥蚀出露多阶段火山喷发产物及岩浆通道、岩浆房等,从而为揭示火山岩浆系统演化和火山活动过程提供重要的研究窗口。本文选择中国东南沿海晚白垩世长屿破火山为研究对象,对其开展火山地质、岩石学、年代学及地球化学研究,以期揭示其火山活动历史及其对中国东南沿海白垩纪古环境的启示意义。长屿火山出露面积约100km^(2),呈近圆形分布,具有较厚的火山地层厚度(总厚度约570m),类似于破火山内的火山堆积特点。由早至晚三个喷发阶段形成的流纹质角砾凝灰岩都显示了典型的火山碎屑流相的特点,发育典型的条纹斑状结构,但表现出不同的晶屑、玻屑及岩屑含量以及熔结程度等岩相学特征,反映火山喷发从初始到高峰、再到减弱的过程,最后岩浆沿火山通道侵出形成流纹斑岩穹隆,标志着火山活动的结束。长屿火山的火山碎屑流式喷发伴随着快速的岩浆房塌陷,以及缺少普林尼式空落堆积,反映了火山活动发生在伸展的构造背景。系统的LA-ICP-MS锆石U-Pb年代学研究获得了不同阶段火山岩一致的形成年龄(97~96Ma),暗示它们具有较短的形成时限,是由同期火山岩浆活动先后喷发形成的。长屿火山岩高的SiO_(2)含量(67%~76%)以及分异的锆石微量元素地球化学特征,表明喷发岩浆来自晶粥提取的熔体,并有晶粥来源晶体的混入。此外,我们在长屿火山岩中发现了南洋杉型丝炭化木(贝壳杉型木属),暗示晚白垩世中国东南沿海地区可能为温暖湿润的亚热带山地气候环境,表明中国东南沿海白垩纪大规模火山活动,在古武夷山脉以东地区形成了地形高耸的海岸山脉。     

大兴安岭嫩江地区中生代双峰式火山岩锆石U-Pb定年、地球化学特征及其地质意义

本文对嫩江地区中生代双峰式火山岩进行了锆石LA-ICP-MSU-Pb年代学和岩石地球化学研究。测年结果显示嫩江地区中生代双峰式火山岩形成于127.5Ma的早白垩世晚期。岩石地球化学研究表明,早白垩世晚期火山岩具有双峰式组合特点,基性端员富碱,富含轻稀土元素和大离子亲石元素,亏损重稀土元素和高场强元素（Nb、Ta、Ti、Y）,形成于富集的岩石圈地幔的部分熔融和分离结晶作用,形成的过程可能含有少量的陆壳混染。酸性端员显示A型流纹岩的特征,为幔源岩浆底侵,使中下地壳岩石发生部分熔融的成因。双峰式火山岩组合的存在暗示其形成于陆内拉张的构造环境。结合区域上中生代火山岩的空间展布特征,嫩江地区早白垩世晚期双峰式火山岩的形成应与太平洋板块向欧亚大陆的俯冲作用有关。     

华南东部陆缘侏罗纪岩浆作用特征及其构造背景——来自浙东南毛弄组火山岩的新证据

华南东部内陆地区在侏罗纪处于陆内伸展背景已逐渐成为学术界共识,但对于该时期东部陆缘的构造环境仍存在争议。本文以浙东南毛弄组火山岩为对象,开展了岩石学、SHRIMP锆石U-Pb年代学、锆石微量元素、全岩元素地球化学和Sr-Nd同位素等研究,为认识华南东部陆缘构造背景提供制约。浙江侏罗纪火山岩以松阳毛弄剖面较具代表性,总体上是一套以英安质晶屑凝灰岩和流纹质玻屑凝灰岩为主的火山岩组合。本次研究在毛弄组下段获得的流纹质玻屑凝灰岩的SHRIMP锆石U-Pb年龄为153±2Ma。综合前人研究表明,毛弄组火山岩主要形成于180～148Ma。毛弄组火山岩属于镁质钙碱性系列,且表现出明显的轻稀土元素富集特征,其中早侏罗世毛弄英安质凝灰岩Eu负异常不明显,而晚侏罗世毛弄流纹质凝灰岩具有显著的Eu负异常;两组凝灰岩均富集K、Rb和Th等大离子亲石元素,亏损Nb、Ta、Zr和Hf等高场强元素。毛弄英安质火山岩的源区残留相组合可能为"斜长石+石榴石+角闪石",而毛弄流纹质凝灰岩则可能为"斜长石+角闪石",这一差异可能代表它们具有不同的源区深度。毛弄组火山岩的Sr-Nd-Hf同位素特征与华夏陆块古元古代基底岩体相似,其可能主要起源于基底地壳物质的部分熔融,并有少量地幔新生物质的加入。结合构造背景分析认为,毛弄组火山岩等陆缘岩浆岩形成环境为相对低温的"安第斯型"俯冲环境。通过不同时代区域岩体锆石氧逸度计算发现,早侏罗世东南海域岩浆岩的氧逸度比大陆陆缘更高,且大陆陆缘岩浆岩的氧逸度从晚三叠世至晚侏罗世不断升高,可能标志着陆缘地区俯冲流体的影响有着从东南海域向大陆陆缘扩散的趋势。综合分析认为,在侏罗纪华南东部陆缘可能发育一个与古太平洋俯冲有关的"安第斯型"陆缘岩浆弧,其时代可能最早可以追溯到早侏罗世早期,并持续扩大到中-晚侏罗世。这一时期浙闽沿海地区总体处于弧后挤压主导的构造环境,与同期内陆地区构造伸展背景形成鲜明对比。     

西天山达巴特火山岩的形成环境及对斑岩型矿化的制约

本文通过对西天山地区比较典型的达巴特斑岩铜钼矿床矿区范围内出露上的英安岩和花岗斑岩进行了系统的岩石地球化学分析,对英安岩和流纹斑岩中的锆石进行了SHRIMP U-Pb定年研究,分别获得了315.9±5.9Ma和278.7±5.7Ma。岩石化学、微量以及稀土元素特征表明从英安岩到花岗斑岩,岩体具有明显的分异演化特征和很好的继承性。火山岩和次火山岩的精确定年为准确厘定火山岩形成的时限和地球动力学背景提供了依据。结合已有的Re-Os法获得的矿化年龄,表明晚石炭世末-早二叠世初（278.7±5.7Ma）,西天山地区进入板块碰撞-板内伸展阶段,由于板内幔根的部分熔化,造成深源斑岩岩浆侵位,在达巴特矿区形成了由花岗斑岩、流纹斑岩和流纹质凝灰熔岩组成的椭圆形火山机构,并导致相关矿床的形成。     

大兴安岭中部柴河——蘑菇气地区早白垩世中性火山岩岩石成因及构造背景

大兴安岭中部柴河—蘑菇气地区早白垩世中性火山岩岩相学研究表明,其主要岩石组合为安山岩、英安岩、安山质晶屑凝灰熔岩、凝灰角砾熔岩等,LA-ICP-MS锆石U-Pb测年结果显示其形成于140~130Ma之间。岩石主量元素具有富钾钠、富铝,贫镁的特点,属高钾钙碱性岩石。相对富集轻稀土元素、亏损重稀土元素,无明显的Eu异常,微量元素主要富集大离子亲石元素(如Rb、K、LREE)和Ba、Sr元素,亏损高场强元素(Ta、Nb、P、Ti)。地球化学特征指示,这些早白垩世中性火山岩来源于新元古代和古生代期间新增生的下地壳玄武质岩石的部分熔融,并可能受到早先俯冲事件带来的流体的影响,形成于蒙古-鄂霍茨克洋闭合陆壳加厚之后的岩石圈伸展环境。     

Sediment-infill volcanic breccia from the Neoarchean Shimoga greenstone terrane,western Dharwar Craton: Implications on pyroclastic volcanism and sedimentation in an active continental margin

We report sediment-infill volcanic breccia from the Neoarchean Shimoga greenstone belt of western Dharwar Craton which is associated with rhyolites, chlorite schists and pyroclastic rocks. The pyroclastic rocks of Yalavadahalli area of Shimoga greenstone belt host volcanogenic Pb–Cu–Zn mineralization. The sediment-infill volcanic breccia is clast-supported and comprises angular to sub-angular felsic volcanic clasts embedded in a dolomitic matrix that infilled the spaces in between the framework of volcanic clasts. The volcanic clasts are essentially composed of alkali feldspar and quartz with accessory biotite and opaques. These clasts have geochemical characteristics consistent with that of the associated potassic rhyolites from Daginkatte Formation. The rare earth elements (REE) and high field strength element (HFSE) compositions of the sediment-infill volcanic breccia and associated mafic and felsic volcanic rocks suggest an active continental margin setting for their generation. Origin, transport and deposition of these rhyolitic clasts and their aggregation with infiltrated carbonate sediments may be attributed to pyroclastic volcanism, short distance transportation of felsic volcanic clasts and their deposition in a shallow marine shelf in an active continental margin tectonic setting where the rhyolitic clasts were cemented by carbonate material. This unique rock type, marked by close association of pyroclastic volcanic rocks and shallow marine shelf sediments, suggest shorter distance between the ridge and shelf in the Neoarchean plate tectonic scenario.     

Provenance,volcanic record,and tectonic setting of the Paleozoic Ventania Fold Belt and the Claromecó Foreland Basin: Implications on sedimentation and volcanism along the southwestern Gondwana margin

This study focuses on the provenance, volcanic record, and tectonic setting of the Paleozoic Ventania System, a geologic province which comprises the Cambro-Devonian Ventania Fold Belt and the adjoining Permo-Carboniferous Claromecó Foreland Basin, located inboard the deformation front. The Ventania Fold Belt is formed of the Curamalal and Ventana groups, which are composed mainly of mature quartzites that were unconformably deposited on igneous and metamorphic basement. The Pillahuincó Group is exposed as part of the Claromecó Basin and it has lithological and structural features totally distinct from the lowermost groups. This group is composed of immature arkoses and subarkoses with intercalated tuff horizons, unconformably overlaying the quartzites and associated with glacial-marine deposits of the lower Late Carboniferous to Early Permian section. The petrography, as well as major and trace elements (including rare earth elements) support that the Ventania quartzites were derived from cratonic sources and deposited in a passive margin environment. For the Pillahuincó Group, we suggest a transition between rocks derived from and deposited in a passive margin environment to those with geochemical and petrographical signatures indicative of an active continental margin provenance. LA-MC-ICP-MS analysis performed on euhedral and prismatic zircon grains of the tuffs revealed an age of 284 ± 15 Ma. The geochemical fingerprints and geochronological data of the tuffs found in the Claromecó Basin support the presence of an active and widespread Lower Permian pyroclastic activity in southwestern Gondwana, which is interpreted as part of the Choiyoi Volcanic Province in Argentina and Chile.     

张广才岭五道岭组火山岩的锆石U——Pb 年代学及地球化学特征

对张广才岭五道岭组火山岩进行锆石U--Pb LA--ICP--MS 年代学和岩石地球化学研究,以确定该组火山岩形成的时代和构造背景。选取样品中的锆石均呈自形--半自形晶,具有清晰的振荡生长环带和较高的Th /U 比值( 0. 52 ～ 2. 28) ,暗示其岩浆成因。测年结果显示,五道岭组火山岩形成于289 ± 3 Ma,是早二叠世岩浆活动的产物。火山岩的岩石组合为玄武岩--流纹岩,显示双峰式火山岩的特点,属于高钾钙碱性--钾玄岩系列,玄武岩具有富集Ｒb、K 等大离子亲石元素( LILE) ,亏损Nb、Ta 等高场强元素( HFSE) 的特征; 流纹岩呈负铕异常,富集Ｒb、Th、U 和K 等大离子亲石元素( LILE) ,亏损Nb、Ta 和Ti 等高场强元素( HFSE) 及Sr、P 元素,并显示A 型流纹岩的特点。结合该时期区域构造演化史,火山岩地球化学特征揭示了五道岭组火山岩的形成与岛弧环境下的局部伸展作用有关,这种构造背景是古亚洲洋板块俯冲于松嫩-张广才岭-佳木斯陆块之下造成的。     

Early Cretaceous volcanism in the northern Songliao Basin,NE China,and its geodynamic implication

The Songliao Basin is characterized by episodic rifting and intense volcanism during its early development, and forms a key concealed part of the Late Mesozoic magmatic province of NE China. Few precise geochronological and geochemical data were previously available for the volcanic elements of this basin, restricting understanding of its geodynamic setting and evolution. We present new SHRIMP U–Pb zircon ages and geochemical data for the volcanic rocks from the northern Songliao Basin, which limit this volcanism to the Early Cretaceous period (115–109 Ma). Although dominated by rhyolite, the rocks cover a wide compositional spectrum encompassing trachyandesite, basaltic trachyandesite, trachyte and dacite. This suite exhibits a range of geochemical signatures characteristic of subduction-related genesis, falling into a high-K calc-alkaline series, with enrichment in large ion lithophile elements (LILE) and light rare earth elements (LREE), and weak depletion in high field strength elements (HFSE) and heavy rare earth elements (HREE). The suite also shares a common isotopic composition, consistent with derivation from partial melting of a single depleted mantle source. This Early Cretaceous volcanism occurred in an extensional back-arc setting associated with the subduction of the Paleo-Pacific plate, large scale upwelling of the asthenosphere, and intensive lithospheric thinning of the eastern continental margin of NE China which may have lasted until ca. 109 Ma.     

Spatial–temporal relationships of Mesozoic volcanic rocks in NE China: Constraints on tectonic overprinting and transformations between multiple tectonic regimes

LA-ICP-MS zircon U–Pb ages and geochemical data are presented for the Mesozoic volcanic rocks in northeast China, with the aim of determining the tectonic settings of the volcanism and constraining the timing of the overprinting and transformations between the Paleo-Asian Ocean, Mongol–Okhotsk, and circum-Pacific tectonic regimes. The new ages, together with other available age data from the literature, indicate that Mesozoic volcanism in NE China can be subdivided into six episodes: Late Triassic (228–201 Ma), Early–Middle Jurassic (190–173 Ma), Middle–Late Jurassic (166–155 Ma), early Early Cretaceous (145–138 Ma), late Early Cretaceous (133–106 Ma), and Late Cretaceous (97–88 Ma). The Late Triassic volcanic rocks occur in the Lesser Xing’an–Zhangguangcai Ranges, where the volcanic rocks are bimodal, and in the eastern Heilongjiang–Jilin provinces where the volcanics are A-type rhyolites, implying that they formed in an extensional environment after the final closure of the Paleo-Asian Ocean. The Early–Middle Jurassic (190–173 Ma) volcanic rocks, both in the Erguna Massif and the eastern Heilongjiang–Jilin provinces, belong chemically to the calc-alkaline series, implying an active continental margin setting. The volcanics in the Erguna Massif are related to the subduction of the Mongol–Okhotsk oceanic plate beneath the Massif, and those in the eastern Jilin–Heilongjiang provinces are related to the subduction of the Paleo-Pacific Plate beneath the Eurasian continent. The coeval bimodal volcanic rocks in the Lesser Xing’an–Zhangguangcai Ranges were probably formed under an extensional environment similar to a backarc setting of double-direction subduction. Volcanic rocks of Middle–Late Jurassic (155–166 Ma) and early Early Cretaceous (145–138 Ma) age only occur in the Great Xing’an Range and the northern Hebei and western Liaoning provinces (limited to the west of the Songliao Basin), and they belong chemically to high-K calc-alkaline series and A-type rhyolites, respectively. Combined with the regional unconformity and thrust structures in the northern Hebei and western Liaoning provinces, we conclude that these volcanics formed during a collapse or delamination of a thickened continental crust related to the evolution of the Mongol–Okhotsk suture belt. The late Early Cretaceous volcanic rocks, widely distributed in NE China, belong chemically to a low- to medium-K calc-alkaline series in the eastern Heilongjiang–Jilin provinces (i.e., the Eurasian continental margin), and to a bimodal volcanic rock association within both the Songliao Basin and the Great Xing’an Range. The volcanics in the eastern Heilongjiang–Jilin provinces formed in an active continental margin setting related to the subduction of the Paleo-Pacific Plate beneath the Eurasian continent, and the bimodal volcanics formed under an extensional environment related either to a backarc setting or to delamination of a thickened crust, or both. Late Cretaceous volcanics, limited to the eastern Heilongjiang–Jilin provinces and the eastern North China Craton (NCC), consist of calc-alkaline rocks in the eastern Heilongjiang–Jilin provinces and alkaline basalts in the eastern NCC, suggesting that the former originated during subduction of the Paleo-Pacific Plate beneath the Eurasian continent, whereas the latter formed in an extensional environment similar to a backarc setting. Taking all this into account, we conclude that (1) the transformation from the Paleo-Asian Ocean regime to the circum-Pacific tectonic regime happened during the Late Triassic to Early Jurassic; (2) the effect of the Mongol–Okhotsk suture belt on NE China was mainly in the Early Jurassic, Middle–Late Jurassic, and early Early Cretaceous; and (3) the late Early Cretaceous and Late Cretaceous volcanics can be attributed to the subduction of the Paleo-Pacific Plate beneath the Eurasian continent.     

赣南版石-蔡坊火山岩年代学、地球化学和锆石Hf同位素特征及其地质意义

赣南版石和蔡坊盆地流纹质火山岩LA-ICP-MS锆石U-Pb定年结果分别为129.2±2.3 Ma和138.0±2.4 Ma。综合报道的同时期火山岩年龄,可以确定武夷山西缘发育的早白垩世火山岩形成时限大约在145~130 Ma。版石和蔡坊火山岩SiO_270%,属于高硅流纹质岩石,具有较低的Fe_2O_3~t/MgO比值(平均值10),富集大离子亲石元素和轻稀土元素,亏损中-重稀土元素,具显著的Eu负异常(δEu=0.06~0.20),类似于湿冷氧化性流纹岩,可能由来自交代岩石圈地幔的富钾岩浆结晶分异形成。湿冷氧化性的版石和蔡坊流纹质火山岩在武夷山西缘出现,并没有扩展到华南内陆,很可能表明古太平洋俯冲对华南地幔的影响范围主要位于武夷山西缘及其以东地区。     

Geochronology,petrogenesis, and tectonic setting of Mesozoic volcanic rocks,southern Manzhouli area,Inner Mongolia

We have undertaken major and trace element analyses of volcanic rocks in Northeast China, as well as U–Pb dating and Hf isotopic analysis of their zircons, in order to determine the petrogenesis and tectonic setting of the volcanics. Mesozoic volcanism in the southern Manzhouli area occurred in two stages: Middle to Late Jurassic (164–147 Ma) and Early Cretaceous (142–123 Ma). The first stage is represented by the Tamulangou, Jixiangfeng, and Qiyimuchang formations. The Jixiangfeng Formation (162–156 Ma) is a rhyolite–trachyte dominated unit that lies between two basalt units, namely the underlying Tamulangou (164–160 Ma) and overlying Qiyimuchang (151–147 Ma) formations. The second igneous stage is dominated by rhyolitic lavas and tuffs of the Shangkuli Formation and basaltic rocks of the Yiliekede Formation, and they yield zircon U–Pb ages of 142–125 and 135–123 Ma, respectively. Basaltic rocks of the Tamulangou and Yiliekede formations have a wide range of MgO contents (1.64–9.59 wt%), but are consistently depleted of Nb and Ta and enriched with incompatible trace elements such as large ion lithophile elements (LILEs) and light rare earth elements (LREEs). Trachytes and rhyolites of the Jixiangfeng and Shangkuli formations are characterized by enrichment in LILEs and LREEs relative to HFSEs and HREEs, and with negative Nb, Ta, P, and Ti anomalies and positive ? _Hf(t) values (3.49–9.98). These data suggest that basaltic volcanic rocks in southern Manzhouli were generated by fractional crystallization of a common parental magma, which was derived by partial melting of metasomatized (enriched) lithospheric mantle, whereas the trachytic and rhyolitic magmas were produced by the melting of lower crustal mafic and felsic granulites, respectively. Geochronological data indicate that Mesozoic volcanism in southern Manzhouli was initiated in the Middle to Late Jurassic and continued into the Early Cretaceous. It was mainly induced by lithospheric extension after the closure of the Mongol–Okhotsk Ocean.