Understanding the evolution of magmatic plumbing systems requires an understanding of the mechanisms of magma ascent from the magma source to the surface. We undertook textural and in situ geochemical studies of clinopyroxene phenocrysts in Early Cretaceous mafic volcanic rocks from the Laiyang Basin, China. Four distinct clinopyroxene populations were recognized based on their textures and zoning patterns in the mafic volcanic rocks (types 1, 2, 3, and 4). Type 1 is reversely zoned and contains rounded, irregularly resorbed, low-Mg cores (Mg# = 60-75) surrounded by clear, high-Mg mantles (Mg# = 75-90). Type 2 phenocrysts are typically normally zoned and characterized by relatively high-Mg cores (Mg# > 85) and thin lower Mg# rims (Mg# = 70-85). Type 3 comprises strong oscillatory zoned crystals (Mg# = 72-85) that are generally normally zoned and, in some cases, exhibit substantial sector zoning. Type 4 crystals are euhedral and unzoned phenocrysts. The textural and compositional features of the clinopyroxenes record complex magmatic processes including fractional crystallization, recycling of early formed crystals, magma convection, and magma recharge and subsequent mixing. Clinopyroxene-melt equilibrium pairs in the volcanic rocks yielded a relatively wide range of temperatures (984-1264 degrees C) and pressures (0.1-10.1 kbar). The P-T array defines two main magma storage zones: (1) a deep, high-T, magma reservoir (similar to 22-28 km), and (2) a shallow, low-T, magma reservoir (similar to 8-19 km). At pressures of >3 kbar, the amount of water in melts in equilibrium with the clinopyroxene is in the range 1.5-3.0 wt.%, but at pressures of <3 kbar, the melt water contents decrease to 0.1 wt.%, indicative of extensive magma degassing. The clinopyroxene phenocrysts have a wide range of Sr-87/Sr-86 ratios from 0.70683 to 0.71366. The broad range of Sr-87/Sr-86 ratios (0.70796-0.71171) for the most primitive clinopyroxene (Mg# > 89) might have been inherited from a heterogeneous mantle source. However, some type 1 crystals with more radiogenic Sr isotopic compositions may record assimilation of crustal material during evolution of the mantle-derived magma. The textural and compositional features of the studied clinopyroxene phenocrysts suggest that Laiyang volcano is fed by a vertically extensive magmatic plumbing system that extends from shallow to deep levels, in which geochemically distinct magmas crystallized and mixed under variable physicochemical conditions.

东北亚大地构造发展经历了古亚洲洋、蒙古—鄂霍茨克洋和古太平洋的俯冲-碰撞作用.如何鉴别和厘定这三种构造体制的时空影响范围和叠合过程一直是一个难题.本文通过巨型岩浆岩带的建库编图,揭示了该地区晚古生代—中生代岩浆岩的时空迁移规律;据此,探讨和厘定了这三大板块构造体制的时空分布范围和构造叠合过程.二叠纪到三叠纪早期间,古亚洲洋体制经历了俯冲到碰撞,主要作用于阿拉善—华北北缘—大兴安岭一带;期间,鄂霍茨克洋主要为陆缘环境,影响范围限于中北部蒙古—外贝加尔一带,并在侏罗纪逐渐向蒙古—鄂霍茨克主缝合带迁移,到白垩纪,其造山带伸展垮塌阶段,影响范围增大,远程效应波及阿拉善—华北北缘—大兴安岭一带,叠加于古亚洲洋体制产物之上.古太平洋构造体制主要发育于三叠纪—侏罗纪时期,其平板俯冲影响范围抵达大兴安岭—太行山,在白垩纪,俯冲板片后撤,影响范围迁移至东亚大陆最东缘.这些作用叠加于古亚洲洋体制产物之上;并与蒙古—鄂霍茨克洋体制同时叠合于大兴安岭一带.

大兴安岭南段黄岗梁火山-侵出隆起由火山灰流相的流纹质晶屑凝灰岩、侵出相的岩穹(流纹质碎斑熔岩)和浅成侵入相的斑状二长花岗岩构成,它们的SHRIMP锆石U-Pb定年结果分别为140.27±0.93 Ma、140.41±0.92 Ma和141.75±0.96 Ma,均属早白垩世初期岩浆活动的产物.3个岩相的同位素年龄在误差范围内一致,表明其间没有明显的间断,为粘稠的富晶岩浆(晶粥)连续作用的产物.这些火山-侵入杂岩属高钾钙碱性系列,主要为准铝质-过铝质岩石,它们的εNd(t)变化范围很小,为-0.43～-0.08,相应的二阶段模式年龄为0.98～0.96 Ga,表明其应起源于相同的源区.岩浆作用产物表现出从早到晚SiO2和K2O含量呈连续降低的趋势,不同岩相间成分上有一定的互补关系,暗示可能是由成分分带的岩浆房近于逐层排出/侵位形成流纹质晶屑凝灰岩和碎斑熔岩,残留岩浆充填到火山根部及火山机构周边的环状裂隙中冷却固结形成斑状二长花岗岩.该火山-侵入杂岩具有A型花岗岩特征,地球化学上均表现为富集Rb、Th、U等大离子亲石元素,强烈亏损Ti、Nb、Ta等高场强元素,具有明显负Eu异常,稀土元素配分图呈右倾的V字型,其可能是早白垩世软流圈上涌或者幔源镁铁质岩浆的底侵作用,诱发上覆地壳发生部分熔融形成的.

The Late Mesozoic granitoid intrusions in the eastern part of the Jiangnan orogenic belt can be divided into three stages: (1) the intrusive rocks formed in the initial stage are small in scales and scattered in distribution, whose ages vary mainly within 181 similar to 167 Ma, with a peak value of about 173 Ma; (2) the intrusions formed in the early stage are widely exposed, dominated by granodiorites, and their ages are mainly between 153 Ma and 137Ma, with a peak value of about 141Ma; (3) the intrusions formed in the late stage are also widely distributed, whose lithologies are mainly alkali feldspar granite-syenogranite, with ages ranging from 135 Ma to 122Ma, with a peak value of about 128 Ma. The early and late magmatic activities overlapped slightly in time, indicating that the regional magmatic activities are unbalanced and asynchronous. The three stages of intrusive rocks have their own geochemical characteristics, indicating they have different but related magma source areas, magmatic processes and dynamic environments. Both the initial and early granitoid intrusions have the characteristics of adakitic and island arc magmatic rocks, but the former generally has higher and more homogeneous whole rock epsilon(Nd) (t) values (close to chondrite) and zircon epsilon(Hf) (t), low Sr-87/Sr-86 initial values, relatively small Nd and Hf isotope depleted mantle two-stage model age (similar to 1.0Ga). It is speculated that the magma source area is basalts which intruded to the bottom of the crust in the Neoproterozoic island arc environment; The latter has the lowest whole rock epsilon(Nd) (t) values (mainly between -9 and -4, with a peak value of about -7) and zircon epsilon(Hf) (t) value (mainly between 10 and +2, with a peak value of about -6), the largest Nd and Hf isotope depleted mantle two-stage model age, Sr-87/Sr-86 initial value is higher and the range of variation is large (from 0.7066 to 0.7121). Combined with the petrochemistry characteristics of Al rich and low MgO content, it indicates that the magma source area is not only the crust source, but also the ancient crustal material (including the crust material experienced supergene) occupies an important position. It is inferred that the magma source area is the lower crust formed by the mixture of ancient crustal materials and Neoproterozoic island arc magmatic rocks. The intrusive rocks formed in the late stage have typical geochemical characteristics of A-type granites. They are closely associated with the I/S-type granitoid intrusions formed in the early stage, often form composite bodies in space and with certain delay in time (with a interval of about 10Myr between them). Their Nd and Hf isotopic compositions are comparable to those of the early intrusive rocks, indicating that they may have the same magmatic source and are the product of remelting of residual components after early partial melting. However, compared with the intrusive rocks formed in the early stage, their epsilon(Nd) (t) and epsilon(Hf) (t) values are higher, and the two-stage model ages of Nd and Hf isotopic depleted mantle are younger, indicating that a larger proportion of new mantle derived magma may have been mixed in them. The Late Mesozoic three stages intrusive rocks in the eastern part of Jiangnan orogenic belt have their own characteristics and internal relations. Their genesis may be due to the long-range tectonic effect of the subduction of the Pacific plate, and the extension state continued to strengthen with the retreat of the subduction plate and/or the steepening of the subduction angle, which triggered successively the thickened (Neoproterozoic) basalts at the bottom of the crust and (mixed) lower crust materials melt. From early to late, the pressure of partial melting decreases gradually (crust thickens to thins), and the contribution of new mantle source materials increases.

火山机构是一切火山岩的源头和绝大多数火山岩、火山岩相的赋存空间,是陆相火山岩区地质调查与研究的中心.本文选择大兴安岭黄岗梁火山构造隆起西南段,通过典型火山机构内火山活动时序的建立和不同火山机构相互关系的厘定,恢复火山构造格架,重溯火山作用过程.研究揭示黄岗梁火山构造隆起西南段包括两个火山隆起、三个破火山、一个凝灰岩环,以及若干个小的火山口,它们之间或并列、或叠套、或切割、或覆盖,构成了复杂的火山构造样式.区内火山活动大致可分为早期、峰期和晚期三个演化阶段,不同阶段在火山作用方式、形成的火山机构类型及主要岩性组合各具特色:早期火山作用主要形成瓦窑沟火山隆起,火山活动除开始阶段有一定烈度的爆发外,喷发强度总体中等偏低,形成产物以溢流相的安山岩和火山颈相的安山玢岩为主;峰期火山作用主要表现为大规模爆发,强烈爆发后塌陷形成多个破火山;晚期火山作用主要表现为压低沸腾外溢侵出侵入,形成黄岗梁火山-侵出隆起,火山活动烈度是三期中最弱的.三期火山作用产物的SHRIMP锆石U-Pb年龄分别为143.7±1.5 Ma、140.1±1.4 Ma和141.1±1.0 Ma,在误差范围内几乎一致,说明黄岗梁火山构造隆起火山活动持续的时间很短,其形成时代对应国际地质年代表为早白垩世贝利阿斯期(Berriasian),部分可能延续到凡兰吟期(Valanginian)初.区域对比表明,大兴安岭南段晚中生代的火山活动主要有两幕,峰值分别为～156 Ma和～132 Ma,中间有约10 Ma的相对宁静期,黄岗梁火山构造隆起形成于宁静期结束后,火山活动重新活跃的发展阶段.大兴安岭南段与北段具有不完全一致的火山活动年龄谱,暗示南、北两段火山作用的动力学机制可能存在着差异.前者与华北北缘晚中生代的火山活动具有可比性,可能与古太平洋板块的俯冲及随后俯冲板片的后撤有关;后者则可能与蒙古-鄂霍茨克洋的俯冲闭合及造山后的伸展有关.

A major and trace element, Sr–Nd–Hf isotope, and zircon U–Pb geochronology study was conducted on Early Cretaceous volcanic rocks from the northern margin of the Sulu orogenic belt in Shandong Province, eastern China. These results constrain the petrogenesis of the volcanic rocks and provide important insights into the significance of crust–mantle interaction. The rocks comprise high‐K basaltic andesite, shoshonites, latites, high‐K dacites, and high‐K rhyolites. U–Pb zircon dating of four representative samples of latite, two high‐K dacites, and high‐K rhyolite indicates that these rocks formed from 126 to 122 Ma. The volcanic rocks are characterized by high K2O (2.04–6.70 wt.%) and total alkalis (Na2O + K2O; 5.3–10.9 wt.%) that plot within the field for shoshonitic rocks. All the rocks are enriched in light rare earth and large‐ion lithophile elements (e.g., Rb, Th, U, and K) and are depleted in high‐field‐strength elements (e.g., Nb, Ta, and Ti). The rocks have high initial 87Sr/86Sr ratios (0.706760–0.708898), low εNd(t) values (−19.5 to −12.5), and negative εHf(t) values (−31.3 to −19.7), similar to the Early Cretaceous Jiaodong mafic dikes and intermediate–mafic volcanic rocks. These geochemical and isotopic characteristics indicate that the volcanic rocks formed through simultaneous fractional crystallization and crustal assimilation of a basaltic magma derived from metasomatized mantle. The metasomatized mantle source might have been produced by the recycling of subducted Yangtze Craton crust into the ancient lithospheric mantle of the North China Craton.

发育于长江中下游构造-岩浆-成矿带最东端宁镇地区的晚中生代中酸性-酸性侵入岩以富钠、高Sr和Ba、富集轻稀土元素,强烈亏损重稀土元素为特征,高场强元素Ti、Nb、Ta等表现出显著的负异常,岩石地球化学的总体特征类似于高Sr/Y的埃达克岩.但与长江中下游其他地区的高Sr/Y岩浆岩相比,宁镇地区的这些侵入岩体还表现出低的放射性成因Pb、更低的重稀土元素含量、相对高的MgO、Cr和Ni含量及M9#值等特征,推测它们的形成过程是由(再)富集的上地幔物质部分熔融形成的岩浆与古老的大陆下地壳物质部分熔融形成的埃达克质岩浆混合,混合岩浆在演化过程中还经历过较强的矿物分离结晶作用以及一定程度的上地壳物质混染.该再富集事件的发生可能与俯冲的古太平洋板块部分熔融所析出的熔体(或流体)交代上覆的地幔楔有关,导致原已富集的陆下岩石圈地幔更进一步富集挥发分以及不相容元素,古老的富集地幔中所累积的放射性成因Sr、Nd同位素被“中和”,该作用在长江中下游地区可能仅影响到最东段的宁镇地区,并没有波及到更靠内陆的其他地区.宁镇地区的这些埃达克岩侵位于100～108 Ma的早白垩世末期,晚于长江中下游其他地区高Sr/Y岩体长达30 Ma左右,其间存在着较长时间的岩浆活动静止期,意味着它们可能形成于不同的动力学背景.后者的形成可能与区内印支期—早燕山期陆内挤压造山后的应力松池,加厚的大陆下地壳及其富集的岩石圈地幔发生拆沉和部分熔融有关,这种发生在长江中下游广大地区的岩石圈减薄事件可能并没有波及到最东段的宁镇地区.而前者可能与早白垩世末期—晚白垩世初期,太平洋板块相对亚洲大陆板块运动方向发生了改变,中国东部大陆边缘进入拉张-裂解的构造环境有关,但其效应在长江中下游地区可能主要影响到了最东段的宁镇地区,其他地区对这次构造变动并没有产生明显的岩浆活动.

翁文灏先生提出“燕山运动”已经整整90周年,燕山运动对中国大地构造历史研究具有特殊的意义.文章回顾了“燕山运动”提出、发展和构造幕划分沿革历史,介绍与燕山运动相关的构造事件研究的最新成果和进展,重点阐述了中国大陆不同地区对燕山运动的沉积、变形和岩浆响应,进一步梳理了燕山运动幕式演化历史及其动力作用性质,探讨了燕山运动发生的板块动力学背景及其全球构造意义.研究认为,燕山运动是三叠纪东亚大陆雏形形成后的一次重大地质构造事件,起始于中侏罗世(170±5)Ma,先后经历175～136Ma主变形期、135～90Ma主伸展期和89～80Ma的弱挤压变形期等3个主构造运动时期.主变形期包含了北京西山和燕山地区发育的2个地层不整合事件:髫髻山底部不整合和张家口底部不整合,对应于翁文灏先生1928年定义的A幕和B幕.从区域上看,晚中生代燕山运动的启动和发展与古太平洋、新特提斯和蒙古-鄂霍茨克三大构造域洋壳俯冲消减历史和板块汇聚碰撞过程密切相关.晚侏罗世,东亚周邻多板块汇聚形成了3个巨型陆缘汇聚造山系统(北部蒙古-鄂霍茨克碰撞造山带、东部陆缘Cordillera型俯冲增生造山系统、西部班公湖-怒江俯冲碰撞造山系统)以及向陆内变形扩展系统,包括多方向的陆内造山带、鄂尔多斯和四川盆地的环形褶皱山系.陆内变形表现为远离汇聚板块边缘的大规模逆冲-褶皱构造、古老造山带的复活和广泛的岩浆成矿作用.结合古大陆分离-聚合过程的周期演变规律,本文提出晚中生代东亚多板块汇聚可能是未来亚美超大陆的起始点,燕山运动应是亚美超大陆诞生的“第一声啼鸣”.

LA-ICP-MS zircon U-Pb dating was carried out for two samples of porphyroclastic lava and rhyolite from the west Taipusi Banner,Inner Mongolia.As a result,their ages were obtained,which are 140.1±0.6Ma and 138.3±0.9Ma,respectively.The results show that all the rocks were produced by magmatic activities in Early Cretaceous. Porphyroclastic lava and rhyolite have the same geochemical features,characterized by high content of SiO2,Na2O+K2O and low CaO,MgO,TiO2and P2O5,and belonging to the high-K calc-alkaline series.A/CNK values of the rocks are from 0.99 to 1.13,suggesting that they are peraluminous.The rocks are characterized by LILE enrichment (Rb, Th, U) and HFSE (Ti, Nb, Ta) strong depletion. They are characterized by enriched LREE patterns with strong negative Eu anomalies(δEu=0.06~0.24),with high TFeO/MgO(5.64~43.29)and 104×Ga/Al(2.96~4.41) ratios,and strong depletion of Ba and Sr.All these geochemical data indicate that they are mainly aluminous A-type granite.Under the regional lithospheric extension,the asthenosphere upwelling and mafic magma underplating provided enhanced heat flux and trig-gered the partial melting of the overlying crust and then produced the porphyroclastic lava and rhyolite.

The Yanshan movement/orogeny has been proposed for 90 years, which is of special significance in the history of geological research in China. This study conducted a review by synthesizing major achievements regarding episodic deformation features, sedimentary and magmatic records of the Yanshan orogeny in China, and clarified the episodic tectono-magmatism and its geodynamic origins. The tectonic implications of the Yanshan orogeny are discussed in the context of global plate tectonics and supercontinent reconstruction. Lines of evidence from structural, sedimentary and magmatic data suggest that the Yanshan orogeny represents a regional-scale tectonic event that affected the entire China continent in late Mesozoic period. Numerous age and structural constraints consistently indicate that the Yanshan orogeny was initiated in the Jurassic (at ∼170±5 Ma). and was characterized by alternating stages of crustal shortening at ∼170–136 Ma, crustal extension at ∼135–90 Ma, and weak shortening at ∼80 Ma. The 170–136 Ma crustal shortening was reflected in the generation of two regional stratigraphic unconformities (the Tiaojishan and Zhangjiakou unconformities), which were initially named the A and B episodes of “the Yanshan Orogeny” by Mr. Wong Wenhao in 1928. Geodynamically, the Yanshan orogeny in East Asia was associated with nearly coeval oceanic subduction and continental convergence in the Paleo-Pacific, Neo-Tethys, and Mongol-Okhotsk tectonic domains. As a consequence, three giant accretionary-collisional tectonic systems were formed along the continental margins of East Asia, i.e., the Mongol-Okhotsk, Bangonghu-Nujiang, and SE China subduction- and collision-related accretionary systems. The Yanshan orogeny induced widespread crustal-scale folding and thrusting, tectonic reactivation of long-lived zones of crustal weakness, and extensive magmatism and mineralization in intraplate regions. Based on the time principle of supercontinent assembly and break-up, we propose that the mid-Late Jurassic multi-plate convergence in East Asia might represent the initiation of the assembly of the Amasia supercontinent, and the Yanshan orogeny might be the first “stirrings” that is a prerequisite for the birth of the Amasia supercontinent.

A combined study of whole-rock major and trace elements, Sr–Nd–Hf isotopes, and zircon U–Pb geochronology was conducted on late Mesozoic volcanic rocks along the Tan-Lu fault zone (the Anqiu, Gaoqiao, Juxian, and Junan regions) of Shandong Province, eastern China. The results constrain the petrogenesis of the volcanic rocks and provide important insights into the significance of the Tan-Lu fault zone for lithospheric thinning. The volcanic rocks are composed of basaltic trachyandesite, trachyandesite, trachydacite, andesite, dacite, and rhyolite, which yielded zircon U–Pb ages of 125.4 ± 0.9, 126.2 ± 1, 125.7 ± 1, 127.1 ± 1.2, 120 ± 0.65, and 122.8 ± 1 Ma, respectively, indicating eruption in the Early Cretaceous. A large amount of Palaeoproterozoic and Archaean inherited zircons exist in Anqiu and Gaoqiao volcanic rocks, but Neoproterozoic inherited zircons in Juxian and Junan volcanic rocks, in agreement with the age spectrum of the basement rocks of the North China Craton (NCC) and Neoproterozoic protolith ages of ultrahigh-pressure metaigneous rocks in Sulu orogenic belt, respectively. The volcanic rocks have high Na2O + K2O concentrations (5.94–11.33 wt.%), indicating that they are alkaline. All the rocks are characterized by enriched in light rare earth elements and large ion lithophile elements (e.g. Rb, Th, U, and K) but are depleted in high field strength elements (e.g. Nb, Ta, and Ti). Anqiu and Gaoqiao volcanic rocks have wide initial 87Sr/86Sr ratios (0.707678–0.711259), variable negative εNd(t) values (–15.2 to −11) and εHf(t) values (−19.5 to −2.2). The varied isotopic compositions and the abundance inherited zircons, together with mineral disequilibrium features, suggest that the Anqiu and Gaoqiao volcanic rocks were produced by the mixing of magmas from enriched lithospheric mantle and lower crust. The enriched lithospheric mantle originated from the ancient lithospheric mantle beneath the NCC, which was modified by the subduction of Yangtze crustal material. Juxian and Junan voalcanic rocks have initial 87Sr/86Sr ratios of 0.707502–0.709238, low εNd(t) values of −20.5 to −16.1, and negative zircon εHf(t) values of −24.6 to −16.4, similar to granitoids in Sulu orogenic belt, suggesting that they derived from similar crustal sources. Combining the existence of the Neoproterozoic inherited zircons and the isotope characteristics, we propose that the Juxian and Junan volcanic rocks were dominantly derived from partial melting of the Subducted Yangtze crust but with contributions from the mantle. The volcanic rocks along the Tan-Lu fault zone were produced under an extensional regime linked with lithospheric thinning in the eastern NCC during the Early Cretaceous. According to the characteristic spatial and temporal distributions of late Mesozoic volcanic activity along the Tan-Lu fault zone, combined with the distributions of regional adakitic rocks and the evolutionary history of the fault, we suggested that the Tan-Lu Fault played an important role in the initiation of lithospheric thinning and provide a favourable channel and beneficial conditions for magma activity.

In this paper,we report the geochronology,major and trace element geochemistry and Sr-Nd-Hf isotope data for the early Cretaceous volcanic rocks of the Qingshan Group in the Linqu area,with an objective to constrain the petrogenesis.The volcanic rocks are mainly intermediate rocks,with a SiO2 content varying between 54.41％～67.81％.Rock association consists mainly of andesite,trachyandesite,trachyte and trachydacite.These volcanic rocks belong to calc-alkaline series.Zircon LA-ICP-MS U-Pb dating yields an age of 121.3 ± 1.5 Ma for trachyandesite,indicating that the rocks crystallized in Early Cretaceous.The rocks are geochemically characterized by enrichment of LREE and LILE (e.g.,Rb,Ba,K),and depletion of HFSE (e.g.,Nb,Ta,Ti).These volcanic rocks have enriched Sr-Nd isotopic compositions ((87Sr/86Sr)t =0.704346～0.705831,εNd (t) =-14.6～-9.5),and have low Hf isotopic composition (εHf(t)=-29.3～-21.6).The rocks have the similar Mg# values as the melts produced by metabasite,with large range of Cr (26.7×10-6～239× 10-6) and Ni (10× 10-6 ～69.7× 10-6) content,and show significant mineral textural disequilibrium.The study further indicates that the Linqu volcanic rocks of the Qingshan Group may be the product of magma mixing between lower crust-derived melts of ancient North China Craton and mantle-derived melts of enriched mantle under the lithospheric extension setting.

Objective Shandong Province is divided into two parts by the Tan–Lu fault zone:the western part（Luxi）and the eastern part（Jiaodong）.Large-scale volcanic activity occurred during the Late Mesozoic in Shandong Province,eastern China（Fig.1b）,and was controlled by the Tan–Lu fault zone and its secondary faults.Mesozoic volcanic rocks in Shandong Province mainly occur within the Cretaceous Qingshan

Mesozoic volcanic rocks are widespread throughout the Great Xing’an range, NE China. Their ages formed from about 180 Ma to 120 Ma, with a strong peak about 125 Ma, and several weak peaks at ∼116 Ma, ∼140 Ma and ∼156 Ma respectively in age histogram. These complicated age spectrum points out that the volcanism may be related not only with the subduction of the Pacific plate, but also with closure of the Okhotsk ocean.

Mesozoic volcanic rocks are widely exposed in Zhenglan Banner of southeast Inner Mongolia.The volcanic rocks mainly consist of rhyolite,trachyte,porphyroclastic lava,ignimbrite,and obsidian,in which the porphyroclastic lava is the most developed.According to the results of the zircon LA-ICP-MS dating,the U-Pb zircon age of rhyolites is (141.4±0.7) Ma,that of felsitic mortar lava is (141.6±0.6) Ma and that of ignimbrite is (139.4±0.7) Ma.Within the error range,the formation ages of the three kinds of rocks are the same,which indicates that the time of the volcanic activity (from effusion to explosion and extrusion) lasted a short time.So they should be assigned to early Cretaceous Zhangjiakou Formation.Except for very few samples,the porphyroclastic lava that extruded in the late phase and the rhyolite-trachyte belonging to the early phase effusion facies are extremely consistent in the geochemical characteristics.They are rich in silicon and potassium,and poor in Ca,Mg and A1.So they could be classified as trachyte-rhyolite combination,and some samples have the features of pantellerite.They are enriched in Rb,Th,U and other largeion lithophile elements,and strongly depleted in Ba,Sr,Ti,P.The chondrite-normalized REE patterns show enrichment of light rare earth elements (LREE),strong negative Eu anomalies,and significant fractionation of LREE and HREE for the volcanic rocks (LaN/YbN=6.87-42.74,except for LQ-38).Compared with the early phase effusion facies lava,porphyroclastic lava has higher silicon and lower alkali,which shows that the magma chamber experienced obvious crystallization differentiation after effusion of the rhyolite and trachyte in the magma event.Then the magma with higher silicon and lower alkali extruded out of the earth's surface.The volcanic rocks of Zhenglan Banner area have the characteristics of A-type granites and possess the geochemical characteristics of A1 type and A1-A2 transition granite.The Nb/Ta ratio of the extrusive porphyroclastic lava and effusive rhyolites is 10.46-24.02,which is between the values of the crust and the mantle magma;Y/Nb,Ti/Yb,Ti/Zr also reflect the characteristics of crust-mantle mixing;Rb/Sr ratio is between 0.61-64.51(＞0.5),reflecting the characteristics of crust source.These data suggest that the volcanic rocks might have been produced in an extension environment of the transportation period of anorogenic and postorogenic activities,mainly being intraplate anorogenic activity.In addition,the volcanic rocks were probably derived from partial melting of the Precambrian lower crust which was strongly transformed by Mesozoic underplating and metamorphism.

The mapping method for continental volcanic rock field with the purpose of reflecting the volcanic characteristics is differ?ent from the traditional method suitable for sedimentary area, and this problem has been groped for over half a century in China. The"diplex mapping method"(lithofacies+stratigraphy) and the"volcanic construction-lithologic rock facies-volcanic sequence"have been explored, with important progress and achievement obtained in local area. Nevertheless, the fact that volcanic rock was mapped as stratum (formation) did not get out of habitual practice in actual mapping at the national level. It is still a significant task to explore and summarize mapping method suitable for continental volcanic rocks. Volcanic facies is a foundation for restoration of the processes of volcanism and ancient volcanic apparatus, and should be shown as key elements in volcanic geological maps, whereas lithological as?sociation is a most reliable basis for assigning types of lithofacies. The continental volcanic characteristics can be well reflected on the basis of lithological association-lithofacies mapping.

Scientific Drilling No.1 in the Lujiang-Zongyang basin is the pilot hole of Chinese Continental Scientific Drilling.The drilling with an end depth of 3008.29 m successfully reveals the internal geological structure of the Luzhong basin.This study carried out a systematic study of geochronology,petrology and geochemistry on the concealed intrusions in LZSD-01.LA-ICPMS zircon U-Pb dating yields the ages of 132.6±1.2 Ma and 133.28 ±0.4 Ma respectively for concealed syenite and monzonite,suggesting that they were the product of magmatic intrusion at the end of Zhuanqiao volcanic cyclic in this basin.Magmatic rocks are characterized by nearly saturated SiO2,high contents of Al2O3 and K2O,and low TiO2.The concealed intrusions of LZSD-01 also have relatively high LILEs such as Rb,K,Pb,but depleted HSFEs such as Nb,Ta and Ti,indicating that the intrusion should be shoshonitic rock.The Sr-Nd isotopic composition suggests that the primary magma of the concealed intrusions in the Qianpu area may derive from enriched mantel type-Ⅰ.Elemental evolution trend shows that fractional crystallization of major minerals such as plagioclase,pyroxene and ilmenite may be the leading mechanism and concealed intrusions likely formed in the tectonic setting of intraplate extension.

Located in the Huzhou-Anji volcanic basin in the northeastern margin of Zhejiang-Ganzhou volcanic rock belt,the volcanic/subvolcanic rocks consist dominantly of intermediate-felsic to felsic rocks with minor intermediate component and lack of mafic component,and represent a intermediate-felsic magmatic rocks series.The rocks are lithochemically characterized by high-K and rich alkali,suggesting that intermediate rocks belong to shoshonite series and the intermediate-felsic and felsic rocks belong to high potassium calc-alkaline series.In geochemistry,the volcanic rocks in the basin are enriched in large-ion lithophile elements (LILE) and light rare earth elements (LREE) and depleted in high field strong elements (HFSE) such as Nb,Ta and Ti.Major and trace elements variation regulation of the volcanic rocks reveals that fractional crystallization is the main mechanism of the magma evolution in the basin.Different mineral facies is produced at different stage of magma evolution,with plagioclase being the key mineral of fractionation and crystallization.Hornblende may be an important fractionation mineral during the intermediate to intermediate-feslic magma evolution,and K-feldspar and biotite minerals also play an important role in the fractionation of intermediate-felsic to felsic rocks.Our dating results show that the LA-ICP-MS zircon U-Pb ages of three episodes of volcanic activities in the basin are around 128～130 Ma,which fall within the error range,indicating that the main volcanic activities lasted for very short time.The SHRIMP zircon U-Pb dating yields an age of 136±1 Ma for the trachyandesite agglomerates,probably indicating small-scale weak mafic volcanic activities at the initial stage of the basin.It can be speculated that the Huzhou-Anji volcanic basin developed in a post-orogenic environment in the active continental margin,the magma formation was probably controlled by lithosphere delamination or subduction slab breakoff,with parent magma formed by partial melting of mafic lower crust material and with barely mantle material involvement,and the resulting andesitic-dacitic magma experienced strong fractional crystallization at the shallow magma chamber.

庐枞火山岩盆地南侧的钾质侵入岩带由正长岩-石英正长岩-正长花岗岩组成,以石英正长岩为主.它们的形成时间介于123～130 Ma之间,峰值约为126 Ma,其中正长岩和石英正长岩的形成时间稍早,而正长花岗岩的形成时间略晚.整个钾质侵入岩带的侵位时间晚于庐枞盆地内的橄榄玄粗质火山作用约4～7 Ma,也是长江中下游地区除最东段的宁镇地区外中生代最晚的岩浆活动产物之一.地球化学上,该钾质侵入岩带以高钾、富碱、富集Rb、Th、U、K等强不相容元素和轻稀土元素、亏损高场强元素Nb、Ta和Ti为特征.它们的母岩浆主要是由富集型上地幔部分熔融形成的,从正长岩经石英正长岩到正长花岗岩的演化主要受矿物的分离结晶作用控制,地壳物质同化所起的影响不大.但与同样来自富集型上地幔部分熔融的庐枞盆地内火山杂岩的母岩浆相比,前者的母岩浆来源深度可能更大些或其中包含了更多来自软流圈地幔的组分.两者的演化路径也完全不同,钾质侵入岩带的母岩浆除经历过高压下的分离结晶作用外,晚期在低压下还经历过长石为主,可能还有黑云母的分离结晶,甚至上地壳物质一定程度的混染作用;而盆地内火山杂岩的母岩浆低压下矿物的分离结晶作用及上地壳物质的混染都不明显.庐枞盆地南缘的富钾侵入岩与盆地内的火山杂岩一样,地球化学上都具有明显的大陆弧的特征,暗示它们的岩浆源区可能形成于俯冲带环境,意味着扬子地块北缘先前(推测为古元古代晚期)曾发生过俯冲作用,上地幔的交代富集可能就与这次的俯冲作用有关.

The volcanic rocks in the Huaining basin,which is one of a series late Mesozoic volcanic basins&nbsp;developed the Middle—Lower Yangtze region,are main belong to shoshonitic series,but appear bimodal volcanic association of high-K calc-alkaline series in the late stage of volcanism.In this work,we used LA-ICP-MS zircon U-Pb technique to date the trachyte and felsophyre samples from the Pengjiakou formation,early volcanism in the basin,and rhyolite from the Jiangzhen formation,late volcanism in the basin,yield emplacement ages of 128.7 ± 0.8Ma,126.3 ±0.7 Ma and 123.5 ±0.7 Ma respectively,which further confirmed that the late Mesozoic volcanism in the Middle—Lower Yangtze region was ended latest in the Huaining basin.Based on comparison with other volcanic basins in the Middle—Lower Yangtze region,the rush time of volcanism in whole volcanic basins are similar (130 Ma),but the finished time of volcanism in the Huaining basin was late about 6 Ma than other volcanic basins.This combined with the earliest volcanism developed in the Liyang basin(140Ma),show that the volcanism migrating currently northwestward with time,and migrating from center area of the volcanic belt outward subtilly.The bidirectional migration of the volcanism may be the result of relative movement of the Pacific plate and the Asia continental plate and late Mosozoic lithospheric thinning happened in the Middle—lower Yangtze region.