SHRIMP dating of volcanic rock in the Zhangwu-Heishan area, West Liaoning province, China: Its relat

Mining Science and Technology( China)21(2011)701-708Contents lists available at SciVerse Science DirectMining Science and Technology( chinaELSEVIERjournalhomepagewww.elsevier.com/locate/mstcshrimP dating of volcanic rock in the Zhangwu-Heishan area, West Liaoningprovince, China: Its relationship with coal-bearing strataCai Houana, b Xu Debin, Li Baofang Shao longyia state Key Laboratory of Coal Resources and Safe Mining China University of Mining 6 Technology, Beving 100083, Chinab College of Energy. China University of Geosciences, Beijing 100083, China"College of Earth Sciences, China University of Geosciences, Beijing 100083, ChinaARTICLE INFOABSTRACTArticle history:The Zhangwu-Heishan area is located to the east of the Fuxin-Yixian Basin and is mostly covered withReceived 22 December 2010volcanic rock. At various periods, different geologists had varying opinions about their age and periodsReceived in revised form 19 January 2011of volcanic eruptions, especially on sequences between volcanic rock and main coal-bearing strata, whichAccepted 17 February 2011Available online 26 October 2011affect the direction of searching for coal, as well as prospecting the entire research area. During our studywe carried out detailed field investigations in this research area: observed and recorded the main repre-sentative outcrops of volcanic rock. We collected over 20 volcanic rock samples and tested the SensitiveHigh Resolution lon Microprobe ll(SHRIMP ll)u-Pb isotope age of 11 samples. The age of our volcanichangwu-Heishan arearock samples ranged between 56.0*2.9 and 132.3* 2.3 Ma. After taking earlier investigations into con-sideration, we concluded that, except for a suite of paleogene olivine basalt the volcanic rock in theHRIMP U-Pb isotopic ageZhangwu- Heishan area is younger than the coal-bearing Shahai Formation. It is therefore most unlikelyoal-bearing stratato find coal seams equivalent to those of the early Cretaceous Shahai Formation in Fuxin Basin below vol-anic rock.e 2011 Published by Elsevier B V. on behalf of China University of Mining Technology1 Introductioncoal-bearing strata were identified and the directions of preciousfossil discoveries and the search for coal definedThe Zhangwu Heishan area is located to the east of the Fuxin-Yixian Basin. Besides the quaternary soil, our research area is mostly 2. Geology backgrounddiate-basic andesite trachyandesite and basaltic andesite and smallWest Liaoning province is located in the eastern section of theamounts of dacite and rhyolite(Fig. 1). At various periods, a number Yanshan Platform fold Belt to the north of the Sino Korean Para-of research units or individuals had different opinions about their platform and belongs to the eastern extension of the Yanshanage and volcanic eruption periods, especially about the sequence Orogenic Belt(see Fig. 1). The Yanshan Orogenic Belt. inside thebetween volcanic rock and main coal-bearing strata which affect North China Platform, experienced intense tectonic deformation,the direction of searching for coal and prospecting of the entire magmatic and volcanic activities and syn-orogenic sedimentationresearch area []. Investigations about the age and sequence of during the period of the Jurassic-Cretaceous Yanshan Movementvolcanic rock, volcanic eruption periods and source regions are In the end, it became a typical intraplate orogenic belt far awayimportant for the discovery of fossil beds, structural evolution of from any contemporary plate boundaries [13]. The subduction ofbasins and accumulation of fossil fuels. Therefore these key prob- the Pacific Plate resulted in a NE-trending thrust nappe structurelems should be solved immediately. Our field investigation started of the late Jurassic Epoch and an extension structure of the earlyat a high degree of intensity with the Yixian Basin and gradually Cretaceous Epoch. Prior to the Mesozoic Period, the research areaadvanced to the north and northeast of the basin, where major rep- was a large tectonic uplift area. The fault-folding at the early stagesresentative volcanic outcrops were observed and recorded. Volcanicof the Yanshan Movement formed the lower-middle Jurassic Seriesoutcrops and rock cores in different horizons were sampled forSHRIMP U-Pb isotopic dating. Based on previous research findings, Beipiao Formation At the middle stages of the Yanshan Movement,the age and main eruption periods of these volcanic rocks were basi- large-scaled fractures occurred and were accompanied by magcally determined; the sequence between volcanic rock and main matic eruption, which essentially formed the Mesozoic tectonicframework. In the middle and late Jurassic Period, due to a south-4 Corresponding author. Tel: +86 13810170035.ward movement of the Siberian Plate and westward subduction ofE-mailaddress:tonnycha@163.com(HCai)the pacific Plate, t中国煤化工 as extruded in1674-5264/S-see front matter o 2011 Published by Elsevier B V on behalf of China University of Mining& Tedoi:lo.016msc2011.02028YHCNMHGH Cai et aL /Mining Science and Technology( China)21(2011)701-708Zhangwu county这将Fig- 1. Geological map of the Zhangwu Heishan area and sampling location.NW-SE direction and mainly features NE- and NNE-trending SHRIMP U-Pb isotope analyses on 11 volcanic rock samplesstructures [14. West Liaoning province is bordered by the Although the research on the sequence of volcanic rock in theChifeng-Kaiyuan Fracture to the north, is adjacent to the Inner study area started early and many units and individuals particiMongolia-Xing 'an Orogenic Belt and the Songliao Basin. It is also pated in the research, little systematic and canonical work wasconnected to the Ew-trending Yanshan Orogenic Belt to the west performed. The history of research can be classified into threeand separated from the liaodong Uplift Zone by the yilan-Yitong stagesfracture Zone to the east. Its tectonic position belongs to the transition zone of the North China Block, the Liaodong Uplift Zone and(1)Before 1970: Sun placed the gangtai volcanic rock in the cat-the Inner Mongolia-Xing an Orogenic Belt [151egory of Badaohao Coal Measures after investigating a Bad-aohao Mine. In the 1950s, wang et al. dug trenches nearGangtai Village to validate their sequence and further iden3. History of studies on volcanic rock in the research areatified the sequaffected later中国煤化工which greatlygeologist Shi-Isotopic dating of volcanic rock in the study area started earlyjingdu performand many results have been published [16-34]. We conductedCNMHGhaffected laterock below theH. Cai et aL Mining Sdence and Technology( China)21(2011)701-708coal strata in the Fuxin Basin with the gangtaishan volcanicof the Fuxin and shahai Formations below the volcanic rock.rock in the Badaohao mining area and viewed the badaohaoWhile others agree with the earlier investigators in terms ofCoal measures as the sum of the shahai and Fuxinsequence, they have different opinions about stratigraphicformationscorrelation, think that it is basic for the lower part and inter-(2)Based on this basic understanding, the principles of explora-mediate to intermediate-acidic for the upper part and conse-on strategies and prospecting work deployed during thequently view this basic rock area as a new target for coal1950s and 1960s were described as follows: the coal-bearingprospecting. Positive aspects of this opinion include astrata in the Fuxin and shahai Formations were the targetcomprehensive analysis of various geological factors, a preli-with the horizon of the final gap in the volcanic rock seriesminary understanding of volcanic geology, material supple(later referred to as the Yixian Formation). The prospectingments to previous opinions and drawing the attentions ofea consisted of non-volcanic rock, especially the negativecolleagues. But volcanic geology, structures and othertectonic area with red variegated rock series, Target areasresearch have not been fully performed due to the difficultwere always selected on the basis of achievements in geo-in drilling through volcanic rock. Hence, our work focused onphysical prospecting. Except for Xielintai and Leijia, thestratigraphic research. We combined previous research findresults are as follows: 1: the volcanic rock series disappearedings, started with field work, focused on volcanic rock seriesafter the red variegated rock series was drilled through withwith low level research and obtained results which will beTaihe and Baishantu as representative areas: Il: limited bydescribed in the following sectionsexploration engineering ability at the time many drillholesonly reached the red variegated rock series and Ill: only a 4 Results and discussionfew drillholes disclosed basal strata of metamorphic rock.(3)Since the 1970s, the Regional Geological Survey Team of Lia-.1. Samples and results of isotopic datingoning province has carried out geological surveys on a scaleof 1: 200 000 in this area and the northeast china Bureau ofThe reported data on the absolute age of volcanic rock in thisCoal Geological Exploration has explored for coalfields in the area are mainly derived by K-Ar or Ar-Ar methods [11, 17.me area. At the beginning of the 1990s, the Northeast 22-27 During our research, 11 volcanic rock samples were colChina Bureau of Coal Geological Exploration and Liaonilected and analyzed with the high-precision SHRIMPU-Pb isotopIcTechnical University conducted studies to find coal below dating method. Specific sample IDs, sampling location, lithologythe volcanic rock. Coal prospecting has been carried out in determined through slice identification are shown as Fig. 1 or prethe Badaohao, Liuhetun and east peripheries. During this sented in Table 1. Detailed test data will be published in anotherperiod, a few scientists objected to the traditional strati- paper Sample Ni is from the bottom of borehole BS13 in the Bad-graphic classification and coal-seeking direction, which aohao exploration area, heishan county [33 Zhangluotun trachyactually had no effect. Their basic understanding can be andesite(N2), a quartz trachyandesite found on the southeast sidesummarized as follows: some geologists think that the vol- of Badaohao, clearly intrudes into the tuffite and tuffaceous clasticcanic rock series(the Gangtai Formation), widely spread in rock, generally inclines to the inside of volcanic conduits and has athe whole area, lies above the Badaohao Coal Measures large dip. Its fluidal structures are developed inside the trachy(Xielintai and Leijia) and suggest seeking coal-bearing strata andesite and seem almost vertical at these volcanic conduits(seeSummary of SHRIMP U-Pb isotopic dating result of volcanic rock in the study area.Sample Sampling locationColorgy by Age( Ma) Volcanic Horizon inOriginal horizon in 1: 50,000 Horizonsliceeruption 1: 200,000 geologic geologic map by the 107th currentlyidentificationmap(1972)ade1160 m in borehole BS. Grayish Trachyandesite1257±17②-③Tuhulu Formation13 at BadaohaoZhangluotun to thePurplish Rhyolite1249±29③Tuhulu Formation Tuhulu Formation J3tTugulusoutheastTohe eastGreyQuartz115.5±15Tuhulu formatioin Heishan dSalishan inco nav angtu560±29Covered withCovered with QuatenaryPaleogeneDongliangshan inTrachyandesite1297±1.6②Tuhulu Formation Daxinzhuang FormationYixianBeizhuanchengzi in the GreyAndesite1323±23①Tuhulu Formation Yixian Formationxiansouthwest of QinghemenHuanghuashan in the Grayish Dacite1263±17Tuhulu Formation Yixian Formationsoutheast of Yi county yellowJtFormation K,tN11 Lijiatai in the southeast Claret Trachyandesite 125.8:1.9 22Yixian FormationDalinghe Formationof Yi countynglonggou in theAndesite1270±5,1②Daxinzhuang Formationsoutheast of Yi countyFormation K,tN13 Tonglvgou of Songbahu Caesious Andesite1223±4.5③Tuhulu Formation Yixian FormationLuotaishan in the north offwhite AndesiteTuhulu FormationJatYH中国煤化工xnCNMHGKIyH Cat et aL/Mining Science and Technology(China)21(2011)701-708(b)(d)(eBack side of(5)BentoniteIndesit(a) Hypabyssal andesite at Xiaoliangshan in the northest of Liangshancommunity. Xinmin counb)Pillow lava and fragmented breccia at dagubentaogaic) Alkaline baslt developed with cleavages at Jianguo of Wuhuanchiunship, Fuxin cityasaltic andesite with vesicular amygdaloidal structure at shirazwinship to the northeast of Xiniitune)Bentonite deposit at Jianshan unconformably covered with hypabyssal(f Baked layer formed through extravasation - facies basaltic andesite atdouyawopu of Zhangwu county covering the mudstone(g) Hypabyssal trachyandesite at Zhangluotun(h) Andesite at Xiashitou of Cangtu county overlying the bentoniteFig. 2. Pictures of rocks.1g. 2g)[34]. At Dongbaizitun of Faku county(see Fig 3c)and otherplaces, we found that the basalt covers or intrudes into the Jiufo. small hills due totang Formation. Liangshan trachyandesite(N3)lies towards the System: a non-confYHnorthwest of Liang中国煤化工 f independentCNMHGthe QuaternaryH Cal et aL/ Mining Science and Technology(China)21(2011)701-708in a small hill to the north of Shuangshanzi and a 30-40 cm thickmiddle of the Jurassic System. Some geologists define thembaked layer lies on top. the trachyandesite is greenish black andas the"Wangijiatun Formation"and think that they belonghas a compact and even structure, with well developed fluidalto an early stage of the Cretaceous palaevolcanic rock seriesstructures and columnar joints. the structures are almost vertical(Yixian Formation )and are equivalent to the "Baiqi FormaThe samples were collected from volcanic conduits(see Fig 2a).tion"or the"Zhangjiakou Formation"in northern HebeiSample N4 is collected from Alishan of Yaocangtu Sample N5province. As well, similar phenomena and bed sets are foundoriginates from Dongliangshan of Heishan county. The samplesin Inner Mongolia, Ningcheng and Zhangjiakou in northernfor isotopic dating of the Fuxin-Yixian Basin were collected fromHebei province. In other words, intermediate-acidic volcanicBeizhuanchengzi in the southwest of Qinghemen, Huanghuashan,rock occurred earlier, covered with Rehe fossil organismsLijiatai, Xinglonggou and Songbahu southeast of Yi countybearing sedimentary rock and basalt strata.(Fig. 3d), Tonglvgou and Luotaishan in the north of Badaohao De-(2)Sedimentary segment. As far as we know, this segment istailed sampling locations are shown in Fig. 1pread over the entire area, differs only in depth, ofunknown thickness, varies in rock assemblage and in a pre4.2. Discussionliminary classification can be divided into two typesL. The Zhujiawobo type. The strata are thick and the sedimen4. 2. 1. Bottom-up lithostratigraphy of volcanic rock seriestary rock is rich in tuff and close to a coal-bearing sedimen-tation type in terms of color, lithology, bedding-plane(1)Acidic, acidic-basic and intermediate-acidic volcanic lavastructure and fossils. it is occasionally mixed with thin coaland its clastic lava, agglomerates, volcanic breccia and varistreaks or high-carbon mudstone and melanocrate: repre-ous tuff segments are always colorful and have distinct feasentative places are gullies in Zhujiawobo village, Haertaotures. They are distributed in the shape of circles or irregularTownship, whose lower part have faulted contact with thecircles and laminated in some segments. Their spatial distrimetamorphic rock series of the pre-sinian system. The com-bution characteristics and occurrence are of the centralposition of basal conglomerate shows no evidence of intenseeruption type with a relatively high explosion index. Perlite,volcanic activity during pre-sedimentation, i. e, it is either apitchstone, obsidian, zeolite tuff and other non-metallicpolymictic or ancient continental substance.ndustrial minerals and rocks are often developed in thisIL The Paozi type. This type is mainly found towards the middlelayer. These are mainly found in Houxinqiu, Fangshan townand east of this area, is generally glaucous, ficelle and isabel-in volcanic clusters south of this area. Its rock assemblage isline, takes the shape of medium-thick lamination, has finemainly characterized by rhyolite, quartz andesite, quartzlithology, is typically characterized by sandstone and silt-trachyandesite, etc In the past, it was generally thought thatstone and is occasionally mixed with thick and laminar conthese acidic volcanics lie at the top of volcanic rock seriesglomerate. It has mild dip angles, crops out in a large area, itswith signs of magma splitting and evolution. These phenomthickness unknown. the former Geological Brigade #101ena found during our investigation can almost confirm thatdrilled borehole #11 at Madewobo, which penetrates volca-they are the bottom strata of the entire volcanic profilenic rock, discloses an apparent thickness of about 300 m, butThe same phenomena are found at the juncture betweendoes not pierce it. Several types of freshwater molluscathe jinyang and Fuxin-Yixian Basins so much so that somefossils(common species of Jehol Biota) were found theregeologists have recently defined them as the"TiaojishanCompared to the Zhujiawobo type, this segment is acidic,Formation"and are of the opinion that they belong to thecontains many tuffaceous (volcanic) substances and(aKg①ADa Sketch of volcanic rock at dawulabac2)Sketch of the relaionship between the bentonite atJianshan and volcanic rock at Jiangtashan()Sketch of contact relationship between volcanic rock ofD) Profile chart for detailed route of cretaceous strata on eastside of Yixian Basin母岡圃圖圖豳嚼〖〖邨國FL 3. Fleld sketch of rescarch area.(1) Conglomerate: 2) sandstone:(3)mudstone;(4)marlite: (5)trachyandesbreccia: (9)breccia-bearing tuff: (10)rhyolitic tuff: (11)femiallophanoid: (12)Quaternary System; ( 13)lower pleistol(16)Yixian Formation: ( 17)hypabyssal trachyandesite: (18) Jiufotang Formation.YH中国煤化工te:(8) volcanicCNMHGshahai FormationH Cat et aL/ Mining Science and Technology( China)21(2011)701-708consequently belongs to the sediments formed after equivalent to the Gangtaishan, Yushugou, Daxingzhuang or Zhanghe eruption of acidic volcanic rocks. The distribution laogongtun formationsof volcanic rock is caused by continental factors.Outcrops of the first set of early cretaceous volcanic rock include(3) Eruptive Basaltic Segment. This segment lies in the basaltic andesite in Shijiazi Township to the northeast of Xinlitunnortheast and middle north of the research area, is (see Fig 2d), which features a large amount of vesicular and amy-wide spread, covers 1/3 of the entire area, but is not daloidal structures and contains abundant agate. Hypabyssalvery thick Sedimentary formation below this segment andesite in Luotaishan overlies the outcrop of a coal-bearing seriesis often found in natural gullies. As far as we know, it of the Beipiao Formation of the early Jurassic Epoch and is the low-could belong to the uppermost section of volcanic est intermediate volcanic rock of the early Cretaceous Epoch in thisstrata without any overlay. In some places, a grayish area. This set of volcanic rock is referred to as the Daxingzhuangclaret lava bed is often found below this segment Formation on the 1: 200,000 geology map, which may be incorrect.and easily defined as andesite or other intermediate- for based on its age of 129.0+ 2.4 Ma, determined by SHRIMP. itbasic rocks. As well, it sometimes takes the form of should be included in the Yixian Formation. Hypabyssal andesitelaminar quartz andesite with a half concentric circle in Shuangshanzi of Liangshan is found in Shuangshanzi towardsshaped cleavage; a few signs indicate that it is related the southwest of Xiliangshan town, Xinmin county, takes the formto the assimilation of basic rock activities. For exam- of independent small hills due to weathering and is covered by theple, the weathering of basic rock coexists with the Quaternary System. Lava flows, showing a lack of conformity, covercrystallization of quartz and it is purple black, so it the sedimentary rock in a small hill, with a 30-40 cm thick bakedcould belong to the early period of this basaltic layer on top. The andesite is dark gray and has a compact and evenstructure. fluidal structures and columnar joints are developed(see(4) Subvolcanic rock and volcanic intrusive facies rockFig 2a), of which the former are almost vertical. The samples werescattered in the area can be ordered in a specific cate- collected from volcanic conduits. this set of volcanic rock is denom-gory in a unified manner and are thought to be related inated as the Daxingzhuang Formation on the 1: 200,000 geologyto acidic rock activities at an early stage and belong to map, has an isotopic age between 129.54 1.6 and 129.7+1.6 Mathe sediment formed after an effusive period. Basic determined by SHRIMP, belongs to older volcanic rock and is corre-volcanic intrusive facies rock is the product after an lated with the Yixian Formation in Yi county. Hypabyssal andesiteeffusive period of basalt and is found along the Jiufu in Zhangluotun to the southeast of the Badaohao Coal Mine clearlyvillage in the northwest of this areaintrudes into the tuffite and tuffaceous clastic rock, generallyinclines to the inside of volcanic conduits and has a dip angle of40-50. Fluidal structures are developed inside the trachyandesite4.2. 2 Age and sequence of volcanic rock in the Zhangwu-Heishan area and are almost vertical in their volcanic conduits. This set of andes-During our field work, we investigated volcanic sequences and ite was originally denominated as the Yushugou Formation or theeruption periods and came to the conclusion that three suites of Daxingzhuang Formation, has an isotopic age of 124.9* 2.9 Ma asCretaceous volcanic rock in the Zhangwu-Heishan area could be determined by SHRIMP. It belongs to older volcanic rock and is cor-distinguished, based on our investigation and the results of isoto- related with the Yixian Formation(see Fig 2g).pic dating. The first set of volcanic rocks lies in the lowest horizonThe second set of early cretaceous volcanic rock features trachconsists of intermediate-basic basaltic andesite, features a large andesites and bentonites. the bentonite deposits are found in halaamount of vesicular amygdaloidal structures, is the result of fissure and Shaojianshanzi in the southwest of zhangwu county. in Xiashitueruption and was formed during tectonic activities. the second set of Yaocangtu in the northwest of Xinlitun and in Douyawopulies in the middle horizon, consists of intermediate trachyandesite, towards the southeast of Zhangwu county. Bentonite deposits arefeatures trachyandesite and bentonite deposits produced by alter mainly composed of montmorillonite minerals, accounting for overtion and was formed during a tectonic stabilization period. The 80% of bentonite deposits and are of volcanic or sedimentary gene.third set lies in the highest horizon, consists of compact intermedi- sis. Sedimentogenic bentonite is the result of hydrolysis, diageneate-basic basaltic andesite, is also the result of fissure eruption and weathering or low-temperature hydrothermal alteration of inter-is mainly characterized by hypabyssal andesite and overlies the mediate-basic volcanic rock, especially trachyandesitic pyroclastbentonite or other older strata of non-conformity. Lava flows and or volcanic ash falling into the lake basin. This bentonite is mostunderlying strata often produce about 30 cm thick baked layers likikely contemporaneous with th(see Fig. 2f) showing lack of conformity and are overlain by a Huanghuashan, in which case it represents the product of the sec-coal-bearing series of the Shahai Formation(the Badaohao Forma- ond set of volcanic eruptions in this area. The outcrops include:tion). this third set of volcanic rock could be of the Gangtaishan (1)bentonite deposits in the Hala and Shaojianshanzi areas andFormation in Xinlitun, referred to by Tan, is contemporaneous with (2)bentonite in Yaocangtu. Bentonite deposits in Hala andthe Yushugou Formation to the west of Yi county, also known as Shaojianshanzi are found towards the southeast of Zhangwu countythe Daxingzhuang Formation in the 1: 200,000 geology map of and between Paozi and Daguben, are covered with andesite, a laterthe Regional Survey Team of Liaoning province, and the Zhanglao- product of erosion, overlying clastic rock(see Fig. 2e and Fig 3b).gongtun Formation as denominated by Wang et al. [1,9. 10]The bentonite is closely related to the trachyandesite in Huanghua-From the aspect of lithology and eruptive sequence, correlated shan in terms of composition and genesis, shows an interruption inwith contemporaneous volcanic rock in Yi county. the first set of deposition with the overlying basalt andesite and should be eitherbasaltic andesite in the Zhangwu Heishan area is equivalent to part of the Gangtaishan Formation(see Fig 3a). the Yushugou orthe second set(the main episode)of basaltic andesite in the Yixian Daxingzhuang Formations. Bentonite in Yaocangtu is found inFormation. The second set of intermediate trachyandesite and Xiashitu of Yaocangtu towards the northwest of Xinlitu(seebentonite is equivalent to the breccia in Huanghuashan and should Fig 2h) is covered with andesite, erupted at a later stage, and showsbe included in the Huanghuashan Formation. The third set of the interruption in deposition between stages. A bentonite layerIntermediate-basic basaltic andesite, overlying the trachyandesite overlies a set of clastiand underlying the Badaohao Formation, could belong to volcanic the bottom-up and中国煤化工 uning expansionrock of the middle stages of the early cretaceous period and is of the lake basin.CNMHGH. Cai et aL Mining Science and Technology(China)21(2011)701-708The third set of early cretaceous volcanic rock features interm108 Ma. It features alkaline basalt in the upper section ofdiate-basic basaltic andesite, overlying the bentonite, the result ofJianguo and Wuhuanchi towns and is mainly found in Doua new round of volcanic eruptions and was formed in the middle ofawopu and Yaocangtu in Zhangwu county.the early Cretaceous Epoch, with an absolute ag(3)No matter whether it is the Yixian Formation of the first110 Ma. It crops out at Hala and Shaojianshanzi in the southwestycle. the Gangtaishan Formation of the second cycle or con-of Zhangwu county, in Xiashitu of Yaocangtu in the northwest oftemporaneous volcanic rock with different names(such asXinlitun and in douyawopu towards the southeast of ZhangwuDaxingzhuang, Yushugou or Zhanglaogongtun Formationcounty. the bottom of this set of basaltic andesite, often baked,the early cretaceous volcanic rock in the Zhangwu-Heishanunderlies the Jiufotang Formation, showing a lack of conformityresearch area is older age and has a lower horizon than thewith the formation. the layer below this set of volcanic rock isBadaohao Formation or the contemporaneous Shahai Formaabundant in"Jehol Biota"fossils. Bentonite deposits represent antion. hence the possibility of finding coal of the Badaohao,ancient denudation plane, contemporaneous with andesitic volca-Shahai or Fuxin formations below this volcanic rock is lownic rock in Huanghuashan. Hypabyssal andesite in Hala andShaojianshanzi is found in the southwest of Zhangwu county andbetween Paozi and daguben and overlies the bentonite which, in Acknowledgementturn, is underlain by clastic rock. The interruption in depositionoccurs between the bentonite and overlying andesite(seeThis study is supported by the National Natural Science Founda-Fig 2e). The andesite in yaocangtu lies in the northwest of Xinlitun. tion of China(No. 40672103 )The basaltic andesite in Xiashitu of Cangtu township overlies thebentonite, indicating that the interruption in deposition occurred Referencesbetween the basaltic andesite and the bentonite. the overlyingbasaltic andesite is the third set of volcanic rock in this area( see[11 Tan XC. Beipiao coal field in Chaoyang county, Rehe city. Geol RepFig. 2h), with an absolute age of 115+ 1.5 Ma. Extravasation-facies1926: 8: 45-57 in Chineselbasaltic andesite in douyawopu of Zhangwu county crops out at/L Zheng SL Zhang LI Pu RG Zharand paleontology in Western Liaoning province-1. Beijing: GeologicalDouyawopu in the southeast of Zhangwu county and is the resultof a new round of volcanic eruptions after the trachyandesitic [3] Ren D, uo ZG, Lu Lw. Ji SA Tang FJin YGet al.A further contribution to theurassic Yixian formation in Western Liaoning. Geoleruption in this area. this shows the interruption in depositionbetween the basaltic andesite and the underlying sedimentary 14] Chen Yx. Chen wj. Mesozoic volcanic rocks in Westem liaoning and adjacentrock. A baked layer was formed between the fissure-eruptionextravasation-facies basaltic andesite and the underlying argilla- 15| Chang Zi wang YQ. Wang XL The late Mesozoic strata and discussionceous rock(see Fig. 2f). Alkaline basalt(see Fig. 2c)in Jianguo ofWuhuanchi Township was observed on site and sampled. ThisHouse: 1999. p. 13-26 [in Chines[6] Sun G, Zheng SL New proposal onand correlation of Mesozoic frombasalt has a low zircon content due to being a basic volcanic rock,hence u-pb isotopic dating analysis was not carried out.[71 Wang GH, Zhang CH. Wang GS.Tectonic framework of WesternPaleogene basalt cropping out at Nalishan of Taogai in Dagubenevolution during Mesozoic. GeoscienceTownship is an olivine basalt. According to U-Pb isotopic datinganalysis, it is 56+ 2.9 Ma old and belongs to basic effusive rock [8] Ji Q Mesozoic jehol biota of Western Liaoning. China. Beijing: GeologicalPublishing House: 2004. p. 95-159 lin Chineseof the paleogene period[9] Wang WL Zhang 4. Zheng SL Zheng Y]. Zhang H u ZT et al. A new study onthe stratotype and biostratigraphy of the Yixian stage in the Yixian-Beilegion. Liaoning. Acta Geol Sin 2004: 78(4): 433-47 lin Chinese110] Wang WL Zhang H Zhang L], Zheng SL Yang FL Li ZT, et al. Standard section of5 ConclusionsTuchengzi stage and Yixian stage and their stratigraphy, palaeontology andtectonic-volcanic actions. Beijing: Geological Publishing House: 2004. p 343434(1)In our investigation, we collected over 20 volcanic rock sam[11 Li DM. Chen CL Li Q Zheng Dw. Constrain the time of the paleocoenosis fossilples from the Fuxin-Yixian Basin and the Zhangwu-Heishanarea and conducted 11 SHRIMP U-Pb isotope analyses. Based006: 22(6): 1627-32 in Chinese).on the age of the Mesozoic volcanic rock in Western Liaoning /121 Cai HA Research on the sequence stratigraphy of Badaohao coalvolcanic horizon in West Liaoning province and the coal-searching proprovince, cretaceous volcanic activities can be divided intoBeijing: China University of Geosciences: 2009. p. 1-115 lin Chineselfive stages, i.e., 132+1, 1261, 12222, 115#2 and [131 Zhang CH A primary discussion on the intraplate orogenic belt. Earth Sci(2)There are two sets of early cretaceous volcanic rock and one I14) Ren: 6(4): 295-308 lin Chinesel100±5MaTectonic evolution map of eastern China and adjacent areasset of paleogene volcanic rock in the research area: early cre-2002. p 6-9 in Chinese ltaceous volcanic rock is thick and widespread and has vari[15]Chen YX. Chen W). Mesozoic volcanic rocks in Western Liaoning and adjacentous lithologies and complicated denominations, while the [16] Wang DF. Variations in isotopic ages of cretaceous volcanic rocks in easternpaleogene basic basalt is found at Alishan to the southeastChina and isog of the lower boundary of the cretaceous system.of Yemataohai and elsewhere. Early cretaceous volcanic rockin the research area can be divided into two cycles. The first 17] Diao NC. Li xz The K-Ar isotopic dating of Mesozoic volcanic rocks in Westemcycle starts with basic basalt, is represented by the narrow- [18] Luo QH. Chen pl. Zhou DY, Sun Xs. u Qs. Age of Sinosauropterys andsense Yixian Formation and ends with intermediate trachyandesite and crater-lake deposits, i.e., the HuanghuashanFormation, NE China Geochimica 1999: 28(4): 405-9 in Chinesebreccia segment and jiufotang Formation. Several lacus- 119] Luo ZK, Miao LC. Guan K, Qiu YS. SHRIMP U-Pb zircon age of magmatic rock intrine-facies deposits, formed during the volcanic dormantperiod, lie between basic and intermediate volcanic rock. [201 Wang SS.Hting. China, Bull Mineral Petrol Geochem 2001: 20(4): 289-91 linVolcanic rock of the second cycle is represented by basic [211 Zhu RX, Pan YX, Shibasalt, shows a lack of conformity with the underlying volca-中国煤化工nic or sedimentary rock, has baked underlying strata and its 22 2Li TS. Pu ZIisotope geology age is estimated to be between 106 andCNMHGon the Mesozoicvents. ChinH Cai et aL/Mining Sdence and Technology( China)21(2011)701-708[231 Peng YD, Zhang LD, Cheng W. Zhang C]. Guo SZ Xing DH, et al. K-Ar [291 Zhang H, Yang FL Zhang U. Li ZT, Wang WL Ma B, et al. New progress in theixian county, Western LiaoninWesterm Liaoning Geochimica 2003: 32(5): 427-35 lin Chineseleosci Sin 2004 25(2 ) 321-6 in Chinese[24] Liu YS, Gao S, Yuan HL Zhou L Liu XM. Wang XC, et al. U-Pb zircon ages and [30] Zhang H, Liu XM. Chen W, Li ZT. Yang FL The age of the top of the YixianNd, Sr, and Pb isotopes of lower crustal xenoliths from North China CratonFormation in the Beipiao- Yixian area, Western Liaoning, and its importanceghts on evolution of lower continental crust. Chem Geol 2004: 211(187-109.[311 Shao JA. Zhang HF. Liu XM, Li ZT. The chronology record of early Mas[251 Zhu RX, Lo CH. Shi RP, Shi GH. Pan JA. Shao YX. Palaeointensities determinedolcanic underplating on north margin of North China: U-Pb dating evidePhys Earth Planet In 2004: 142: 49-59 ning Province, north-eastern China.of Masonic andesite from Western Liaoning. China. Prog Nat Sci2007:17(5)609-13| in Chinese[26)Zhu RX. Kenneth A, Hoffman, Sebastien N, Paul RR, Shi RP, et al. Geomagnetic[32 Xiao Go, Gao S, Huang H, Xie SW. Zhang H. Zircon u-Pb geochronology andnsity and direct age determination of the ISEA(MOr)chron. Earthgeochemistry of mesozoic volcaZhangwuz7 biotite iw mesozoic ng n. Psi ve. Complex from theinorth chile black: 133I StraHA. unE e zircon SH RIMPatioph dad g s sioni ricin ceck oo theploration 2008: 38(4): 17-20 [in Chinese2004:33(3)221-31| in Chinesel[34] Cai HA, Xu DB. Li BF, Shao LY. The discovery of thrust nappe structure in8] Zheng JP. Zhang RS, Yu CM, Tang HY, Zhang P. Zircon U-Pb dating, Hf isotopeZhangwu- Heishan area, Liaoning province and its significance for coalnd trace elements of monzonitic enclave in basalt of eastern Hebei-westernearching. Coal Geol Exploration 2010: 38(5): 1-6 [in Chinese lYanshan-Liaoxi belt Sci China 2004: 34(SuppL ) 32-44 lin Chinese].中国煤化工CNMHG