Geochronology and geochemistry of Late Triassic bimodal igneous rocks at the eastern margin of the Songnen–Zhangguangcai Range Massif,Northeast China: petrogenesis and tectonic implications

Abstract

New zircon laser ablation inductively coupled plasma mass spectrometry and secondary ion mass spectroscopy U–Pb ages, and Hf isotope and whole-rock geochemical data are reported for Mesozoic igneous rocks from the eastern margin of the Songnen–Zhangguangcai Range Massif, Northeast China, in order to document the petrogenesis of the igneous rocks and reconstruct the early Mesozoic tectonic setting of the region. Zircons from five representative igneous rocks are euhedral–subhedral and display oscillatory growth zoning or striped absorption in cathodoluminescence images, suggesting a magmatic origin. The dating results indicate that granite, gabbro, and rhyolite from the eastern Songnen–Zhangguangcai Range Massif formed during Late Triassic (204–211 Ma). The Late Triassic granitoids and rhyolites have an affinity to A-type granites or rhyolites. Their zircon ε_Hf(t) values and Hf two-stage model ages range from –3.8 to +3.8 and from 999 to 1485 Ma, respectively, indicating that their primary melts were derived from the partial melting of the Meso-Proterozoic crust. The geochemistry of coeval gabbros, which reflects primary magma composition, shows a significant large ion lithophile element (e.g. Ba and Sr) enrichment and high field strength element (i.e. Zr, Hf, Nb, Ta, and Ti) depletion. Based on zircon ε_Hf(t) values (–4.2 to +2.8) and Hf single-stage model ages (746–1031 Ma), we conclude that the mafic magma is the product of partial melting of lithospheric mantle that was metasomatically enriched by fluids derived from the subducted oceanic crust. The Late Triassic magmatism along the eastern margin of the Eurasian continent has bimodal magma compositions, indicating an extensional setting after the final closure of the Palaeo-Asian Ocean rather than being related to subduction of the Palaeo-Pacific Plate beneath the Eurasian continent. The occurrence of Late Triassic igneous rocks on the eastern side of the Mudanjiang Fault suggests that this fault does not represent the suture zone between the Songnen–Zhangguangcai Range and Jiamusi massifs.     

Age and geochemistry of the Neoproterozoic granitoids in the the Songnen–Zhangguangcai Range Massif, NE China: Petrogenesis and tectonic implications

<正>1 Introduction The Songnen–Zhangguangcai Range Massif(SZRM)crops out over an extensive part of NE China and was thought to contain Precambrian crystalline basement material,as evidenced by the presence of what appears to bePaleoproterozoicbasementmaterialwithin exploration drillholes(Pei et al.,2007).An alternative view is that the basement within the SZRM is     

Early–Middle Ordovician volcanism along the eastern margin of the Xing’an Massif,Northeast China: constraints on the suture location between the Xing’an and Songnen–Zhangguangcai Range massifs

We present new zircon U–Pb and Hf isotopic as well as whole-rock geochemical data for volcanic rocks from the eastern margin of the Xing’an Massif, Northeast China, in order to further our understanding of the suture location between the Xing’an and Songnen–Zhangguangcai Range massifs. Zircon secondary ion mass spectrometry U–Pb dating indicates that the volcanic rocks formed during the Early–Middle Ordovician (473–463 Ma). Compared with the coeval Moguqi basalts (rare earth element [REE] = 171–183 ppm; εHf_(t) = +0.3 to +2.7; T_DM1 = 1074–977 Ma), the Duobaoshan andesites exhibit lower overall REE abundances (109–131 ppm) with relatively high heavy REE contents, stronger high-field-strength element depletion, higher εHf_(t) values (+13.0 to +14.8), and much younger T_DM1 ages (559–484 Ma). This suggests that the primary magma for the andesites was generated by the partial melting of a relatively depleted mantle wedge that was metasomatized by subduction-related fluids. The primary magma for the basalts in the Moguqi area was probably derived from the partial melting of a relatively enriched lithospheric mantle that was also modified by fluids sourced from a subducted slab. These interpretations suggest that the andesites in Duobaoshan formed in a newly accreted island arc setting, whereas the coeval basalts in Moguqi formed along an active continental margin. We therefore attribute the Early–Middle Ordovician volcanism along the eastern margin of the Xing’an Massif to the northwestward subduction of the Nenjiang–Heihe oceanic plate beneath the Xing’an Massif. Furthermore, considering coeval igneous activity in the southern parts of the Xing’an Massif, we suggest that a magmatic arc existed along the margin of the Xing’an Massif in the early Palaeozoic (490–420 Ma). We conclude that the location of the suture between the Xing’an and Songnen–Zhangguangcai Range massifs runs from Airgin Sum, via south of Xilinhot, to Ulanhot, Moguqi, Nenjiang, and finally Heihe.     

Geochronology and Geochemistry of Early Cretaceous Granitic Plutons in the Xing’an Massif, Great Xing’an Range, NE China: Petrogenesis and Tectonic Implications

In this study, we present zircon U-Pb ages, whole-rock geochemical data and Hf isotopic compositions for the Meiguifeng and Arxan plutons in Xing'an Massif, Great Xing'an Range, which can provide important information in deciphering both Mesozoic magmatism and tectonic evolution of NE China. The zircon U-Pb dating results indicate that alkali feldspar granite from Meiguifeng pluton was emplaced at ～145 to 137 Ma, and granite porphyry of Arxan pluton was formed at ～129 Ma. The Meiguifeng and Arxan plutons have similar geochemical features, which are characterized by high silica, total alkalis, differentiation index, with low P_2O_5, CaO, MgO, TFe_2O_3 contents. They belong to high-K calc-alkaline series, and show weakly peraluminous characteristics. The Meiguifeng and Arxan plutons are both enriched in LREEs and LILEs(e.g., Rb, Th, U and K), and depleted in HREEs and HFSEs(e.g., Nb, Ta and Ti). Combined with the petrological and geochemical features, the Meiguifeng and Arxan plutons show highly fractionated I-type granite affinity. Moreover, the Meiguifeng and Arxan plutons may share a common or similar magma source, and they were probably generated by partial melting of Neoproterozoic high-K basaltic crust. Meanwhile, plagioclase, K-feldspar, biotite, apatite, monazite, allanite and Ti-bearing phases fractionated from the magma during formation of Meiguifeng and Arxan plutons. Combined with spatial distribution and temporal evolution, we assume that the generation of Early Cretaceous Meiguifeng and Arxan plutons in Great Xing'an Range was closely related to the break-off of Mudanjiang oceanic plate. Furthermore, the Mudanjiang Ocean was probably a branch of Paleo-Pacific Ocean.     

Middle Devonian Picrites of the Southern Margin of Altay Orogenic Belt and Implications for the Tectonic Setting and Petrogenesis

INTRODUCTION Inrecentyears,greatprogressonthegeologic tec tonicevolutionandmineralresourcesofXinjianghas beenachieved.However,manyissuesarestilldebated, suchasancienttectonicpatternsandtheclosuretimeof theancientoceanicbasin(LiandXu,2004).Theseis sueshavelimitedourknowledgeoftheformationande volutionofAsiancontinents,aswellastheexploration anddevelopmentofmineralresources. Recently,theHilaketehalasuporphyrycopperde positwasdiscoveredinthestrataoftheMiddleDevoni anBeitashanFormatio…     

Geochronology and Geochemical Characteristics of the Early Mesozoic Tangquan Pluton in Southwestern Fujian and Its Tectonic Implications

The Tangquan granodioritic pluton in Dalian County, southwestern Fujian, China, which extends in a NE direction with an exposed area of about 130 km2, used to be considered a product of Early Cretaceous magmatism. The present study suggests for the first time that the pluton was formed in the Early Jurassic by using multiple methods for isotopic dating, which give zircon U-Pb ages of 186.8 Ma and 179.0 Ma, Rb-Sr isochron age of 162.02±4.5 Ma, and biotite 40Ar/39Ar plateau age of 158.1±0.7 Ma. The cooling rate for the pluton was relatively low (4.76℃/Ma) during the early stage (183-162 Ma) because of the compressional environment. It was emplaced in a higher cooling rate (50℃/Ma) in an extensional environment during the later stage (162-158 Ma). The granodiorites are metaluminous-peraluminous, relatively enriched in Na2O and depleted in K2O, and characteristic of I-type granites of crust-mantle mixed sources. They are moderately enriched in Rb, Th, Hf and LREE, and depleted in Ti, Nb, Ta and Sr, and     

Tectonic ore-controlling in the middlesouthern segment of Da Hinggan Ling, Northeast China

1INTRODUCTION THEMIDDLE SOUTHERNSEGMENTOFDAHINGGANLING ISONEOFTHEIMPORTANTORE CONCENTRATEDAREASOFCHI NA.INRECENTYEARSGREATSTRIDESHAVEBEENMADEIN THEORETICALGEOLOGICALRESEARCHANDGEOLOGICALEXPLOITA TION(SHAOJI’ANETAL.,1998,1999;ZHANGLUQIAOET AL.,1998;XIAOCH…     

Sr,Nd,Pb Isotope Geochemistry and Magma Evolution of the Potassic Volcanic Rocks,Wudalianchi,Northeast China

Wudalianchi volcanic rocks are the most typical Cenozoic potassic volcanic rocks in easten China.Compositional comparisons between whole rocks and glasses of various occurrences indicate that the magma tends to become rich in silica and alkalis as a result of crystal differentiation in the course of evolu-tion.They are unique in isotopic composition with more radiogenic Sr but less radiogenic Pb.^87Sr/^86Sr is higher and ^143Nd/^144Nd is lower than the undifferentiated global values.In comparison to continental pot-ash volcanic rocks,Pb isotopes are apparently lower.These various threads of evidence indicate that the rocks were derived from a primary enriched mantle which had not been subjected to reworking and shows no sign of incorporation of crustal material.The correlation between Pb and Sr suggests the regional heterogeneity in the upper mantle in terms of chemical composition.     

鄂尔多斯盆地三叠系延长组层序地层格架与沉积相构成

运用高分辨率层序地层学的原理和方法,综合鄂尔多斯盆地野外地质露头、岩心、测井及地震资料,确定了层序界面的识别标志,在上三叠统延长组识别出不整合面和沉积作用转换面两种类型的层序界面。延长组发育7个具有等时意义的层序界面,将其划分为6个长期基准面旋回。根据短—中期基准面旋回的叠加样式,SQ1层序至SQ3层序基准面上升旋回地层样式总体上以长期基准面上升半旋回为主,构成上升不对称型旋回结构;SQ3层序基准面下降旋回至SQ6层序地层样式则以长期基准面下降半旋回为主,构成下降不对称型旋回结构。沉积相类型及其展布受基准面升降变化控制明显,沉积微相类型以(辫状)河流—(辫状河)三角洲前缘水下分支河道为主。有利储层发育于长期基准面旋回上升半旋回的早中期以及下降半旋回的中晚期。     

鄂尔多斯盆地三叠系延长组长7沉积相分析

三叠纪延长期长7沉积期是鄂尔多斯盆地中生代湖盆发育的鼎盛时期,沉陷幅度大,湖盆范围广。通过研究明确了长7沉积期物源来自盆地周边五个方向,其中东北部、西南部为主要物源方向,西部、南部、西北部为次要物源方向;长7主要发育三角洲相和湖泊相,进一步划分出5种亚相10种微相,其中长73期湖盆面积最大,半深湖—深湖相浊积砂体不发育,暗色泥岩及高阻泥岩发育,为中生界主要优质烃源岩;长72期,半深湖—深湖相沉积面积明显减少,浊积砂体较发育;长71期,湖盆面积及半深湖-深湖相沉积面积继续减少,浊积砂体最为发育,是长7油藏的主力储层。     

大型坳陷湖盆浅水辫状河三角洲沉积特征及模式:以鄂尔多斯盆地陇东地区延长组为例

浅水三角洲是当今沉积学研究热点和油气勘探重点对象。鄂尔多斯盆地陇东地区三叠系延长组发育了大型浅水辫状河三角洲,并在其中发现了丰富的油气资源。在大量野外露头、岩心和地球物理资料分析的基础上,明确鄂尔多斯盆地延长组具有利于浅水辫状河三角洲发育的大型坳陷湖盆地质背景,形成的辫状河三角洲具有粒度较粗、塑性岩屑较多、成分和结构成熟度较低、发育交错层理和间断正韵律、水下分支河道多叉、砂厚、延伸远等沉积特征。鄂尔多斯盆地浅水辫状河三角洲沉积时期,沉积区距物源区相对较近,河道宽深比较大,发育浅水沉积构造和沉积韵律,构造活动和湖平面变化共同控制了三角洲的发育,形成了"小平原、大前缘"的浅水辫状河三角洲沉积体系。     

鄂尔多斯盆地中及上三叠统延长组沉积相与油气勘探的突破

鄂尔多斯盆地位于中国的中西部,跨陕、甘、宁、蒙、晋5省区,盆地本部面积25万km2.中及上三叠统延长组在盆地内广为展布,厚逾千米,发育冲积扇、河流、三角洲、湖泊等沉积相,是该地区重要的油气产层.根据盆地腹地100多口井的钻井资料及盆地周边地区的露头资料,以及长庆油田长时期对延长组的油气勘探经验,编制出了鄂尔多斯盆地中及...     

鄂尔多斯盆地上三叠统延长组长10油层组沉积特征及物源*

鄂尔多斯盆地上三叠统延长组为大型拗陷湖盆沉积,长10油层组为延长组初始期沉积物。但其物源特征、沉积体系划分、沉积相类型等基础问题尚不清楚,严重制约了全盆地长10油层组的勘探发现。针对这些问题,作者采用了轻重矿物、锆石测年等分析方法,明确了长10油层组主要发育东北、西北、西南三大物源,根据物源特征沉积体系划分为东北、西北和西南沉积体系。综合野外露头、岩心、钻井、测井等资料揭示了长10主要发育河流-三角洲沉积,其中,西北沉积体系主要发育辫状河沉积,东北沉积体系发育曲河流-三角洲沉积,西南沉积体系发育辫状河-三角洲沉积,沉积中心位于太白-宜君一带,为浅湖相沉积。     

鄂尔多斯盆地西南地区上三叠统延长组沉积相及石油地质意义

鄂尔多斯盆地三叠系延长组主要发育东北和西南两大沉积体系,东北的河流三角洲体系已为大量的勘探研究资料所证实,而西南体系因受勘探程度限制,目前研究不够。本文通过最新钻探成果,结合盆地西南部露头资料,确立盆地西南地区三叠系延长组为冲积扇-扇三角洲沉积体系,发育冲积扇、扇三角洲、湖泊（浊积）相。冲积扇以西南缘平凉崆峒山和汭水河剖面为代表,扇三角洲及湖泊（浊积）相为区内钻井剖面所证实。长6-长8为区内主力油层组,地层保存完整,钻探程度相对较高。扇三角洲前缘砂体类型以水下分流河道为主,局部发育河口坝,浊积体以厚层块状为主。长8亚期为扇三角洲前缘亚相最发育期,横向形成自西南向东北延伸的三支前缘砂体带,是石油聚集的重要区带;长7亚期随着湖盆沉降,周边抬升强烈,湖岸较陡,大量发育浊积体系;长6亚期湖退导致扇三角洲再次发育,但规模较长8亚期弱。扇三角洲前缘砂体单层厚度大,砂岩粒度较粗,颗粒分选及物性好,是石油富集的最有利相带。     

鄂尔多斯盆地陇东地区延长组重力流沉积特征及其模式

利用岩心、测井资料和重力流沉积理论,系统研究了鄂尔多斯盆地陇东地区延长组重力流沉积特征及其沉积模式。该区重力流沉积物可分为浊积岩、砂质碎屑流沉积物、泥质碎屑流沉积物和滑塌岩。其中,浊积岩发育正粒序;砂质碎屑流沉积物以冻结块状沉积为特征;泥质碎屑流沉积物以泥质为主,内部含少量砂质颗粒和砂质团块;滑塌岩发育包卷层理等液化构造。不同重力流沉积物发育程度差异明显,浊积岩和砂质碎屑流沉积物的钻遇井数最多,泥质碎屑流沉积物最少。在重力流单期沉积厚度方面,砂质碎屑流沉积物单期沉积厚度平均为0.986m,明显高于其他类型;浊流沉积厚度最低,平均厚度为0.414m。本区重力流是由三角洲前缘沉积物失稳滑塌所致,砂质碎屑流沉积物和浊积岩是主要的重力流沉积类型,其次为滑塌岩和泥质碎屑流沉积物。砂质碎屑流沉积物主要发育于北东向曲流河三角洲前缘前方的深水区;浊积岩主要发育于西部、西南部和南部物源形成的辫状河三角洲前缘前方的深水区域;泥质碎屑流沉积物和富含泥砾砂质碎屑流沉积物在平面分布极少,且规律不明显。     

鄂尔多斯盆地南缘岐山剖面中奥陶统平凉组沉积环境分析

鄂尔多斯盆地南缘岐山剖面平凉组以碎屑岩和碳酸盐岩混积为特征,根据岩性特征可将平凉组分为七段。其中碎屑岩约占80%,主要分布在平一、三、五、七段;碳酸盐岩约占20%,主要分布在平二、四、六段。研究表明,岐山剖面平凉组属于大陆斜坡环境,是一套多旋回沉积,其中一-二段、三-四段、五-六段分别构成一个海进海退旋回,属于上斜坡-下斜坡交互沉积环境,第七段单独构成一个海进旋回。至唐陵组初期,海水开始退去。     

鄂尔多斯盆地上三叠统延长组长9油层组沉积相及其演化*

鄂尔多斯盆地延长组长9油层组发育三角洲—湖泊沉积相,三角洲平原分流河道砂体和三角洲前缘水下分流河道砂体是最有利的储集砂体。在沉积相研究的基础上,根据单因素分析多因素综合作图法,选取了地层厚度、较深水沉积岩含量、砂岩厚度、砂地比、自生绿泥石分布、古生物化石分布和沉积构造分布等单因素,对鄂尔多斯盆地延长组长9油层组上下2段的沉积相平面展布特征进行了深入研究,并探讨了其演化规律。研究表明,鄂尔多斯盆地以发育多水系、多物源注入的环湖分布的多个三角洲为特色,东北部地区主要发育曲流河三角洲,西部发育辫状河三角洲,其中以三角洲平原分流河道和三角洲前缘水下分流河道微相较为发育。长9₂沉积期,半深湖沉积在盆地内较为局限,长9₁沉积期湖盆初始扩张达到最大范围,湖岸线向陆推移,湖域面积扩大,半深湖沉积较发育。由长9₂沉积期到长9₁沉积期,鄂尔多斯盆地沉积水体经历了由浅变深的过程,由此在长9₂的顶部沉积了一套具有生烃潜力的油页岩。     

四川盆地中三叠统雷口坡组有利沉积相带及岩相古地理特征

依据四川盆地古地理背景和古气候条件,结合中三叠统雷口坡组野外剖面、岩心和薄片的观察以及单井和连井沉积相等的分析认为,盆地周边水下隆起的障壁作用和干旱炎热气候条件共同影响雷口坡组的沉积相特征,海平面升降变化是控制沉积相发育和空间分布的重要因素。雷口坡组总体为一套障壁蒸发潟湖沉积,可分潟湖边缘坪、潟湖、潮坪和台缘障壁四种沉积亚相类型,并可进一步划分出多种微相。台缘障壁亚相潟湖边缘白云岩坪和颗粒浅滩是有利的沉积相带。雷口坡组可划分出SQ1—SQ4四个层序。绘制了雷口坡期各时段体系域的岩相古地理图,并分析了它们的岩相古地理特征。