松辽盆地长岭断陷营城组火山岩的时代与岩石成因

对松辽盆地长岭断陷查干花次凹营城组火山岩进行了LA--ICP--MS U--Pb 年代学和岩石地球化学研究。确定研究区内火山岩形成于104 ～ 112 Ma 的早白垩世晚期。营城组火山岩主要由粗面岩、流纹岩、钠闪碱流岩、流纹质岩屑晶屑凝灰岩组成,化学成分显示均为流纹岩,属碱性系列。火山岩高硅富碱、贫铝钙镁; 铕负异常明显( δEu = 0. 16 ～ 0. 65) ,轻重稀土元素分馏较强［( La /Yb) N］ = 7. 15 ～ 10. 38; 富集大离子亲石元素K、Ｒb 和LＲEE。Ba、Sr 出现强烈的负异常,强烈亏损高场强元素P、 Ti,而Nb、Ta 并不亏损。该区中酸性火山岩由玄武质岩浆底侵导致新生地壳岩石部分熔融形成。     

松辽盆地营城组两类酸性火山岩地球化学特征与成因

松辽盆地断陷期营城组发育一套厚层火山岩,钻井岩心及薄片观察发现,火山岩以流纹岩、英安岩、流纹质凝灰岩及熔结凝灰岩等酸性火山岩为主,中基性岩相对较少。在对样品精细挑选基础上,开展了岩石主量元素、微量元素及Sr-Nd同位素测试分析。结果显示,该套酸性火山岩依据TiO2含量可明显分为两类,其中高Ti酸性火山岩(TiO2>0.45%),规模较小,SiO2含量介于64.87%～68.79%之间,其主量元素、微量元素与亚碱性中基性岩呈连续变化趋势且具有相似的Sr-Nd同位素组成;低Ti酸性火山岩(TiO2<0.4%)SiO2含量为68.93%～76.69%,该类岩石为营城组酸性火山岩主体,与碱性基性岩呈双峰式组合,元素含量及同位素比值变化范围较大。研究表明,两类酸性火山岩的形成都与晚中生代东北地区受古太平洋板块俯冲引起的岩石圈拆沉减薄软流圈上涌有关。在板块俯冲影响下,被富集的亏损地幔源区发生部分熔融,在岩浆演化过程中经历了一定分离结晶作用形成了少量高Ti酸性火山岩岩浆。与此同时,在底侵作用下新生地壳与下地壳物质发生混合熔融,受上地壳不同程度混染后形成了大规模的低Ti酸性火山岩岩浆。     

松辽盆地南部早白垩世火山岩的地球化学特征及其成因

对松辽盆地南部早白垩世火石岭组和营城组火山岩进行的岩石地球化学研究表明,火石岭组火山岩主要以玄武质粗面安山岩和粗安岩为主,存在少量粗面英安岩,其Si O2=53.8%~68.6wt%、K2O+Na2O=7.70%~9.59%、Mg#=26.72~33.89,以富集轻稀土和大离子亲石元素(LILEs,如Rb、Ba、Th、U等),亏损重稀土和高场强元素(HFSEs,如Nb、Ta、Ti、P等)为特征,这些特征与俯冲带火山岩类似。营城组火山岩以流纹岩为主,存在少量的玄武质粗面安山岩、粗面安山岩和英安岩,基性端元具有低硅(Si O2=49.3%~56.6%)、低碱(K2O+Na2O=4.57%~6.60%)、富镁(Mg#=33.49~59.51)的特征,主要属于钙碱性系列,暗示其原始岩浆主要来源于地幔;酸性端元的Si O2=65.4%~74.9%,K2O+Na2O=3.23%~7.75%,低镁(Mg#=21.76~39.18)。营城组火山岩稀土配分型式呈右倾型,富集轻稀土和大离子亲石元素,亏损重稀土和高场强元素,与俯冲环境火山岩相似。其中,营城组流纹岩地球化学特征类似A型花岗岩,暗示形成于伸展环境。结合区域研究成果,认为松辽盆地南部早白垩世火山岩的形成与古太平洋板块向欧亚大陆之下的俯冲作用有关。火石岭组火山岩形成于活动大陆边缘环境,营城组火山岩的形成与岩石圈拆沉作用引发的伸展背景有关。     

松辽盆地北部营城组火山岩地球化学特征及地质意义

松辽盆地北部早白垩世营城组发育一套以流纹岩为主的中酸性火山岩,其具有高硅、铝,富碱和低镁、铁的特征,不同类型火山岩均具有轻稀土富集、重稀土亏损、轻重分异严重的特征。其中：酸性流纹岩表现为富集Pb、U、Th、Ta、Hf和Zr等元素,亏损Sr、Ba、Eu等元素;中性安山岩、粗安岩和基性玄武岩则亏损不明显;中酸性英安岩介于两者之间。地化特征分析表明,营城组岩浆来源于亏损地幔,是地幔底侵导致地壳部分熔融,并受到地幔物质的混染,酸性岩喷出前经历了较强的岩浆分异作用。构造判别图解指示营城组火山岩形成于板内伸展环境,具有与板块俯冲作用有关的、发育于活动陆缘或岛弧的火山岩类似的演化特征。结合中国东部构造环境演化特征,认为松辽盆地北部早白垩世火山活动可能是古太平洋板块北北西方向高速俯冲导致地壳岩石圈减薄、地幔物质上涌的产物。     

松科二井东孔营城组火山岩测井响应特征及岩性评价

为开展松辽盆地深部长期观测、流体实验和探索白垩纪火山事件,利用松科二井东孔丰富、齐全的测井资料,对营城组火山岩岩性进行评价。通过测井响应特征分析发现,松科二井东孔营城组凝灰岩具有最强的放射性和导电性,高孔隙度的集块熔岩密度为低值,流纹岩表现出高密度和低导电性。利用测井交会图和成像识别模式,识别出松科二井东孔营城组火山岩以流纹岩、凝灰熔岩和集块熔岩为主,少量的凝灰岩。结合凝灰岩处测井曲线变化特点,证明了火山喷发间断的存在。流纹岩具有高碱、高Si、低Fe和低黏土矿物特征。T_2谱分析认为流纹岩有利于后期深部长期观测和流体实验的开展。研究成果对松科二井东孔后续火石岭组火成岩及整个松辽盆地火山岩研究具有一定的参考价值。     

Basalt-rhyolite volcanism by MORB-continental crust interaction: Nd,Sr-isotopic and geochemical evidence from southern San Joaquin Basin,California

The early miocene Tecuya volcanic center in the southern San Joaquin basin of California consists of flows and tuffs of basalt and rhyolite that erupted, closely spaced in time, in both submarine and subaerial conditions. The rhyolites are overlain by the basalts and constitute approximately 45% of a total of at least 180 km³ of the Tecuya volcanic rocks. The basalts have _Nd(t) values of +2 to +6 and (⁸⁷Sr/⁸⁶Sr)_i values between 0.7035 and 0.7052. These rocks show LREE enrichment [(La/Yb)_N =2.4–5.5; La=28–150 times chondrite] and higher Th/U, Th/Ta, Rb/Ta, Ba/Ta, Cs/Rb but lower K/Rb ratios than MORB. Combined major- and trace-element, and Sr–Nd isotopic data suggest the involvement of subcontinental lithosphere, depleted upper mantle source (MORB), and local continental crust in the basalt petrogenesis. _Nd(t) values in rhyolites vary from +1.5 to +3.7 while (⁸⁷Sr/⁸⁶Sr)_i ratios range from 0.7051 to 0.7064. The rhyolites display LREE enrichment [(La/Yb)_N=10; La=100 times chondrite] along with a distinct negative Eu anomaly (Eu/Eu^*=0.75) and depletion of Ti and P. Mixing relations in (⁸⁷/⁸⁶Sr)_i – _Nd(t) space among basalts, rhyolites, and local continental crust indicate that the Tecuya rhyolites were produced by assimilation of variable amounts of continental crust by MORB-related magmas and subcontinental lithosphere-derived melts. This conclusion is supported by the synchroneity of Tecuya volcanism at 22 Ma with interaction of a segment of the East Pacific Rise along the southern California margin. The Tecuya volcanic rocks thus provide an example for the generation of rhyolitic melts owing to crustal assimilation by basaltic melts during mid-oceanic ridge-induced magmatism along a continental margin.     

新疆阿尔泰南缘康布铁堡组钾-钠质流纹岩锆石U-Pb年龄和地球化学

阿尔泰南缘分布着大量的晚古生代康布铁堡组火山岩系,是许多铁矿、铜矿以及铅锌矿的赋矿围岩。阿尔泰南缘麦兹和克朗火山-沉积盆地内的钾-钠质流纹岩的年龄分别为396.7±1.4Ma和394.0±6.0Ma,结合近期研究成果,进一步表明阿尔泰南缘火山岩主要形成于晚古生代早期,锆石U-Pb年龄峰期在400Ma左右。钾-钠质流纹岩具有高硅(SiO₂的含量范围为73%~82%)、高碱(总碱含量介于4%~7%)和过铝质(高A/CNK值>1)的特征,并见有白云母和黑云母的矿物组合,属于高硅高碱过铝质的钙碱性火山岩。此外,它们的Sr和Nd同位素分别为⁸⁷Sr/⁸⁶Sr=0.7074~0.7144,¹⁴³Nd/¹⁴⁴Nd=0.512072~0.512252,具有上地壳来源的特征,说明其岩石成因与初生地壳的部分熔融作用有着密切关系。结合区域地质背景分析,它们都产在与俯冲消减作用有关的陆缘岛弧的地质环境中。因此,我们推断本区钾-钠质流纹岩的原始岩浆为高硅高碱的花岗质岩浆,是由进入陆壳的高侵位玄武岩浆的底侵作用导致其上部地壳近固相线的低程度部分熔融的产物。     

松辽盆地徐家围子营城组流纹岩地球化学特征及构造指示意义

松辽盆地徐家围子营城组发育一套以流纹岩为主的中酸性火山岩。岩石薄片观察和主量、微量元素研究发现,后期热液蚀变、区域埋深及低温水合作用对流纹岩的Si、K、Rb等元素含量产生一定影响; 流纹岩明显富集Rb、Th、U、Pb等强不相容元素,Ba、Sr、Ti、Eu、P 负异常,暗示其经历了斜长石、磷灰石和钛铁矿分离结晶作用。流纹岩的(⁸⁷Sr/⁸⁶Sr)_i(0.705265 ~ 0.711895)值变化范围较大,大多数ε_Nd(t)为正值(1.83 ~ 3.38),Pb同位素比值相对集中,(²⁰⁶Pb/²⁰⁴Pb)_i=18.09～18.32,(²⁰⁷Pb/²⁰⁴Pb)_i=15.50 ~ 15.54,(²⁰⁸Pb/²⁰⁴Pb)_i=37.80 ~ 38.10。研究表明,岩石的源区为大比例年轻成分与少量古老地壳的混合部分熔融,其演化过程中经历了不同程度的地壳混染。松辽盆地早白垩世火山岩为板内伸展环境喷发的产物,可能与太平洋板块俯冲导致的中国东部岩石圈减薄、软流圈上涌密切相关。     

松辽盆地白垩纪火山期后热液活动的岩石地球化学和年代学及其地质意义

在松辽盆地东南隆起区营城组标准剖面营三段古火山口附近识别出岩浆期后热液活动的地质记录。岩石学特征表现为隐爆角砾岩,即,原有的近火山口相岩石(原岩)被高压流体炸碎形成原地角砾、之后又被灌入的富含矿物质"岩汁"胶结形成的原地角砾岩。采集隐爆角砾岩及其上覆和下伏三个层位共10个样品进行地球化学和年代学对比研究,包括两套4个对应的原岩和岩汁、下伏4个玄武粗安岩和上覆2个流纹岩。原岩高精度~(39)Ar/~(40)Ar坪年龄113.4±0.7Ma;岩汁为含铁酸性流体的隐晶质析出物,其~(39)Ar/~(40)Ar坪年龄112.9±19.6Ma;二者的年龄差反映岩浆主期与期后热液活动的时代间隔(1Ma之内)。10个样品的共性是:(1)稀土总量中-高(∑REE=81×10~(-6)～202×10~(-6))且轻重稀土分异明显((La/Yb)_N=4.91～11.45);(2)MORB标准化蛛网图上P和部分不相容元素(Cs、Th、La和Zr)正异常,而另一部分不相容元素(Sr和Pb)负异常。整体表现为双峰式裂谷火山岩特点。主要差别在于:(1)铕和钡表现为两种情况,下伏玄武粗安岩和隐爆角砾岩中的粗面岩具正异常,而隐爆角砾岩中的流纹岩和岩汁及其上覆的流纹岩具负异常;(2)只有2个岩汁样品显示K负异常,其它8个岩石样品均为K正异常;(3)下伏玄武粗安岩(4个样)显弱的Ti正异常且Rb/Sr比低(0.04～0.05),而其它6个样品为Ti负异常且Rb/Sr比高(0.62～2.83),其中的2个岩汁样品Ti负异常最强。岩汁与其下伏粗面质原岩差别显著,而与其上覆流纹岩(SHRIMP年龄110.6Ma)的地化特征相似(见正文)。该火山期后热液活动是深源热流体萃取壳源物并沿古火山通道(构造薄弱带)运移到近地表的,可能是后续流纹质火山活动的先驱。这种高压的岩浆期后热液导致围岩炸裂、发生角砾岩化、形成大量角砾间孔和裂缝。这是造成火山口-近火山口相带成为优质储层的重要因素。该类火山岩储层改善作用早于烃类运移,可构成有利于成藏的时空配置。与该期热液活动相伴生的深源天然气早于上覆圈闭的形成,因此对成藏没有贡献。     

松辽盆地北部地层水同位素特征及其地质意义

盆地流体是沉积盆地中非常活跃的因子,盆地流体的水文地球化学特征主要是受控于流体-岩石相互作用。本文以松辽盆地北部为研究对象,基于地层水的水文地球化学特征、锶-氢-氧同位素数据分析,初步探讨了水-岩反应与锶-氢-氧同位素的关系。这一研究对于丰富同位素示踪、水-岩相互作用等基础理论具有重要研究意义。分析表明,位于盆地西部地区地层水明显受到古大气降水的影响,中央凹陷地区δ18O正偏移可能是由水岩作用加强引起的。地层水为大气水与原生沉积水的混合,较轻的δD值反映出原始沉积水属陆相沉积水。地层水的87Sr/86Sr值略低而Sr2+含量又较高,是高87Sr/86Sr值流体端元与低87Sr/86Sr值流体端元的混合,即地表来源水与深部水的混合,也更多地受到高Sr2+含量低87Sr/86Sr值的火山-地热水等幔源深部水的补给。     

Zircon U-Pb Geochronology and Geochemical Characteristics of the Volcanic Host Rocks from the Tongyu VHMS Copper Deposit in the Western North Qinling Orogen and Their Geological Significance

Precise in situ zircon U-Pb dating and Lu–Hf isotopic measurement using an LA-ICP-MS system, whole-rock major and trace element geochemistry and Sr–Nd isotope geochemistry were conducted on the volcanic host rocks of the Tongyu copper deposit on the basis of further understanding of its geological characteristics. Three zircon samples from the volcanic host rocks yielded 206Pb/238 U weighted average ages ranging from 436±4 Ma to 440±5 Ma, which are statistically indistinguishable and coeval with the ca. 440 Ma northward subduction event of the Paleo-Qinling oceanic slab. The volcanic host rocks were products of magmatic differentiation that evolved from basalt to andesite to dacite to rhyolite, forming an integrated tholeiitic island arc volcanic rock suite. The primitive mantle-normalized trace element patterns for most samples show characteristics of island arc volcanic rocks, such as relative enrichment of LILE(e.g. Th, U, Pb and La) and depletion of HFSE(e.g. Nb, Ta, Ti, Zr and Hf). Discrimination diagrams of Ta/Yb vs Th/Yb, Ta vs Th, Yb vs Th/Ta, Ta/Hf vs Th/Hf, Hf/3 vs Th vs Nb/16, La vs La/Nb and Nb vs Nb/Th all suggest that both the volcanic host rocks from the Tongyu copper deposit and the volcanic rocks from the regional Xieyuguan Group were formed in an island arc environment related to subduction of an oceanic slab. Values of ISr(0.703457 to 0.708218) and εNd(t)(-2 to 5.8) indicate that the source materials of volcanic rocks from the Tongyu copper deposit and the Xieyuguan Group originated from the metasomatised mantle wedge with possible crustal material assimilation. Most of the volcanic rock samples show good agreement with the values of typical island arc volcanic rocks in the ISr-εNd(t) diagram. The involvement of crustal-derived material in the magma of the volcanic rocks from the Tongyu copper deposit was also reflected in the zircon εHf(t) values, which range from-3.08 to 10.7, and the existence of inherited ancient xenocrystic zircon cores(2616±39 Ma and 1297±22 Ma). The mineralization of the Tongyu copper deposit shows syn-volcanic characteristics such as layered orebodies interbedded with the volcanic rock strata, thus, the zircon U-Pb age of the volcanic host rocks can approximately represent the mineralization age of the Tongyu copper deposit. Both the Meigou pluton and the volcanic host rocks were formed during the ca. 440 Ma northward subduction of the Paleo-Qinling Ocean when high oxygen fugacity aqueous hydrothermal fluid released by dehydration of the slab and the overlying sediments fluxed into the mantle wedge, triggered partial melting of the mantle wedge, and activated and extracted Cu and other ore-forming elements. The magma and ore-bearing fluid upwelled and erupted, and consequently formed the island arc volcanic rock suite and the Tongyu VHMS-type copper deposit.     

Geochemistry and Genesis of the Late Jurassic Granitoids at Northern Great Hinggan Range: Implications for Exploration

<正>The Longgouhe and Ershiyizhan intrusions of the Late Jurassic,located in the Upper Heilongjiang Basin of the northern Great Hinggan Range,are closely related to porphyry Cu-Au mineralizations.In lithology the intrusions are quartz diorite,quartz monzodiorite and granodiorite of high-K calc-alkaline series,with minor aspects of shoshonite series.Their SiO_2 and Al_2O_3 contents range from 61.37%to 66.59%and 15.35%to 17.06%,respectively.The MgO content ranges from 2.02%to 3.47%,with Mg~# indices of 44-59.The(La/Yb)_N and Eu/Eu~* values range from 16.85 to 81.73 and 0.68 to 0.93,respectively,showing strong differentiation rare earth element(REE) patterns similar to those of adakites.The rocks are enriched in Ba,Sr and light REE(LREE),obviously depleted in Nb and Ta,slightly depleted in Rb and Ti,and poor in Yb and Y,with Yb and Y contents of 0.31-1.32 ppm and 4.32-12.07 ppm,respectively.As indicated by Sr/Y ratios of 67.74-220.60,the rocks are characterized by low-Y and high-Sr contents,which characterize the adakites in the world.Holistically, geochemical tracers suggest that the interested intrusions are adakitic rocks.Given that the Paleo-Asian Ocean and Mongol-Okhotsk Ocean were closed in the Late Paleozoic and Permian-Middle Jurassic,respectively,the interested intrusions should be formed by partial melting of delaminated crust,which had been thickened during collisional orogeny between the Siberian and Mongolian-Sinokorean continents.     

松辽盆地庆深气田储层火山岩锆石地质年代学研究

庆深气田储层火山岩由多期火山喷发叠置形成,分布于白垩系下统营城组,以酸性喷发岩为主。火山岩离子探针(SHRIMP)U-Pb锆石年龄测定结果表明,储层火山岩年龄集中在111~115Ma,介于早白垩世晚期阿普第阶(Aptian)和阿尔布阶(Albian)分界线附近。兴城与升平两个天然气产区储层火山岩测年结果对比表明,它们是同一时代火山作用产物,并非以前所认为的兴城地区火山岩属营城组一段,升平地区火山岩属营城组三段。该成果对于松辽盆地火山岩气藏的勘探开发具有重要的实际意义。     

松辽盆地三台地区营城组珍珠岩地球化学特征及地质意义

松辽盆地东南缘的三台地区营城组火山岩分布广泛,其中一部分为珍珠岩。通过岩石薄片鉴定,挑选了三台地区北山上的6块珍珠岩样品,进行了主量元素、微量及稀土元素分析测试。珍珠岩的主量元素组成表明,它们与流纹岩成分相当,具有高SiO_2、较高(NaO_2+K_2O)、低TiO_2和低CaO含量,属于铝饱和-弱过饱和的钙碱性系列。稀土元素配分模式以轻稀土富集、Eu负异常强烈为特征。在不相容元素蛛网图上,珍珠岩相对于洋脊花岗岩总体上富集大离子亲石元素和轻稀土元素,而明显亏损高场强元素Sr、Nb、Y。在Nb-Y和Rb-(Y+Nb)判别图上,它们分别落入板内和火山弧区。这些结果显示,所研究的珍珠岩应为类似弧后盆地的引张环境。     

松辽盆地庆深气田储层火山岩锆石U-Pb同位素年龄及其地质意义

庆深气田储层火山岩是由多期火山喷发叠置形成,分布在白垩系下统的营城组,以酸性喷发岩为主。火山岩离子探针(SHRIMP)锆石U-Pb年龄测定结果表明,储层火山岩年代集中在111～115 Ma,介于早白垩世晚期阿普第阶(Aptian)和阿尔布阶(Albian)的分界线附近。对比兴城与升平两个天然气产区的储层火山岩的形成年代,发现它们是同一时代的火山作用产物,并不是以前所认为的兴城地区火山岩属于营城组一段,升平地区火山岩属于营城组三段。这一结果对于松辽盆地火山岩气藏的勘探开发具有实际意义。     

Neoproterozoic Volcanic Rocks in the Southern Quruqtagh of Northwest China:Geochemistry,Zircon Geochronology and Tectonic Implications

The Early Neoproterozoic Beiyixi Formation volcanic rocks of the southern Quruqtagh comprise mainly of a suite of tholeiitic basalts,alkaline andesites,and calc-alkaline rhyolites.The rhyolites are characterized by variably fractionated enrichment in light rare earth elements（LREE） and flat in heavy rare earth elements（HREE）,and strongly negative Eu anomalies.Compared to the rhyolites,the andesites also exhibit enrichment in LREE and flat HREE（chondrite-normalized values of La/Yb,and La/Sm are 13.30-41.09,3.18-6.89 respectively）.Their rare earth element patterns display minor negative Eu anomalies.Both of them exhibit coherent patterns with strongly to moderately negative anomalies of Nb,Zr,Ti,and Hf on spider diagrams.Two rhyolite and one andesite magmatic zircons with defined oscillatory zoning yielded weighted mean ²⁰⁶Pb/²³⁸U ages of 743±7 Ma,741±2 Ma,and 727±4 Ma.These ages are interpreted to represent the timing of volcanic eruptions. According to geochemistry and rock type,these volcanic rocks formed within a continental island-arc environment following subduction of the oceanic crust during the Early Neoproterozoic period.     

松辽盆地长岭断陷中基性火山岩的时代与其成因

锆石U-Pb定年结果显示,松辽盆地长岭断陷松南180井中基性火山岩形成于101～116 Ma的早白垩世晚期,属于营城组,非火石岭组火山岩。岩相学观察主要由安山岩和橄榄玄武岩组成,化学成分显示为玄武岩、粗面玄武岩和玄武质粗面安山岩,属碱性系列,镁质量分数较低,镁值较小（Mg^#=0.27~0.53）。稀土元素总量较高（w（∑REE）=（164.98~257.27）×10^-6）,轻重稀土分馏明显（（La/Yb）_N=6.60~10.96）,铕异常微弱（δEu=0.85~1.02）。富集大离子亲石元素和轻稀土元素, Rb,K 相对亏损,相容元素（Cr、Co、Ni）质量分数低,高场强元素Nb、Ta弱富集,整体表现出与 OIB(洋岛玄武岩)一致的稀土图谱和微量元素特征。岩浆源区为软流圈地幔,经历了深部地幔流体的交代富集作用,岩浆未遭受地壳物质的混染。     

内蒙古中部红格尔地区白音高老组流纹岩地球化学特征及成因

内蒙古中部红格尔地区白音高老组主要由流纹岩组成, 含少量英安岩和粗安岩。流纹岩具有高硅、铝和钾,低钙镁的特点;富集大离子亲石元素K、Rb、Th和U, 高场强元素Nb、Ta、Ti和P强烈亏损, 具负异常;高w(Sr)/w(Y)和w(La)/w(Yb), 低w(Y)和w(Yb)。稀土元素总量较低, 轻重稀土元素分馏强烈, 具有中等的铕负异常。εNd(t)值为正值(+088~+266), tDM变化于5883~7164 Ma之间。主量、微量元素地球化学和Sr Nd Pb同位素组成显示红格尔地区白音高老组流纹岩为高钾钙碱性C型埃达克质岩, 其形成与蒙古—鄂霍茨克洋的闭合碰撞有关, 形成于早白垩世造山后加厚岩石圈跨塌阶段的板内伸展环境, 是加厚下地壳部分熔融的产物。岩浆源区部分熔融残留相为石榴子石, 在岩浆上升演化过程中经历了斜长石、钛铁矿和磷灰石的分离结晶作用。     

Chronology, Geochemistry and Tectonic Settings of the Hadamiao Granodiorite on the Northern Margin of the North China Platform

<正>The Hadamiao granodiorite,located on the northern margin of the North China platform and acting as the country rock of gold deposits in the Hadamiao region,was formed in the same age and similar tectonic settings with the Hadamiao gold deposit and the large-scale Bilihe gold deposit in the same area.By using the LA-ICP-MS method,the U-Pb age obtained is 267±1.3 Ma,which represents the crystallized age of the granodiorite,and that of the xenolithic zircon is 442.8±5 Ma. Base on the main elements,it exhibits the features of calc-alkaline to high-potassium calc-alkaline series,low silicon,and quasi-aluminous I-type granites,and with high magnesium(Mg~#=0.45-0.57) and high sodium contents(Na_2O/K_2O=0.98-2.29).The SREE values(81.6-110.15 ppm) are relatively low,the fractionations between LREE and HREE are obvious,showing a right-inclined dispersion in the REE distribution diagram.Compared with the primitive mantle,the rock is relatively rich in LREE(La and Ce),LILE(K,Sr,and Th),and intensively depleted in HFSE(Ti,P,Nb and Ta).The ratios of Sr/Y and(La/Yb)_N and the contents of Rb,Nb and Y are relatively low,the Sr values are high (436.35-567.26 ppm),and the Yb contents of most samples are low(1.25-1.8),which indicate the features of typical continental margin arc and adakitic rocks.According to the values ofε_(Nd)(t)(-2.4 to +0.2) and I_(Sr)(0.7028-0.7083),and variations of the La/Sm ratios,the Hadamiao granodiorite was formed from mixing of the thickened molten lower crust and the mantle wedge substances.The rock was related to the southward subduction and accretion of the Paleo-Asia Ocean in the Late Paleozoic, being Late Paleozoic magma of the continental margin arc formed on the basement of the Early Paleozoic accretion complexes,and showing a trend of turning into adakitic rocks,which indicates their great metallogenic(Au) potential.