【作者】 赵亮亮；

【导师】 张兴洲； 周建波；

【作者基本信息】 吉林大学 ， 构造地质学， 2011， 博士

【摘要】 黑龙江杂岩是佳木斯地块与松嫩地块裂解与拼合过程中形成的构造混杂岩。这套混杂岩主要出露于黑龙江省东部的牡丹江-穆棱、桦南-依兰和萝北-嘉荫三个地区。大地构造上,混杂岩总体呈近南北向分布在佳木斯地块西侧,西界受南北向展布的牡丹江断裂所控制。组构上,混杂岩以北东走向、强烈变形的长英质糜棱岩为主体,其中含有大量规模不等、变形程度各异的变橄榄岩、变辉长岩、蓝闪石片岩(变玄武岩)及变硅质岩和大理岩等岩块或岩片,构成典型的变形基质+岩块的构造混杂岩组构。岩块与基质间的变质变形关系及变质矿物组合特征显示,虽然多数变玄武岩岩块在后期变质变形过程中遭受了强烈的变质改造和构造改造作用,形成宽窄不一、延伸有限,以含青铝闪石、冻蓝闪石、黑硬绿泥石、多硅白云母和钠长石等新生变质矿物组合为代表的蓝闪绿片岩条带或岩片夹裹在长英质糜棱岩之间,但局部地区仍保存有规模较大,且未受后期变质变形作用改造的块状变玄武岩岩块,岩块变质矿物组合以出现大量的蓝闪石(含量大于50%)为特征。本文将这种变玄武岩岩块称为块状蓝闪石片岩。野外产状特征表明,部分蓝闪石片岩岩块的边部片理化特征明显,片理产状与区域上长英质糜棱岩片理产状一致。这一特征清楚地表明,黑龙江杂岩至少经历了两期重要的变质事件,即以蓝闪石片岩岩块为代表的早期高压变质事件和以片理化糜棱岩为代表的晚期变质-变形事件。为揭示黑龙江杂岩的构造背景及形成时代,本文重点对依兰地区出露的未变形的蓝闪石片岩岩块及其边部变形部分的蓝片岩进行了岩石地球化学和锆石LA-ICP-MS U-Pb定年研究。结果显示,蓝闪石片岩的原岩主体为亚碱性玄武岩和玄武安山岩,具有OIB型玄武岩稀土配分特征,而非以往所认为的大洋中脊环境。特别是在变玄武岩中发现有形态复杂的锆石。测年结果显示,这些锆石的年龄可分为5组,年龄区间分别为210-330Ma(峰值240Ma)、380-420Ma(峰值400Ma)、480-540 Ma(峰值503Ma)、1600-1900Ma(峰值1824Ma)和2400-2500Ma(峰值2512Ma)。这一证据进一步说明黑龙江杂岩中含蓝闪石的变玄武岩的原岩不可能形成于大洋中脊环境。结合区域年龄事件分析,峰值年龄为503Ma的事件是黑龙江杂岩东、西两侧的佳木斯地块和松嫩地块内最为普遍的峰值变质作用和花岗岩侵入年龄,而且这两个地块中也都存在年龄大于1000Ma的捕获锆石或碎屑锆石。这说明变玄武岩中以503Ma、1824Ma和2512Ma三期峰值年龄为代表的锆石是玄武岩侵位过程中从裂解的古老地块中捕获的锆石。380-420Ma的年龄组占所获锆石年龄的主体,其锆石形态及其成分特征具有玄武岩岩浆结晶特点。目前,这组年龄在两侧地块内尚无记录。变玄武岩的岩石地球化学及其锆石年代学证据表明,佳木斯地块和松嫩地块在380-420Ma之前曾是一个统一的陆块,该陆块不但具有前寒武纪和早前寒武纪结晶基底,而且在503Ma前后的早古生代普遍遭受了强烈的区域变质作用和花岗质岩浆侵入作用。380-420Ma的大陆裂谷型玄武岩的形成标志着早古生代固结的基底陆块在晚志留世-早中泥盆世期间发生裂解,并逐渐形成了佳木斯和松嫩两个独立演化的地块。根据黑龙江杂岩中普遍存在变橄榄岩、变辉长岩、变玄武岩(部分具枕状构造)以及变硅质岩和大理岩等岩块,说明裂谷作用已演化到洋壳形成阶段。210-330Ma(峰值240 Ma)的锆石年龄是本次测年研究获得的时代最年轻的一组锆石。这组锆石的形态及组成等显示具有变质成因特点,鉴于这种变玄武岩是以蓝闪石为主的高压变质岩石,因此,我们推测这组年龄可能与蓝片岩的形成有关。结合黑龙江杂岩西侧的小兴安岭-张广才岭地区广泛发育一套近南北向展布的碰撞后花岗岩,时代为210-180Ma,我们有理由将蓝片岩的形成与伸展型花岗岩的形成联系起来。240 Ma的峰值年龄代表佳木斯地块与松嫩地块的碰撞时代,也即蓝闪石片岩的形成时代,而小兴安岭-张广才岭地区210-180Ma的花岗岩形成与两地块碰撞后的伸展事件有关。在上述以玄武岩及其变质形成的蓝闪石片岩地球化学及锆石年代学研究基础上,本文对构成黑龙江杂岩主体的长英质糜棱岩进行了地球化学及变质矿物年代学研究。地球化学结果表明,这套长英质糜棱岩的原岩多为大陆边缘的杂砂岩,具有浊积岩特点;糜棱岩中新生白云母的(40)~Ar/(39)~Ar年龄为176-184Ma,这一年龄在萝北、依兰和牡丹江等地的糜棱岩中普遍存在,说明黑龙江杂岩在早-中侏罗世遭受了一次重要的变质-变形事件。鉴于这次事件以韧性变形为特点,而且是早期高压变质矿物组合向低压变质矿物组合的转变,因此,我们认为作为黑龙江杂岩主体的糜棱岩目前所表现的变质变形组构的形成和黑龙江杂岩中蓝闪石片岩岩块的保存,与早-中侏罗世的快速构造折返事件有关。更多还原

【Abstract】 Heilongjiang complex, bounded by the Mudanjiang fault on the west, is distrubuted between the Jiamusi and Songnen massifs. The complex as a melange zone resulted from rupture and collision of Jiamusi and Songnen massifs. The complex is mainly exposed in three regions of Mudanjiang - Muling, Huanan - Yilang and Luobei– Jiayin areas in the eastern part of Heilongjiang Province, and is composed predominately of strongly deformed mylonites with a large number of blocks or slices of ultrabasite, blueschist, metasilicatite and marble in varied sizes and deformation, constituting a typical tectonic mélange with matrix and blocks.The relationship of metamorphism and deformation between blocks and mylonites ,and metamorphic mineral assemblage features show that, although most metabasalt blocks are strongly deformed and transformed to be mylonites marked by new metamorphic mineral assemblage of crosstie, stilpnomelane, phengite and albite, some undeformed glaucophane schist blocks with assemblage of glaucophane, albite and epidote are locally preserved in mylonites.The relationships of metamorphism and deformation between undeformed masses and deformed mylonites indicate the Heilongjiang complex was at least subjected to two phase metamorphism of early high-pressure metamorphism and late lower P/T metamorphism associated by ductile deformation.In order to further insight into the tectonic setting of Heilongjiang complex and its relation with the Jiamusi and Songliao massifs, we present geochemical and LA-ICP-MS U-Pb Zircon data for undeformed blueshist facies metabasalts and deformed blueshist facies metabasalts in Heilongjiang Complex.The results show that the protolith of the blueschists is subalkali-basalt with OIB features,instead of ocean rift. The zircon datings futher surport the result above. The zircons from metabasalts are complex. LA-ICP-MS U-Pb dating from 96 zircon analyses gives five age groups of 210~330Ma with a peak age of 240Ma, 380~420Ma with a 400Ma, 480~540Ma with a 503 Ma, 1600~1900Ma with a 1824Ma and 2400~2500Ma with a 2512Ma. These imformation from zircons in the metabaslts also prove that the protolith of the metabaslts is not formed in ocean rifting.The zircons with age group of 380~420Ma are predominent in dated zircons. The crystal forms and composition of the zircon indicate they are originated from baslt magma.At present, this age group has not been reported in Jiamusi and Songnen massifs. Consequently, it is suggested that Jiamusi and Songnen massifs was an united microcontinent block before 380~420Ma. The block not only has a Precambrian crystaline basement, but also subjected to the strongly metamorphism and granitic magmatism in 503Ma. Therefore we favour the view that the basalt most likely formed in a rift environment within the Jiamusi-Songnen microcontinent similar to the current Red Sea.The age group of 210~330Ma with a peak age of 240Ma is the youngest zircon ages with metamorphogenic features. According to the fact that the basalt had been metamorphosed to be glaucophane schist,we suggest this age group from zircons records the form time of bluschist metamorphism in Heilongjiang complex. Combined with postorogenic granites with the ages of 210-180Ma widely developed in XiaoXinganLing and Zhangguangcailing regions to west of Heilongjiang complex, it is reasonable that this age group of 210~330Ma represents the time of blueschist metamorphism and the collision of Jiamusi with Songnen massifs.In order to reveal the metamorphic and deform age of predominent mylonites in Heilongjiang Complex,we present the results of geochemical analysis and muscovite Ar-Ar dating from mylonites.The results indicate that the protolith of mylonites for the most part formed in continental margin envirorment. The muscovites coexisting with crossite in mylonites in Huanan area give the (40)~Ar/(39)~Ar ages of 176.5±1.9Ma and 184.5±2.1Ma, respectively. This event is prevalently recorded in Heilongjiang complex in Jiayin, Yilan and Mudanjiang areas, indicating that the entire Heilongjiang complex experienced a major tectonic exhumation in the early - middle Jurassic. This event not only had exhumated the early blueschists to the surface, but also form the general tectonic framwork in NE direction in the northeast China.更多还原