辽南地块新太古代2.52～2.46Ga构造-热事件的识别及地质意义

发布时间：2018-03-11 10:02

  本文选题：辽南地块　切入点：太古宙　出处：《岩石学报》2017年09期 　论文类型：期刊论文

【摘要】：胶-辽-吉活动/造山带是华北克拉通早前寒武纪基底三条古元古代构造带之一,对其邻区内太古宙地质体的岩石组合和时空分布的研究,可为制约胶-辽-吉带的构造属性以及华北克拉通东部在古元古代时期的构造格局提供重要依据。胶-辽-吉带的北侧为龙岗地块,南侧为辽南和狼林地块,本文对辽南地块中典型前寒武纪基底变质岩石进行了详细的野外地质、岩石学和锆石LA-ICP-MS U-Pb年代学研究,结果显示原岩为石英闪长岩或英云闪长岩的黑云角闪片麻岩(DL05-1)和侵入其中的花岗质脉体(DL05-2)分别形成于2523±11Ma(MSWD=0.62)和2505±13Ma(MSWD=0.67),原岩为TTG岩系的黑云斜长片麻岩(DL10-1)形成于2521±12Ma(MSWD=1.15)。2件斜长角闪岩样品(DL12-1和DL07-1)分别给出2521±16Ma(MSWD=1.9)和2464±20Ma(MSWD=0.72)的~(207)Pb/~(206)Pb加权平均年龄,前者的锆石形态、结构和Th-U体系组成具有高温岩浆成因的特征,因此2521±16Ma代表基性原岩的形成时代,后者的锆石没有明显的内部结构,且Th、U含量低(分别为6×10~(-6)~29×10~(-6)、9×10~(-6)~26×10~(-6))具变质重结晶锆石的特征,2464±20Ma代表区域变质事件的年龄。侵入斜长角闪岩的2件花岗片麻岩样品(DL12-2和DL07-2)207Pb/206Pb加权平均年龄分别为2498±18Ma(MSWD=1.4)和2.1Ga,1件钾质花岗岩样品(DL17-1)由于强烈的Pb丢失未能获得准确的形成年龄,根据野外产状和锆石U-Th-Pb组成推测该钾质花岗岩形成于新太古代晚期。虽然辽南地块内太古宙表壳岩的时空分布规律目前还不清楚,但本文的研究结果进一步确认,辽南地块内存在新太古代2.52Ga基性岩、闪长岩和TTG组合,它们的形成时代总体上不晚于共生的花岗岩(2.50Ga),而后辽南地块经历了新太古代晚期2.46Ga区域变质作用的改造。侵位时代接近2.1Ga花岗岩的存在表明辽南地块太古宙陆壳在形成后受到2.1Ga构造-热事件的影响。另一方面,本文研究的花岗质岩石样品中残余锆石核年龄分布于2.61~2.51Ga,表明辽南地块内古老大陆地壳物质的形成时代至少可以追溯至新太古代早期。辽南地块内太古宙岩浆、变质作用时限和陆壳物质的形成时间都与华北克拉通东部可以对比,具有华北的太古宙基底属性。与狼林地块相比,辽南地块内太古宙的岩石类型更加丰富,规模也更大;与胶-辽-吉活动/造山带北侧龙岗地块相比,辽南地块内尚没有发现大规模条带状铁建造(BIF)和形成于新太古代之前(2.8Ga)的岩石,且变质程度相对较低。目前的地质和年代学证据尚不支持辽南地块与胶-辽-吉带北侧的龙岗地块原属于同一陆壳基底。
[Abstract]:The Jiao-Liaoji active / orogenic belt is one of the three ancient Gu Yuan tectonic belts in the early Precambrian basement of the North China Craton. The rock assemblages and temporal and spatial distribution of the Archean geological bodies in the adjacent area are studied. It can provide an important basis for restricting the tectonic properties of the Jiao-Liaojia-Ji belt and the tectonic pattern of the eastern North China Craton in the Paleoproterozoic period. The north side of the Jiao-Liaojian-Ji belt is the Longgang block, and the south side is the southern Liaoning and Langlin blocks. In this paper, the typical Precambrian basement metamorphic rocks in the southern Liaoning block have been studied in detail in the field geology, petrology and zircon LA-ICP-MS U-Pb chronology. The results show that the quartz diorite or dolomite gneiss DL05-1) and the intrusive granitic vein DL05-2) were formed in 2523 卤11 Ma-MSWD0.62) and 2505 卤13Ma-MSWD0.67, respectively, and the TTG series of rubric gneiss DL10-1) was formed in 2521 卤12MaMMSWD1.15.2 pieces of plagioclase. The results show that the diorite is composed of quartz diorite or quartz diorite (DL05-1) and the intrusive granitic vein (DL05-2) was formed at 2521 卤12MaMMSWD1.15.2. For diorite samples DL12-1 and DL07-1), the weighted average age of 207Pb / L / 206U Pb for 2521 卤16MaM MSWDU 1.9) and 2464 卤20MaM MSWDU 0.72), respectively, is given. The zircon morphology, structure and Th-U system composition of the former have the characteristics of high-temperature magmatic genesis, so 2521 卤16Ma represents the age of the formation of the basic protolith, while the zircon of the latter has no obvious internal structure. Moreover, the low content of Thu (29 脳 10 ~ (10)) (9 脳 10 ~ (10)) ~ (9) ~ (6) ~ (6) ~ (6) ~ (-) ~ (26 脳 10 ~ (10)) zircon is characteristic of metamorphic recrystallization zircon representing the age of regional metamorphism. Two granitic gneiss samples (DL12-2 and DL07-2)207Pb/206Pb weighted average age of 2498 卤18MaMMSWD1.4) and 2.1 ~ (1) kalitic zircons intruding into amphibolite are characterized by metamorphic recrystallitic zircon age of 2464 卤20Ma. The weighted mean ages of DL12-2 and DL07-2)207Pb/206Pb are 2498 卤18MaMSWD1.4 and 2.1 ~ (-1), respectively. DL17-1) due to strong Pb loss, an accurate age of formation has not been obtained. According to the field occurrence and zircon U-Th-Pb composition, the potash granite was formed in the late NeoArchean. Although the temporal and spatial distribution of Archean epidermal rocks in the southern Liaoning massif is not clear, the results of this paper further confirm that, NeoArchean 2.52Ga basic rocks, diorite and TTG assemblages exist in the southern Liaoning massif. Their forming age was not later than that of the INTERGROWTH granite (2.50GaN) in general, and the southern Liaoning massif underwent the reformation of late NeoArchean 2.46Ga regional metamorphism. The presence of the emplacement age close to 2.1 Ga granite indicates the Archean continental crust of the southern Liaoning block. After formation, it was influenced by 2.1 Ga tectonic-thermal events. The age distribution of the residual zircon in the granitic samples studied in this paper is 2.61 ~ 2.51 Ga, which indicates that the formation of the ancient continental crustal material in the southern Liaoning block can be traced back to the early NeoArchean period at least, and the Archean magma in the southern Liaoning block. The time limit of metamorphism and the forming time of continental crust material can be compared with the eastern part of North China craton, which has the Archean basement attribute of North China. Compared with the Langlin block, the Archean rock types in southern Liaoning block are more abundant and the scale is larger. Compared with the Longgang massif on the north side of the Jiao-Liaojia-Jiagi active / orogenic belt, no large scale banded iron formation (BIFs) and rocks formed before the NeoArchean (2.8Ga) have been found in the southern Liaoning massif. The present geological and chronological evidence does not support that the southern Liaoning block and the Longgang block on the north side of the Jiao-Liaojia-Ji belt belong to the same continental crust basement.
【作者单位】： 中国地质科学院地质研究所;
【基金】：国家自然科学基金重点项目(41430210) 中国地质调查局地质大调查项目(DD20160121) 中国地质科学院基础科研业务费(YYWF201703、J1714)联合资助
【分类号】：P534.2;P542
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本文编号：1597669