河北平泉光头山碱性花岗岩的时代、Nd-Sr同位素特征及其对华北早中生代壳幔相互作用的意义

doi:10.3321/j.issn:1000-0569.2004.06.007

CORC > 北京大学 > 地球与空间科学学院

	河北平泉光头山碱性花岗岩的时代、Nd-Sr同位素特征及其对华北早中生代壳幔相互作用的意义; Age and Nd-Sr isotopic geochemistry of the Guangtoushan alkaline granite,Hebei province,China:implications for early Mesozoic crust-mantle interaction in North China Block
	韩宝福 ; 加加美宽雄 ; 李惠民
刊名	岩石学报
	2004
关键词	锆石U-Pb年龄同位素地球化学 A型花岗岩壳幔相互作用中生代华北 zircon U-Pb age isotopic geochemistry A-type granite crust-mantle interaction mesozoic North China
DOI	10.3321/j.issn:1000-0569.2004.06.007
英文摘要	光头山碱性花岗岩产出在华北北部的前寒武纪基底变质岩系之中,造岩矿物组合为石英+碱性长石+钠铁闪石+霓辉石+钠铁非石±星叶石,副矿物有锆石、钛铁矿、硅钛铈铁矿等.晚期的伟晶岩囊状体由颗粒粗大的石英、碱性长石和钠铁闪石等组成.全岩Rb-Sr等时线年龄为T=200±16 Ma,(87Sr/86Sr)i=0.705±0.008,MSWD=11.2,代表冷却年龄,单颗粒锆石U-Pb谐和年龄为220±1 Ma,代表岩体侵位时代.光头山碱性花岗岩以A/CNK＜1和A/NK＜1,Al2O3、MgO、CaO和Ba、Sr含量低,全碱含量、MnO和Rb、Ga等含量高,负Eu异常特别显著等为特征.矿物学和地球化学完全符合A型花岗岩的特征.光头山碱性花岗岩是华北地区早中生代后造山环境下岩浆活动的产物.光头山碱性花岗岩的εNd(T=220Ma)平均值为-8.9,明显高于华北前寒武纪下地壳岩石的范围,而冀北地区前寒武纪高压麻粒岩地体虽具有大陆地幔的特征,但未经历过部分重熔,表明至少前寒武纪下地壳不可能是岩浆主要的或唯一的来源.同样,现今华北下地壳由于时代较新,也不可能成为岩浆的源岩.对比时代相近的超镁铁岩和煌斑岩的Nd同位素特征,推测最可能的源区是1.8～1.9Ga形成的富集的岩石圈地幔.光头山碱性花岗岩和华北北缘早中生代侵入岩带规模很大,以富集地幔来源的岩浆为主,反映了当时的岩浆活动已经具有相当的规模和强度.如果130Ma前后中国东部大规模岩浆活动之时,是岩石圈减薄已经达到最大程度之际,那么,此前一定时间段内的幔源岩浆活动都有可能与岩石圈减薄从开始到鼎盛的过程有关.所以,华北北缘早中生代岩浆活动可能是华北中生代岩石圈减薄过程早期阶段的产物.与岩石圈减薄过程有关的早中生代岩浆活动还在中国东北地区东部和阿拉善北部形成了后造山A型花岗岩.与岩石圈减薄过程相关的早中生代侵入岩在一定范围内的带状分布,表明当时岩石圈减薄过程可能并没有涉及到整个中国东部地区.只有到了侏罗纪-白垩纪,岩石圈减薄过程才在更大的区域内广泛发生.所以说,中国东部中新生代岩石圈减薄过程是在时间上从早中生代就已经开始、在空间上从华北北缘-中国东北地区东部开始向外逐渐扩展的一个深部过程.这个深部过程对应的地表表现是,先在华北北缘和中国东北东部地区形成规模很大的早中生代侵入岩带.而后,当岩石圈减薄过程扩展到整个中国东部时,岩浆活动才达到鼎盛时期.这可能就是中国东部侏罗纪-白垩纪大规模岩浆活动的深部原因所在.而以富集地幔源区为主的岩浆活动还导致了华北北缘地壳垂向生长.; The Guangtoushan alkaline granite occurs in the Precambrian metamorphic rocks of the North China block and contains the assemblage of quartz + alkaline feldspar + arfvedsonite + aegirine augite + aenigmatite +/- astrophyllite, accessory minerals are zircon, ilmenite, and chevkinite. Late pigmatitic pods in the granite are composed of coarse-grained quartz + alkaline feldspar + arfvedsonite. A whole-rock Rb-Sr isochron age is 200 +/- 16 Ma, with ((87) Sr/(86) Sr)(i) = 0.705 +/- 0.008 and MSWD = 11.2, in correspondence to a cooling age. A concordia age of 220 +/- 1 Ma yielded by the single-grain zircon U-Pb dating is considered to represent the emplacement age of the granite. Geochemically, the granite is characterized by A/CNK < 1 and A/NK < 1, low Al2O3, MgO, CaO, Ba, Sr and high total alkali, MnO, Rb, Ga contents and pronounced negative Eu anomalies. Mineralogy and geochemistry of the granites are consistent with those of post-orogenic A-type granites. Therefore, it is suggested that the Guangtoushan alkaline granite was produced by magmatism in a post-orogenic setting. The averaged epsilon(Nd) (T = 220 Ma) value is -8.9, higher than that for the lower crust of the North China block, implying that the parent magma for the granite could not be produced from the partial melting of the lower crust. It is also impossible that the parent magma was originated from the Precambrian high-pressure granulite terranes in northern Hebei province, because the granulites have no evidence for partial melting. Similarly, the magma could not be derived from the present-day lower crust beneath the North China block because of its young age of 120 to 140 Ma. An enriched mantle source in subcontinental lithosphere is suggested for the Guangtoushan alkaline granite, which was contaminated by the crustal materials subducted in early Proterozoic. The early Mesozoic intrusive zone in northern North China block, including the Guangtoushan alkaline granite, has been considered to be derived mainly from enriched mantle sources. The most intense magmatism in eastern China at around 130 Ma is in correspondence to the peak time of lithospheric thinning, but the mantle-derived magmatism before 130 Ma would be related to a process from initial to extreme lithospheric thinning. It is thus suggested that the early Mesozoic intrusions in northern North China block were formed in the early stage of lithospheric thinning. The early Mesozoic magmatism related to initial lithospheric thinning generated a post-orogenic A-type granite belt from eastern Northeast China through northern North China block to northern Alaxa region. The distribution of these early Mesozoic intrusions in either eastern Northeast China or northern North China block is limited to a long and narrow zone, indicating that not whole of eastern China was involved in initial lithospheric thinning. The lithospheric thinning would not occur widely until Jurassic and Cretaceous. It is concluded that the Meso-Cenozoic process of lithospheric thinning started temporally in early Mesozoic and spatially in northern North China block and eastern Northeast China. As more and more eastern China was involved in such a process of lithospheric thinning, the peak magmatism occurred at around 130 Ma. This would be the reason at depth for the Jurassic-Cretaceous magmatism in eastern China. In addition, the addition of mantle-derived magmas to the crust also resulted in the vertical growth of continental crust during the initial lithospheric thinning.; 国家重点基础研究发展计划(973计划); 教育部跨世纪优秀人才培养计划; http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000226179100007&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=8e1609b174ce4e31116a60747a720701 ; SCI(E); 中文核心期刊要目总览(PKU); 中国科技核心期刊(ISTIC); 中国科学引文数据库(CSCD); 54; 6; 1375-1388; 20
语种	中文
内容类型	期刊论文
源URL	[http://ir.pku.edu.cn/handle/20.500.11897/243450]
专题	地球与空间科学学院
推荐引用方式 GB/T 7714	韩宝福,加加美宽雄,李惠民. 河北平泉光头山碱性花岗岩的时代、Nd-Sr同位素特征及其对华北早中生代壳幔相互作用的意义, Age and Nd-Sr isotopic geochemistry of the Guangtoushan alkaline granite,Hebei province,China:implications for early Mesozoic crust-mantle interaction in North China Block[J]. 岩石学报,2004.
APA	韩宝福,加加美宽雄,&李惠民.(2004).河北平泉光头山碱性花岗岩的时代、Nd-Sr同位素特征及其对华北早中生代壳幔相互作用的意义.岩石学报.
MLA	韩宝福,et al."河北平泉光头山碱性花岗岩的时代、Nd-Sr同位素特征及其对华北早中生代壳幔相互作用的意义".岩石学报 (2004).