摘要
山东胶莱盆地大西庄的王氏群玄武岩属于高钛碱性岩系列,全岩40Ar-39Ar年龄为73.2±0.3Ma,形成于晚白垩世岩石富N2O,Mg#值为63-66,(Ne-Hy-Q)值为6.03-10.05,轻稀土富集,(La/Yb)N比值为11.18-12.56,重稀土有一是程度的分异,富集大离子亲石元素,Tb显著正异常,Zr轻微正异常,具有与大陆板内碱性玄武岩类似的特征。εNd(T)值为7.08-7.55,87Sr/86Sr(T)比值为0.7035-0.7038,反映了玄武岩浆来源于亏损的地幔源区,在上升过程中几乎没有受到地壳物质的混染,原始玄武岩浆由软流圈和新生岩石圈地幔分别部分熔融产生的熔体相混合而形成,起源深度为50-70km。玄武岩含有幔源包体,岩石类型为尖晶石二辉橄榄岩。包体的温压估算结果为T=1010-1140℃,P=20kb。包体的矿物相与平衡温压估算值以及玄武岩浆起源深度估计值表明,胶州地区晚白垩世时岩石圈厚度大约为60-70km,岩石圈地幔具有新生的性质。因此,中国东部岩石圈减薄发生在125-73Ma之间。此后,中国东部进入了统一的以拉张为主的动力学背景之下。
The Wangshi group basalts cropped out in Daxizhuang, Jiaolai basin, eastern Shandong, belong to high-Ti alkaline basalt series. The basalt was emplaced at Late Cretaceous with 40Ar-39 Ar plateau age of 73.2±0.3 Ma. The basalt is enriched in Na2O and has Mg# values of 63 -66 and normative ( Ne-Hy-Q) of 6. 03-11.05 , suggesting a depths of generation of 50 -70 km for the basalt. The enrichment of light rare earth elements ( LREE) with ( La/Yb) N of 11. 18 - 12. 56 and large ion lithophile elements ( LILE) , such as Th and Zr, and reletively differentiated heavy rare earth element ( HREE) patterns suggest a continental intraplate setting. High positive εNd( T) value of 7.08 -7.55 and low 87Sr/86Sr( T) ratio of 0. 7035 -0. 7038 for basalt in Daxizhuang suggest that the basalt was virtually not contaminated by crustal materials during their ascending and the initial basltic magma was generated by a depleted mantle source. The parantal basaltic magma was a mixture of melts derived from the asthenospheric mantle and young depleted lithospheric mantle. Mantle derived spinel-iherxolite xenoliths have been discovered in the basalt. The estimated equilibrium P-T condition of xenoliths was about 20 kb and 1010 - 1140℃. The estimated equilibrium P-T condition of xenoliths and depth of the generation o( the basaltic magma suggested that the lithosphric thickness in Jiaozhou area was about 60 - 70 km in Late Cretaceous. This further inferred that the lithospheric thinning and asthenospheric upwelling in eastern China took place at 125 to 73 Ma B. C. Hereafter, there was a uniform dynamic setting in eastern China.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2005年第1期99-112,共14页
Acta Petrologica Sinica
基金
中国科学院知识创新工程重大项目(KZCX2-107)资助
