摘要
晚白垩世 (95Ma)、白垩纪末 (6 9Ma)和古新世 (6 76 5Ma)玄武质岩石 ,呈脉状零星露头产于燕山期崂山花岗岩体中 ,岩性分别为碱性玄武岩、碧玄岩和拉斑玄武岩。碱性玄武岩和碧玄岩以高度富集LILE和LREE为特征 ,(La/Yb) N=2 5 .5～ 4 6 .6 ,两者表现为程度不等的Nb、Ta、Zr、Ti等高场强元素亏损 ,与我国华北新生代碱性玄武岩相比 ,Ba、Rb、Th更为富集 ,Sr、Nd同位素比值 (碧玄岩 )为87Sr/ 86Sr =0 .70 5 5 17,14 3 Nd/ 14 4 Nd =0 .5 12 777,它们很可能均起源于早中生代扬子板块向华北板块之下消减而形成的古老岩石圈地幔楔的部分熔融 ;拉斑玄武岩则与华北早第三纪拉斑玄武岩类似 ,微量元素总量及LILE和LREE含量均较低 ,(La/Yb) N=4 .7～ 6 .4 ,其典型的微量元素比值 (如Zr/Nb、Rb/Nb、Nb/Ta等 )与EM1型OIB类似 ,87Sr/ 86Sr =0 .70 6 0 5 4～ 0 .70 6 146 ;14 3Nd/ 14 4 Nd =0 .5 72 387～ 0 .5 12 392 ,它可能起源于受上涌软流圈交代的大陆岩石圈 (软流圈顶部的“metasome”)的部分熔融 ,是软流圈流体与大陆岩石圈相互作用的产物。上述不同类型玄武岩的顺序侵位 ,可能反映在晚白垩世—早第三纪期间 。
The scattered outcrops of the Late Creraceous (95Ma), end Creraceous (69Ma), and the Oligocene(67 65Ma) basalitic rocks occur in the Laoshan Yanshanian granitic intrusives, estern China. The rock types are alkaili basalt, basanite and tholeiite, respectively. The alkaili basalt and basanite are all characterized by higher contents of LILE and LREE, with (La/Yb) N=25.5～46.6, depleted in Nb,Ta,Zr,Ti , and enriched in Ba, Rb, Th, as compared to those of the Cenozoic alkaili basalt in North China. The Sr, Nd isotopic ratios of basanite are 87 Sr/ 86 Sr=0.705517, 143 Nd/ 144 Nd=0.572777. Both alkaili basalt and basanite should be derived by partial melting of an older mantle wedge that formed by the Early Mesozoic subduction of the Yangtze plate beneath the North China plate. Compared to alkaili basalt and basanite, the tholeiite has lower contents of total trace elements, LILE and LREE, and with (La/Yb) N= 4.7～ 6.4 . Their typical ratios of trace elements are similar to those of EM1 OIB. 87 Sr/ 86 Sr= 0.706054～ 0.706146 ; 143 Nd/ 144 Nd=0.572387～0.512392. They should be originated by partial melting from the 'metasome'-the lithospheric mantle metasomatised by the rising asthenospheric fluid. The intrusions of different kinds of basalts may reflect the dynamic process in the area of gradual crustal extension, thinning, and asthenospheric elevation from Late Creraceous to Eogene.
出处
《高校地质学报》
CAS
CSCD
2001年第4期435-443,共9页
Geological Journal of China Universities
基金
国家自然科学基金 (4 990 30 0 3)
山东省自然科学基金 (Y2 0 0 0E6 )资助项目
