摘要
三塘湖盆地早石炭世安山岩（ECA）、早二叠世粗面岩类（EPT）以及中二叠世玄武岩（MPB）样品都具有大离子亲石元素（LILE）相对于高场强元素（HFSE）富集，Nb和Ta强烈亏损，轻稀土元素（LREE）相对于重稀土元素（HREE）富集，类似于和俯冲带相关的岩浆特征。ECA具有高的Zr／Nb（4．67～12．39），低的Nb／La（0．27～0．30），Ce／Ce＊=0．63～0．89，Sr／Sr＊=1．32．2．49，并具有Ti的负异常，另外（^87Sr／^86Sr）i=0．70408～0．70451，εNd（t）=＋7．42-＋7．88。与ECA相比，EPT大离子亲石元素更为富集，Ti和P的负异常明显，特别是Ce／Ce＊=0．72—1．64，Sr／Sr＊=0．38～1．87，相对较低的Al2O3和CaO含量以及（^87Sr／^86Sr）；=0．70414～0.70481和εNd（t）=＋4．93～＋6．13而区别于ECA。MPB与ECA相比具有较低的大离子亲石元素含量和较高的Nb、Ta含量，Ce／Ce＊=0．69～0．84，Sr／Sr＊=1、44～2．13，未有明显的Ti负异常，（^87St／^86Sr）i=0．70388～0．70396，εNd（t）=＋7．10-＋7．99。所有的地球化学特征表明：早石炭世或更早，三塘湖盆地为与俯冲带相关的构造背景，ECA是典型的弧火山岩，其岩浆主要源于被流体或沉积物交待改造的亏损地幔楔。早石炭世以后，三塘湖地区逐渐进入碰撞后伸展拉张阶段，EPT和MPB都为后造山火山岩。EPT岩浆主要源于亏损软流圈底侵前二叠纪形成的造山组分的部分熔融；MPB的岩浆主要源于亏损地幔的部分熔融，并被前二叠纪形成的造山组分或是年轻地壳混染。三塘湖地区二叠纪伸展拉张的动力学机制主要是由于造山带增厚的岩石圈大范围拆沉而导致的大范围亏损地幔部分熔融岩浆和上部造山组分或是年轻地壳的相互作用，这种造山组分或是年轻地壳具有低的（^87Sr／^86Sr），比值和正的εNd（t）值。火山岩地球化学特征指示没有明显地幔柱的作用特征。
The major element, trace element and isotopic data of the latest-Paleozoic volcanic rocks which include early- Carboniferous andesites （ECA）, early-Permian trachytoids （EPT） and middle-Permian basalts（ MPB）, from Santanghu basin, Eastern Xinjiang, NW China, are reported in this paper. The majority of samples have enriched large ion lithophile elements （LILE） relative to high field strength elements （HFSE）, strongly negative anomalies in Ta and Nb relative to rare earth element （REE）, enriched light rare earth element （LREE） relative to heavy rare earth element （HREE）, as a typical characteristics of subduction-related magmas. Additionally, ECA have high Zr/Nb （4.67 - 12.39）, low Nb/La ratios （0.27 - 0.30）, Ce/Ce ＊ = 0.63 - 0.89, Sr/Sr＊ = 1.32 - 2.49, negative anomalies in Ti, （^87Sr/^86Sr） i = 0. 70408 - 0. 70451 and εNd （t） = ＋ 7.42 - ＋ 7.88. In contrast with ECA, EPT are characterized by higher LILE concentrations and more negative anomalies in Ti and P, especially, by Ce/Ce ＊ = 0.72 - 1.64, Sr/Sr＊ = 0.38 -1.87, and relatively low Al2O3 and CaO, and by （^87Sr/^86Sr）i = 0.70414 -0.70481 and εNd（t） = ＋4.93 - ＋6. 13 distinguished from ECA. MPB have distinct characteristics with low LILE concentrations, higher Nb and Ta concentrations, Ce/Ce＊ = 0.69 -0.84,Sr/Sr＊ = 1.44 -2.13, no negative anomalies in Ti, and with （^87Sr/^86Sr）i = 0.70388 -0.70396 and εNd（t） = ＋7. 10 - ＋ 7.99 from ECA. All the geochemical characteristics of latest-Paleozoic volcanic rocks from Santanghu Basin indicate ECA were typical of subduction-related magmas and shared a convergent margin setting in early Carboniferous or earlier, and magmas were generated by partial melting of the depleted mantle wedge modified by sediments or fluids. After late Carboniferous, Santanghu basin was under collapse setting of post-collision and shared extensional tectonic setting. EPT and MPB were all anorogenic volcanic rocks. The generation of EPT magmas origined from melting of orogenic components prior to early Permian underplated by upwelling of new asthenospheric mantle and the magmas of MPB derived from partial melting of asthenospheric mantle and were contaminated by orogenic components prior to Permian. Conclusionally, the dynamic model of stretch and extension in Permian in Santanghu basin was a result from interaction between upwelling of partial melting asthenospheric mantle induced by delamination of thickened subcontinental mantle root and orogenic components or juvenile crust formed before Permian with low （^87 Sr/^86Sr）;and positive εNd （t）. All the geochemical characteristics of latest-Paleozoic volcanic rocks also indicate they have no obvious characteristics related to mantle plume.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2006年第1期199-214,共16页
Acta Petrologica Sinica
基金
国家重点基础研究规划项目(2001CB409804)
国家自然科学基金项目(40572123)的资助。
关键词
三塘湖盆地
古生代晚期
火山岩
地球化学特征
构造-岩浆演化
Santanghu basin, latest-Paleozoic, volcanic rocks, geochemical characteristics, tectonic-magmatic evolution
