| 江西会昌盆地晚白垩世站塘高钠埃达克质岩石的地球化学特征及岩石成因 |
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| 引用本文： | 蔡志勇,熊小林,孙三才.江西会昌盆地晚白垩世站塘高钠埃达克质岩石的地球化学特征及岩石成因[J].大地构造与成矿学,2004,28(4):355-369. |
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| 作者姓名： | 蔡志勇 熊小林 孙三才 |
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| 作者单位： | 中国科学院广州地球化学研究所,广东,广州,510640;中国科学院研究生院,北京,100039;鄂西北地质矿产调查所,湖北,襄樊,441003;中国科学院广州地球化学研究所,广东,广州,510640;鄂西北地质矿产调查所,湖北,襄樊,441003 |
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| 基金项目： | 中国科学院知识创新工程项目 |
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| 摘 要： | 江西会昌盆地晚白垩世喷发的站塘安山岩,其形成与晚中生代岩石圈伸展和玄武质岩浆的底侵作用有关。这些岩石是高Na(6.59%～8.46%Na2O)、高Al的奥长花岗质岩石,具有与埃达克岩相似的高Sr和Ba、低Y和HREE、高Sr/Y和La/Yb比等特点。与埃达克岩相比,它们的Na2O较高而CaO较低,其εNd(t)值-2.3～-3.8和87Sr/86Sr初始比值0.707～0.708也与具大洋同位素组成特征的埃达克岩有明显区别。这些化学的和同位素特征,表明它们并非消减板片部分熔融的产物。站塘埃达克质岩浆可能源自底侵玄武质下地壳,其异常的高Na和低Ca特点反映其源岩成分的特殊性。因其成分与由实验产生的富碱玄武岩部分熔融体组成相当,因此,我们认为站塘高钠安山质岩浆可能是富碱玄武质岩石部分熔融的产物。
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| 关 键 词： | 高钠安山岩 埃达克岩 富碱玄武岩熔融 底侵作用 江西 |
| 文章编号： | 1001-1552(2004)04-0355-15 |
| 修稿时间： | 2004年6月15日 |
CHARACTERISTICS AND ORIGIN OF HIGH-NA ADAKITE-LIKE ROCKS:THE LATE CRETACEOUS ZHANTANG ANDESITES IN THE HUICHANG BASIN, JIANGXI PROVINCE |
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| CAI Zhiyong.CHARACTERISTICS AND ORIGIN OF HIGH-NA ADAKITE-LIKE ROCKS:THE LATE CRETACEOUS ZHANTANG ANDESITES IN THE HUICHANG BASIN, JIANGXI PROVINCE[J].Geotectonica et Metallogenia,2004,28(4):355-369. |
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| Authors: | CAI Zhiyong |
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| Institution: | CAI Zhiyong~ |
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| Abstract: | The Zhantang andesites occur in the Cretaceous Huichang Basin, Eastern Nanling Range of SE China, and were formed under an intracontinental, extensional tectonic setting that was not associated with subduction. They are high-Na (up to 8.46% Na_2O), high-Al trondhjemitic rocks, with high concentrations of Sr and Ba, low concentrations of MgO, CaO, Cr, Co Ni, Y and HREE, and high Sr/Y and La/Yb and low Rb/Sr ratios. Partial melting of mantle lithosphere, magmatic mixing or fractional crystallization cannot explain the origin of these compositionally distinctive magmas, while partial melting of garnet-containing basaltic protolith such as subducted slab or basaltic underplate can account for many features of these magmas. The high Na, Al and high Sr/Y and La/Yb features of the Zhantang andesites are similar to those of adakite resulted from slab-derived melting. However, the Zhantang andesites were not derived from subducted slab. As compared with adakite, they are much higher in Na_2O but lower in CaO. The ε_(Nd)(t) (-2.3～-3.8) and initial ()~(87)Sr/~(86)Sr (0.707～0.708) are also significantly different from those of most adakites which have like-MORB isotopic compositions. These chemical and isotopic data together with the geological setting suggest that subducted slab was not involved in producing these magmas. Alternative derivation of these magmas is therefore the partial melting of underplated basaltic lower crust. Partial melt composition of basalt is closely related to source composition. The high Na_2O and low CaO signature for the Zhantang magmas suggests a compositionally particular source. Comparison shows that the Zhantang andesites are generally compositionally similar to the high-pressure partial melts of the alkali-rich, high Na_2O and low CaO basalt (Rapp and Watson, 1995). We therefore suggest that the Zhantang high-Na and low-Ca adakite-like magmas were produced, at a pressure high enough to stabilize garnet (≥10×~8 Pa), by melting of an alkali-rich basaltic (amphibolitic) underplate. The melting probably took place in response to the continued magma underplating and thickening at the base of the crust of the Eastern Nanling Range. |
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| Keywords: | high-Na andesites adakite melting of alkali-rich basaltic underplate Jiangxi province |
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