Geochemical and isotopic investigation of the Laiwu–Zibo carbonatites from western Shandong Province, China, and implications for their petrogenesis and enriched mantle source
Geochemical and isotopic investigation of the Laiwu–Zibo carbonatites from western Shandong Province, China, and implications for their petrogenesis and enriched mantle source
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DOI：
10.1016/j.lithos.2004.04.037
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发表时间：
2004-08
期刊：
影响因子：
3.5
通讯作者：
Jifeng Ying;Xin-hua Zhou;Hong‐fu Zhang
中科院分区：
文献类型：
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作者：
Jifeng Ying;Xin-hua Zhou;Hong‐fu Zhang
鲁西莱芜-淄博中生代碳酸岩的主量元素、微量元素和Nd-Sr同位素数据为岩石成因和地幔源区性质提供了线索。莱芜-淄博碳酸岩可分为钙、镁、铁碳酸岩。所有这些碳酸岩在地球化学上都显示出相似性。一方面，它们与全球碳酸岩相似，Ba、Sr和LREE极度富集，K、Rb和Ti显著偏低;另一方面，它们具有极高的初始87 Sr/86 Sr（0.7095-0.7106）和极低的εNd（−18.2 ~ −14.3），与全球碳酸岩完全不同。Sr和Nd同位素比值的微小变化表明，地壳混染并不能改变LZC岩浆的原始同位素组成，这些比值代表了LZC岩浆的地幔来源。LZCs的Nd-Sr同位素组成及其与中生代防城玄武岩的相似性表明它们来自富集的岩石圈地幔。这种富集的岩石圈地幔的形成与华北板块和扬子板块的大碰撞有关。扬子板块的地壳物质俯冲到华北克拉通之下，扬子板块俯冲地壳的熔融物产生了富集的中生代地幔，这是LZCs和防城玄武岩的源区。碱性硅酸盐岩石，这通常是与碳酸盐岩的缺席表明，LZC起源于地幔直接部分熔融。
Major and trace element and Nd–Sr isotope data of the Mesozoic Laiwu–Zibo carbonatites (LZCs) from western Shandong Province, China, provide clues to the petrogenesis and the nature of their mantle source. The Laiwu–Zibo carbonatites can be petrologically classified as calcio-, magnesio- and ferro-carbonatites. All these carbonatites show a similarity in geochemistry. On the one hand, they are extremely enriched in Ba, Sr and LREE and markedly low in K, Rb and Ti, which are similar to those global carbonatites, on the other hand, they have extremely high initial87Sr/86Sr (0.7095–0.7106) and very low εNd(−18.2 to −14.3), a character completely different from those global carbonatites. The small variations in Sr and Nd isotopic ratios suggest that crustal contamination can not modify the primary isotopic compositions of LZC magmas and those values are representatives of their mantle source. The Nd–Sr isotopic compositions of LZCs and their similarity to those of Mesozoic Fangcheng basalts imply that they derived from an enriched lithospheric mantle. The formation of such enriched lithospheric mantle is connected with the major collision between the North China Craton (NCC) and the Yangtze Craton. Crustal materials from the Yangtze Craton were subducted beneath the NCC and melts derived from the subducted crust of the Yangtze Craton produced an enriched Mesozoic mantle, which is the source for the LZCs and Fangcheng basalts. The absence of alkaline silicate rocks, which are usually associated with carbonatites suggest that the LZCs originated from the mantle by directly partial melting.