内蒙古莫尔道嘎佳疙瘩组变质岩地球化学特征及构造意义
Geochemistry and Its Tectonic Implictions of Metamorphic Rocks of Jiageda Formation in Moerdaoga Area, Inner Mongolia

莫尔道嘎地处额尔古纳地块中北段，该区发育一套中低级变质的佳疙瘩组变质岩，如千枚岩、云母片岩和变质砂岩；但是目前其原岩类型、物质来源以及沉积环境尚不明确.基于全岩主微量元素测试和LA-ICP-MS U-Pb定年，结果表明千枚岩类和云母片岩类总体富Al和K，变质砂岩类总体富Si.岩石轻稀土明显富集，具负铕异常特征，高场强元素相对富集，Sr强烈亏损，Nb、Ta、P、Ti相对亏损.原岩性质及构造环境分析表明，原岩类型主要是杂砂岩和粘土岩，物源以长英质成分为主，并混有少量古老沉积物.它们形成于活动大陆边缘，并存在较多大陆岛弧性质物质，成熟度不高，属于近源沉积.岩石样品中的碎屑锆石多为岩浆成因,且显示了较大的年龄变化，主要集中在新元古代(1.0～0.8Ga)和古元古代(2.0～1.8Ga)，说明佳疙瘩组的沉积物源时代主要为新元古代和古元古代.
The Moerdaoga area is situated in the centralnorthern Erguna block, where a set of low-medium grade metamorphic rocks of Jiageda Formation develops, such as phyllites, mica schists and metamorphic sandstones. However, the origin, source and sedimentary environment of the protolith are not clear yet. The results of the major and trace elements analysis and LA-ICP-MS zircon U-Pb dating in this study show that phyllite and mica schists are enriched in Al and K and metamorphic sandstones are enriched in Si. These three groups exhibit similarity in trace element geochemistry, with strong enrichment in light REEs and negative Eu anomalies. The primitive mantle normalized trace element pattern shows strong depletion in Sr. Furthermore, Nb, Ta, P, Ti are relatively depleted, and most high field strength elements are enriched. The protoliths of the studied samples are mainly sandy sedimentary rocks with a small amount of muddy sedimentary rocks. The sediments show low maturity with moderate chemical weathering. The uppercrust felsic sources with possible old sediment component make a contribution to their provenance. The tectonic discrimination diagrams show that the protoliths were deposited in an active continental margin setting and had a large number of clastic rocks deposited in continental island arc setting. Most detrital zircons are of magmatic origin. The detrital zircon ages show great variations, yet mainly concentrated in Neoproterozoic (1.0-0.8Ga) and Paleoproterozoic (2.0-1.8Ga), which suggests that they provided the main sedimentary materials