辽北中太古代栾家街TTG岩石成因及对华北克拉通东部陆块早期地壳生长的制约

The Eastern Block of the North China Craton had experienced complicated crustal growth and reworking in Archean. Currently, this is a general consensus that the major crustal growth of the Eastern Block occurred during Neoarchean. However, the crustal growth and its mechanism in pre-Neoarchean were poorly constrained. The Luanjiajie TTG gneiss is located at the northeastern margin of the Eastern Block, and is known as the only Mesoarchean geological body in this area, which was formed at ca. 3.07 Ga. The Luajiajie TTG was derived from partial melting of lower mafic crust, and thus recorded critical information about the crustal growth. The study on petrogenesis could provide important constraints on the process of the Eastern Blocks’s crustal growth during early Archean. Large-scale field mapping will be combined with petrology, geochemistry, zircon U-Pb dating, Hf-O-Sr-Nd isotope as well as thermodynamic modelling, to determine the distribution, protolith, forming age, petrogenesis and tectonic setting of the TTG gneisses and mafic enclaves. The results will help to clarify the Archean crustal growth and evolution processes in the Eastern Block. And the results also have significant implications for understanding the difference in crustal evolution of different ancient continental cores of the Eastern Block.

华北克拉通东部陆块在太古宙期间经历了复杂的地壳生长与再造过程。目前，普遍认为东部陆块主要的地壳生长发生在新太古代，但新太古代之前是否也经历过重要的地壳生长及其动力学机制等问题的研究还相对较少。栾家街TTG片麻岩位于东部陆块东北缘，是该地区保存的唯一的一处中太古代地质体，形成时代约3.07Ga。栾家街TTG片麻岩来自幔源基性岩的部分熔融，保留了重要的地壳生长信息，其成因研究可以为重塑东部陆块太古宙早期的地壳生长过程提供重要制约。本项目将结合大比例尺地质填图与岩石学、地球化学、锆石U-Pb年代学与Hf-O-Sr-Nd同位素联合示踪及热力学相平衡模拟等手段，理清栾家街TTG片麻岩及其中的基性岩包体的空间分布、原岩属性、形成时代、岩石成因及构造背景，阐明东部陆块东北缘太古宙早期大陆地壳的形成与演化过程。同时，本项目对深入理解东部陆块各古陆核地壳演化史的异同与多样性也具有重要意义。

本项目以华北克拉通东部陆块栾家街杂岩为主要研究对象，以年代学、岩石地球化学、同位素地球化学为主要研究手段，重点研究了栾家街杂岩的岩石组合、岩石成因及形成构造环境，同时研究了东部陆块新太古代-古元古代构造演化历史，进一步揭示了华北克拉通自中太古代-古元古代构造体制的演变过程，为华北克拉通内板块构造的启动提供了有效制约。项目取得了如下进展：（1）揭示了栾家街杂岩主要由~3.1Ga的TTG片麻岩、闪长质片麻岩和斜长角闪岩组成，~3.1Ga TTG片麻岩为中-低压型，是经历低温水岩反应的古老水化基性地壳物质在麻粒岩相变质作用条件下部分熔融的产物；闪长质片麻岩可能源自同时期的TTG岩浆经历角闪石主导的结晶分异作用，同期的~3.1Ga斜长角闪岩具有OIB特征，其母岩浆源自亏损的石榴石橄榄岩低程度部分熔融；进而认为东部陆块辽北栾家街地区在中太古代构造演化可能受控于地幔柱构造体制。（2）冀东-辽北-吉南地区~2.55Ga的TTG岩石主要为中低压型，相平衡模拟结果表明它们形成于较高的地温梯度下（>730℃/GPa；图5），明显高于现代板块冷俯冲或热俯冲，对冀东地区的新太古代构造变形特征研究表明构造变形样式为典型的doom-and-keel，其演化受控于垂向构造体制。因此，上述地区新太古代构造演化仍主要受控于垂向构造体制。（3）古元古代胶-辽-吉带内沉积-岩浆作用研究表明其为典型的碰撞型造山带，表明华北克拉通东部陆块在新太古代末期-古元古代早期经历了由垂向构造体制为主向板块构造体制的转变。本项目资助期间共发表SCI论文8篇，其中第一标注论文2篇，培养博士后1名，硕士生1名。