2026-06-08 北京大学（PKU）
◆第1のサイクルは27～23.5億年前の新始生代に発生し、衝突後の地殻伸張と造山帯崩壊を示す双峰性火成岩複合体が形成された。第2のサイクルは22～16億年前の後期古原生代に起こり、アダカイト質岩体、A型花崗岩複合体、および複数世代の苦鉄質岩脈群が形成された。この活動は超大陸コロンビアの形成と関連し、最終的なクラトン安定化をもたらしたと考えられる。
◆研究は、衝突・造山・崩壊・安定化というプレートテクトニクス過程が少なくとも古原生代には現代と類似した形で機能していたことを示し、地球最初期の超大陸形成と分裂の理解に重要な知見を提供している。
Zircon U–Pb concordia diagrams of adakitic rocks, A-type complex, and mafic dykes from the Yinshan Block.
＜関連情報＞
- https://newsen.pku.edu.cn/news_events/news/research/15570.html
- https://www.sciencedirect.com/science/article/abs/pii/S0301926826001531
華北クラトン陰山ブロックにおける後期古原生代のアダカイト質A型複合岩体および苦鉄質岩脈：コロンビア超大陸形成後の長期にわたる造山帯崩壊に関する考察 Late Paleoproterozoic adakitic, A-type complexes and mafic dykes in Yinshan Block, NCC: insights into long-lived orogen collapse after assembly of Columbia supercontinent
Shabbir Jawad, Shuguang Song, Yuanyuan Liu, Chao Wang, Mark B. Allen, Chunjing Wei
Precambrian Research Available online: 27 May 2026
DOI:https://doi.org/10.1016/j.precamres.2026.108165
Highlights
- Syn-to-post-collisional magmatism (1900-1663 Ma) reveals orogenic collapse after assembly of Columbia Supercontinent.
- Adakitic rocks formed by melting of thickened mafic lower crust during collision, and the A-type rocks and mafic dykes mark the initiation of orogenic collapse at ∼1860 Ma.
- Lithospheric delamination occurred at 1.7-1.6 Ga with formation of Yanliao Basin.
- The orogenic cycle for assembly of Columbia supercontinent had lasted for 400 Myr from 2.2 Ga to1.6 Ga.
Abstract
The assembly and dispersal of the Columbia supercontinent record the earliest collisional orogenic cycle on Earth. Syn- and post-collisional magmatism provides critical insights into key orogenic processes, including the timing and crustal evolution of orogenic belts from continental collision to orogenic root detachment and collapse. This study investigates adakitic rocks, A-type igneous complexes, and mafic dykes in the Yinshan Block of the North China Craton, with zircon U-Pb ages ranging from 1890 Ma to 1663 Ma. The adakitic rocks, formed between 1890 and 1875 Ma, indicating partial melting of thickened Neoarchean mafic lower crust. The A-type complex comprises gabbro, diorite, and granite, with zircon U-Pb ages of 1827–1692 Ma. Geochemical classification of A2 subgroup implies post-collisional extensional melting of the metasomatized mantle. Two distinct types of mafic dykes are identified. Type I mafic dykes are older (∼1860–1848 Ma), subalkaline, and display relatively high MgO and Mg#, along with negative εNd(t) values, suggesting derivation from high-degree melting of metasomatized lithospheric mantle during the early stages of orogenic unrooting, driven by thermal erosion from upwelling asthenosphere. In contrast, Type II dykes are younger (1663 Ma) and spatially and genetically associated with the A-type complex. They are alkaline and exhibit elevated trace element concentrations, but have low MgO (Mg#), Cr, and Ni, indicative of low-degree melting of metasomatized lithospheric mantle during mantle delamination. After the final assembly of the Columbia supercontinent, post-collisional extension in the Yinshan Block followed terminal compression at approximately 1860 Ma. Orogenic collapse triggered asthenospheric upwelling, leading to melting of the metasomatized lithospheric mantle and the generation of A-type granites and alkaline mafic dykes. This thermo-mechanical weakening likely culminated in lithospheric delamination, with the dense lithospheric root foundering at around 1663 Ma. This geodynamic process drove mountain belt collapse and basin development and ultimately contributed to cratonic stabilization, marking the onset of the quiescent interval known as the Boring Billion.
