China Geological Survey: Bedrock Geological Map and Digital Database of the Baidunzi-Heishankou Area (K46F037044, K46F037045, K46F037046, K46F038044, K46F038045 and K46F038046, and parts of K46F037043 and K46F038043), Guazhou, Gansu, scale 1:25,000

The Baidunzi map sheet comprises an imbricate stack of six structural panels, each characterised by a distinctive tectonostratigraphy of greenschist- to amphibolite facies tectonites and/or style of tectonism. The stack assembled rock units formed in diverse tectonic settings. Deformation and formation of the imbricate stack was polyphase (D1−3) and occurred during the Permian to early Triassic. Final assembly of the structural panels occurred during D3, which led to north-directed ductile-brittle thrusting and folding, following an earlier phase of south-directed D2 thrusting. The structurally two highest thrust nappes in the stack (Panels 1 and 2) comprise a distinct collage of structurally interleaved metasedimentary and metaplutonic tectonites of the Baidunzi Complex. The mafic to intermediate igneous rocks of Panel 1 are largely early Carboniferous (ca. 335-325 Ma) and late Permian (ca. 270-255 Ma), whereas Panel 2 mainly contains early Permian gabbroic to granitic rocks (ca. 295-280 Ma), which intruded syntectonically. The metasedimentary rocks include orthoquartzite, which may be Neoproterozoic, marble (≤ ca. 330 Ma) and a unit of immature siliciclastic rocks (≤ ca. 305 Ma), which are all older than ca. 295 Ma. Panel 4 comprises calc-alkaline felsic to intermediate tuffs (ca. 295 Ma) of the Ganguan Group, which are unconformably overlain by red beds and minor tuff dated at ca. 282 Ma. Rocks typical of the Baidunzi Complex are absent in the Ganguan Group, indicating that these two units represent different tectonic settings. Panels 3 and 5 comprise a structural collage of Baidunzi Complex rocks of Panel 2 and Ganguan Group of Panel 4. Juxtaposition and/or interleaving of these two units occurred after intrusion of the ca. 281Ma Baidunzi Complex gabbro, which nowhere intruded rocks of the Ganguan Group. Panel 6 mainly comprises pillow basalt and chert of the ophiolitic Liuyuan Complex, which were thrust southwards over Panel 5. The immature clastic rocks of the Shuanbaotang Group unconformably overlie rocks of Panels 4, 5 and 6 and were deformed during D2 and D3.