## 2 Geological Setting and Samples  
Baiyinhushuo ploton is located in the northern part of Xi Ujimqin town, which is located on the southeastern margin of the CAOB (Figure 1a), north of the Solonker-Xar Moron River ophiolite belt and south of the Erenhot-Hegenshan ophiolite belt (Figure 1b). In the Paleozoic period, it experienced multi-stage subduction and the accretion of the Paleo-Asian Ocean, which is a typical accretionary orogenic belt [2,3]. The exposed strata are mainly the Late Paleozoic Amushan Formation and the Gegenaobao Formation, as well as the Early Cretaceous Baiyingaolao Formation and the Quaternary sediments [15]. The main lithology of the Gegenaobao Formation is siltstone and fine siltstone, which  
Figure 1: (**a**) Distribution range of the Central Asian Orogenic Belt (CAOB; modified from [9]). (**b**) Sketched tectonic map of the adakite in Baiyinhushuo, Inner Mongolia (modified from [20,21]). (**c**) Simplified geologic map of the study area [15].  
experienced strong metamorphism. The metamorphism of the clastic rocks is mainly carbonatization and silicification.  
The magmatic rocks in the study area are abundant and have a large outcropping area; the ophiolite of Wusinihei is located in the western part of the study area. Baiyinhushuho granodiorite intrudes into the Gegenaobao Formation. The intermediate acidic dikes are widely distributed in the Baiyinhushuho granodiorite, in which the main lithologies are quartz-diorite porphyrite, granite porphyry, and quartz porphyry, and Early Cretaceous andesite and rhyolite and other volcanic rocks can be found in some places (Figure 1c).  
The granodiorite is overall grayish-white and massive, with a medium-coarse-grained structure, and the rock can be seen as slightly fractured (Figure 2a,b). It is mainly composed of plagioclase (45%), quartz (\(\pm\)20%), K-feldspar (15%), biotite (5%), and hornblende (10%). Observed under the microscope, plagioclase is subhedral and haphazardly distributed; its size is generally 1-2 mm; some parts are 2-4 mm, with the development of polysynthetic twins, and some particles show an obvious zoning structure. The quartz crystals has a granular structure and generally has a size of 0.5-1 mm; parts of it are 0.2-0.5 mm, with a small portion being 0.1-0.2 mm. It has a gap-filling distribution, and the surface is fresh and clean; a wave-like extinction is common, and a band extinction can be seen. Potassium feldspar is subhedral and plate-like; it has a size of about 0.5-1 mm and parts are 1-1.5 mm; it has haphazard distribution and showing kaolin alteration. Hornblende is subhedral and columnar; its size is generally 0.5-1 mm; a few parts are 1-1.5 mm and haphazardly distributed. Biotite is flaky with a flake diameter of 0.5-1 mm; parts of it are 1-1.5 mm; showing epidote and chlorite alteration. Biotite, which is present in small amounts, exhibits a flaky habit and pronounced pleochroism, which is indicative of its color variation when viewed from different directions. The accessory minerals primarily consist of zircon and apatite. Zircon occurs as idiomorphic crystals, and the size ranges from approximately 0.012 to 0.20 mm. Apatite presents a more complete crystalline structure, appearing as tabular or short prismatic, with visible zoning characteristics.  
Figure 2: Field outcrop (**a**,**b**) and photomicrograph (**c**,**d**) of granodiorite.