Magmatic activity in the Sanqingshan area and its surroundings began in the Meso-Neoproterozoic, with the most frequent and intense activity occurring during the Mesozoic Yanshanian Period. The granites exhibit a characteristic "two-belt, three-type" distribution, forming a granite field of typical significance.
Meso-Neoproterozoic M-type Oceanic Plagiogranite
Meso-Neoproterozoic M-type oceanic plagiogranite is distributed within the metamorphic peridotite of the Xiwan area, located in the northern part of Sanqingshan. According to the research of Shu Liangshu et al. (1995), this rock is a differentiation product of the basic components within an ophiolite suite. Along the fault contact zone between the Xiwan metamorphic peridotite and phyllite, high-pressure metamorphic blueschist can be observed.
Yanshanian Granites
The Yanshanian granites are characterized by a "two-belt, three-type" pattern.
"Two Belts":
Northern Belt (Tongchang - Yinshan Tectono-Magmatic Belt): This is a Middle-Late Jurassic intermediate-acid hypabyssal porphyry-subvolcanic rock belt. Rock bodies in this belt occur as small stocks and apophyses, characterized by negative topography.
Southern Belt (Huaiyushan - Lingshan Tectono-Magmatic Belt): Distributed in the Huaiyushan area and its southeastern side, this is a Cretaceous granite belt, mainly composed of the Lingshan and Huaiyushan batholiths. According to geophysical data, the two batholiths are connected at depth, forming the Huaiyu Mountains, and are significant rock units for landscape formation.
"Three Types":
This refers to the three different genetic types of granite exposed in the Sanqingshan area: I-type, S-type, and A-type. Over time (from early to late), the genetic types evolve from I-type → S-type → A-type, with the rock composition generally evolving towards an ultra-acid, alkali-rich trend.
Detailed Characteristics of the Granite Belts:
1. Tongchang - Yinshan Tectono-Magmatic Belt
This belt consists of the Fujiawu, Tongchang, and Zhushahong hypabyssal granodiorite porphyry stocks, and the Yinshan subvolcanic cryptovolcanic diorite porphyrite body. According to research by Shao Kezhong (1957) and Zhu Xun (1989), these are I-type granites, belonging to an intermediate-acid rock assemblage (SiO2 content: 60%-66%). They are deep-sourced crust-mantle mixed magma rocks. Rb-Sr isochron ages of 170-160 Ma indicate they are products of the early orogenic stage in the Middle-Late Jurassic.
2. Huaiyushan - Lingshan Tectono-Magmatic Belt
This belt exposes two genetic types of granite.
The Lingshan Complex: It occurs as a NW-trending ellipsoid.
The Wangxian Pluton in the central part is an S-type rapakivi granite, lithologically characterized as megaporphyritic rapakivi hornblende-biotite monzogranite. It contains abundant microdiorite enclaves formed by magma mingling. It was emplaced under localized extensional conditions at the intersection of NE and NW faults during a late orogenic environment. K-Ar ages of 140 Ma place it from the late Late Jurassic to the early Early Cretaceous.
The Lingshan Pluton from the late Early Cretaceous is a miarolitic granite, lithologically characterized as hornblende-biotite alkali-feldspar granite or biotite alkali-feldspar granite, with well-developed miarolitic cavities. The rock evolves towards a sodium-rich composition (Na2O content up to 3.7%). Research by Jiang Yaohui et al. (1999) classifies it as A-type granite. The Lingshan Pluton formed in an extensional setting during the post-orogenic stage, emplaced passively along the remnant conduit of the earlier Wangxian Pluton. K-Ar ages are 115.6 Ma. The Wangxian Pluton, occupying the inner part of the circular complex, forms gentle terrain, while the Lingshan Pluton in the outer part creates peak forest landscapes.
The Huaiyushan Granitic Complex: Exposed from Sanqingshan through Huaiyushan to Damaoshan, this complex belongs to the A-type granite category. It is a complex granitic body formed by multiple magmatic intrusions. The main intrusive phase yields K-Ar ages of 115 Ma, while the supplementary phase yields ages of 96.6-87.4 Ma, representing the latest intrusive granitic bodies in the region. The Sanqingshan granite is an integral part of the Huaiyushan Granitic Batholith, located in its eastern segment.
