The magma evolution sequence and geodynamic setting in the Qibaoshan ore area, Wulian County, Shandong Province, China

摘要

The Qibaoshan ore area is located in Wulian town, Shandong Province, which is an important polymetallic metallogenic zone containing gold, copper, lead, and zinc. The polymetallic mineralization is mostly related to the Qibaoshan complex. The Qibaoshan complex is composed mainly of pyroxene diorite, andesitic porphyrite, pyroxene andesite porphyrite, amphibole andesite porphyrite, diorite porphyrite, and granodiorite porphyry, among which granodiorite-porphyry is the main wall rock of gold and copper ore body, whereas lead and zinc mineralization is closely related to diorite porphyrite. A combined study of laser ablation-inductively coupled plasma-mass spectrometry zircon U-Pb dating and geochemical analyses (major and trace elements) for 5 Mesozoic plutons from the Qibaoshan complex was carried out to determine their ages, petrogenesis, and tectonic setting. The U-Pb zircon ages measured by laser ablation-inductively coupled plasma-mass spectrometry indicate that the Qibaoshan complex was emplaced in 3 stages, represented by the similar to 175Ma pyroxene diorite, similar to 129Ma andesitic porphyrite/ porphyrite, similar to 125Ma granodiorite-porphyry, and similar to 112Ma diorite porphyrite. Systematic diagenetic chronology and rock geochemistry show that formation of similar to 175Ma pyroxene diorite in Qibaoshan ore-concentrated area is possibly related to the transformation environment from compression to extension of the Sulu orogenic belt and/or of the subduction of the Pacific Plate, whereas the formation of the Early Cretaceous subvolcanic rock has a volcanic arc affinity related to subduction of the Pacific Plate. Based on the previous studies, this paper argues that the metallogenic age of Qibaoshan polymetallic ore-concentrated area is 125-105Ma, which is formed in the volcanic arc dynamics environment of the Pacific Plate subduction in the Late Yanshanian. In addition, a small amount of 610-799Ma and 1.8Ga was developed in the samples of the pyroxene d