Petrogenesis of ore-bearing porphyry in non-subduction setting: a case study of the Eocene potassic intrusions in the western Yangtze Block

• Published in: Mineralogy and petrology Vol. 112; no. 6; pp. 801 - 817
• Main Authors: Liu, Zheng, Liao, Shi-Yong, Zhou, Qing, Zhang, Xin
• Format: Journal Article
• Language: English
• Published: Vienna Springer Vienna 01.12.2018; Springer Nature B.V
• Subjects: Aluminum oxide; Anomalies; Barium; Case studies; Copper; Earth; Earth and Environmental Science; Earth Sciences; Eocene; Fugacity; Geochemistry; Heavy metals; Inorganic Chemistry; Isotopes; Magma; Mantle; Mineralogy; Original Paper; Oxygen enrichment; Petrogenesis; Porphyry copper; Rare earth elements; Ratios; Removal; Rock; Rocks; Silica; Silicon dioxide; Strontium; Subduction; Ytterbium; Yttrium; Lithospheric mantle; Western Yangtze; Eocene; Porphyry copper deposit; Potassic rocks
• ISSN: 0930-0708; 1438-1168
• DOI: 10.1007/s00710-018-0597-4

In the western Yangtze Block, abundant Eocene (~38–34 Ma) potassic adakite-like intrusions and associated porphyry copper deposits are exposed in non-subduction setting, including Machangjing, Beiya, Binchuan, Habo and Tongchang intrusions. All these ore-bearing porphyries share many geochemical characteristics of adakite such as depletion in heavy rare earth elements (HREEs), enrichment in Sr and Ba, absence of negative Eu anomalies, high SiO 2 , Al 2 O 3 , Sr/Y, La/Yb and low Y, Yb contents. They also exhibit affinities of potassic rocks, e.g., alkali-rich, high K 2 O/Na 2 O ratios and enrichment in light rare earth elements (LREEs) and large ion lithophile elements (LILEs). Their Sr-Nd isotopic ratios are similar to coeval shoshonitic lamprophyres. Geochemical data indicate that they were probably produced by partial melting of newly underplated potassic rocks sourced from a modified and enriched lithospheric mantle. These underplated rocks have elevated oxygen fugacity, water and copper contents, with high metallogenic potential. We propose that all the studied potassic rocks were emplaced in a post-collisional setting, associated with the local removal of lithospheric mantle.