Mantle-derived immiscible characteristics for fluid inclusions in special xenoliths from Cenozoic alkalic-rich porphyry in west Yunnan

Zhao, Fufeng; Liu, Xianfan

doi:10.1109/rsete.2011.5964525

Cited by 2 publications

(1 citation statement)

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“…According to the previous studies, the chemical compositions of the Tongchang-Chang'anchong fertile porphyries have high SiO2 and low MgO contents, typical of igneous rocks formed from crust-derived melts. Based on the similar Sr-Nd isotope compositions of these rocks with the mafic lower crust beneath the Yangtze Craton ( 87 Sr/ 86 Sr = 0.7060-0.7100; εNd(t) = −10.0 to 0) [84] and the adakitic characteristics according to the geochemical data of whole-rock and apatite, the magmatic source of Tongchang-Chang'anchong fertile intrusions is restricted to the mafic lower crust. The zircons from these fertile intrusions have Neoproterozoic Hf isotope model age, indicating that the Tongchang-Chang'anchong fertile intrusions were derived from partial melting of the Neoproterozoic juvenile lower crust [52,83].…”

Section: Discriminant For Adakite From Apatite Geochemistrymentioning

confidence: 97%

In Situ Mineralogical Constraints on Magmatic Process for Porphyry Deposits in the Upper Crust: A Case from Tongchang–Chang’anchong Porphyry Deposits, SW China

Wang

Zheng

et al. 2023

Minerals

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The magmatic process within upper crust encompasses various contents such as the transition between magmatic and hydrothermal systems and changes in oxygen fugacity (ƒO2), which ultimately play key roles in the formation of porphyry Cu deposits (PCDs). However, tracing these magmatic processes, especially in porphyry systems, is not an easy task. This study reported the detailed process of magmatic fluid exsolution and systematical variation of magmatic ƒO2 within the upper crust of a Tongchang–Chang’anchong porphyry Cu deposit, based on detailed investigations of mineral crystallization sequences and compositional features of the minerals in the fertile porphyries. Results indicate that the fertile porphyries show a high initial ƒO2, with ΔFMQ ≥ +3.0 (ΔFMQ is the deviation of logƒO2 from the fayalite–magnetite–quartz (FMQ) buffer). The magmatic ƒO2 (ΔFMQ) continued to decrease to ~+2 until fluid exsolution occurred at ~790 °C due to wall-rock contamination. The magmatic fluid exsolution process caused a temporary increase in the ƒO2 (to ΔFMQ = ~+3.4). The high magmatic ƒO2 during this process (790–750 °C) resulted in a higher content of ore-forming materials in the exsolved magmatic fluid. When the temperature dropped below 750 °C, the magmatic ƒO2 began to continuously decrease and eventually reached ΔFMQ = ~+0.6. The lower magmatic ƒO2 hindered the further migration of ore-forming materials through the exsolved fluid during this process (< 750 °C). Results of this study indicate that the initial magma during the upper crustal magmatic process of PCDs generally has a high ƒO2, and the contamination of reduced components can significantly decrease the magmatic ƒO2. The early magmatic fluid exsolution process can maintain a high magmatic ƒO2 condition, thereby efficiently extracting ore-forming minerals and producing ore-forming fluids, which is the key to the formation of PCDs. The latter continuous decrease in magmatic ƒO2 during the fluid exsolution process may be the reason preventing the Tongchang–Chang’anchong porphyry Cu deposit to form a giant PCD.

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Section: Discriminant For Adakite From Apatite Geochemistrymentioning

confidence: 97%