Oxygen isotopic compositions and geological significance of zircons from the Yanshanian felsic intrusions in the Xidamingshan cluster, southeastern margin of the Youjiang fold belt, South China : In situ SHRIMP analysis

Abstract

The source and petrogenesis of the Late Cretaceous magmatism and associated Sn-W mineralization in the South China are yet well documented. This paper reports the oxygen isotope compositions of previously analyzed zircons from the Yanshanian felsic intrusions in the Xidamingshan cluster, along the southeastern margin of the Youjiang fold belt, Guangxi, South China. Zircon (Zrn) delta(18) O for quartz porphyry ranges from 5. 31 parts per thousand to 9. 31 parts per thousand, VSMOW, averaging at 7. 61 +/- 2. 17 parts per thousand. delta(18) O-Zrn for beresitization biotite granite, fine biotite granite and medium biotite granite range from 7. parts per thousand to 9. 79 parts per thousand ( average = 8. 36 +/- 1. 33 parts per thousand) , from 5.48 parts per thousand to 9. 27 parts per thousand ( average = 7. 73 +/- 2. 23 parts per thousand) and from 6. 27 parts per thousand to 9. 77 parts per thousand (average =8. 04 +/- 1. 75 parts per thousand) , respectively. Monzonitic granite records a wide range in delta(18) O-Zrn. (5. 48 parts per thousand similar to 10. 99 parts per thousand) with average of 7. 55 +/- 2. 77 parts per thousand. The majorities are greater than the "mantle-like" values (delta(18) O: 5. 3 +/- 0. 6 parts per thousand 2 sigma). Except beresitization biotite granite, five samples have bimodal or multi-modal distribution characteristics and Hf-O plots of zircons have a negative correlation, indicating a crust-mantle interaction. Hf-O isotopic compositions suggest that the source of the magma was mainly derived from partial melting of crustal material with input of mantle-derived components. The mantle-derived melts imply that these melts not only provided necessary heat energy for crust partial melting, but also put got involved in the generation of granitic melts. Low oxygen fugacity as indicated by low Ce(IV)/Ce(III) ratios may be responsible for formation of large Pb-Zn-dominated skarn deposits. Our current research illustrates that combination of zircon Hf-O isotope could more accurately trace the source of magma through distinguish juvenile components and parental magmas derived from reworking of pre-existing crustal material. And zircon O isotope is one of the most efficient techniques to study the metallogenetic regularity.