Abstract:

The Yangxin pluton is the largest intrusion in southeast Hubei Province, and is also the section in which mineral resources
are the most concentrated. The complex is mainly composed of quartz diorites and small-scale biotite quartz diorites. This paper
presents high-precision zircon U-Pb ages and Hf isotopes of the Yangxin intrusion. The result indicates that its emplacement took place
around 143~139 Ma, and the quartz diorites were emplaced earlier than the biotite quartz diorites. Both of them were products of
magmatic activities in the peak period of this area. The calculation results of Ti-in-zircon thermometer show that the quartz diorites
were mainly formed in the temperature ranging from 787℃ to 876℃ , and the biotite quartz diorites were mainly formed in the
temperature ranging from 686℃ to 805℃. The zircon Hf isotopic data show that εHf(t) values of the quartz diorites range from-11.42
to-3.31, and εHf(t) values of the biotite quartz diorites are obviously lower and have a wider distribution (from -21.75 to -1.44). Combined
with geochemical, Sr and Nd isotopic and mineral chemical characteristics, both quartz diorites and biotite quartz diorites were likely
derived from enriched lithospheric mantle, as well as fractional crystallization and assimilation followed. Moreover, quartz dioritescrystallized earlier in higher temperature, while the biotite quartz diorites crystallized later in the lower temperature with addition of
more crustal materials.

Key words: southeast Hubei Province, Yangxin pluton, zircon U-Pb ages, Hf isotope, Ti-in-zircon thermometer