关键词: 两河口岩体, 锆石U-Pb年龄, 同位素地球化学, 北秦岭

Abstract: The Lianghekou pluton is located in Taibai area of North Qinling terrane and was emplaced into Qinling Group complex. The
pluton is mainly composed of augen granite, gneissic granite and monzogranite. In this study, crystallized ages of 928±19 Ma and 940±12
Ma with the inherited zircons grains ranging from Paleoproterozoic to Mesoproterozoic are obtained from augen granite and gneissic
granite, respectively. Augen granite contains aluminum minerals of garnet and muscovite. Most granites show the characteristics of A/
CNK＞1.1, high silica and aluminum content as well as high-K calc-alkaline series. Chondrite-normalized REE patterns show a
rightward inclination with medium negative Eu anomalies. The trace element geochemistry is characterized by enrichment in LILEs
(such as Rb, Ba, K, et al.), depletion in HFSEs (such as Nb, Ta, Ti, et al.) and obviously negative anomalies of Ba, P, Sr. Mineralogical
and geological characteristics indicate that the gneissic granites and augen granites of Lianghekou pluton are typical S-type granites.
Lianghekou granites show large range of initial 87Sr/86Sr(t) ratios of 0.701067-0.739451, lower εNd(t) values varied from -5.7 to -3.3 with
two-stage Nd modal ages of TDM2=1.9-2.1 Ga and highly radiogenic Pb composition, indicating a crustal magmatic origin and the source
rocks may be amphibolite and gneiss of Qinling Group. Combined with the regional geological background, we conclude that granites of
Lianghekou pluton originated from melting of ancient middle-lower crust under tectonic transition stage of late continental crust collision
during Neoproterozoic in response to the assembly of Rodinia supercontinent.

Key words: Lianghekou pluton, zircon U-Pb age, isotopic geochemistry, North Qinling terrane.