Chronology, geochemistry, petrogenesis and tectonic setting of Chaganhake granitic pegmatite in North Qaidam

Objective The determination of the formation age, petrogenesis, and tectonic environment of Chaganhake granite pegmatite is of great significance for the study of the evolution of the Paleo−Tethyan and the metallogenesis of rare metals in the northern margin of the Xizang Plateau.

Methods In this paper, monazite U−Pb dating and zircon U−Pb dating have been carried out for granite pegmatite and its surrounding rocks, and their geochemistry has been studied.

Results The results show that the monazite U−Pb age of granite pegmatite is 250.4±0.7 Ma(MSWD=0.1, n=27), while the zircon U−Pb age of biotitite syenogranite is 374.3±8.5 Ma(MSWD=0.15, n=8). The granite pegatite is characterized by high Si, alkali, Al and low Ti, with A/CNK value of 1.15 to 1.32 and low rare earth element contents, showing a right−leaning partition pattern with weak enrichment of light rare earth elements (LREE), strong Eu deficit, δEu of 0.07 to 0.18, showing a four−group effect of M−type rare earth elements, significant enrichment of Rb, K, U and P, strong depletion of Ba, Sr and Ti, moderate enrichment of high field strength elements(HFSE) Nb, Ta, Zr, Hf. Biotite synenite granite is rich in Si, K, and poor Ti, with A/CNK value of 1.13 to 1.32 and moderate rare earth element contents, showing a right−leaning partition pattern of strong enrichment of LREE, obvious Eu deficit, δEu of 0.19 to 0.32, strong enrichment of Rb, K, Th, and strong depletion of Sr, P and Ti.

Conclusions Combined with the regional geological background, it is believed that the Chaganhake granite pegmatite in the western part of the North Qaidam margin is different from the Zongwulong granite pegmatite. The Zongwulong granite pegmatite evolved from the granite formed in the process of accretionary orogeny and collision orogeny of the Paleo−Tethys Ocean continental margin through high differentiation, while the Chaganhake granite pegmatite was formed in the continental interior of the Qaidam block under the Paleo−Tethys Ocean subduction environment of the Early Triassic. It is the product of small proportion partial melting of the Dakendaban rock group during the process of extrusion migmatization within the continent, and has the metallogenic potential of niobium−tantalum deposit.