Citation: | LU Lin, PAN Liang, ZHOU Bin, HAN Kui, QIAO Xinxing. Geochronology, geochemistry and tectonic setting of the Dianzhong Formation volcanic rocks in the Riduo area, Eastern Gangdese belt, Tibet[J]. Geological Bulletin of China, 2021, 40(8): 1314-1329. |
The Linzizong Group is a typical Paleogene volcanic assemblage in the Gangdise belt, which records the orogenic history of subduction and collision between India and Eurasia.Zircon U-Pb chronology and Lu-Hf isotope studies were conducted on the Dianzhong Formation basic and intermediate volcanic rocks at the bottom of the Linzizong Group in the Riduo region of the Eastern Gangdese belt.LA-ICP-MS zircon U-Pb dating results show that ages of the Dianzhong Formation basalt and andesite crystalline tuff are 57.9±1.2 Ma and 57.4±1.2 Ma respectively, indicating that they were formed in the Late Paleozoic.Geochemically, the volcanic rocks generally belong to high-K(calc-alkaline) series.The basic volcanic rocks have low SiO2(48.67%~49.34%), high Al2O3(15.25%~18.59%) and high MgO(3.76%~8.69%).They are characterized by LREE enrichment and positive Eu anomalies(δEu=1.15~1.37).The intermediate volcanic rocks have high SiO2(54.92%~64.16%), high Al2O3(15.85%~16.72%), high K2O(0.65%~2.14%) and low MgO(1.34%~3.67%).They are relatively enriched in LREE and weak negative Eu anomalies(δEu=0.77~0.92).Both volcanic rocks exhibit fractionated REE and rightward patterns, strong enrichment of LILE(Rb, Ba, Sr), and depletion of HFSE(Nb, Ta, Ti).The zircon εHf(t) values of the basic volcanic rocks range from 4.86 to 8.97, and the εHf(t) values of the intermediate volcanic rocks are from 0.26 to 6.37.Based on previous results, it is suggested that the Dianzhong Formation volcanic rocks in Riduo area were formed in the syn-collision tectonic setting of the collision between India and Eurasia.The basic volcanic rocks were mainly derived from the partial melting of overlying mantle wedge metasomatized by the fluids of subducting plate, while the intermediate volcanic rocks were originated from partial melting of the juvenile crust materials, both of which were influenced by the contamination of old crustal materials to various degrees.
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Tectonic position of Lhasa terrane(a, b)and geological map of the Riduo area(c)
Collumn of Dianzhong Formation volcanic rocks in Riduo area
Outcrop(a~c)and microscopic(d, e)photos of the Dianzhong Formation volcanic rocks in the Riduo area
TAS(a)and FAM(b)diagrams of the Dianzhong Formation volcanic rocks in the Riduo area
SiO2-K2O diagram of the Dianzhong Formation volcanic rocks in the Riduo area
Chondrite-normalized REE patterns(a)and primitive mantle normalized spider diagram(b) of the Dianzhong Formation volcanic rocks in the Riduo area
CL images and analyzing locations of zircons from the Dianzhong Formation volcanic rocks in the Riduo area
Zircon U-Pb concordia diagram and 206Pb/238U age weighted average value diagram of the Dianzhong Formation volcanic rocks in the Riduo area
Petrogenesis diagrams of the Dianzhong Formation volcanic rocks in the Riduo area
(Y+Nb)-Rb(a)and Hf-Th-Ta(b)diagrams of the Dianzhong Formation volcanic rocks in the Riduo area