40Ar/39Ar ages of Quaternary volcanic rocks from the midwest of the Leizhou Peninsula, and their geologic significance

Quaternary volcanic rocks are widely distributed in the Leizhou Peninsula, but the age of volcanic formation remains controversial. This study used the high-precision laser stepwise heating 40Ar/39Ar method to date the age of volcanic samples from the midwest of the Leizhou Peninsula, and two volcanic cycles were determined by combining the contact relationship with the neighboring strata. Volcanic rocks of the first cycle (Ⅰ) occur as interlayers in the Zhanjiang Formation, only seen in Borehole ZKC12, and the lithology is olivine tholeiite; volcanic rocks of the second cycle (Ⅱ) are the most widely distributed in the study area, unconformably overlaying on the Zhanjiang Formation, with 40Ar/39Ar ages ranging from 2.02 to 0.88 Ma, indicating that they were erupted from the early stage of the early Pleistocene to the end of the early Pleistocene. On the combination of contact relationship with surrounding strata, the second cycle can be further divided into four eruption stages. The first eruption stage (Ⅱ1) has the largest scale and the most extensive area, forming two eruption centers with 40Ar/39Ar age of 2.02±0.03 Ma. The second eruption stage (Ⅱ2) centers in the areas of Guokailing and Beicha with 40Ar/39Ar ages of 1.77±0.03 Ma and 1.70±0.03 Ma, respectively. The eruptional center of the third eruption stage (Ⅱ3) lies at Huoju Farm, and the age of 40Ar/39Ar is 1.51±0.07 Ma. The lithology of the fourth eruption stage (Ⅱ4) is dominated by basaltic lava of overflow phase formed by fissure eruption, and the 40Ar/39Ar age is 0.88±0.14 Ma. The volcanic activity is obviously controlled by NE-trending and NW-trending basement faults. These results provide reliable age data to constrain Leizhou Peninsula’s forming age, eruption periods, and the law of volcanic activity.