COVERED DEPTH OF SUPERFICIAL MAGMA CHAMBER ON THE NORTHERN SLOPE OF TIANCHI VOLCANO IN CHANGBAI MOUNTAIN BASED ON BOREHOLE TEMPERATURE

The crustal thermal structure in Changbaishan volcanic area has not been established yet and there are differences about the covered depth of superficial magma chamber in Tianchi Volcano by means of geophysical exploration. The covered depth of superficial magma chamber on the northern slope of Tianchi Volcano is estimated through the temperature measurement of CZK07 borehole, data evaluation and geothermal gradient calculation, combined with the temperature data of Holocene magma chamber. The CZK07 borehole is located right above the superficial magma chamber speculated by geophysical exploration, close to the historic crater of volcanic eruption, with relatively high and stable temperature (102.5-106.8℃) at the depth about 610 m. The continuous temperature measurement data indicates that the borehole temperature shows a positive correlation with depth, with the geothermal gradient ranging from 134 to 178℃/km (averagely 153℃/km), roughly representing the geothermal gradient of the overlying crust of superficial magma chamber. Based on previous temperature studies of superficial magma chamber, the covered depth of superficial magma chamber on the northern slope of Tianchi Volcano is estimated to be 5.25-7.21 km below the surface of Tianchi Lake, which is similar to the inversion results of geophysical exploration.