A temperature exceeding a thousand degrees; if Zhou Tian wasn't protected by various powers, just coming into contact with magma of that kind of temperature would likely cause him to be incinerated completely. Thus, even if Zhou Tian managed to block the surrounding magma using various methods now, if he were to fight the Vermilion Bird in that environment, he would surely be at a disadvantage.
However, from the moment Zhou Tian jumped into the volcano, he was somewhat aware that he would encounter various discomforts. Although the actions of the Vermilion Bird made him uncomfortable, he was not entirely unsettled by the bird's actions.
The lethal nature of such high temperature is significant, but the power is too rigid. As long as one prepares for the situation and prevents high-temperature damage, it is a simple matter for Zhou Tian.