一般とは半波長遅れて使ってみました。
Q what type of rocks the rokko mountain made of?
A Rokko Mountain is predominantly made up of granite, which is a type of igneous rock formed from the slow cooling of magma beneath the Earth's surface. Additionally, there are some sedimentary rocks, such as sandstone and shale, found in the lower elevations of the mountain.
Q thanks. Did granite constituted a magma chamber?
A Yes, granite is typically formed from cooled magma that has slowly solidified deep beneath the Earth's surface in large, slowly cooling bodies known as plutons or magma chambers. Over time, the overlying rock and sediment can erode away, exposing the cooled magma chamber up to the surface, where it may form visible features such as mountains or rock outcroppings.
Q. In the northern part of Rokko mountain, granite intrudes contemporaneous volcanic rocks, suggesting the contact is not so deep, I.e. less than 2km deep. How do you think?
A. You are correct that if granite intrudes contemporaneous volcanic rocks, it is an indication that the contact is not very deep, as you mentioned, probably less than 2 km deep. The exact depth, however, can vary based on a number of factors such as the size and viscosity of the magma, surrounding rock types and geologic structures, and the pressure and temperature conditions at the time of intrusion. It is likely that in the northern part of Rokko Mountain, the magma chamber was relatively shallow and had less overlying rock and sediment compared to other parts of the mountain, allowing it to be exposed at the surface and intrude into the surrounding volcanic rocks.
Q. At such shallow depth, granitic magma is over saturated with water, and vesiculation, degassing and crystallization occurs, together increase the bulk viscosity. Highly viscous magma is non-eruptible, and we wonder if Rokko granite represents magma chamber, which usually contain eruptible magma. How do you think?
A You are correct that granitic magma at a shallow depth may be over-saturated with water and undergo vesiculation, degassing and crystallization, which can increase its bulk viscosity. Highly viscous magma is indeed generally non-eruptible, and this would suggest that the Rokko granite might not represent a typical magma chamber, which usually contain more eruptible magma.
However, it is worth noting that the formation of granite itself can involve a complex interplay of different factors, such as the composition of the magma, the temperature and pressure conditions, and the presence of certain minerals and chemicals. So while the Rokko granite might not represent a typical magma chamber, it is still possible that it formed in some other unique way that produced a lower degree of viscosity or greater volume of eruptible magma. More research would be needed to better understand the specific geological processes at play in the formation of the Rokko granite.