Low-pressure area Low-pressure area A low-pressure area, low, depression or cyclone is a region on the topographic map where the atmospheric pressure is lower than that of surrounding locations. Low-pressure systems form under areas of wind divergence that occur in the upper levels of the troposphere. The formation process of a low-pressure area is known as cyclogenesis. Within the field of meteorology, atmospheric divergence aloft occurs in two areas. The first area is on the east side of upper troughs, which form half of a Rossby wave within the Westerlies (a trough with large wavelength that extends through the troposphere). A second
High pressure metamorphic terranes along the Bangong-Nujiang Suture Zone are generally associated with subduction zones. Protoliths of serpentinites are olivine- and pyroxene-dominated. The formation of serpentinites is caused by the release of fluids from subducting hydrated oceanic slabs as they become heated with depth to a maximum temperature of 650-700 °C. Eclogites are high-pressure (HP) to ultrahigh-pressure (UHP) metamorphic rocks that are indicative of subduction zone metamorphism. The eclogites in central Tibet are of Early Mesozoic origin, and they appear to be the result of diachronous collision between the eastern Qiangtang terrane and the western Qiangtang-Lhasa plate, along the linked eastern Bangong-Nujiang-central Qiangtang zone. Located along the western sector