Cenozoic tectonic units and their stratigraphic characteristics of southern west Pacific region: Implication for Himalayan orogeny

In this paper, based on the study of tectono-stratigraphic characteristics of some representative tectonic units of southern Western Pacific region which include South China, Southwest Japan, Philippines, and East Indonesia, the authors present a review of the age, periods and background of Himalayan orogeny.Within the study region, after the late Yanshanian orogeny, most of regions were uplifted with the absence of Paleocene to lower Eocene strata.Cenozoic strata generally cover the pre-Cenozoic basement in angular unconformity form.According to stratigraphic and volcano-sedimentary characteristics of different tectonic units, they can be divided into three structural layers, i.e., Eocene or Eocene-Lower Oligocene(E₂ or E₂-E₃¹), Miocene or Upper Oligocene-lowest Miocene(N₁/E₃-N₁¹)and Pliocene till now(N₂-Q).The above three structural layers are in contact with two regional angular unconformities, and correspond to the early Himalayan orogeny(E₃-N₁¹, 33~20 Ma)and the late Himalayan orogeny(N₂, 5.3~2.6 Ma), respectively, with he former being most intense.In different regions, both orogenic movements were usually related to the collision of arcs or detached micro-terranes towards the edge of the Eurasian plate.Obviously, Himalayan orogeny was accretionary orogenesis rather than collision between two continents, and was controlled by changes in the direction and rate of movement of the Pacific and Indian Ocean-Australian plates.Between the episodic tectonic events, it was an intensive extensional setting, which led to the flattening of the palaeocathysian mountain system and the opening of the marginal seas.