Large-scale metallogenesis and petroleum field formation in continental China—constraints from the lithosphere

Abstract: Continental China consists of five types of lithospheres, namely, cratonic, orogenic, rift, oceanic, marginal sea crust and island-arc. As different types of lithospheres have different dynamic mechanisms and effects, the junction zones between the different types of lithospheres are bound to be discontinuity zones and have close relationship with continental metallogenesis. The greater majority of known metallic mineral deposits in continental China are distributed along the lithospheric discontinuities or reactivated discontinuities, indicating that the lithospheric discontinuities provide favorable spaces for migration and accumulation of large ore deposits (deposit clusters). A comparison of the sequences of the tectono-magmato-metallogenic events in the northwestern, eastern and southwestern regions of continental China indicates that the lithospheric crust-mantle petrological structures and large-scale metallogenesis depend on the latest and strongest magmatism, and that large-scale metallogenesis was initiated in the period of instability and de-rooting of the orogenic lithosphere and large-scale upwelling of the asthenospheric material. The occurrence of C-type adakite may be regarded as one of their indications. The Yangtze, Ordos, Tarim and Junggar basins distributed in China inland, which are called "cold basins" due to their low surface heat flow values, belong to the setting of the cratonic type lithosphere and tectonically are usually foreland basins of orogenic belts. The tectonic stability of the cratonic type lithosphere determined that these basins were swallowed, buried and modified continuously by their surrounding orogenic belts. Although many oil-gas fields have been found in these basins now, the areas outside these basins which are now covered by the front thrust sheets of orogenic belts should also be favorable areas for occurrence of oil-gas fields, i.e., those areas under granites of orogenic belts outside the basins are still important potential areas for oil-gas field finding. The plains and epicontinental seas such as the Yellow Sea, East China sea and South China sea in eastern China, which are called "hot basins" due to their high surface heat flow values, correspond with the rift- or oceanic-type lithosphere. They were formed when the coastal areas of eastern China entered a new tectonic evolution stage—the continental rifting stage—during the Cenozoic, which is marked by extensive eruption of basalt. The input of convective mantle material and heat resulted in the increase of terrestrial heat flow values in basins and thus the basins became "hot basins" with the corresponding rift-type lithosphere and even oceanic-type lithosphere (e.g. the Central basin of the South China Sea). The large-scale eruption of mantle-derived basaltic magma occurring concomitantly with rifting and tectonic extension and rapid deposition and burial of abundant sediments are favorable for the formation of oil-gas fields, in which some components, such as CO2 in CO2 fields, might be mainly derived from the mantle. It is suggested that the plains and epicontinental sea areas in eastern China are one of the most potential oil-gas fields.