The Character and Petrogenetic Model of the Permian Tarim Large Igneous Province

Tarim Large Igneous Province(TLIP)is the second Late Paleozoic LIPs in China after the recognition of the Emeishan LIP.The residual distribution range of TLIP is up to 250000 km2,and the largest residual thickness is 780 m.The eruption of basalt happened during 290–288 Ma and belongs to LIPs magmatic event with fast eruption of magma.The lithological units of the TLIP include basalt,diabase,layered intrusive rock,breccia pipe mica-olivine pyroxenite,olivine pyroxenite,gabbro,ultramafic dyke,quartz syenite,quartz syenite porphyry and bimodal dyke.The basalt and diabase of TLIP exhibit OIB-like trace element patterns and enrichment of LILE and HFSE,and mainly belong to high TiO2 series.There is an obvious difference in isotope among the basalt from Keping and the basalt and dibase from the northern Tarim Basin.The basalt from Keping with negative Nd and high REE value derives from enriched mantle,and the diabase and basalt from the northern Tarim Basin with positive Nd and low REE value are related to depleted mantle.The crust uplifting in the Early Permian and the development of picrite and large scale dyke and formation of large scale V-Ti-magnetite deposit in Wajilitag area support the view that the TLIP is related to mantle plume.The TLIP has a temporal-spatial relationship with Permian basicultrabasic igneous rock,which is distributed widely in Central Asia,and they represent a tectono-magmatic event with very important geodynamic setting.This study also systematically demonstrates the two-stage melting model for the TLIP based on our previous research work and predecessor achievements,and highlights the two types of magmatic rocks within the TLIP.The two-stage melting model suggests that the formation of the TLIP is mantle plume related.The early hot mantle plume caused the low-degree partial melting of the lithosphere mantle,while in the later stage,the plume partially melted due to adiabatic uplift and decompression.Therefore,this model carries signatures of both the"Parana"and"Deccan"models in terms of mantle plume activity.During the early stage,the mantle plume provided the heat required for partial melting of sub-continental lithosphere mantle(SCLM),similar to the"Parana Model",while later the plume acted as the main avenue for melting,as in the"Deccan Model".Basalts that erupted in the first stage have higher 87Sr/86Sr,lower 143Nd/144Nd ratios,and are enriched in large ion lithophile elements and high field strength elements,indicating a possible origin from the enriched continental lithosphere mantle,similar to the Parana type geochemical features.The basic-ultrabasic intrusive rocks in the second stage exhibit lower 87Sr/86Sr,higher 143Nd/144Nd ratios relative to the basalts,consistent with the involvement of a more depleted asthenospheric material,such as a mantle plume,similar to the Deccan type geochemical features.The first stage basalts can be further subdivided into two categories.Developing this petrogenetic model for the TLIP aids in comprehensively understanding its magmatism and deep geological and geodynamic processes.Furthermore,this work enriches the theories describing the origin of large igneous province and mantle plume activity.

Characteristics of the Cretaceous Magmatism in Huanghua Depression and Their Relationships with Hydrocarbon Enrichment

The Huanghua depression located in the hinterland of the Bohai Bay Basin in eastern China is a typical area for the research of multistage magmatic activities with hydrocarbon enrichment,many high-yield wells related to igneous rocks were discovered within the Cretaceous strata in recent years.However,the spatial and temporal distribution of Cretaceous igneous rocks remains unclear,and the relationships among magmatic sequence,lithology,and hydrocarbon enrichment have been poorly studied.In order to solve these problems,core observation,logging analysis,major element analysis,zircon U-Pb chronology,oil-bearing grade statistics and reservoir spaces analysis were used to subdivide the magmatism cycles and to investigate the characteristics of igneous reservoirs.Our results show that the Mesozoic magmatism in Huanghua depression started in 140.1±1.4 Ma and could be divided into two stages including the Early Cretaceous stage and Late Cretaceous stage.The Early Cretaceous magmatism principally developed basic-intermediate rocks in the north zone,and could be subdivided into 3 cycles with their forming ages of 140,125–119,and 118–111 Ma,respectively.By contrast,the late stage mainly developed intermediate-acid rocks centralized in the south zone and formed at 75–70 Ma.The GR and SP curves are good indicators for the contrast of different lithologies,lithofacies and for magmatic sequences division.Intensive magmatism may have an advantage to form reservoirs,since basalt in cycle III in the Early Cretaceous and dacite porphyrite in the Late Cretaceous have great exploration potential.Lithology and tectonic fractures have an important influence on the formation of reservoir spaces and hydrocarbon enrichment.The characteristics of Cretaceous magmatism and igneous reservoirs in Huanghua depression and adjacent areas are summarized,providing important information for igneous reservoirs research and oil-gas exploration in the Cretaceous in related areas.