This study is focused on geothermal heat flow and the origin of non-hydrocarbons in natural gases in terms of the isotope geochemical characteristics of Ar,He,CO2 and N2 in natural gases from the Sanshui Basin,Guangdong Province,China,^3He/^4He,ratios are of from the Sanshui Basin,Guangdong Province,China,^3He/^4He ratios are of (1.60-6.39)×10^-6,and ^40Ar/^36Ar ratios of 450841.The carbon isotopic composition (δ^13 C PDB)of carbon dioxide ranges from -20‰to -2‰,δ^15N (air) ratios have a wider range of -57‰-+95‰.The isotope geochemical characteristics of non-hydrocarbons indicate that He,Ar and N2 in the gas reservoirs enriched in non-hydrocarbons were derived largely from the upper mantle.Non-hydrocarbons in gaseous hydrocarbon reservoirs consist mainly of crustal radiogenic ^4He and ^40Ar and some mantle-derived He and Ar, as well as of ^13C-depleted carbon dioxide and nitrogen generated as a result of thermal decomposition of organic matter in strata.Carbon dioxide enriched in ^13C was derived largely from carbonate rocks and partially from the lower crust and upper mantle.Based on the relationship between geothermal heat flor(A)and ^3He/^4He ration in natural gases,the Q values for the area studied have been calculated.Similar Q values are reported from the upper mantle uplift area(77mWm^-2)in Huabei and the Tancheng Lujiang Rift Zone (88mWm^-2).More than 60 percent of geothermal heat flow in the Sanshui Basin may haee been derived from the upper mantle.
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