UC San Diego

The Baja California Peninsula represents an area of anomalous heat flow evidenced by an abundance of subaerial geothermal manifestations and submarine hydrothermal vents. We report helium and carbon isotopic and relative abundance data from 13 geothermal springs throughout northern Baja California. Results of this study reveal 3He/4He values ranging from 0.11 to 1.74 RA (where RA = air 3He/4He) and concentrations of 4He, corrected for air contamination, vary from 0.284 to 1207 (×10-6) cm3 STP/gH2O. Carbon isotopes (δ13CO2) vary between -19.39 to +9.08‰ (vs. PDB) and CO2/3He values vary over several orders of magnitude (2.02 × 105 to 1.06 × 1013). 3He/4He values are attributed to mixing between mantle-derived helium and a radiogenic component derived from the crust. The highest 3He/4He values lie toward the east in the Gulf Extensional Province (GEP), are proximal to spreading centers, and are in agreement with low mantle velocity zones observed in recent tomography studies. Variable δ13CO2 and CO2/3He values at these localities are consistent with phase separation and/or calcite precipitation in shallow-level hydrothermal systems. Both processes result in CO2 loss which exacerbates the effects of contamination by crustal gases. The value of the majority of samples in the present study lies with discerning the potentially complicating effects of degassing and/or crustal contamination on the resulting CO2 record. Ultimately, the Puertecitos and Punta Estrella regions can be considered a promising geothermal prospect with a potential to satisfy the increasing energy demands of the Baja California Peninsula.