Fig. 7
Secular change of CO2 (as carbonate) content in the altered subseafloor crust. a DSDP/ODP drill cores that penetrated basaltic basement (Alt and Teagle 1999; Gillis and Coogan 2011). The CO2 content in the Jurassic/Cretaceous crusts is generally higher than that of younger crusts. Because the crusts with shallower penetration depth have large variation of CO2 content, the crusts with penetration depth > 200 m is mainly discussed in the text. b The CO2 content in Precambrian greenstones with geologically reconstructed depth > 1000 m from the ancient seafloor. Data from 3.5 Ga Apex Basalt in the Marble Bar area (Nakamura and Kato 2004), 3.5 Ga Mount Ada Basalt in the North Pole area (Kitajima et al. 2001; Terabayashi et al. 2003), 3.2 Ga Regal Formation in the Cleaverville area (Shibuya et al. 2012), 2.6 Ga Jeerinah and Bunjinah Formations in Beasley River area (Shibuya et al. 2013a) in the Pilbara Craton (Western Australia), and this study. Note that the CO2 contents in the 3.5 Ga Mount Ada Basalt and the 3.2 Ga Regal Formation were calculated from the modal abundance of carbonate minerals in greenstones