Abstract
The crystallochemical variations of clinopyroxene in response to changes in fO2 and melt composition have been determined for a basalt-pantellerite suite (Boseti Complex, Main Ethiopian Rift) by crystal structure refinement and microprobe analysis. The pyroxene evolutionary trend has both a “Ca-minimum” and late iron enrichment. During crystallization from basalts to trachytes, clinopyroxene geometry depends mainly on the relationships between T and M2 sites; for example, high SiO2 activity in the magma causes high Si occupancy in T site, which in turn requires low Ca occupancy in M2 site in order to fulfill the local charge balance requirements. In contrast, clinopyroxene crystallized from acid melts is characterized by high Fe2+ (M1) content and therefore by a very large M1 site. Longer 〈M1-O1〉 and M1-O2 bond lengths require shorter T-O1 and T-O2 bond lengths and high Si occupancy in T site. It is concluded that the “Ca-minimum” in the clinopyroxene structure is regarded as the lowest value at which the charge balance requirements are satisfied in a C2/c clinopyroxene structure.
Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
