Mineral chemistry as a tool for understanding the petrogenesis of Cryogenian (arc-related)–Ediacaran (post-collisional) gabbros in the western Arabian Shield of Saudi Arabia

摘要: Metagabbros and gabbros in the Ablah-Shuwas belt (western Saudi Arabia) represent part of significant mafic magmatism Neoproterozoic Arabian Shield. The metagabbros are Cryogenian, occasionally stratified bear calcic amphiboles (hornblende, magnesio-hornblende actinolite) typical calc-alkaline complexes. These suggest low pressure (~1–3 kbar), high $$f_{{{\text{O}}_{2} }}$$ crystallization temperature up to 727 °C, whereas it is 247–275 °C case retrograde chlorite. Rutile titanite Fe-rich replace Mn-bearing ilmenite precursors at . On other hand, younger fresh, layered comprised olivine gabbro olivine–hornblende with an uppermost layer anorthositic gabbro. fresh biotite-bearing. They characterized by secondary magnetite–orthopyroxene symplectitic intergrowth outer peripheries olivine. symplectite forms deuteric alteration from residual pore fluids moving along grain boundaries sub-solidus state. In gabbros, ortho- clinopyroxenes indicate 1300–900 800–600 °C, respectively. Geochemically, Cryogenian (~850–780 Ma) tholeiitic composition interpreted as arc-related. Younger, post-collisional (~620–590 Ma, i.e., Ediacaran), forming during late stages arc amalgamation southern related a lithospheric mantle source previously modified subduction. were probably produced partial melting enriched (e.g., garnet lherzolite).