The Mechanism Of Fault-related Dolomitization In Musandam Peninsula, United Arab Emirates

Structurally controlled dolomitization may be more common and widespread all over the world than we thought before,and it has a significant impact on carbonate reservoir quality in many cases.The Upper Triassic limestones in Ras Al Khaimah,have been subjected to pervasive dolomitization and dolomite cementation along the main faults and associated fractures.Two regional orogenic events(i.e.the obduction of Oman-UAE ophiolites and the Cenozoic thrusting phase)make it possible for hot basinal brines(referred to as hydrothermal fluids in literature)to flow through active faults and fractures.Field observations,petrographic,fluid inclusion micro-thermometry and carbon,oxygen,strontium and magnesium isotope analyses have been combined to constrain the timing of dolomitization episode(s),as well as the origin and evolution of dolomitizing fluids.Associated with fracturing and brecciation,saddle dolomite and host dolostones have similar stable isotope data and high strontium isotope ratio,thus formed from the same hot Mg-rich basinal brines,followed by precipitation of blocky calcite and minor prismatic quartz.Moreover,saddle dolomite with high temperature shows lower magnesium isotope content than that in host dolostones with relatively low temperature.Late columnar calcite cements with extremely low stable isotope values and low strontium ratio show nearly no salinity,indicating the involvement of meteoric water during the uplift and erosion phase.This study thus elucidates the influence of regional tectonic history and related basinal fluids on the diagenetic and reservoir-quality evolution of carbonate succession.