Geochemical characteristics and geological significance of biotite in granite of Dahongliutan area in the West Kunlun Orogen
The West Kunlun Dahongliutan rock mass is thought to be closely related to pegmatite type lithium(beryllium)mineralization.In order to constrain the physical-chemical conditions,petrogenesis and source,backscattering observation(BSE)and electron probe analysis(EPMA)are performed on biotite collected from the Dahongliutan granite.The results show that the biotite from two mica granite and syenogranite is ferrugaceous biotite,and featured by high rich silicon,aluminum,iron and potassium,but low magnesium,manganese,sodium,and calcium.Biotite in biotite granite is ferrugaceous biotite and magnesia biotite,which is magnesium rich,but poor in aluminum and iron.The biotite from two mica granite and syenogranite has a high AlⅥ(0.7～0.9),and biotite coexists with tourmaline,garnet,and muscovite.Biotite from biotite granite has high MgO content(9.30%～10.11%),and coexists with hornblende.The biotite composition further constrains crystallization temperatures of 661℃～673℃for two mica granite,621℃～669℃for syenogranite,and 685℃～714℃for biotite granite.Corresponding consolidation pressures 332～404 MPa,356～377 MPa,248～270 MPa,respectively,with estimated intrusion depths of 12.46～14.98 km,13.18～14.38 km and 9.18～10.01 km.Estimated oxygen fugacity fall into the range of-15.8～-15.0 for two mica granites,-16～-15 for syenogranite,-14.9～-14.0 for biotite granite.The comprehensive research results indicate that the two-mica granite and syenogranite in the Dahongliutan area are products of crustal source material re-melting,exhibiting typical characteristics of strongly peraluminous S-type granite.In contrast,the biotite granite is an I-type granite formed by the involvement of mantle source material.The results of this study provide new data for the physical-chemical conditions,rock genesis types and source of different lithological granites from the Dahongliutan rock mass.
GraniteBiotiteMineral chemical compositionDiagenetic mineralizationDahongliutan
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