GRV 99027火星陨石的岩石学和矿物学特征  

Petrology and mineralogy of Martian meteorite GRV 99027.

作　　者：王鹤年[1] 梁英[1] 徐伟彪[2] 

机构地区：[1]南京大学地球科学系内生金属矿床成矿机制研究国家重点实验室,南京210093 [2]中国科学院紫金山天文台天体化学和行星科学实验室,南京210008

出　　处：《岩石学报》2006年第2期491-502,共12页Acta Petrologica Sinica

基　　金：国家自然科学基金(40232026)资助。

摘　　要：GRV 99027陨石是二辉橄榄岩质辉玻无球粒陨石(L-S)的火星陨石新成员,具有嵌晶、非嵌晶和冲击熔融袋结构。矿物模式组成以橄榄石(55%)、辉石(37．5%)为主,有少量熔长石(6%)、铬铁矿(1．5%)以及微量白磷钙石、陨硫铁等。其矿物的化学成分较为均一,无分带现象。橄榄石组分为Fo_(69．1～76．6)Fa_(23．4～30．9),平均Fo_(72．4)Fa_(27．6),低钙易变辉石为En_(59．3～75．1) Fs_(20．5～26．9)Wo_(3．1～14．9),平均En_(68．6)Fs_(23．5)Wo_(8．0),普通辉石为En_(46．6～53)Fs_(13．1～16．1)Wo_(31．9～37．8),平均En_(50．7)Fs_(14．5)Wo_(34．8),熔长石为An_(43．6～59．3) Ab_(40．2～54．6)Or_(0．5～1．8),平均An_(52．4)Ab_(46．7)Or_(0．8)。该陨石的结晶顺序是：亏损的火星幔源区部分熔融形成的原始母岩浆最先结晶的是嵌晶区的橄榄石和铬铁矿,随后易变辉石晶出,呈主晶包裹橄榄石和铬铁矿；此后,橄榄石、易变辉石、普通辉石持续结晶,直到残余熔体在晶隙形成斜长石和白磷钙石等。在这陨石中的易变辉石和普通辉石共存,二辉石温度计显示平衡温度为1000～1190℃(平均≈1146℃)。GRV 99027经历的亚固相再平衡,其程度为ALH 77005≈GRV 99027＞LEW 88516＞Y 793605。GRV 99027经受的冲击压力为30～45 GPa,,局部达到60～80GPa,冲击后温度可能＜600℃。GRV 99027 is a new member of the martian lherzolitic shergottites （L-S） consisting of poikilitic, non-poikilitic and melt pocket textures. Its mineral modal composition is olivin （55vo1%）, pyroxene （37.5vo1%, pigeonite and augite）, a few maskelynite （6vo1%）, chromite （1.5vo1%）, and trace whitlockite, troilite and so on. The mineralogical chemistry of GRV 99027 are relatively homogeneous： olivine（ Fo69.1-76.6 Fa23.4-30.9, avg. Fo72.4 Fa27.6 ） , pigeonite （ En59.3 -75.1 Fs20.5 -26.9 Wo 3.1-14.9 , avg. En68.6 Fs23.5 Wo8.0 ） , augite（ En46.6-53 FS13.1 -16.1 Wo31.9 -37.8 , avg. En50.7 Fs14.5 Wo34.8 ） and maskelynite （ An43.6 -59.3 Ab40.2 -54.6 Or0.5 -1.8, avg. An52.4 Ab46.7 Or0.8 ）. The crystallization sequence of GRV 99027 was two stages： firstly the primitive parent magma which originated from depleted martian mantle source region crystallized olivine and chromite in poikilitic area. Subsequently, a great deal of pigeonite crystallized into large oikio-crystals enclosing olivine and chromite, followed by abundant olivine, pigeonite, augite continuous crystallization in non- poikilitic area, the interstitial melts in between crystals finally crystallized plagioclase, ilmenite and whitlockite etc. The coexistence of low-calcium pyroxene and angite in GRV 99027 indicated that the equilibrium temperature was about 1000 - 1190°C （avg, 1146°C ）. Sub-solidus re-equilibration experienced by GRV 99027 is ALH 77005 ≈GRV 99027 〉 LEW 88516 〉 Y 793605. The shock pressure of GRV 99027 was probablv 30-45 G Pa and the hOSt-shock temperature tended to be slightlv lower than 600°C.

关 键 词：火星陨石 GRV 99027 二辉橄榄岩辉玻无球粒陨石 结晶顺序 平衡温度 冲击压力 

分 类 号：P185.83[天文地球—天文学]