龙泉关韧性剪切带同变形花岗岩的构造特征及其独居石测年

On the M i n era l Che m istry of Apa tite i n Eclogites Fro m the CCS D M a i n Borehole and the Geoche m i ca l Behav i ors of F,Cl,Sr and
O ther Ele m en ts i n Eclogites
CH EN Zhenyu1),ZEN G L ingsen2),L I A N G Fenghua2),ZHAN G Ze m ing2)
1)Institute of M ineral R esources,Chinese A cad e m y of Geolog ical S ciences,B eij ing,100037
2)K ey laboratory of Continental D y na m ics,Institute of Geolog y,Chinese A cad e m y of Geolog ical S ciences,B eij ing,100037
Abstract
T he100～600m m afic and ultra m afic rock s(ecl ogites and garnet pyroxenites)recovered from the Ch inese Continental Scien tific D rilling(CCSD)m ain ho le have been show n to have h igh ly variable w hole rock geoche m istry and P2O5contents by2orders of m agnitude.To address the role of apatite in shap ing the apatite2 compatible ele m en t geoche m istry of the CCSD ecl ogites,w e have perfor m ed w ho le rock m aj o r and trace ele m en t analyses on a suite of11ecl ogites from500to540m deep,and m easure m ents on apatite m ineral che m ical compositi on s.In conjuncti on w ith petrography observati on s,these data de monstrate that(1)T hese ecl ogites can be divided in to two group s by their m ineral m blages and bulk rock geoche m istry,the ecl ogites from500～530m are o rdinary ecl ogites,and tho se from530～540m are h igh T i or h igh T i2Fe ecl ogites;(2)apatites from these ecl ogites are exclusively fluor2apatites,rich in F and poo r in C l;(3)these apatites contain fair a moun ts of Sr,S and Fe,and trace a moun t of Cu,Pb and Zn;(4)good correlati ons betw een w hole rock P2O5 and apatite2host ele m ents(e.g.F,Sr,and C l)in these ecl ogites,regardless of their sign ificant differences in m ineral asse m blages and w ho le2rock geoche m istry.P resence of F2apatites in these ecl ogites m ay be the m aj o r factor that cause h igh salin ity fluid inclusi on and elevated F C l rati o s in ecl ogites.A patite is the most i m portan t reservoir for F,als o is an i m portan t reservo ir fo r Sr,but just partly contro l C l in ecl ogite.It see m s that apatites from these ecl ogites are not a m aj o r host for S.T hese data als o i m p ly that the geoche m ical behavi ors of F,Sr and C l in ecl ogites are m ainly controlled by apatites,and their mobility during p rograde to retrograde m eta mo rph ic reacti on s is li m ited by the stabilities of apatite.
Key words:apatite;ecl ogite;m ineral che m istry;F,C l,Sr;CCSD
龙泉关韧性剪切带同变形花岗岩的构造特征及其独居石测年
张进江,赵兰,刘树文
北京大学地球与空间科学学院,100871
龙泉关韧性剪切带(LQ GSZ)为华北克拉通内一条重要构造带,并将下伏阜平杂岩与上覆五台杂岩分割开来。

该带经历了3期变形,第一期为主期变形,变形性质为韧性剪切,上盘沿WNW缓倾的面理向ESE运动,其他两期为后期垮塌滑动。

剪切带内强变形部位发育一系列平行剪切面理展布的花岗岩,并构成剪切带的一个主要组分。

这些花岗岩在其侵位时经受剪切带主期变形作用,形成糜棱状岩石。

变形特征及其与围岩接触关系证明这些花岗岩可能是剪切作用下的原地部分重熔产物,即同变形花岗岩。

花岗岩内独居石为岩浆成因矿物,所以独居石结晶年龄可代表岩浆事件年龄,也即龙泉关韧性剪切带主期变形年龄。

两个样品的独居石电子探针定年得出了LQ GSZ同变形花岗岩的多峰值年龄,其中1846M a和1877M a为两样品的主峰值年龄,代表龙泉关韧性剪切带的主期变形年龄。

这与华北地区1850M a左右的区域地质事件年龄完全一致,该事件被认为是华北东、西部地块的碰撞所致,证明了龙泉关韧性剪切带的发育是这次拼合事件同期的韧性剪切带。

0581地　质　学　报2006年。