摘要
最近的研究证实,在大别-苏鲁超高压变质带的多硅白云母榴辉岩和超基性岩中的磷灰石矿物内普遍发育有针柱状出溶晶体,初步研究证明这些出溶晶体多为各种硫化物:如黄铁矿、黄铜矿等。本文重点研究苏鲁青龙山地区的多硅白云母榴辉岩和退变榴辉岩中磷灰石内的出溶晶体,通过扫描电镜、电子探针和X-光能谱的线扫描分析,确认这些出溶晶体是铜的硫化物,并根据无标样定量的分析结果初步推测有可能是CuS2晶体。目前已知的CuS2晶体都是在高温高压(T=700- 1000℃和P=4．5-5．0GPa)条件下人工合成的。这样的温压条件与青龙山榴辉岩的超高压变质条件是吻合的。在磷灰石中能保存超高压的硫化物,可能是由于磷灰石自身的稳定性和化学惰性。因此推测在超高压变质作用中,磷灰石晶体中易于保存硫化物出溶体与石榴石和绿辉石中易于保存柯石英和金刚石的作用相类似。
Recent studies have shown that apatites with needle-like exsolution lamellae are widely found in eclogites as well as in ultramafic rocks in the Dabie-Sulu UHP metamorphic belt. These studies demonstrated that most of these exsolution lamellae are sulfides （e. g. pyrite and chalcopyrite） with an intriguing mineral chemistry. In this contribution, we focus on the composition of solid exsolution lamellae in apatites from a fresh phengite eclogite and a highly retrograded eclogite from the Qinglongshan, Jiangsu province. Scanning electron microscope （SEM） examinations, electron microprobe and X-ray energy-dispersive （EDS） analyses show that exsolution lamellae in these apatites are dominantly copper-bearing sulfide, possibly CuS2. Experimental studies have shown that CuS2 crystal can only be synthesized under high temperature and high pressure conditions （T = 700 - 1000℃ and P = 4.5 -5.0GPa）. Such a condition is consistent with the UHP metamorphism experienced by the Qinglongshan eclogites. The preservation of UHP sulfide phases in apatites can be understood by considering the shielding effect of apatite which is extremely stable and chemically inert in the Sulu eclogites. Therefore, apatites may have behaved similarly to garnet or omphacite （ primary phases that host coesite and diamond） to facilitate the preservation of UHP sulfide phases.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2006年第7期1921-1926,共6页
Acta Petrologica Sinica
基金
国家自然科学基金重大项目(编号40399141)
中国地质科学院重点开放实验室专项资金(编号KL05-1和KL05-3)
关键词
磷灰石
出溶结构
榴辉岩
超高压变质带
Apatite, Exsolution lamellae, Eclogite, UHP metamorphic belt
