变质砾岩

变质砾岩(英语:metaconglomerate)是砾岩经过变质作用后形成的岩石类型。砾岩是由卵石或较大的碎屑颗粒和基质组成,其基质为沙、淤泥或黏土。变质砾岩与砾岩组成相似,但其碎屑颗粒会经过变质而变形。砾岩的基质固结不如其碎屑颗粒,因此当破碎时,砾岩中的碎屑颗粒会从基质破裂而出。然而,变质砾岩破碎时其碎屑颗粒和基质会同时破裂,因其基质已经变质重结晶[1]

美国加州圣地亚哥县侏罗纪变质砾岩
巴西变质砾岩

变质砾岩有时呈叶片状,其生成变质环境与板岩千枚岩相同,但母岩(原岩)是砾岩,而不是黏土[2]

西澳大利亚杰克山的变质砾岩是碎屑锆石的源岩,这些碎屑锆石的历史可追溯至44亿年[3][4]

参考文献

  1. ^ Metaconglomerate
  2. ^ Essentials of Geology, 3rd Ed, Stephen Marshak
  3. ^ VALLEY, John W.1, CAVOSIE, A.J., WILDE, S.A., GRANT, M., and LIU, Dunyi, JACK HILLS METACONGLOMERATE: EVIDENCE OF EARLY AND LATE ARCHEAN HYDROSPHERE, The Geological Society of America, 2002 Denver Annual Meeting http://gsa.confex.com/gsa/2002AM/finalprogram/abstract_39602.htm
  4. ^ ftp://rock.geosociety.org/pub/reposit/2002/2002034.pdf from: Peck, W.H., Valley, J.W., Wilde, S.A., and Graham, C.M., 2001, Oxygen isotope ratios and rare earth elements in 3.3 to 4.4 ga zircons: Ion microprobe evidence for high δ18O continental crust in the early Archean: Geochimica et Cosmochimica Acta, v. 65, p. 4215-4229.