Petrogenesis And Tectonic Significance Of The Marble Within Hongqiyingzi Complex In North Hebei Province, China

A mass of marble blocks widely distribute in Hongqiyingzi complex in North Hebei,but the rock association, geochemical features, the nature of original rocks, formingenvironment, petrogenesis and tectonic significance of marble blocks in different areas arenot the same. The occurrences of Hongqiyingzi complex in different areas are different.The strike of Hongqiyingzi complex in Chicheng is entirely from NW to SE, while thestrike is near EW in Chongli which is consistent with the general strike ofChongli-ChiCheng fault zone. The occurrence of marble are also different: marble in(garnet) biotite plagioclase-gneiss in Chicheng, extends along NW-SE integrally.Marble occurs as lens in (garnet) biotite plagioclase-gneiss in Chongli, while occur asstratoid beds in local area, and is interbedded with (garnet) biotite plagioclase-gneiss.The marble in Hongqiyingzi complex in Chicheng area is mainly serpentinizationolivine marble and epidotization marble, while mainly diopside marble in the Chongliarea.(1)The mineral assemblage of serpentinization olive marble is mainlyDol+Srp+Fo+Cal+Qtz.The content of dolomite is86.65%-95.87%. The olivine ismetamorphogenetic forsterite (Fo：97.50-99.32). The chemical constituents are mainlyMgO+CaO（42.97%-51.76%）. The value of Ca/Mg is0.96-1.24. The contents of otheroxides are less than1%. The content of∑REE is low. There was a losses in thecomparation on the trace elements in the serpentinization olive marble and thephanerozoic limestone, which was lesser affected by terrigenous detrital sediments.(2)The mineral assemblage of epidotization marble is Cal+Ep+Qtz. The contents of calcitechange a lot which is from58.28%to93.85%.The chemical constituent is mainly CaO(32.66%-52.59%).The value of Ca/Mg is14.30-61.24. The contents of Al2O3andK2O+Na2O which reflects the shale content are1.09%-8.59%and0.34%-4.23%respectively. The content of∑REE in epidotization marble is higher than that inserpentinization olivine marble. There is an enrichment in the comparation on the trace elements in the epidotization marble and the phanerozoic limestone, which was greateraffected by terrigenous detrital sediments.(3) The mineral assemblage of diopside marbleis mainly Cal+Di+Ep+Or+Qtz. The contents of calcite change a lot which is from63.62%to98.97%. The chemical constituent is mainly CaO (53.39%-55.46%). The value ofCa/Mg is22.32-81.62. The contents of other oxides are less than1%. The affection of thediopside marble by terrigenous detrital sediments is less than marble in Chicheng area.The content of P2O5in the marble of Hongqiyingzi complex in North Hebei is0.01%-0.06%, which is much less than that0.8%in the carbonate rock of magmaticorigin.The contents of Nb、Ti、Zn、Pb、Th、U and∑REE are much more similar tocarbonate rock of sedimentary origin. Through geochemical analysis, the nature oforiginal rocks and forming environment of marble in different areas are quite different.(1)The original rock of serpentinization olivine marble in Chicheng area is mainlysiliceous-argillaceous dolostone which forming environment probably is enclosedsemi-enclosed lagoonal face fore-arc basins in dry climates.(2) The original rock ofepidotization marble probably is siliceous-argillaceous limestone which formingenvironment is marine sedimentary environment at passive continental margin.(3) Theoriginal rock of diopside marble probably is marine limestone which was formed in thetransitional environment from infraneritic environment to epeiric sea environment. Theforming environment was of strong oxidizing.Combining with the chronology information study, the research shows that the protolith of serpentinization olivine marble probably experienced regional metamorphism of amphibolite facies during321-326Ma and generated serpentinization olivine marble whichcontacted with gneissic granite intrusion and resulted in the contact metamorphism during(239.5±7.5) Ma. Marble in Hongqiyingzi complex in Chongli probably only experiencedregional metamorphism of amphibolite facies during (268.7±3.3) Ma. The chronology ofmetamorphisms of marble in Hongqiyingzi complex in these two areas were not alwaysconsistent which illustrated that Hongqiyingzi complex in Chicheng and Chongli probably belong to different tectonic blocks.