地质论评
地質論評
지질론평
GEOLOGICAL REVIEW
2015年
3期
499-510
,共12页
张亚冠%杜远生%徐亚军%余文超%黄虎%焦良轩
張亞冠%杜遠生%徐亞軍%餘文超%黃虎%焦良軒
장아관%두원생%서아군%여문초%황호%초량헌
震旦纪(埃迪卡拉纪)-寒武纪之交%华南%硅质岩%地球化学%沉积环境
震旦紀(埃迪卡拉紀)-寒武紀之交%華南%硅質巖%地毬化學%沉積環境
진단기(애적잡랍기)-한무기지교%화남%규질암%지구화학%침적배경
Sinian (Ediacaran) Cambrian%South China%siliceous rock%geochemistry%sedimentary environment
震旦纪（埃迪卡拉纪）—寒武纪之交华南地块处在伸展扩张的构造背景下，在扬子板块东南缘发育了广泛的硅质岩沉积。湘中地区发育了自震旦系陡山沱组、留茶坡组及寒武系牛蹄塘组连续的深水相沉积，岩性以层状硅质岩为主，夹炭质、硅质页岩。通过对硅质岩的主量、稀土元素的地球化学特征分析表明，本区硅质岩 SiO2含量极高（普遍＞92％），Al／（Al ＋Fe ＋Mn）比值普遍大于0．6，稀土元素澳大利亚后太古代平均页岩（PAAS）标准化配分曲线显示中—弱 Ce 负异常且有明显的重稀土富集特征。震旦纪陡山沱期硅质岩样品中 Ce ／Ce*值、LaN ／YbN 值、Y／Ho 值分别为0．34～0．54、0．05～0．10、38．00～51．44；灯影期硅质岩样品中 Ce ／Ce*值、LaN ／YbN 值、Y／Ho 值分别为0．70～0．85、0．06～0．37、35．91～46．79；寒武纪初期硅质岩样品中的稀土元素地球化学特征与灯影期相似，Ce ／Ce*值、LaN ／YbN 值、Y／Ho 值分别为0．58～0．78、0．26～0．40、34．75～45．58。湘中地区震旦纪—寒武纪之交的硅质岩地球化学特征显示本期硅质岩为正常的海水沉积成因，整体受热液和陆源影响较小，但从震旦纪陡山沱期至寒武纪初期陆源输入有增加趋势，硅质来源可能与硅质浮游生物有关，硅质岩沉积环境始终保持在深水盆地中，湘中地区沉积盆地符合被动大陆边缘伸展型盆地特征。
震旦紀（埃迪卡拉紀）—寒武紀之交華南地塊處在伸展擴張的構造揹景下，在颺子闆塊東南緣髮育瞭廣汎的硅質巖沉積。湘中地區髮育瞭自震旦繫陡山沱組、留茶坡組及寒武繫牛蹄塘組連續的深水相沉積，巖性以層狀硅質巖為主，夾炭質、硅質頁巖。通過對硅質巖的主量、稀土元素的地毬化學特徵分析錶明，本區硅質巖 SiO2含量極高（普遍＞92％），Al／（Al ＋Fe ＋Mn）比值普遍大于0．6，稀土元素澳大利亞後太古代平均頁巖（PAAS）標準化配分麯線顯示中—弱 Ce 負異常且有明顯的重稀土富集特徵。震旦紀陡山沱期硅質巖樣品中 Ce ／Ce*值、LaN ／YbN 值、Y／Ho 值分彆為0．34～0．54、0．05～0．10、38．00～51．44；燈影期硅質巖樣品中 Ce ／Ce*值、LaN ／YbN 值、Y／Ho 值分彆為0．70～0．85、0．06～0．37、35．91～46．79；寒武紀初期硅質巖樣品中的稀土元素地毬化學特徵與燈影期相似，Ce ／Ce*值、LaN ／YbN 值、Y／Ho 值分彆為0．58～0．78、0．26～0．40、34．75～45．58。湘中地區震旦紀—寒武紀之交的硅質巖地毬化學特徵顯示本期硅質巖為正常的海水沉積成因，整體受熱液和陸源影響較小，但從震旦紀陡山沱期至寒武紀初期陸源輸入有增加趨勢，硅質來源可能與硅質浮遊生物有關，硅質巖沉積環境始終保持在深水盆地中，湘中地區沉積盆地符閤被動大陸邊緣伸展型盆地特徵。
진단기（애적잡랍기）—한무기지교화남지괴처재신전확장적구조배경하，재양자판괴동남연발육료엄범적규질암침적。상중지구발육료자진단계두산타조、류다파조급한무계우제당조련속적심수상침적，암성이층상규질암위주，협탄질、규질혈암。통과대규질암적주량、희토원소적지구화학특정분석표명，본구규질암 SiO2함량겁고（보편＞92％），Al／（Al ＋Fe ＋Mn）비치보편대우0．6，희토원소오대리아후태고대평균혈암（PAAS）표준화배분곡선현시중—약 Ce 부이상차유명현적중희토부집특정。진단기두산타기규질암양품중 Ce ／Ce*치、LaN ／YbN 치、Y／Ho 치분별위0．34～0．54、0．05～0．10、38．00～51．44；등영기규질암양품중 Ce ／Ce*치、LaN ／YbN 치、Y／Ho 치분별위0．70～0．85、0．06～0．37、35．91～46．79；한무기초기규질암양품중적희토원소지구화학특정여등영기상사，Ce ／Ce*치、LaN ／YbN 치、Y／Ho 치분별위0．58～0．78、0．26～0．40、34．75～45．58。상중지구진단기—한무기지교적규질암지구화학특정현시본기규질암위정상적해수침적성인，정체수열액화륙원영향교소，단종진단기두산타기지한무기초기륙원수입유증가추세，규질래원가능여규질부유생물유관，규질암침적배경시종보지재심수분지중，상중지구침적분지부합피동대륙변연신전형분지특정。
The South Block was in the background of extensional tectonics during the transition from Sinian (Ediacaran)to Cambrian,and the siliceous rocks developed widely in southest margin of Yangtze block.The deep-water Sinian— Cambrian sections in central Hunan include the Doushantou Formation,Liuchapo Formation, composed mainly of bedded siliceous rocks with Si-rich and C-rich shale deposits,which is also overlain by the Niutitang Formation.Based on the analyses of major elements and rare earth elements,it was conclude that the Sinian— Cambrian siliceous rocks of central Hunan contain high contents of SiO2 (generally over 92%)and have high Al /(Al +Fe +Mn)value (generally higher than 0.6).The shale PAAS-normalized REE patterns for the Sinian—Cambrian siliceous rocks show weak to intermediate negative Ce anomalies and strong enrichment in HREEs relative to LREEs.Ce /Ce*,LaN /YbN and Y /Ho values for the siliceous rocks of Sinian Doushantuo Formation are 0.34 ~0.54,0.05 ~0.10 and 38.00 ~51.44;the siliceous rocks from Sinian Liuchapo Formation and Cambrian Niutitang Formation have similar REE geochemical characteristics,Ce /Ce*,LaN /YbN and Y /Ho values for two groups of samples are 0.70 ~0.85,0.06 ~0.37,35.91 ~46.79 and 0.58 ~0.78,0.26 ~0.40, 34.75 ~45.58 respectively.The characteristics of major and rare earth elements reflect that these siliceous rocks formed in the deep-water basin far from continent and extensional faulting belts where terrestrial material and hydrothermal activities had no obvious effect on them.Although terrestrial input had an increasing tendency from Sinian to Cambrian,the origin of silica may derived from the thriving of the siliceous plankton.Sedimentary basin in central Hunan seemed like a passive continental margin basin during the transition from Sinian to Cambrian.
