西北地质
西北地質
서북지질
NORTHWESTERN GEOLOGY
2015年
2期
31-42
,共12页
大巴山构造带%灯影组%硅质岩系%热水成因
大巴山構造帶%燈影組%硅質巖繫%熱水成因
대파산구조대%등영조%규질암계%열수성인
tectonic belts of Daba Mountain%Dengying formation%cherts%hydrothermal origin
通过野外调研,表明大巴山构造带和米仓山构造带震旦系灯影组发育多套硅质岩系,并与海相碳酸盐岩相伴产出。微量、稀土元素分析结果表明,硅质岩系具有热水成因特征。其中,Ba 含量较高,Ba/Sr 值大于1；Th/U 值小于1,Th U 图解中所有样品均投到热水沉积物区；Zr 元素较为富集,Zr Cr 图解中样品全部投到热水沉积物趋势线附近；硅质岩系 REE 总量低,Ce 总体为负异常,Eu 正异常明显,硅质岩 HREE 富集,硅质白云岩 HREE 富集不明显。Ce/Ce?、LaN/CeN 、V/Y 值表明灯影组硅质岩形成于大洋盆地到大陆边缘的过渡地带；Th/Sc、Th/U、V/Cr、V/(V+Ni)值表明硅质岩主要形成于还原环境中,部分形成于氧化环境中。综合硅质岩稀土、微量元素特征并结合震旦纪区域地质构造演化,本区硅质岩应形成于复杂大陆边缘富氧的浅海陆棚环境及缺氧的陆内裂陷槽环境中。
通過野外調研,錶明大巴山構造帶和米倉山構造帶震旦繫燈影組髮育多套硅質巖繫,併與海相碳痠鹽巖相伴產齣。微量、稀土元素分析結果錶明,硅質巖繫具有熱水成因特徵。其中,Ba 含量較高,Ba/Sr 值大于1；Th/U 值小于1,Th U 圖解中所有樣品均投到熱水沉積物區；Zr 元素較為富集,Zr Cr 圖解中樣品全部投到熱水沉積物趨勢線附近；硅質巖繫 REE 總量低,Ce 總體為負異常,Eu 正異常明顯,硅質巖 HREE 富集,硅質白雲巖 HREE 富集不明顯。Ce/Ce?、LaN/CeN 、V/Y 值錶明燈影組硅質巖形成于大洋盆地到大陸邊緣的過渡地帶；Th/Sc、Th/U、V/Cr、V/(V+Ni)值錶明硅質巖主要形成于還原環境中,部分形成于氧化環境中。綜閤硅質巖稀土、微量元素特徵併結閤震旦紀區域地質構造縯化,本區硅質巖應形成于複雜大陸邊緣富氧的淺海陸棚環境及缺氧的陸內裂陷槽環境中。
통과야외조연,표명대파산구조대화미창산구조대진단계등영조발육다투규질암계,병여해상탄산염암상반산출。미량、희토원소분석결과표명,규질암계구유열수성인특정。기중,Ba 함량교고,Ba/Sr 치대우1；Th/U 치소우1,Th U 도해중소유양품균투도열수침적물구；Zr 원소교위부집,Zr Cr 도해중양품전부투도열수침적물추세선부근；규질암계 REE 총량저,Ce 총체위부이상,Eu 정이상명현,규질암 HREE 부집,규질백운암 HREE 부집불명현。Ce/Ce?、LaN/CeN 、V/Y 치표명등영조규질암형성우대양분지도대륙변연적과도지대；Th/Sc、Th/U、V/Cr、V/(V+Ni)치표명규질암주요형성우환원배경중,부분형성우양화배경중。종합규질암희토、미량원소특정병결합진단기구역지질구조연화,본구규질암응형성우복잡대륙변연부양적천해륙붕배경급결양적륙내렬함조배경중。
Field survey indicates that a large scale of cherts occur in Dengying formation of Sinian Systemin the tectonic belt of Dabashan and Micangshan,together with carbonatite.The results of trace and rare earth elements analysis indicate that the cherts have the characteristics of hydro-thermal origin.Among the trace elements,Ba is enriched and most of the Ba/Sr ratio is greater than 1.Th/U ratio is less than 1 and the values from all samples fall into the hydrothermal sedi-ment area in the Th-U diagram.Zr is also enriched and its content in all samples are neighboring the hydrothermal sediment trend line in the Zr-Cr diagram.The ∑REE of cherts is very low.Ce is negative anomaly in general while Eu is obviously positive.HREE is enriched in the radiolariancherts,but not distinctly enriched in the siliceous dolostone.The Ce/Ce?,LaN/CeN ,V/Y rati-os indicate that the cherts are formed in the transition zone from oceanic basin to continental mar-gin.The Th/Sc,Th/U,V/Cr,V/ (V+Ni)ratios indicate that the cherts are mostly formed in the reducing environment,with a small number formed in the oxidation environment.Consider-ing the trace and rare earth elements characteristics and regional evolution of tectonics during Sin-ian period,it is inferred that the cherts are formed in shallow-sea shelf oxygen-enriched environ-ment and anoxic intracontinental taphrogenic trough environmentin the complex continental margin.
