浙东南地区磨石山群祝村组地层及其区域对比  

Lithological Characteristics and Regional Comparison of the Zhucun Formation of the Early Cretaceous Moshishan Group Volcanics in Southeastern Zhejiang

作　　者：陈小友 王加恩 汪发祥 

机构地区：[1]浙江省地质调查院,杭州311203

出　　处：《上海国土资源》2012年第3期91-95,共5页Shanghai Land & Resources

基　　金：中国地质调查局地质调查项目"1:5万区域地质调查"(200013000122)

摘　　要：早白垩世期间浙东南地区火山岩地层磨石山群的祝村组的建组一直存有争议。近年在浙江宁海地区深入开展的1:50000区域地质调查,发现此套中—酸性火山碎屑岩、凝灰质沉积岩夹酸性或中性熔岩地层,在岩性组合、岩相类型、岩石化学成分、火山活动类型等方面与下伏的九里坪组存在较大差异,并在宁海水车、永嘉大箬岩、丽水祝村等地出露广泛、厚度较大。依火山岩地层划分原则,这套地层可作为一个组级岩石地层单位——祝村组。通过对浙东南地区祝村组地层的区域对比认为:祝村组属早白垩世火山活动产物;岩性组合随当时火山活动强度及所处位置有所不同:分布于火山活动较强的破火山口内的祝村组地层,以火山碎屑流相为主,另有崩落相、火山泥石流相、空落相等岩相类型,岩石化学类型属中—酸性;分布于火山活动时喷时歇的火山洼地内的祝村组,以空落相火山碎屑岩与湖相、冲积扇相沉积岩互层产出为主,并有少量火山碎屑流相与喷溢相岩相类型,岩石化学类型属酸性。The Zhucun Formation is a constituent part of the Early Cretaceous-aged Moshishan Group volcanics within southeastern Zhejiang Province, and is of controversial origin. Recent mapping at 1：50,000 scale by the Zhejiang Province regional geological survey has identified a set of acidic pyroclastic rocks and tuffaceous sedimentary rocks associated with acid or mafic lavas. This set of pyroclastics and tuffaceous sediments is lithologically, geochemically, and volcanologically distinct from the underlying Jiliping Formation, and contains significantly different lithofacies units. These rocks are widely exposed in the study area, with units thickening towards the Shuiche area of Ninghai County, the Daruoyan area of Yongjia County, and the Zhucun area of the city of Lishui. Here, we define these units as a distinct lithostratigraphic formation, hereby termed the Zhucun Formation. A comparison with the Zhucun Formation outcropping in southeast Zhejiang suggests that this set of pyroclastics and tuffaceous sediments is associated with Early Cretaceous volcanism, with the lithologies preserved within these units spatially varying with the intensity of volcanic activity. The Zhucun Formation present in distinct calderas associated with more intense volcanic activity is preserved as pyroclastic flow, avalanche, volcanic mudslide, and fallout lithofacies, and is geochemically mafic to acidic; in comparison, Zhucun Formation units located in volcanic depressions that formed during low intensity periods of volcanism are acidic and preserve evidence of interbedding between airfall pyroclastic and lacustrine facies, in addition to alluvial fans and associated sediments, with only small amounts of pyroclastic flow and effusive facies present in these areas.

关 键 词：火山岩地层 祝村组 区域对比 浙东南地区 

分 类 号：P534.53[天文地球—古生物学与地层学]