山西忻定盆地断层崩积楔OSL年龄及其对古地震事件的指示意义

断层陡坎崩积楔是断层活动的直接产物,是古地震事件的重要证据。对于崩积楔的准确定年是解决古地震事件的关键。近几年得益于释光技术与方法的发展,简单多片再生法(SMAR)已成功应用于130 ka以来黄土类型沉积物的定年。以山西忻定盆地五台山北麓南峪口探槽为例,对该探槽中的两期崩积楔(D1、D2)各个部位不同类型沉积物进行系统采样,对样品采用细颗粒石英(4~11μm)简单多片再生法(SMAR)进行光释光(OSL)测年,根据光释光年龄,得出如下认识:(1)D1、D2崩积楔演化过程与常规的正断层崩积楔演化模式有些差别;(2)D1崩积楔古地形面由断层处向外延伸堆积而成,D2崩积楔古地形面由水平堆积形成,且较D1厚;(3)D1崩塌结束后经历较强的水流作用;(4)两次古地震事件分别发生于(42.77±2.46)~(61.72±2.82)ka、(32.80±2.87)~(47.92±0.94)ka,时间间隔为10~15 ka。

OSL Age of Fault Collapse Wedge in Xinding Basin,Shanxi Province and Its Significance for Paleoearthquake Events

The fault scrap collapse wedge is the direct result of fault activity, it is also signification of paleoearthquake events, its accurate dating is the key to solve the problems about paleoearthquake events.Luminescence techniques are rapidly progressing in recent years.Simplified multiple aliquot regenerative-dose (SMAR) protocol is already applied successfully in loessial sediments after 130 ka.The studied samples are collected detailedly in two fault scarp collapse wedges(D1 and D2) from the schematic section of Nanyukou in north piedmont zone of Wutai Mountain in Xinding basin, Shanxi Province.The sample ages are acquired with fine grain quartz (4-11 μm) SMAR protocol.The results of the OSL dating show that evolutional models of D1 and D2 are different from general model of normal fault collapse wedge.The palaeotopography of D1 is formed by accumulating nearby the fault to stretch out far, whereas the palaeotopography of D2 is formed by accumulating horizontally and is thicker than D1.After dilapidation powerful current has rised in D1. The results indicate that the older paleoearthquake event occurred between (42.77±2.46) ka and (61.72±2.82) ka, the younger paleoearthquake event occurred between (32.80±2.87) ka and (47.92±0.94) ka.The interval of the two paleoearthquake events is between 10 ka and 15 ka.