长江中下游成矿带抛刀岭金矿裂变径迹研究及大地构造意义

抛刀岭金矿位于长江中下游成矿带中的安庆-贵池矿集区,是长江中下游多金属成矿带中首次发现的斑岩型独立金矿床。通过磷灰石裂变径迹研究分析区内的构造演化特征,裂变径迹长度处于11.9±1.8μm和13.2±1.6μm之间,表明样品在后期受构造热事件的影响,样品长时间处于退火带温度,长度直方图总体呈现单峰特征,受隆升冷却作用控制明显。通过对同组年龄(x2检验值>5%)和混合年龄(x2检验值<5%)进行分析,所测年龄位于123Ma和19Ma之间,可以将年龄分为5组:123.0Ma,107Ma,86Ma,52Ma,19Ma。裂变径迹热历史可以分为4个时期:缓慢冷却期,从150～90Ma;快速冷却期,从90Ma至65～58Ma;缓慢冷却期,从65～58Ma至18～12Ma;快速降温期,从18～12Ma至今。自中侏罗世以来,江南隆起带受控于太平洋板块构造,太平洋板块在不同时期有着不同的活动,其运移方向和活动强度直接控制着中国东部的构造演化。研究地区所测裂变径迹年龄划分时代与太平洋形成后不同产状洋岛链出现的时代吻合,热历史模拟结果和太平洋板块不同期次活动相关。通过热历史模拟和构造分析,可推测热历史不同阶段的形成是不同时期太平洋板块运动的结果,样品混合年龄亦证明了构造活动的多期次性。可以推断贵池地区自白垩纪以来的构造运动与太平洋构造带活动密切相关,其多期构造演化是对太平洋板块活动的响应。

Fission Track Dating on the Paodaoling God Deposit in Middle-Lower Part of Yangtze Metallogenic Belt: Its significance to Tectonic Setting

The Paodaoling gold deposit regarding as an independent prophyry gold deposit is firstly found in Anqing-Guichi ore district within the middle-lower Yangtze River polymetallic metallogenetic belt.One the study of fission tracks,we analyze the characteristics of structural evolution in the Paodaoling gold deposit.Results show that the mean track lengths range between 11.9±1.8μm and 13.2±1.6μm,respectively,indicating that intrusions are infulenced by tectonic-thermal events in late stage and controlled by the temperatures of annealing belts in long time.There are unimodal characterstics in the histogram of track lengths.Analysises of central age(P(x2)x2>5%) and mixed ages(P(x2) x2 <5%)reflect that the measured AFT ages lie between 123Ma and 19Ma,which is all significantly younger than those of their host rocks.These ages can be divided into five phases,i.e.,123.0Ma,107Ma,86Ma,52Ma,and 19Ma,respectively.The AFT data modeling identifies a four-stage regional cooling history,i.e.,the first cooling phase of cooling took place from 150Ma to 90Ma with slow cooling rates;the second phase of cooling took place from 90Ma to 65~58Ma with rapid cooling rates;the third phase of cooling took place from 65~58Ma to 18~12Ma with slow cooling rates;the fourth phase of cooling took place from 18~12Ma to now with rapid cooling rates.Since Middle Jurassic,Jiangnan uplifted belt is controlled by Pacific Plate tectonics.The movements of Pacific Plate are different in various periods,whose directions and intensities directly control the tectonic evolution of Eastern China.Subdivision of measured fission track ages in this area corresponds with the ages of island chains with different occurrences after the formation of the Pacific Ocean.The results of thermal history modeling are related to movements of the Pacific Plate in different periods.Based on the tectonic-thermal history models and tectonic analysises,we concluded that various stages of thermal history are related to Pacific plate movements in different stages,mixed ages also indicate multiple phases of tectonic activities.Thus we further prove that the stages of tectonic movements in the Guichi area,lower Yangtze metallogenic belt are closely direct response to the Pacific plate activities since Cretaceous.