Natural Radioactivity Logs and Interpretation from the CCSD Main Hole
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摘要: 为了认识江苏东海超高压变质带上地壳岩石自然放射性的垂向分布特征, 榴辉岩退变质程度对放射性元素浓度的影响, 以及放射性产热率对地温梯度的影响, 利用中国大陆科学钻探(CCSD) 主孔100~5000m自然放射性测井(自然伽马和自然伽马能谱) 资料统计了CCSD主孔各类岩石的自然放射性强度和铀、钍、钾元素的浓度, 计算出产热率曲线.自然伽马, 铀、钍、钾浓度和产热率从蛇纹岩到榴辉岩、角闪岩、副片麻岩、正片麻岩依次增大.随着榴辉岩退变质程度的增强, 其铀、钍、钾元素的浓度值逐渐增大.CCSD主孔自然放射性的垂向分布特征主要受岩性控制, 自然放射性随深度增加有增强趋势.产热率与自然伽马测井值之间有很好的线性关系, 在高放射性岩层的上部, 地温梯度会出现较强扰动和低值异常.
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关键词:
- 中国大陆科学钻探主孔 /
- 超高压变质岩 /
- 自然放射性测井 /
- 产热率
Abstract: In order to understand the vertical distribution of natural radioactivity of the upper crust of the ultra-high pressure (UHP) metamorphic belt in Donghai County, Jiangsu province, as well as the influence of the retrogression intensity of eclogite on the concentration of radioelement, and the influence of radiogenic heat production rate on the geothermal gradient, the natural radioactivity logs (gamma ray and gamma spectrometry logs) from the main hole of the Chinese Continental Scientific Drilling (CCSD) were utilized to obtain the natural gamma intensity and the concentration of U, Th and K of main lithologies and the heat production rate log. The natural gamma intensity and concentration of U, Th and K gradually increase from serpentine to eclogite, amphibolite, paragneiss, and orthogneiss. With the strengthening of the retrogression of eclogite, the concentration of U, Th and K of eclogite increase. This indicates that some exotic fluids with U, Th and K elements join in the retrograde metamorphism. The vertical distribution of the natural gamma intensity and concentration of U, Th and K is dominated mainly by lithology. The natural gamma intensity approximately increases with the depth. The heat production rate and the natural gamma log have a good linear relationship. The formation with high radioactivity could cause disturbance and low anomalies on geothermal gradient on its upper formation. -
图 2 CCSD主孔100~2 000 m的测井和岩心样品CK, CTh测量结果的对比(岩心测试数据引自曾令森等, 2005)
Fig. 2. Curves showing the contrast of CKand CThfrom well logs and core test in 100~2 000 m interval of CCSD main hole
图 4 超高压榴辉岩退变质过程的P-T轨迹及其CU, CTh, CK的变化(图(a) 引自张泽明等(2005))
M.角闪岩; EA.绿帘角闪岩相; EC.榴辉岩相; GR.麻粒岩相; GS.绿片岩相; BS.蓝闪片岩相; P.葡萄石相; PA.绿纤石阳起石相; PP.葡萄石阳起石相; Qtz.石英; Coe.柯石英; Pg.钠云母; Omp.绿辉石; Ky.蓝晶石; W.水; Gr.石墨; Dia.金刚石; FR.新鲜榴辉岩; WM.弱至中等退变质榴辉岩; SR.强退变质榴辉岩; TR.完全退变质榴辉岩
Fig. 4. P-T path and variation of CU, CTh, CK of ultra-high pressure eclogite
图 5 CCSD主孔A、T、G与λc的分布(地温、地温梯度与热导率资料来源于何丽娟等(2006))
Fig. 5. The distribution of heat ptoduction rate, temperature, thermal gradient and thermal conductivity in CCSD main hole
表 1 CCSD主孔UHP变质岩γt、CK、CU、CTh的统计结果
Table 1. Statistics data of γt、CK、CU、CTh of UHP rocks in CCSD main hole
表 2 不同退变质程度榴辉岩的γt、CU、CK、CTh的统计结果
Table 2. Statistics data of γt、CU、CK、CTh of eclogites of different retrogressions
表 3 CCSD主孔UHP变质岩的密度和生热率
Table 3. Density and heat production rate of UHP metamorphic rocks in CCSD main hole
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