钦-杭成矿带南段庞西垌断裂带热年代学证据

丁汝鑫; 虞鹏鹏; 胡光明; 邹和平; 曾长育; 周永章

doi:10.3799/dqkx.2018.609

钦-杭成矿带南段庞西垌断裂带热年代学证据

doi: 10.3799/dqkx.2018.609

丁汝鑫^1,2,3,,
虞鹏鹏^1,2,
胡光明⁴,
邹和平^1,2,
曾长育^1,2,
周永章^1,2

1.
中山大学地球科学与工程学院, 广东广州 510275
2.
广东省地质过程与矿产资源探查重点实验室, 广东广州 510275
3.
Low-T实验室, 上海 201101
4.
长江大学地球科学学院, 湖北武汉 430100

基金项目:

国家自然科学基金项目 41472097

中国地质调查局 12120113067600

国家留学基金项目 201206385013

广东省自然科学基金项目 2015A030313193

国家自然科学基金项目 41102131

详细信息

作者简介:
丁汝鑫(1978-), 男, 副教授, 博士, 主要从事构造地质学研究

中图分类号: P548
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- 被引次数: 0
出版历程
- 收稿日期: 2018-01-24
- 刊出日期: 2018-06-15

Thermochronology of Pangxidong Fault Zone in Southern Section of Qin-Hang Metallogenic Belt

1.
School of Earth Science and Engineering, Sun Yat-Sen University, Guangzhou 510275, China
2.
Guangdong Provincial Key Lab of Geological Processes and Mineral Resource Survey, Guangzhou 510275, China
3.
Low-T Lab, Shanghai 201101, China
4.
School of Geosciences, Yangtze University, Wuhan 430100, China

摘要

摘要: 庞西垌断裂带是钦-杭成矿带南段众多NE向韧性剪切带的其中一条，控制着一系列韧性剪切带型银金矿床的分布.对其进行热年代学研究有助于了解钦-杭成矿带南段NE向韧性剪切带的构造演化及其对伴生矿床的控制作用.获得的庞西垌断裂带内糜棱岩中两件白云母⁴⁰Ar/³⁹Ar总气体年龄分别为221.98±1.16 Ma和223.77±1.16 Ma.据此认为庞西垌断裂带在印支期发生韧性剪切活动，为伴生矿床的形成提供了有利空间；在同一糜棱岩样品中获得的磷灰石、锆石裂变径迹年龄分别为64.83±4.13 Ma和75.69±2.88 Ma，结合热史模拟结果可以得出，庞西垌断裂带在75~60 Ma期间发生了快速冷却作用（6.2 ℃/Ma），与区域整体缓慢冷却过程（1.5 ℃/Ma）差别显著，据此推测庞西垌断裂带可能在约75~60 Ma期间再次发生活动，而庞西垌银金矿床可能形成于晚白垩世.
- 钦-杭成矿带 /
- 庞西垌断裂带 /
- ⁴⁰Ar/³⁹Ar测年 /
- 裂变径迹 /
- 石油地质
Abstract: The Pangxidong fault zone is one of many NE-strength ductile shear zones in the southern section of the Qin-Hang metallogenic belt and controls the distribution of a series of ductile shear zones related Ag-Au deposits. Study on its thermochronology is helpful to understand the tectonic evolution of the NE-trending ductile shear zone in the southern part of the Qin-Hang metallogenic belt and its effect on the associated mineral deposits. A set of muscovite ⁴⁰Ar/³⁹Ar and fission track analysis were carried out in this paper. Two muscovite samples from the mylonite yielded ⁴⁰Ar/³⁹Ar isotopic total gas ages of 221.98±1.16 Ma and 223.77±1.16 Ma, respectively. It is interpreted that the ductile shearing happened in Pangxidong fault zone during the Indosinian period, which is believed to have provided favorable space for the formation of associated mineral deposits.Apatite and zircon fission track ages from the same mylonite sample yield 64.83±4.13 Ma and 75.69±2.88 Ma, respectively. Combined with the thermal history modeling results, it is shown that the fault zone had experienced a rapid cooling process during~75-60 Ma(6.2 ℃/Ma), which is much different from the slow cooling process of the Yunkai region (1.5 ℃/Ma). The results suggest that the Pangxidong fault zone was active again during~75-60 Ma and the Pangxidong Ag-Au deposits possibly formed in the Late Cretaceous.
- Qin-Hang metallogenic belt /
- Pangxidong fault zone /
- ⁴⁰Ar/³⁹Ar dating /
- fission track analysis /
- petroleum geology

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图 1 云开地区及庞西垌银金矿地质图

断裂名称：1.博白-梧州断裂；2.庞西垌断裂；3.黎村-文地断裂；4.廉江-信宜断裂；5.吴川-四会断裂；据Wang et al.(2013)修改

Fig. 1. Tectonic background of Yunkai area and Pangxidong Ag-Au ore deposit

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图 2 庞西垌银金矿1号矿体3、13线剖面

Fig. 2. Geological profiles of No.3, 13 for 1^# ore body, Pangxidong Ag-Au ore deposit

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图 3 庞西垌断裂带内的糜棱岩显微照片

Fig. 3. Microphotograph of mylonite in Pangxidong fault zone

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图 4 白云母⁴⁰Ar/³⁹Ar阶段激光剥蚀年龄谱

Fig. 4. ⁴⁰Ar/³⁹Ar age spectra of muscovite obtained by stepwise laser heating

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图 5 磷灰石、锆石颗粒裂变径迹年龄分布及磷灰石裂变径迹围限径迹长度分布

Fig. 5. The apatite and zircon fission track grain ages and apatite confined track length distribution

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图 6 裂变径迹热史模拟

图 6a、6b中分别搜索了100 000和10 000条热史曲线.绿色模拟区域代表可以接受的模拟结果(拟合优度＞0.05)，紫色模拟区域代表良好的模拟结果(拟合优度＞0.5)，黑色粗实线代表最终的结果.a.庞西垌断裂带糜棱岩样品裂变径迹热史模拟结果，数据为磷灰石、锆石颗粒裂变径迹年龄(62.68±1.73 Ma、75.69±2.88 Ma)；b.云开地区裂变径迹热史模拟结果，数据为区域上前人所有样品(李小明等，2005)的平均磷灰石、锆石裂变径迹年龄(54.56±2.83 Ma、114.91±6.86 Ma)

Fig. 6. Thermal history modeling of fission track

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表 1 糜棱岩白云母⁴⁰Ar/³⁹Ar测年结果

Table 1. ⁴⁰Ar/³⁹Ar dating results of muscovite from mylonite

阶段	累积³⁹Ar释放率	激光功率 (mW)	气体体积(10^-13 mL)					t(Ma)	年龄误差(Ma)
阶段	累积³⁹Ar释放率	激光功率 (mW)	³⁶Ar	³⁷Ar	³⁸Ar	³⁹Ar	⁴⁰Ar	t(Ma)	年龄误差(Ma)
ZMT-B1白云母，J=0.002 2±0.000 011 9
1	0.002	100	0.41	0.33	0.29	3.74	255.79	136.83	21.51
2	0.004	150	0.41	0.21	0.25	4.76	274.05	122.18	17.29
3	0.008	200	0.37	0.70	0.22	7.63	409.18	149.56	15.37
4	0.014	250	0.39	0.61	0.15	11.20	595.69	162.72	8.98
5	0.022	300	0.33	0.53	0.22	15.93	832.43	173.96	4.44
6	0.050	400	0.68	0.88	0.24	52.54	3 049.22	202.90	2.24
7	0.107	500	1.20	0.84	0.23	111.22	6 651.19	211.44	1.08
8	0.195	600	1.34	0.60	0.43	170.14	10 397.04	219.04	0.68
9	0.366	800	2.41	1.28	0.71	331.37	20 598.97	223.36	0.46
10	0.485	1 000	1.82	0.61	0.43	231.08	14 354.32	222.56	0.66
11	0.614	1 200	1.78	0.36	0.55	249.29	15 552.21	224.27	0.73
12	0.825	1 600	2.06	0.48	0.69	408.41	25 578.92	227.29	0.60
13	0.922	2 000	0.73	0.26	0.37	186.66	11 594.56	226.64	0.86
14	0.980	2 600	0.37	0.15	0.22	112.12	7 016.10	228.89	1.06
15	0.996	3 200	-0.10	-0.13	0.07	32.33	2 012.24	234.42	2.32
16	1.000	4 000	0.07	0.32	-0.04	7.01	441.99	223.00	13.35
ZMT-B2白云母，J=0.002 2±0.000 011 9
1	0.001	100	0.42	0.18	0.09	4.04	264.75	133.58	20.75
2	0.003	150	0.44	0.22	0.07	5.07	317.02	140.87	19.79
3	0.006	200	0.38	0.45	0.15	7.40	436.80	165.57	10.32
4	0.010	250	0.18	0.47	0.07	11.09	624.53	193.81	7.83
5	0.016	300	0.56	0.66	0.11	15.41	881.59	175.38	6.59
6	0.041	400	1.24	1.10	0.34	69.36	4 310.23	212.34	1.92
7	0.077	500	1.29	1.51	0.49	99.68	6 096.28	213.98	1.10
8	0.129	600	1.87	1.50	0.59	142.56	9 104.64	223.29	0.81
9	0.234	800	2.95	1.54	0.90	289.20	18 030.43	220.97	0.65
10	0.316	1 000	2.48	1.10	0.49	225.96	14 081.27	220.07	0.76
11	0.447	1 200	2.76	1.20	0.87	360.45	22 440.23	223.26	0.52
12	0.622	1 600	4.23	1.39	1.24	482.38	30 697.55	226.96	0.55
13	0.759	2 000	3.15	1.25	0.94	379.72	24 185.75	227.64	0.68
14	0.887	2 600	2.47	1.15	0.79	350.14	22 317.35	229.07	0.50
15	0.954	3 200	1.23	0.81	0.37	186.50	11 726.24	226.53	0.78
16	1.000	4 000	0.58	0.63	0.26	126.18	7 911.37	228.01	1.16

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表 2 糜棱岩磷灰石、锆石裂变径迹测试数据

Table 2. Fission track analysis results of apatite and zircon from mylonite

矿物	颗粒数	自发径迹		诱发径迹		P(χ²)	标准玻璃		总体年龄t(Ma)	1σ (Ma)	平均年龄t(Ma)	1σ (Ma)	平均径迹长度L
矿物	颗粒数	ρ_s(径迹数) (cm^-2)	N_s	ρ_i(径迹数) (cm^-2)	N_i	P(χ²)	ρ_d(径迹数) (cm^-2)	N_d	总体年龄t(Ma)	1σ (Ma)	平均年龄t(Ma)	1σ (Ma)	径迹数量	L±σ(μm)
磷灰石	70	0.39×10⁶	3 073	1.60×10⁶	12 592	0.92	12.84×10⁵	7 312	64.83	4.13	62.68	1.73	124	12.33±1.85
锆石	56	7.22×10⁶	6 589	8.98×10⁶	8 203	0.51	20.10×10⁵	10 330	75.69	2.88	75.67	1.20	-	-
注：N_s表示自发径迹数；N_i表示诱发径迹数；N_d表示铀标准玻璃的诱发径迹数.

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