ISSN 1009-6248CN 61-1149/P 双月刊

主管单位:中国地质调查局

主办单位:中国地质调查局西安地质调查中心
中国地质学会

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    冈底斯斑岩铜矿带东段早中新世剥蚀作用及对渐新世—中新世斑岩矿床时空分布的影响

    Early Miocene Exhumation History in the Eastern Gangdese Porphyry Copper Belt and Its Influence on the Spatiotemporal Distribution of Oligocene-Miocene Porphyry Deposits

    • 摘要: 冈底斯渐新世—中新世斑岩铜矿带是特提斯成矿域重要组成部分,已经发现了多处超大型-大型斑岩-矽卡岩型铜-钼-金矿床。然而,渐新世以来铜矿带所处的青藏高原经历了强烈抬升与剥蚀作用,在此背景下带内矿床是如何保存下来的尚未清楚,带内剥蚀作用的发育特征及对渐新世—中新世斑岩矿床的分布影响如何,控制机制有待解决。笔者通过泽当以北40km处冈底斯弧内部垂直剖面锆石和磷灰石(U-Th)/He定年,发现成矿带内部发育了早中新世(17.3~15.1 Ma)快速剥蚀作用,期间平均剥蚀速率>1.82 km/Ma,剥蚀量为4.0 km,而后剥蚀速率降低至0.14~0.19 km/Ma,15.1 Ma至今剥蚀量~2.5 km。结合前人数据,笔者发现成矿带内早中新世强快速剥蚀区呈东—西向带状分布,且受谢通门-沃卡剪切带向南逆冲作用控制,其南、北两侧也发育同期剥蚀作用,强度明显低于剪切带活动区域,说明高原内部中新世以来的隆升与剥蚀作用具有差异性。冈底斯带渐、中新世斑岩矿床分别分布在早中新世强剥蚀区南、北两侧弱剥蚀区内,指示差异剥蚀作用是成矿带内已发现的渐新世—中新世矿床时空分布的重要影响因素。

       

      Abstract: Gangdese Oligocene-Miocene porphyry copper belt is the important component of Tethys metallogenic domain, where numerous giant and large porphyry-skarn Cu-Mo-Au deposits have been discovered. However, the Tibetan Plateau that hosts this copper belt has suffered intense and rapid uplifting and erosion since Oligocene. How these Oligocene-Miocene deposits preserved in that environment suffering rapid uplifting and erosion remains as mystery and how the temporal and spatial distribution of erosion dominate the Oligocene-Miocene deposits in the belt remains unsettled. Basing on the zircon and apatite (U-Th)/He dating on the vertical section inner Gangdese arc 40km north of Zedong area, the author discovered an early Miocene (17.3~15.1 Ma) intense and rapid erosion event in the Gangdese porphyry Cu belt, during which the average erosion rate was >1.82 km/Ma, the erosion amount was 4 km. And then the erosion rate decreased to 0.14~0.19 km/Ma with the erosion amount from 15.1 Ma to present of ~2.5 km. Integrating the previous thermo-chronological data, the author reveals that the early Miocene intense erosion zone in the Gangdese porphyry Cu belt was E-W trending and controlled by the southward thrusting of Xietongmen-Oiga shear zone. Even though the contemporaneous erosional event was also developed on the southern and northern sides, the intensities were significantly lower than the shear zone area, indicating that the uplifting and erosion in the plateau has varied temporally and spatially since Miocene. Besides, the Oligocene and Miocene porphyry deposits are distributed in the weak erosion zones on the southern and northern sides of the early Miocene E-W trending intense erosional belt respectively, indicating that the differential erosion is one of the restrictive factors for the temporal and spatial distribution of Oligocene-Miocene deposits in the belt.

       

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