近日，中国科学技术大学张海江团队研究了地壳增生、多成因改造和广泛的斑岩-矽卡岩Cu-Au/Fe和W-Mo矿化，数据来自中国东部长江中部矿带和邻近地区的案例。该项研究成果发表在2025年5月19日出版的《中国科学：地球科学》杂志上。

大多数巨型斑岩矽卡岩铜金矿系统要么与俯冲大洋地壳脱水形成的交代地幔楔有关，要么与富含铜的新生下地壳熔融有关。成矿母岩通常为贫化埃达克岩。相比之下，陆内铜金矿系统中的母岩表现出富集的同位素组成，但其形成机制和深部过程尚不清楚。为了解决这个问题，研究组重点分析长江中部矿带（CYROB）和邻近地区。通过汇编区域岩石学和年代学数据，进行了多同位素示踪和Hf同位素测绘，结合区域地震速度层析成像和大地电磁探测结果，重建了岩石圈结构及其演化过程。

研究结果表明，CYROB在中元古代和新元古代经历了显著的地壳增生，形成了新生地壳。中生代晚期，地壳经历了两个不同的时期（156-136Ma和136-120Ma）的多成因改造。在晚侏罗世到早白垩世（156-140Ma）的过渡时期，在高潭断裂附近和北部地区，伸展环境中的岩石圈拆沉促进了地幔对流和富集岩石圈地幔的部分熔融。这一过程改变了先前存在的幼年下地壳，导致εHf值略微为负（5至0）的埃达克岩和相关的斑岩矽卡岩铜金矿床的形成。 同时，埃达克质岩浆的上升偶尔会掺入富含钨的中上地壳物质，富集钨中的熔体，形成局部的中小型矽卡岩钨矿床。

140-136Ma期间，随着岩石圈应力的持续松弛，安庆西部和庆阳北部发生了富集地幔对下地壳更强烈的改造。这导致了εHf值为强负（24至8）的埃达克岩浆和相关的矽卡岩铜铁矿床的形成。在江南断裂以南，地壳较深，地幔对流导致元古代改造地壳重熔，将钨和钼释放到地壳衍生熔体中，最终形成了一系列大中型斑岩矽卡岩钨钼矿床。 

在晚期（136-120Ma），渐进的岩石圈伸展引发了大规模的岩石圈分层和从东南向西北的斜向软流层上涌，进一步改变了下地壳。由贫化地幔物质输入的改造地壳的重熔导致了广泛的富碱花岗岩基的形成。研究结果表明，在晚中生代的伸展体制下，由持续的岩石圈尺度拆沉和软流圈上升流驱动的新生地壳的多基因改造和先前改造的地壳的重熔，在控制CYROB和邻近地区金属矿石系统的时空分布方面发挥了关键作用。

附：英文原文

Title: Crustal accretion, polygenetic reworking, and extensive porphyry-skarn Cu-Au/Fe and W-Mo mineralization: A case study from the central Yangtze River ore belt and adjacent areas, eastern China

Author: Zhiyu ZHANG, Zengqian HOU, Xiaofei PAN, Xianke FAN, Xiaowei ZHANG, Chenguang WANG, Haijiang ZHANG, Kun ZHANG

Issue&Volume: 2025/05/19

Abstract: Most giant porphyry-skarn Cu-Au ore systems are associated with either the metasomatic mantle wedge, formed by the dehydration of subducting oceanic crust, or the melting of Cu-rich juvenile lower crust. The ore-forming parent rocks are typically depleted adakites. In contrast, parent rocks in intracontinental Cu-Au ore systems exhibit enriched isotopic compositions, yet their formation mechanisms and deep processes remain unclear. To address this, our study focuses on the central Yangtze River ore belt (CYROB) and adjacent areas. By compiling regional petrological and chronological data, we conducted multi-isotope tracing and Hf isotope mapping, integrated with regional seismic velocity tomography and magnetotelluric detection results, to reconstruct the lithospheric architecture and its evolutionary processes. Our findings indicate that the CYROB underwent significant crustal accretion during the Meso- and Neo-proterozoic, forming a juvenile crust. In the Late Mesozoic, the crust experienced polygenetic reworking, through two distinct periods (156–136Ma and 136–120Ma). During the transition from the Late Jurassic to the Early Cretaceous (156–140Ma), in the area near and north of the Gaotan fault, lithospheric delamination in an extensional setting facilitated mantle convection and partial melting of enriched lithospheric mantle. This process modified the pre-existing juvenile lower crust, leading to the formation of adakites with slightly negative εHf values (5 to 0) and associated porphyry-skarn Cu-Au deposits. Concurrently, ascent of adakitic magma occasionally incorporated W-rich middle-to-upper crustal materials, enriching the melts in W and forming localized small- to medium-sized skarn W deposits. During 140–136Ma, with the continued relaxation of lithospheric stress, a more intense modification of the lower crust by enriched mantle occurred west of Anqing and north of Qingyang. This led to the formation of adakic magmas with strongly negative εHf values (24 to 8) and related skarn Cu-Fe deposits. To the south of the Jiangnan fault, where the crust was deeper, mantle convection induced the remelting of Proterozoic reworked crust, releasing W and Mo into crust-derived melts, ultimately forming a series of large- and medium-sized porphyry-skarn W-Mo deposits. During the late period (136–120Ma), progressive lithospheric extension triggered large-scale lithospheric delamination and oblique asthenospheric upwelling from the southeast to the northwest, further modifying the lower crust. The remelting of reworked crust with input from depleted mantle materials, led to the formation of extensive alkali-rich granitic batholiths. This study demonstrates that, under the extensional regime of the Late Mesozoic, the polygenic reworking of juvenile crust and the remelting of previously reworked crust—driven by ongoing lithosphere-scale delamination and asthenospheric upwelling—played a key role in controlling the temporal and spatial distribution of metal ore systems in the CYROB and adjacent areas.

DOI: 10.1007/s11430-024-1562-6

Source: https://www.sciengine.com/10.1007/s11430-024-1562-6