Rapid transition to long-lived deep crustal magmatic maturation and the formation of giant porphyry-related mineralization (Yanacocha, Peru)
Rapid transition to long-lived deep crustal magmatic maturation and the formation of giant porphyry-related mineralization (Yanacocha, Peru)
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DOI：
10.1016/j.epsl.2009.10.012
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发表时间：
2009-11-15
影响因子：
5.3
通讯作者：
Spikings, Richard
中科院分区：
文献类型：
--
作者：
Chiaradia, Massimo;Merino, Daniel;Spikings, Richard
亚纳科查岩浆区(秘鲁北部)拥有地球上最大的高硫化金矿。矿化与沿NE向岩浆构造走廊分布的斑岩侵入体有关。其中8个侵入岩的年龄范围为12.4~8.4 Ma，并显示出系统的化学和同位素随时间的变化。它们被解释为来自含水镁铁质岩浆，在较深的层面上，通过角闪石-单斜辉石+/-石榴石分馏和下地壳熔融(留下石榴石残留物)，导致不同程度的强烈埃达克岩特征，在较浅层面，通过斜长石-角闪石分馏，伴随着地壳同化和补给(补给同化分离结晶，RAFC过程)。随着侵入年龄的系统地球化学和同位素变化，再加上斜长石分带和角闪石大地测量，表明岩浆系统的演化是通过地幔熔体与地壳柱长的增加相互作用而发生的，并随着时间的推移从深到浅的地壳水平传播。这可能是稳步增加的挤压作用的结果，这种挤压逐渐减缓了岩浆上升的速度，迫使岩浆在下地壳和上地壳之间的一系列中层洞穴中演化。压力的增加可能与浮力印加海洋高原开始俯冲有关，据估计，俯冲发生在大约12 Ma，即从正常“到埃达克岩样特征”的快速转变开始的同一时间。巨型亚纳柯查成矿系统与上述过程形成的埃达克岩类岩浆(12.4/12.0-8.4 Ma)长3.6~4.0 Ma侵入上地壳小体积相吻合，并在类似于2.4 Ma(10.8-8.4 Ma)的岩浆活动末期达到顶峰，类似于1.4 Ma(12.4-11.0 Ma)的深部马龙岩浆的成熟期。需要进一步研究，以了解埃达克岩类岩浆与矿石的组合是不是高压条件下形成的氧化岩浆中不相容挥发分和金属聚集的结果，是低地壳富硫化物堆积物循环的结果，还是岩浆从地壳深层次向浅层长期集中转移的结果。(C)2009爱思唯尔B.V.保留所有权利。
The Yanacocha magmatic field (northern Peru) hosts the largest high sulfidation gold deposit on Earth. Mineralization is associated with porphyritic intrusions distributed along a NE-trending magmatic structural corridor. Eight of these intrusions investigated in this study range in age from 12.4 to 8.4 Ma and show systematic chemical and isotopic changes through time. They are interpreted to derive from hydrous mafic magmas evolving through amphibole-clinopyroxene +/- garnet fractionation and lower crust melting (leaving a garnet residue) at deeper levels, which led to variably strong adakite-like signatures, and through plagioclase-amphibole fractionation at shallower levels, both accompanied by crustal assimilation and recharge (recharge assimilation fractional crystallization, RAFC, processes). Systematic geochemical and isotopic changes with intrusion ages, coupled with plagioclase zoning and amphibole geobarometry, suggest that the evolution of the magmatic system occurred through interaction of mantle-derived melts with an increasing length of the crustal column and propagation from deep towards shallower crustal levels through time. This was probably the result of a steadily increasing compression that has progressively slowed down magma ascent forcing magmas to evolve at a series of intermediate level chambers between the lower and upper crust. Increased compression might have been related to the onset of subduction of the buoyant Inca oceanic plateau, estimated to occur at similar to 12 Ma, i.e., the same time of the onset of the rapid transition from normal" to adakite-like signatures. The giant Yanacocha ore system developed in coincidence with the similar to 3.6-4.0 Ma-long intrusion of the adakite-like magmas (12.4/12.0-8.4 Ma) formed by the above processes into a small upper crustal volume and peaked during the last similar to 2.4 Ma (10.8-8.4 Ma) of magmatic activity after a similar to 1.4 Ma long (12.4-11.0 Ma) maturation of magmas at deep crustal levels. Further investigation is needed to understand whether the association of adakite-like magmas with ore, which is typical of other giant porphyry-systems, is the result of the build-up of incompatible volatiles and metals in oxidized magmas that evolve under high-pressure conditions, of recycling of lower crustal sulfide-rich cumulates, and/or of a long-lived, focused transfer of magmas from deep to shallow crustal levels. (C) 2009 Elsevier B.V. All rights reserved.