Eclogite-, amphibolite- and blueschist-facies rocks from Diego de Almagro Island (Patagonia): Episodic accretion and thermal evolution of the Chilean subduction interface during the Cretaceous
Eclogite-, amphibolite- and blueschist-facies rocks from Diego de Almagro Island (Patagonia): Episodic accretion and thermal evolution of the Chilean subduction interface during the Cretaceous
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迭戈德阿尔马格罗岛（巴塔哥尼亚）的榴辉岩、角闪岩和蓝片岩相岩石：白垩纪期间智利俯冲界面的幕式增生和热演化
DOI：
10.1016/j.lithos.2016.09.001
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发表时间：
2016
期刊：
影响因子：
3.5
通讯作者：
Chopin
中科院分区：
文献类型：
--
作者：
Hyppolito;Angiboust;Juliani;Glodny;Garcia-Casco;Calderon;Chopin
在巴塔哥尼亚安第斯山脉，很少有地方暴露出中生代智利古增生复合体的遗迹。我们重点研究了Diego de Almagro岛高压/低温（HP/LT）杂岩，这是一个多公里厚的层序，由具有海洋亲性的变质火山岩和变质沉积岩组成。本研究首次对巴塔哥尼亚智利俯冲界面最深段进行了表征。尽管表面上呈均匀性，但杂岩体实际上是由两个变质和热演化时代不同的构造单元组成：石榴石角闪岩（GA）和其下的蓝片岩（BS）单元。GA单元基性岩在渐进式石榴石I中表现为绿帘石、云母石、钛石、金红石、绿绿石和paragonite包裹体，在石榴石II中表现为透辉石+钠长石互生取代辉辉石包裹体，在岩屑-寄生角闪石中表现为残余辉辉石（XJd45）。热压测量结果表明，这些岩石沿较冷的进积路径（c. 11℃/km）埋藏，接近峰值压力条件（c. 550 ~ 600℃，1.6 GPa）达到榴辉岩相。在c. 1.3 GPa的减压过程中，GA单元经历了普遍的两角化阶段。野外和岩石学观察以及多矿物Rb-Sr测年表明，GA单元的角闪石化发生在距今约120 Ma的俯冲界面上，在略暖的俯冲状态下（约13-14°c /km），与距今约35 km的古海角闪岩形成一致。下伏的BS单元(i)产生了4个一致的Rb-Sr变形年龄，约为80 Ma，即比GA单元的上覆岩石年轻40 Ma；（ii）表现出略冷的峰值变质条件（c. 520-550°c, 1.6 GPa），表明沿c. 10°c /km的递进路径埋藏；（iii）不显示GA单元中所见的角闪岩相覆印。在角闪岩相条件下长时间停留后，GA单元角闪岩在80 Ma左右的蓝片岩相变形过程中发生了部分再结晶，表现为白云岩周围的富硅边缘和角闪石周围的蓝闪石过度生长。这些新结果：(i)阐明了智利深部古增生楔的动力学，（ii）揭示了GA单元经历了两个阶段的挖掘，可能与40 km深度附近的BS单元并在一起，（iii）表明Diego de Almagro岛的俯冲热梯度在白垩纪时期在c. 10-11°c /km和13-14°c /km之间波动。
Few localities in the Patagonian Andes expose remnants of the Mesozoic Chilean paleo-accretionary complex. We focus on the Diego de Almagro Island high-pressure/low-temperature (HP/LT) Complex, a pluri-kilometer thick sequence comprising metavolcanic rocks with oceanic affinities and metasedimentary rocks. In this study, the deepest segments of the Chilean subduction interface in Patagonia are characterized for the first time. Despite its apparent homogeneity, the complex is actually composed of two tectonic units with distinct ages of metamorphism and thermal evolution: the garnet amphibolite (GA) and the underlying blueschist (BS) units.The GA unit mafic rocks exhibit epidote, phengite, titanite, rutile, chloritoid and paragonite inclusions in prograde garnet I, diopside + albite intergrows replacing omphacite inclusions in garnet II, and relict omphacite (XJd45) included in edenitic-pargasitic amphiboles. Thermobarometric results show that these rocks were buried along a relatively cold prograde path (c. 11 °C/km) and reached eclogite-facies near peak pressure conditions (c. 550–600 °C, 1.6 GPa). The GA unit underwent a pervasive stage of amphibolitization during decompression at c. 1.3 GPa. Field and petrological observations, together with multi-mineral Rb-Sr dating, indicate that amphibolitization of the GA unit took place along the subduction interface at c. 120 Ma in a slightly warmer subduction regime (c. 13–14 °C/km), in agreeement with the formation of coetanoeus amphibolites at c. 35 km. The underlying BS unit (i) yields four consistent Rb-Sr deformation ages of c. 80 Ma, i.e. 40 Ma younger than the overlying rocks from the GA unit; (ii) exhibits slightly cooler peak metamorphic conditions (c. 520–550 °C, 1.6 GPa) indicating burial along a prograde path of c. 10 °C/km (iii) does not show amphibolite-facies overprint as seen in the GA unit. After a long residence time under amphibolite-facies conditions, the amphibolitized rocks of the GA unit partly recrystallized during blueschist-facies deformation at around 80 Ma, as shown by silica-richer rims around phengite and glaucophane overgrowths around hornblende.These new results: (i) shed light on the dynamics of the deep Chilean paleo-accretionary wedge, (ii) reveal that the GA unit underwent two stages of exhumation, likely juxtaposed with the BS unit near 40 km depth, and (iii) suggest that the subduction thermal gradient on Diego de Almagro Island fluctuated between c. 10–11 °C/km and 13–14 °C/km during Cretaceous times.
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影响因子：
3.4
作者：
S. Inger;R. Cliff
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DOI：
--
发表时间：
1991
期刊：
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DOI：
--
发表时间：
2008
期刊：
影响因子：
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作者：
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Villa, I. M.;De Bievre, P.;Renne, P. R.
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DOI：
--
发表时间：
1985
期刊：
影响因子：
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作者：
Terence T. Kato
通讯作者：
Terence T. Kato