Unraveling crustal growth and reworking processes in complex zircons from orogenic lower-crust: The Proterozoic Putumayo Orogen of Amazonia
Unraveling crustal growth and reworking processes in complex zircons from orogenic lower-crust: The Proterozoic Putumayo Orogen of Amazonia
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DOI：
10.1016/j.precamres.2015.06.014
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发表时间：
2015-09-01
影响因子：
3.8
通讯作者：
Ruiz, Joaquin
中科院分区：
文献类型：
--
作者：
Ibanez-Mejia, Mauricio;Pullen, Alex;Ruiz, Joaquin
暴露在安第斯山脉北部的高级基底地块和邻近的普图马约前陆盆地的埋藏的基底，包含了亚马逊参与罗迪尼亚超大陆的记录。变质麻粒岩和正片麻岩在大约0.99Ga的至少一个变质幕中强烈变形，为中元古代大陆边缘的碰撞前历史提供了重要信息。本文报道了来自Garzon和Las Minas Cordilleran基底地块露头样品的新的U-Pb、Lu-Hf、Sm-ND和O同位素数据，以及在普图马约盆地基底中发现的钻芯碎片。我们探索了用双电感耦合等离子体质谱方法从造山带下地壳中同时获得复杂分带的锆石U-Pb和Lu-Yb-Hf信息的应用，并证明了尽管混合区烧蚀和热致重结晶对U-Pb体系的同位素扰动可能带来的复杂性，该方法仍可用于提取可靠的变质前信息。结合同一锆石生长域中的三角洲O-18组分和块体岩石的Nd同位素信息，我们重建了中元古代大部分时间沿亚马孙(现代)西北缘发育的长寿增生造山带的构造和地壳演化段。科迪勒地块变质岩样品中继承的锆石，其原岩结晶年龄约为1.47~1.15Ga，具有Hf-O成分，表明其源区有显著的地壳再作用，但表明随着年龄的降低，Hf-176/Hf-177有增加的趋势，这可归因于在此时间间隔内逐渐增加的放射成因成分的返老性。在加尔松地块的变质麻粒岩中发现的这一年龄范围内的碎屑锆石也遵循这一趋势，进一步支持了以前的推断，即它们的原岩是在弧形近端盆地中沉积的，几乎没有来自较老的克拉通区域的粗粒碎屑。大约1.15-1.10Ga左右开始的造山变形样式的转变，被推测与边缘弧形地体对大陆边缘的增生有关，触发了早期的角闪岩级变质事件；伴随着富饶的变质沉积单元中普遍存在的部分熔融和混合岩类的发育，从加尔松和拉斯米纳斯地块的碎屑和变质锆石的年龄趋势来看，Hf-176/Hf-177变浅证明了地壳改造的加强。沿普图马约边缘的会聚构造作用在亚马逊与罗迪尼亚超大陆核心的最后合并期间结束，可能是在0.99Ga与波罗的海的斯维孔诺威西段碰撞期间。尽管亚马逊在Rodinia中的位置和作用仍然存在争议，但新的Nd和Hf同位素数据提供了更多的证据，将这一造山段的演化与瓦哈奎亚的基底联系起来，并继续与亚马逊西南部Sunsas-Aguapei造山带发展相关的构造过程的时间和性质产生根本差异。(C)2015爱思唯尔B.V.保留所有权利。
High-grade basement massifs exposed in the northern Andes and the buried basement of the adjacent Putumayo foreland basin contain a record of Amazonia's involvement in the supercontinent Rodinia. Metasedimentary granulites and orthogneisses, strongly deformed during at least one metamorphic episode dated at ca. 0.99 Ga, provide critical information on the pre-collisional history of the Mesoproterozoic continental margin. Here, new U-Pb, Lu-Hf, Sm-Nd and O isotopic data from outcrop samples of the Garzon and Las Minas Cordilleran basement massifs as well as fragments of drill-core recovered from the Putumayo basin basement are reported. We explore the application of a dual-ICP-MS approach to obtain concurrent U-Pb and Lu-Yb-Hf information on complexly zoned zircon from orogenic lower-crust, and demonstrate its use to retrieve reliable pre-metamorphic information despite possible complexities introduced by mixed-domain ablation and isotopic disturbance of the U-Pb system by thermally induced recrystallization. In combination with delta O-18 compositions from the same zircon growth domains, and bulk-rock Nd isotope information, we reconstruct segments of the tectonic and crustal evolution of a long-lived accretionary orogen that developed along the (modern) NW margin of Amazonia during most of the Mesoproterozoic. Inherited zircons in metaigneous samples from the Cordilleran massifs, with protolith crystallization ages in the range from ca. 1.47 to 1.15 Ga, have Hf-O compositions that indicate significant crustal reworking in their source region, but denote a trend of increasing Hf-176/Hf-177 with decreasing age that can be attributed to rejuvenation by progressive addition of radiogenic components during this time interval. Detrital zircons within this same age range found in metasedimentary granulites of the Garzon massif also follow this trend, further supporting previous inferences that their protoliths were deposited in arc-proximal basins with little to no coarse-grained detritus delivered from an older cratonic domain. A shift in orogenic deformation style starting at similar to 1.15-1.10 Ga, inferred to be associated with the accretion of fringing-arc terranes against the continental margin, triggered an early amphibolite-grade metamorphic episode; this was accompanied by pervasive partial melting and migmatite development in fertile metasedimentary units and is interpreted to be responsible for enhanced crustal reworking evidenced from the shallowing of Hf-176/Hf-177 vs. age trends in detrital and metamorphic zircons from the Garzon and Las Minas massifs. Convergent tectonism along the Putumayo margin came to an end during the final incorporation of Amazonia to the core of the Rodinia supercontinent, possibly during collision against the Sveconorwegian segment of Baltica at 0.99 Ga. Although the position and role of Amazonia within Rodinia remains controversial, the new Nd and Hf isotope data provide additional evidence to link the evolution of this orogenic segment with the basement of Oaxaquia, as well as continue to draw fundamental differences with the timing and nature of the tectonic processes associated with the development of the Sunsas-Aguapei Orogen of SW Amazonia. (C) 2015 Elsevier B.V. All rights reserved.