40Ar/39Ar chronostratigraphy of Altiplano-Puna volcanic complex ignimbrites reveals the development of a major magmatic province
40Ar/39Ar chronostratigraphy of Altiplano-Puna volcanic complex ignimbrites reveals the development of a major magmatic province
复制标题
DOI：
10.1130/b30280.1
复制
发表时间：
2011-05-01
影响因子：
4.9
通讯作者：
Ort, Michael H.
中科院分区：
文献类型：
--
作者：
Salisbury, Morgan J.;Jicha, Brian R.;Ort, Michael H.
玻利维亚西南部的利佩兹地区是一个主要的新近纪熔结凝灰岩耀斑的所在地，但它是安第斯山脉中部的阿尔蒂普拉诺-普纳火山复合体中研究最少的部分。最近的绘图和激光熔融40 Ar/39 Ar测年的透长石和黑云母从56个地点，再加上古地磁数据，完善的时间和量的熔结凝灰岩侵位在玻利维亚和北方智利揭示，单调的中间火山活动是惊人的，在整个复杂的情节。新的研究结果揭示了位于玻利维亚的两个大型多循环破火山口复合体--帕托大破火山口和瓜查破火山口的喷发历史。这两个破火山口，与Vilama和La Pacana破火山口复合体和较小的熔结凝灰岩盾一起，是大约1000万年期间产生熔结凝灰岩的喷发的主要来源。阿尔蒂普拉诺-普纳火山复合体的历史。最古老的熔结凝灰岩在11 ~ 10 Ma之间喷发，代表了分布在整个火山杂岩中的相对较小的岩浆体积（约数百km（3））。第一个主要脉冲分别出现在8.41 Ma和8.33 Ma的Vilama和Sifon熔结凝灰岩。在脉冲1期间，至少有2400 km（3）的英安质岩浆喷发超过0.08百万年。脉冲2涉及三个主要破火山口的几乎同时喷发，产生了5.60 Ma的Pujsa、5.65 Ma的Guacha和5.45 Ma的Chuhuilla熔结凝灰岩，总的最小岩浆体积为3000 km（3）。脉冲3是最大的，在0.1百万年的时间里产生了至少3100 km（3）的岩浆。4.09 Ma的Puripicar、4.00 Ma的Chaxas和3.96 Ma的Atana熔结凝灰岩喷发。在第三次脉冲之后，又发生了两次火山爆发指数（VEI）为8的喷发，产生了3.49 Ma的塔拉（800 km（3）致密岩石当量[DRE]）和2.89 Ma的大帕托（1500 km（3）DRE）熔结凝灰岩。除了这些与大破火山口有关的喷发，新的年龄测定完善了两个鲜为人知的熔结凝灰岩盾，5.23马Alota和1.98马拉古纳科罗拉多中心的时间。此外，40 Ar/39 Ar年龄测定的13个熔结凝灰岩从北方智利以前的K-Ar法提高了整体的时间分辨率高原-普纳火山杂岩的发展。连同更新的体积估计，新的年龄测定表明，一个明显的开始高原-普纳火山复杂的熔结凝灰岩火山活动与适度的输出率，一个情节的中期阶段，最高的喷发率，其次是在火山输出下降。个别破火山口复合体的周期性和火山场作为一个整体的时空格局是一致的，增量建设的岩体，以及复合Cordillennium岩基。
The Lipez region of southwest Bolivia is the locus of a major Neogene ignimbrite flareup, and yet it is the least studied portion of the Altiplano-Puna volcanic complex of the Central Andes. Recent mapping and laserfusion 40Ar/39Ar dating of sanidine and biotite from 56 locations, coupled with paleomagnetic data, refine the timing and volumes of ignimbrite emplacement in Bolivia and northern Chile to reveal that monotonous intermediate volcanism was prodigious and episodic throughout the complex. The new results unravel the eruptive history of the Pastos Grandes and Guacha calderas, two large multicyclic caldera complexes located in Bolivia. These two calderas, together with the Vilama and La Pacana caldera complexes and smaller ignimbrite shields, were the dominant sources of the ignimbrite-producing eruptions during the similar to 10 m.y. history of the Altiplano-Puna volcanic complex. The oldest ignimbrites erupted between 11 and 10 Ma represent relatively small volumes (approximately hundreds of km(3)) of magma from sources distributed throughout the volcanic complex. The first major pulse was manifest at 8.41 Ma and 8.33 Ma as the Vilama and Sifon ignimbrites, respectively. During pulse 1, at least 2400 km(3) of dacitic magma was erupted over 0.08 m.y. Pulse 2 involved near-coincident eruptions from three of the major calderas resulting in the 5.60 Ma Pujsa, 5.65 Ma Guacha, and 5.45 Ma Chuhuilla ignimbrites, for a total minimum volume of 3000 km(3) of magma. Pulse 3, the largest, produced at least 3100 km(3) of magma during a 0.1 m.y. period centered at 4 Ma, with the eruption of the 4.09 Ma Puripicar, 4.00 Ma Chaxas, and 3.96 Ma Atana ignimbrites. This third pulse was followed by two more volcanic explosivity index (VEI) 8 eruptions, producing the 3.49 Ma Tara (800 km(3) dense rock equivalent [DRE]) and 2.89 Ma Pastos Grandes (1500 km(3) DRE) ignimbrites. In addition to these large caldera-related eruptions, new age determinations refine the timing of two little-known ignimbrite shields, the 5.23 Ma Alota and 1.98 Ma Laguna Colorada centers. Moreover, 40Ar/39Ar age determinations of 13 ignimbrites from northern Chile previously dated by the K-Ar method improve the overall temporal resolution of Altiplano-Puna volcanic complex development. Together with the updated volume estimates, the new age determinations demonstrate a distinct onset of Altiplano-Puna volcanic complex ignimbrite volcanism with modest output rates, an episodic middle phase with the highest eruption rates, followed by a decline in volcanic output. The cyclic nature of individual caldera complexes and the spatiotemporal pattern of the volcanic field as a whole are consistent with both incremental construction of plutons as well as a composite Cordilleran batholith.