Volcanic evolution of Volcán Aucanquilcha: a long-lived dacite volcano in the Central Andes of northern Chile

Volcán Aucanquilcha, northern Chile, has produced ∼37 km³ of dacite (63–66 wt% silica), mainly as lavas with ubiquitous magmatic inclusions (59–62 wt% silica) over the last ∼1 million years. A pyroclastic flow deposit related to dome collapse occurs on the western side of the edifice and a debris avalanche deposit occurs on the eastern side. The >6,000-m high edifice defines a 9-km E–W ridge and lies at the center of a cluster of more than 15 volcanoes, the Aucanquilcha Volcanic Cluster, that has been active for at least the past 11 million years. The E–W alignment of vents is nearly orthogonal to the arc axis. A majority of Volcán Aucanquilcha was constructed during the first 200,000 years of eruption, whereas the last 800,000 years have added little additional volume. The peak eruptive rate during the edifice-building phases was ∼0.16 km³/ka and the later eruptive rate was ∼0.02 km³/ka. Comparable dacite volcanoes elsewhere show a similar pattern of high volcanic productivity during the early stages and punctuated rather than continuous activity. Volcán Aucanquilcha lavas are dominated by phenocrysts of plagioclase, accompanied by two populations of amphibole, biotite, clinopyroxene, Fe–Ti oxides and (or) orthopyroxene. Accessory phases include zircon, apatite and rare quartz and sanidine. One amphibole population is pargasite and the other is hornblende. The homogeneity of dacite lava from Volcán Aucanquilcha contrasts with the heterogeneity (52–66 wt% silica) at nearby Volcán Ollagüe, which has been active over roughly the same period of time. We attribute this homogeneity at Aucanquilcha to the thermal development of the crust underneath the volcano resulting from protracted magmatism there, whereas Volcán Ollagüe lacks this magmatic legacy.     

基于激光雷达的自然资源三维动态监测现状与展望

激光雷达作为一种主动的三维遥感观测技术,在不同尺度的土地、矿产、森林、草原、湿地、水、海洋等自然资源的三维动态监测中发挥着越来越重要的作用.本文将在简要介绍激光雷达技术发展现状的基础上,重点阐述激光雷达技术在各类自然资源三维动态监测中的应用现状,同时对激光雷达在自然资源调查中的应用潜力和局限性进行综合分析,最后探讨以激...     

Structural information derived from ambient noise tomography over a hydrocarbon-producing region in the Cachar fold belt,lower Assam,northeast India

Ambient noise tomography is a powerful tool that has found increasing application in reservoir analysis and imaging. The Cachar fold belt in lower Assam, northeast India encompasses several wells under active hydrocarbon production, along with several dry wells. To overcome the lack of active seismic data over the entire fold belt, a passive seismic study was carried out to image the concealed three-dimensional sub-surface structures. The data were recorded from February to November 2011 by a network of 65 wideband seismometers spanning an area of about 40 × 60 km². The data are crosscorrelated in the 2–5 s band, followed by phase-weighted stacking to estimate noise correlation functions with surface wave signatures. The traveltimes picked from the frequency-time analysis are utilized in a tomographic inversion for Rayleigh wave group velocities. The group velocity anomalies have a lateral resolution of ~ 3.5 × 5.5 km² and variations of up to $\pm 20\%$ for each period. The group velocities are in turn inverted for S-wave velocity distribution as a function of depth. The three-dimensional S-wave velocity tomograms reveal the tight anticlines and broad synclines, with high- and low-velocity zones corresponding to structural highs and lows, respectively. The structural interpretation is supported for the part of the region with producing wells and covered by active seismic data, wherein the post-stack time migrated seismic section shows anticlinal and synclinal features similar to those obtained from ambient noise tomography. The structures revealed by ambient noise tomography can help identify zones of interest to be targeted by active seismic surveys in the Cachar fold belt.