Ever since its scientific discovery, the great Nasca site of Cahuachi on the south coast of the Central Andes has captured the attention of archaeologists, art historians, and the general public. ...Until Helaine Silverman's fieldwork, however, ancient Nasca culture was seen as an archaeological construct devoid of societal context. Silverman's long-term, multistage research as published in this volume reconstructs Nasca society and contextualizes the traces of this brilliant civilization (ca. 200 B.C.-A.D. 600).
Silverman shows that Cahuachi was much larger and more complex than portrayed in the current literature but that, surprisingly, it was not a densely populated city. Rather, Cahuachi was a grand ceremonial center whose population, size, density, and composition changed to accommodate a ritual and political calendar. Silverman meticulously presents and interprets an abundance of current data on the physical complexities, burials, and artifacts of this prominent site; in addition, she synthesizes the history of previous fieldwork at Cahuachi and introduces a corrected map and a new chronological chart for the Rio Grande de Nazca drainage system.
On the basis of empirical field data, ethnographic analogy, and settlement pattern analysis, Silverman constructs an Andean model of Nasca culture that is crucial to understanding the development of complex society in the Central Andes. Written in a clear and concise style and generously illustrated, this first synthesis of the published data about the ancient Nasca world will appeal to all archaeologists, art historians, urban anthropologists, and historians of ancient civilizations.
Both the Caribbean and Nazca plates subduct beneath northwestern South America. The configuration of the two subducted slabs and the nature of any interaction between them has long been a matter of ...debate. Based on the location of intermediate-depth seismicity and active and extinct volcanism, as well as on seismic imaging, several different tectonic scenarios have been proposed. In this paper, we use teleseismic data recorded by the Colombian National Network and the temporary CARMA array in Venezuela and Colombia to produce a finite-frequency tomography model for the region. Our results show several distinct subduction segments. Through synthetic tests, we show that our results require a zone of overlap between Nazca and Caribbean subduction north of the “Caldas Tear” as has been proposed by previous studies. Additionally, we find that the Bucaramanga Nest occurs within the Caribbean Plate and coincides with bending of the slab in two planes, where both the strike and the dip of the slab change. We infer that elevated stresses are an important factor in producing the very high rates of seismicity in the nest.
•Teleseismic tomography illuminates the geometry of subduction in NW South America.•There is a zone of overlap between Caribbean and Nazca subduction.•The offset at the Caldas Tear corresponds to seismicity in two different slabs.•The Bucaramanga Nest occurs within the Caribbean Plate.
This study analyzes up‐to‐date gravity data in the Galapagos triple junction region to understand crustal structure and melt distribution beneath the propagating Cocos‐Nazca spreading center (CNSC). ...Application of a standard thermal model to the mantle Bouguer gravity anomaly (MBA) does not appear to result in a realistic crustal thickness in this region. The cross‐CNSC MBA profiles flatten and axial values increase from east toward the western end of the CNSC. A simple smoothing filter applied to the standard thermal model with different filter widths can explain the progressive flattening of the MBA and is interpreted as different distribution widths (concentrations) of partial melt in the mantle. The east‐west residual MBA gradient along the CNSC is similar to the east flank of the East Pacific Rise (EPR), suggesting that the along‐CNSC gradient could partly reflect the shallow mantle properties associated with the EPR.
Plain Language Summary
This study investigates changes in crustal thickness and shallow mantle properties beneath the westward propagating Cocos‐Nazca spreading center (CNSC) by analyzing shipboard gravity data combined with satellite gravity data in the Galapagos triple junction region. By assuming a general 1‐D plate cooling model, we correct the age‐induced thermal effect of the lithosphere with a standard thermal model, which suggest thinner crust near the western tip of the CNSC increasing in thickness toward the east. However, results also indicate that the crust continues to thicken from the CNSC axis to the north and south edges of the gore, which does not seem realistic. Instead, these gravity signals most likely reflect properties within the shallow mantle, specifically a eastward decrease in the width (and hence increase in concentration) of melt within the shallow mantle beneath the CNSC. The residual gravity gradient along the CNSC axis is similar to that on the east flank of the East Pacific Rise (EPR), suggesting that the CNSC axis gravity gradient could in part reflect variation in the mantle density beneath the EPR.
Key Points
Shipboard and satellite gravity data were used to explore the crustal structure in the Galapagos triple junction region
The gravity‐derived crustal thickness with a standard thermal model does not appear to be realistic in this region
A simple smoothing filter applied to the standard thermal model could explain gravity variation along the Cocos‐Nazca spreading center
Nasca society arose on the south coast of Peru 2000 years ago and evolved over the course of the next 700 years. This text examines the range of sites occupied by the people responsible for some of ...the most exquisite art and ingenious hydraulic engineering of the pre-Columbian world.
•Peru hosts a 1300 km long flat slab region and active aseismic ridge subduction.•We examine the role of flat slab versus ridge subduction in inducing exhumation.•Thermochronology/geomorphology show ...elevated exhumation in areas of ridge passage.•The subducting ridge induces transient uplift & exhumation in the overriding plate.•Our findings reconcile paleoflat slab regions with corridors of focused exhumation.
Subduction of aseismic ridges and flat slab subduction are important processes that punctuate Cordilleran orogenesis and may enhance exhumation and rock uplift in the overriding plate. Distinguishing between the two drivers is often challenging, as many modern flat slabs spatially coincide with subducting buoyant ridges. The Peruvian flat slab is the largest region of active flat slab subduction on Earth, spanning over 1300 km of the subducting Nazca plate along the western margin of South America. The flat slab is associated with two seafloor ridges: the Nazca Ridge at the southern terminus and the fully subducted Inca Plateau in the north. These aseismic ridges are spatially confined with respect to the flat slab, allowing assessment of the relative roles of aseismic ridge interactions and flat slab subduction in driving upper plate exhumation. We present: (1) a regional compilation of geochronologic ages of Andean igneous rocks, which track the spatio-temporal evolution of Neogene magmatic arc cessation and hence slab flattening; (2) calculated geomorphic indices, which document landscape perturbations and climatic or lithologic changes, (3) a summary of erosion rates from river catchments on the western Andean slope, and; (4) a regional synthesis of thermochronologic ages that reflect the timing and magnitude of upper crustal cooling.
Thermochronometric cooling ages systematically track the progressive passage of the Nazca Ridge, suggesting that the buoyant ridge focused exhumation in the overriding plate. Geomorphic indices demonstrate enhanced topography and steeper channels closer to the position of the subducted ridge. The spatial progression of basement block uplifts in Peru also coincides with the timing of ridge passage. In hinterland regions, >2 km of exhumation occurred since ca. 15 Ma above the Peruvian flat slab. For individual locations within the orogen, active rock uplift declines after ridge passage, suggesting that increased coupling is not maintained across the entirety of the flat slab. We argue that above broad zones of flat slab subduction, focused areas of aseismic ridge subduction concentrate upper-plate exhumation and uplift. These observations may be relevant to other flat slab systems, which exhibit a broad zone of arc shutoff with corridors of focused exhumation.
Ocean-continental subduction zones are commonly associated with compressional stress fields, which ultimately result in regional uplift of the overriding plate. This has particularly been inferred by ...most studies for the western margin of the Peruvian Andes. However, local geological observations have contested this idea. Here, we present a review of existing local and international literature supplemented by new structural and geomorphic observations that suggest that nearly the entire central (15° to 11° S latitude) and northern Peruvian forearc (11° to 6° S latitude) are under extension with a slight tendency to transtension instead of compression, and that this region has experienced a prolonged period of subsidence since the middle-late Eocene, interrupted by short pulses of uplift. In contrast, the southern Peruvian forearc (15° to 18° S latitude) has experienced (trans)tension from the middle-late Eocene until recent in combination with uplift. The central and southern Peruvian forearc that was influenced by the passage of the Nazca ridge experienced transtension and subsidence until the middle-late Miocene and alternating phases of compressional and transtensional tectonics afterwards. These new findings on the geodynamic development of the Peruvian forearc need to be considered in future reconstructions of the mechanisms at work within this subduction zone.
•Revision of relevant literature on tectonics of the Peruvian forearc•New DEM-and field-based data on lineaments and faults•Peruvian margin is largely transtensional instead of compressive.
For almost eight hundred years (100 BC–AD 650) Nasca artists modeled and painted the plants, animals, birds, and fish of their homeland on Peru’s south coast as well as numerous abstract ...anthropomorphic creatures whose form and meaning are sometimes incomprehensible today. In this first book-length treatment of Nasca ceramic iconography to appear in English, drawing upon an archive of more than eight thousand Nasca vessels from over 150 public and private collections, Donald Proulx systematically describes the major artistic motifs of this stunning polychrome pottery, interprets the major themes displayed on this pottery, and then uses these descriptions and his stimulating interpretations to analyze Nasca society. After beginning with an overview of Nasca culture and an explanation of the style and chronology of Nasca pottery, Proulx moves to the heart of his book: a detailed classification and description of the entire range of supernatural and secular themes in Nasca iconography along with a fresh and distinctive interpretation of these themes. Linking the pots and their iconography to the archaeologically known Nasca society, he ends with a thorough and accessible examination of this ancient culture viewed through the lens of ceramic iconography. Although these static images can never be fully understood, by animating their themes and meanings Proulx reconstructs the lifeways of this complex society.
Inhabited for over 5,000 years before European colonization, the site of La Tiza in Peru's Nasca Desert provides an unprecedented opportunity to examine the dynamics of ancient complex societies. ...This volume takes a long temporal perspective on La Tiza from the Preceramic through the Inca era, studying the site within the context of broader developments such as the rise of Nasca culture, subsequent conquest by the Wari Empire, collapse, abandonment, and the reformation of a new society.
Christina Conlee synthesizes data she obtained while directing a multi-year excavation at the site with data from other investigations to reconstruct the development of social complexity over time. She includes detailed descriptions of the stratigraphy and artifacts, carefully separating materials from each period. Exploring how political integration, religious practices, economics, and the environment shaped societal transformations at La Tiza, Conlee offers patterns that can be found in other areas and can be used to understand the development of other long-lasting civilizations.
Using global multiresolution topography, we estimate new transform‐fault azimuths along the Cocos‐Nazca plate boundary and show that the direction of relative plate motion is 3.3° ± 1.8° (95% ...confidence limits) clockwise of prior estimates. The new direction of Cocos‐Nazca plate motion is, moreover, 4.9° ± 2.7° (95% confidence limits) clockwise of the azimuth of the Panama transform fault. We infer that the plate east of the Panama transform fault is not the Nazca plate but instead is a microplate that we term the Malpelo plate. With the improved transform‐fault data, the nonclosure of the Nazca‐Cocos‐Pacific plate motion circuit is reduced from 15.0 mm a−1 ± 3.8 mm a−1 to 11.6 mm a−1 ± 3.8 mm a−1 (95% confidence limits). The nonclosure seems too large to be due entirely to horizontal thermal contraction of oceanic lithosphere and suggests that one or more additional plate boundaries remain to be discovered.
Key Points
Transform fault azimuths from multibeam sonar show that the direction of Cocos‐Nazca plate motion is ~3 degrees clockwise of prior estimates
The plate east of the main part of the Panama transform fault is not the Nazca plate but the Malpelo plate
Pacific‐Nazca‐Cocos plate circuit nonclosure is less than that found before but large enough that more undiscovered plate boundaries may exist
Plain Language Summary
The central tenet of plate tectonics is that the tectonic plates are rigid. In sharp conflict with this assumption is the prior result that the relative motions between the Cocos, Nazca, and Pacific tectonic plates, which lie in the Pacific Ocean basin, do not sum to zero as expected if the plates are indeed rigid. From an analysis of plate‐motion data, we show that part of the traditionally defined Nazca plate, which lies off the west coast of South America, is really a separate tectonic plate, which we refer to as the Malpelo plate. Recognition of this new tectonic plate reduces the inconsistency in the plate‐motion circuit, but a large and significant inconsistency remains. This remaining inconsistency suggests that there may be one or more plate boundaries still remaining to be discovered within these three plates.
The morphology and composition of subducted slabs in the upper mantle transition zone (400 to 700 km depth) have direct implications for the style of mantle convection. Here we investigate the ...seismic reflectivity structure at transition zone depths beneath South America by combining the arrival times and amplitudes of an updated data set of SS precursors. We observe broad regions with up to 20 km depressed 410- and 660-km discontinuities and diminished precursor amplitudes beneath the back-arc region of Nazca subduction, which are incompatible with temperature-dominated mineral phase boundary perturbations. A probabilistic inversion is applied to simultaneously determine mantle temperature and composition, and the outcomes suggest a mechanically mixed transition zone with basalt enrichment beneath the Amazon basin. This is corroborated by a novel amplitude-versus-offset inversion that measures the changes in density and shear velocity across the discontinuities. Our observations offer direct evidence for thermochemical anomalies within the mantle, which are largely associated with temporary slab stagnation. The slab-transition zone interactions suggest that the Nazca-South American convergence may represent a later-stage analog to the Pacific plate subduction in northeast Asia.
•SS precursors resolve high-resolution transition zone structures in South America.•We image a thickened transition zone with diminished amplitudes beneath Amazonia.•North-south differences exist as the Nazca slab interacts with transition zone.•A thermochemical anomaly is detected, likely enriched in basalt.•Nazca subduction may represent a later-stage analog to Pacific plate subduction.
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