75°

50°

25°

75°

25°

–25°

0°

50°

0°

270° 300° 330° 0° 30° 60° 90°

–25°

–50° –50°

–75° –75°

V–1

V–20 V–21 V–31

V–43

V–62

V–32

V–30

V–29

V–18

V–17

V–19

V–7

V–42 V–33

V–9

V–54 V–45

V–8

V–55 V–44

V–2

V–61 V–56

V–6 V–3

V–60 V–57

V–10

V–53 V–46

V–22

V–41 V–34

U.S. Department of the Interior

U.S. Geological Survey

2013

Prepared for the National Aeronautics and Space Administration

Geologic Map of the Lada Terra Quadrangle (V–56), Venus

By P. Senthil Kumar and James W. Head

Pamplet to accompany

Scientific Investigations Map 3249

Contents

Introduction.....................................................................................................................................................1

Magellan SAR Data and Analysis ...............................................................................................................1

General Geology.............................................................................................................................................2

Map Units........................................................................................................................................................3

Heavily Deformed Terrain Material....................................................................................................3

Tessera Terrain Material ............................................................................................................3

Tessera-like Terrain Material.....................................................................................................3

Densely Lineated Terrain Material............................................................................................4

Regional Plains Material .....................................................................................................................4

Wrinkle Ridged Plains Material.................................................................................................4

Regional Plains Material ............................................................................................................4

Volcanogenic Plains Material.............................................................................................................4

Shield Plains Material.................................................................................................................4

Intra-tessera Basin Plains Material .........................................................................................5

Lobate Plains Material................................................................................................................5

Impact Crater Material ........................................................................................................................5

Structures........................................................................................................................................................5

Primary Structures................................................................................................................................5

Shields ...........................................................................................................................................5

Channels........................................................................................................................................5

Lobate Flow Fronts.......................................................................................................................6

Impact Crater Rim........................................................................................................................6

Secondary Structures..........................................................................................................................6

Lineaments....................................................................................................................................6

Fractures .......................................................................................................................................6

Faults..............................................................................................................................................6

Grabens .........................................................................................................................................6

Linear Ridges................................................................................................................................6

Wrinkle Ridges .............................................................................................................................6

Stratigraphic Relations .................................................................................................................................7

Geologic History.............................................................................................................................................8

Summary..........................................................................................................................................................8

Acknowledgments ........................................................................................................................................9

References Cited............................................................................................................................................9

Table

1. Morphology of impact craters in Lada Terra quadrangle (V–56), Venus ....................................11

iii

1

By P. Senthil Kumar1,2 and James W. Head2

Introduction

Geologic mapping provides fundamental information on 

the distribution of material units and structural geologic features 

on a planetary surface and establishes age relations among these 

units. By understanding the petrogenesis of mapped material 

units and the tectonic history from the deformational structures, 

the geologic map provides significant insight into the processes 

of crustal evolution. On Earth, geologists prepare geologic maps 

in various spatial scales by carrying out field geologic analyses, 

whereas orbiter images are extensively used in preparing global 

or local geologic maps of other planetary surfaces. On Venus, 

although previous missions such as Venera 15/16 and Arecibo 

Earth-based radar observations showed a variety of surface geologic features, the Magellan mission provided a global coverage 

of radar images (~98%), and these images were used in preparing a global geologic map (Ivanov and Head, 2011). 

This publication provides a geological map of Lada Terra 

quadrangle (V–56), a portion of the southern hemisphere of 

Venus that extends from lat 50° S. to 70° S. and from long 0° E. 

to 60° E. V–56 is bordered by Kaiwan Fluctus (V–44) (Bridges 

and McGill, 2002) and Agnesi (V–45) quadrangles in the 

north and by Mylitta Fluctus (V–61) (Ivanov and Head, 2006), 

Fredegonde (V–57) (Ivanov and Head, 2010a), and Hurston 

(V–62) quadrangles in the west, east, and south, respectively. 

The geological map of V–56 quadrangle reveals evidence 

for tectonic, volcanic, and impact processes in Lada Terra in 

the form of tesserae, regional extensional belts, coronae, and 

volcanic plains. In addition, the map also shows relative age 

relations such as overlapping or cross-cutting relations between 

the mapped geologic units. The geology observed within this 

quadrangle addresses (1) how coronae evolved in association 

with regional extensional belts and (2) how tesserae, regional 

plains, and impact craters, which are also significant geological 

units observed in Lada Terra quadrangle, were formed. 

Several previous works have addressed the formation 

mechanisms and relations observed between coronae and 

regional extensional belts within Lada Terra quadrangle. One 

important previous work pertaining to Lada Terra quadrangle is 

by Baer and others (1994), who observed overlapping age relations between the coronae and extensional belts and suggested 

an inter-linked origin. The studies by Magee and Head (1994, 

1995) and Schubert and Sandwell (1995) discussed the mantle 

1

National Geophysical Research Institute, Council of Scientific and Industrial 

Research 

2

Department of Geological Sciences, Brown University

processes relating to the convergence and divergence in Lavinia 

Planitia, Lada Terra, and Derceto Corona. Lopez and others 

(1999) found similarities between the coronae-extensional 

belts in Lada Terra and the East African rift system on Earth. 

Stofan and others (1992) studied the morpho-structural characteristics of some of the coronae (Quetzalpetlatl, Eithinoha, 

and Sarpanitum) in Lada Terra and suggested the mechanism 

of coronae formation related to the mantle plumes. Kratter and 

others (2007) studied the Arecibo radar images of Quetzalpetlatl 

Corona and surrounding regions and identified several pahohae 

lava flows emanating from Quetzalpetlatl Corona and a few new 

impact craters. Based on a detailed geological mapping and topographic analysis, Ivanov and Head (2010b) showed that Lada 

Terra rise and Quetzalpetlatl Corona form a region of long-lived 

mantle upwelling and recent volcanic activity. Although the 

above studies provided many insights to the material units and 

structural features and the attendant geologic processes in Lada 

Terra, this publication provides a geologic map of the entire 

Lada Terra (V–56) quadrangle and reconstructs the geologic 

history within the quadrangle.

Magellan SAR Data and Analysis

The orbiting phase of the Magellan mission extended from 

August 10, 1990, to October 12, 1994. During mission cycles 1, 

2, and 3 from September 1990 to September 1992, the spacecraft collected synthetic aperture radar (SAR) images, passive 

microwave thermal emissions, and measurements of backscatter 

power at small angle of incidence, covering ~98 percent of the 

surface of Venus. During mission cycles 4, 5, and 6 from September 1992 and October 1994, high-resolution gravity measurements were made. The SAR instrument operated at a wavelength of 12.6 cm (S-band) with horizontal transmit/receive 

polarization that allowed cloud penetration and discrimination 

of wavelength-scale surface roughness. The catalogue of SAR 

image data and image interpretation methods are provided by 

Wall and others (1995) and Ford and others (1993), respectively, 

in addition to compilations made by various other researchers.

Geological mapping of Venus has been undertaken at a 

wide variety of scales and by a large number of individuals, 

including broad terrain maps derived from Earth-based radar 

images (Campbell and others, 1991), classifications and geologic mapping based on Pioneer-Venus topography (Masursky 

and others, 1980) and imaging (Senske, 1990), comprehensive 

geological mapping based on the northern area covered by 

Geologic Map of the Lada Terra Quadrangle (V–56), Venus
2

Venera-15/16 radar and altimetry data (Barsukov and others, 1986), specific thematic areas using all available data sets 

(Ivanov and Head, 2010b), generalized global terrain maps 

compiled using Magellan data (Tanaka and others, 1997; Ivanov 

and Head, 2011), and specific areas (quadrangles) mapped at 

specific scales. An example of the latter is the currently ongoing 

NASA program administered by the U.S. Geological Survey 

that involves many individual geologists and their co-workers. 

These NASA/USGS mapping efforts have resulted in publication of more than half of 62 1:5,000,000-scale quadrangles that 

cover about 45 percent of the surface of Venus. These maps 

provide valuable documentation of the local to regional geological settings and processes. Although there are general guidelines 

and conventions for geological mapping (Tanaka, 1994), the 

goal of compilation of these individual maps is to study specific 

geologic problems and processes. Therefore, individual maps 

often employ different guidelines and conventions in terms 

of the details of unit definition and mapping. For example, a 

worker mapping a quadrangle to study the volcanic history of a 

region might map individual lava flows emanating from different volcanic sources separately (McGill, 2004), while a worker 

assessing rift zones and tectonics problems might lump these 

flows into a larger unit of volcanic origin (Basilevsky, 2008). 

Although this approach produces valuable results for individual 

areas, it often makes it difficult to compare these individual 

maps in adjacent areas and across the planet in order to assess 

the general global geological evolution of Venus.

We used 250 m/pixel Magellan SAR images to prepare the 

geologic map at a scale of 1:5,000,000. Wherever necessary, 

full-resolution (75 m/pixel) images were used to observe finer 

details. We used ArcGIS 10.0 software for carrying out geologic 

mapping, following the methods of geologic unit definition and 

characterization of planetary surfaces (Head and others, 1978; 

Wilhelms, 1990), suitably modified for the Magellan SAR 

image data (Tanaka, 1994; Basilevsky and Head, 2000; Ivanov 

and Head, 2001; Hansen, 2000). For the Magellan data, emissivity and radar reflectivity are used to characterize the geologic 

units based on geomorphology. Although geomorphologic 

maps do not necessarily represent stratigraphic rock units, they 

are very useful in determining the local, regional, and global 

distribution of features (such as ridge belts, scarps, and lobes) 

defining morphostratigraphic material units. Primary structures 

formed by material emplacement processes, such as volcanism 

and impact cratering, are also analyzed to infer the attendant 

geologic processes. Well-known primary structures include 

channels, shields, and lobate flow fronts. The SAR images 

are also useful to map the various secondary structures on the 

surface of Venus (Farr, 1993; Stofan and others, 1993; Solomon 

and others, 1992; Tanaka, 1994). Observed secondary structures 

include wrinkle ridges, folds, fractures, and shear zones or fault 

systems. These features are manifested in SAR images as lineaments and surfaces with radar brightness or darkness and tonal 

contrast that are used to characterize the form, position, and 

orientation of these structures, as well as to establish the relative 

age relations between them (such as cross-cutting relations).

General Geology

Geological units in V–56 quadrangle were products 

of tectonics, volcanism, and impact cratering showing their 

characteristic landforms. The surface is characterized by the 

lowlands and highlands; the boundary between these two lies at 

~1.5 km above the mean planetary radius (fig. 1). The highlands are characterized by heavily deformed landforms such as 

tesserae, coronae, and large-scale extensional belts, suggesting 

that crustal deformation played an important role in the regional 

highland formation. The lowlands, in general, are plains characterized by lava-flow materials that traveled for several hundreds 

of kilometers. The slopes of the highlands enabled the lava 

flows to travel for longer distances and pond over the regional 

to local depressions in the lowlands. Aibarchin Planitia and 

Mugazo Planitia are typical examples of lowlands that are filled 

with volcanic materials.

Lada Terra is a broad region of midlands (0–2 km above 

mean planetary radius, MPR) at high southern latitudes (lat 

60°–80° S.; long 300°–90° E.). Its western portion is dominated 

by a large (~2,000 km across) dome-shaped structure, a topographic rise whose summit reaches elevations 2.5–3 km above 

MPR. The vast lowland of Lavinia Planitia (1–1.5 km below 

MPR) surrounds the western portion of Lada Terra. Before 

the Magellan mission, the regional geology of Lada Terra was 

known on the basis of topographic data acquired by the PioneerVenus altimeter (Masursky and others, 1980; Pettengill and others, 1980) and radar images received by the Arecibo telescope 

(Campbell and others, 1991; Senske and others, 1991). Arecibo 

radar images and early Magellan results showed that Lada Terra 

is the site of numerous coronae including one of the largest 

coronae on Venus, Quetzalpetlatl Corona (Stofan and others, 

1992), interconnected by belts of fractures and grabens (Baer 

and others, 1994; Magee and Head, 1995). One of these belts, 

Kalaipahoa Linea in V–61, extends from the east to the west 

along a regional break in slope in the marginal zone between 

Lada Terra and Lavinia Planitia. In contrast to Lada Terra, 

there are no coronae within Lavinia Planitia and the floor of 

the lowland is populated by complex patterns of deformational 

features in the form of ridge belts and grooves (see Ivanov and 

Head, 2006). Among the most spectacular morphologic features 

of Lada Terra are large complexes of lava flows emanating from 

coronae.

The most prominent tectonic features of V–56 are the 

traverses of four large-scale extensional belts (fig. 2) (Baer and 

others, 1994). These include the (1) north-northwest-trending, 

6,000-km-long and 50–200-km-wide Alpha Regio-Lada Terra 

belt (Alpha-Lada belt), (2) north-northeast-trending, 2,000-kmlong and 300-km-wide Derceto Corona-Quetzalpetlatl Corona 

belt (Derceto-Quetzalpetlatl belt), (3) north-south-trending 

Dyamenyuo Corona belt (Dyamenyuo belt), and (4) east-northeast-trending Geyaguga Chasma belt (Geyaguga belt). The latter two extensional belts form branches of the Alpha-Lada belt. 

Corona structures are also very abundant in this quadrangle and 

they occur preferentially along the extensional belts (fig. 2). 
3

Lineaments are abundant in V–56 and are principally secondary deformation features such as fractures, faults, grabens, 

linear ridges, and wrinkle ridges. According to the classification of Stofan and others (1992), V–56 contains three concentric coronae (Quetzalpetlatl, Eithinoha, and Sarpantium), one 

double-ringed corona (Otygen), seven asymmetric coronae (for 

example, Derceto, Demvamvit, Toyo-uke, Dyamenyuo, and 

Ekhe-Burkhan), and one astra-like structure (Loo-Wit Mons). 

Radial and concentric fractures, faults, and grabens define the 

coronae. The large extensional belts are composed of fractures, 

grabens, and strike-slip zones. The areas between the largescale extensional belts are occupied by other geological units, 

such as tessera terrain materials, tessera-like terrain materials, 

densely lineated terrain materials, regional and wrinkle ridged 

plains materials, shield plains materials, intra-tessera basin 

materials, lobate plains materials, and impact crater materials. 

Map Units

Material units and primary and secondary structures are 

described on the basis of their radar brightness, roughness, 

morphology, and stratigraphic relations. The material units are 

shown as polygons filled with distinct color for each individual 

unit, whereas the structures are shown as points for volcanic 

features (for example, shields) and lines for channels and deformational structures, such as grabens, fractures, and faults. The 

material units are divided into three groups: heavily deformed 

terrain material, regional plains material, and volcanogenic 

plains material. The first group, the heavily deformed terrain 

material, is categorized based on unique deformational structures observed exclusively within these units. They constitute 

about 17 percent of V–56, including tessera terrain material, 

tessera-like terrain material, and densely lineated terrain material. The second group, the regional plains material, is characterized by relatively smooth radar surfaces, which host a variety of 

younger deformational structural features that also traverse the 

adjoining material units. Two types of plains characterize these 

geologic units (the regional plains materials and the wrinkleridged plains materials) and both constitute about 35 percent of 

V–56. The third group, volcanogenic plains material, is characterized by primary volcanic structures, for example, shields, 

channels, and lobate features. These units are also characterized 

by smooth surfaces that vary in small-scale surface roughness to yield a range of radar brightness with well-defined unit 

boundaries. They are classified into the shield plains materials, 

intra-tessera basin plains materials, and lobate plains materials; 

they are the most abundant material units in V–56, covering 

48 percent of the surface area. V–56 contains 15 impact craters 

(table 1). Impact craters occupy only a fraction of the total surface in V–56 (~0.5%). 

Heavily Deformed Terrain Material

Tessera Terrain Material

Tessera terrain materials (unit tt, fig. 3) are radar bright and 

high surface-roughness areas characterized by multiple orientations of lineaments (Barsukov and others, 1985; Basilevsky and 

others, 1986; Bindschadler and Head, 1991; Solomon and others, 1992; Hansen and Willis, 1998; Ivanov and Head, 1996). In 

V–56, at least two sets of lineaments are abundant: north-northwest-and east-southeast-oriented lineaments. Tightly spaced 

ridges and troughs generally characterize the tessera. The ridges 

(folds) and troughs (grabens) are the products of compression 

and extension, respectively. Cocomama Tessera and Lhamo 

Tessera are among the largest exposures of the tessera terrain 

materials in V–56. Tessera terrain materials occupy about 570.6 

x 103 km2 (8.9% of V–56 map area).

Tessera terrain material was discovered during the Venera 

15/16 mission (Barsukov and others, 1985) and represents one 

of the most tectonically deformed types of terrain on Venus. 

Both the material and tectonic structures play an important role 

in the definition of tessera and tessera terrain material representing a classic example for the structural-material terrain unit. 

The material that forms the bulk of tessera is heavily deformed 

tectonically and the surface of the unit is characterized by at 

least two sets of intersecting structures, but usually several sets 

are visible. Tectonic features of both contractional (ridges) and 

extensional (grabens and fractures) origin occur at different 

scales, from a few hundred meters to several tens of kilometers 

in width and to several hundreds of kilometers in length. A 

diagnostic characteristic of tessera is its high radar-backscatter 

cross section, which is noticeably higher than that of the surroundings. The surface is rough at all scales, compared to most 

other units, and usually stands topographically higher than the 

surroundings. The tessera terrain material occupies about 7.3 

percent of the mapped area (Ivanov and Head, 2011).

Tessera-like Terrain Material

The tessera-like terrain material (unit tlt, fig. 4) is also 

known as tessera transitional terrain material (Ivanov and Head, 

2001; Basilevsky, 2008). It is radar bright and has high surfaceroughness areas characterized by multiple orientations of 

lineaments but with wider spacing between the lineaments. The 

lineaments are north-northeast- to northeast-oriented ridges and 

troughs, which are cut by east-southeast- to northwest-oriented 

troughs. The spacing of these structures is greater than the structures in the tessera. In the northeastern part of the quadrangle, 

unit tlt is abundant. The tessera-like terrain material occupies 

about 315.2 x 103 km2 (4.9% of V–56 map area). Unit tlt is also 
4

found elsewhere on Venus. Ivanov and Head (2001) showed 

some examples of tessera-like terrain materials along the 30° N. 

global geo-traverse, and Basilevsky (2008) found these materials in Beta Regio (V–17) quadrangle.

Densely Lineated Terrain Material

The densely lineated terrain material (unit tdl, fig. 5) forms 

radar-bright areas with moderate surface roughness characterized by tightly spaced parallel lineaments (Basilevsky and 

Head, 2000; Ivanov and Head, 2001; Basilevsky, 2008). The 

characteristic pattern of deformation plays a very important 

role in the definition of densely lineated plains and, thus, this 

unit represents a typical structural-material unit. The lineaments form a near-parallel arrangement of ridges, grooves, and 

troughs. In most places, these units are also spatially associated 

with the tessera and tessera-like terrain materials, except for a 

few isolated exposures. The lineaments that characterize the 

tdl unit are also common in the adjoining tessera and tesseralike terrain materials. They occupy a small area of the global 

map, about 7.2 x 106 km2 or 1.6 percent of the global map and 

are observed as slightly elevated and usually small (tens of 

kilometers across) occurrences (Ivanov and Head, 2011). In the 

majority of occurrences, the lineaments in unit tdl are packed 

so densely that they completely obscure the morphology of the 

precursor materials. Unit tdl occupies about 168.3 x 103 km2

(2.6% of the mapped area) in V–56.

Regional Plains Material

Wrinkle Ridged Plains Material

The wrinkle ridged plains material (unit pwr, fig. 6) is 

plains material containing dense concentrations of wrinkle 

ridges (McGill, 1993; Bilotti and Suppe, 1999). Large exposures of unit pwr are seen in Aibarchin Planitia, Mugazo Planitia, and Kaiwan Fluctus regions. The wrinkle ridges, in general, 

occur only in the plains material. Unit pwr constitutes about 

365.5 x 103 km2 or 5.7 percent of V–56.

Regional Plains Material

The regional plains material (unit pr, fig. 7) occurs extensively in V–56 and is characterized by a smooth surface on 

radar images with varying radar brightness. Regional plains 

are defined by the characteristic morphology of their material 

and, thus, belong to the class of true material units. The unit is 

interpreted to be regional plains of volcanic origin. Volcanic 

edifices and sources of the plains are commonly not obvious 

at the resolution of Magellan data. Regional plains represent 

the most widespread material unit in V–56, occupying about 

1,817.9 x 103 km2 or 28.3 percent of V–56 compared to 40.3 

percent of the map area globally (Ivanov and Head, 2011), and 

are composed of morphologically smooth, homogeneous plains 

materials of intermediate-dark to intermediate-bright radar 

backscatter. Materials of the plains are deformed by narrow, 

linear to anastomosing fractures and faults of the large-scale 

extensional belts and coronae. In the areas of densely occurring 

later deformational structures, the nature of original surface 

properties of the regional plains material has been substantially 

modified. 

Volcanogenic Plains Material

Shield Plains Material

Shield plains material (units psh, pshc; figs. 5, 8) is 

characterized by smooth surfaces in radar images with clusters 

of small shields (1–20 km in diameter); the shields are circular 

volcanic features with illumination on the radar-looking slopes. 

The summit portion of many of the shields contains pits. Each 

shield is mapped as an individual structure (fig. 9), and shield 

plains are mapped as a unit when lava flows originate and 

surround the shields. Although shields are present in almost 

all material units, they are also abundant in coronae and are 

mapped as the shield plains corona material, unit pshc (fig. 8). 

Some of the shield plains in the densely lineated plains appear 

to be older and are mapped as shield plains material, unit psh

(fig. 5). 

Shield plains material is also one of the most dominant 

material units of Venus (for example, Basilevsky and Head, 

1988, 1995; Head and others, 1992; Crumpler and Aubele, 

2000; Ivanov and Head, 2001; Hansen, 2009). It covers a 

significant portion of the surface of Venus, about 79.3 x 106 km2

or 17.4 percent of the global map (Ivanov and Head, 2011), and 

typically occurs as more or less equidimensional patches several 

tens to hundreds of kilometers across. In many cases, the shields 

occur close to each other and form groups of structures. The 

surface of both the shields and the plains surrounding them is 

morphologically smooth. Shield plains represent the first unit in 

the stratigraphic scheme that displays no pervasive deformation; 

unit psh is only mildly deformed by tectonic structures (wrinkle 

ridges and sparse fractures/grabens). Because of this, the priority in the definition of shield plains was given to the morphologic characteristics of their surface material and this unit thus 

represents a true material unit. 

The small shields and related plains material are not completely confined to the stratigraphic interval between the heavily 

deformed terrain units and the regional plains (for example, 

the shields occurring in the densely lineated terrain materials). 

Some groups of small shields postdate regional plains and are 

associated, spatially and temporarily, with the youngest plains 

units (for example, the psh unit in Mugazo Planitia). The shield 

plains material units (psh, pshc) have a very similar morphology everywhere on Venus and occur in all published geological 

maps of this planet (Ivanov and Head, 2011). They constitute 

about 282.9 x 103 km2 or 4.4 percent of the mapped area in 

V-56. On the other hand, unit pshc is less abundant than unit 

psh and occupies about 146.6 x 103 km2 or 2.3 percent of V–56.
5

Intra-tessera Basin Plains Material

The intra-tessera basin plains material (units itbl, itbm, 

itbu; figs. 10, 11) is radar smooth with varying degrees of 

brightness and (or) darkness that fill the isolated basins occurring inside the tessera terrain materials (Ghent and Hansen, 

1999; Hansen and others, 1999). This material is interpreted 

to be lava flows of different ages; most are derived from the 

units both outside and inside the tessera terrain. Stratigraphically these flows are classified into the intra-tessera basin plains 

lower unit material (itbl), intra-tessera basin plains middle unit 

material (itbm), and intra-tessera basin plains upper unit material (itbu), with decreasing age, respectively.

The intra-tessera basin plains material occurs in the form 

of patches within the outcrops of the tessera terrain material, which are made up of low viscosity lava flows filling the 

topographic lows in the tessera terrain. This plains material was 

recognized as “inter-tessera plains” in Pioneer Venus, Venera, 

and Magellan datasets (Bindschadler and others, 1992; Hansen 

and others, 1999). In V–56, the plains-filled basins are irregularly shaped, although some are quasi-circular, and the margins 

of the basins lack boundaries defining normal faults. Unit itbl

constitutes about 66.2 x 103 km2 or 1 percent of the mapped 

area. The middle unit (itbm) constitutes about 53.7 x 103 km2

or 0.8 percent of the mapped area. The upper unit (itbu) is more 

abundant than the lower and middle units and constitutes about 

117.7 x 103 km2 or 1.8 percent of the mapped area in V–56.

Lobate Plains Material

Lobate plains material (units pll, plm, plu; figs. 12, 13) 

show dark to bright smooth surfaces on radar images and are 

characterized by primary structures such as lobate flow fronts 

(Head and others, 1992). Occurrences of the material units of 

the lobate plains usually have morphologically smooth surfaces 

that are occasionally disturbed by a few extensional features 

related to the rift zones. The most characteristic feature of lobate 

plains is their non-uniform albedo pattern consisting of numerous bright and dark flow-like features. The flows can be as long 

as several hundred kilometers and as wide as tens of kilometers 

(fig. 12). These materials are interpreted to be lava flows and are 

mostly derived from coronae (fig. 13). Stratigraphically, these 

materials are classified into lobate plains material, lower unit 

(pll), lobate plains material, middle unit (plm), and lobate plains 

materials, upper unit (plu). 

Globally, the lobate plains make up a significant portion 

of the surface of Venus, about 37.8 x 106 km2 or 8.3 percent of 

the global map area (Ivanov and Head, 2011). In V–56, all the 

lobate plains units together make up 38.7 percent of the map 

area, which is one of the most extensive mapped units. The 

lower, middle, and upper units constitute about 276 x 103 km2

(4.3%), 1,303 x 103 km2 (20.3%), and 908.1 x 103 km2 (14.1%), 

respectively. Aibarchin Planitia and Mugazo Planitia are typical examples of lowlands that are filled with these volcanic 

materials. 

Impact Crater Material

V–56 contains 15 impact craters (table 1), of which eight 

are complex craters, while the others are simple craters. Complex crater material is composed of ejecta material (unit ce), 

rim and wall material (unit cw), floor material (unit cf), and 

central peak material (unit cp) (fig. 14). The simple craters lack 

the central peak material, while containing the ejecta (unit ce), 

wall (unit cw), and floor (unit cf) materials similar to the complex craters. Impact craters are generally the youngest geologic 

units identified. The impact crater, Dinah, is cut by faults and 

fractures of Tsects Chasma, which is an extensional belt (fig. 

15). Impact craters occupy only a fraction of the total surface 

in V–56 (29.5 x 103 km2 or 0.5%). The impact craters, Marsh 

and Flagstad, depict outflow features that originate near the rim 

crest and flow outward, inundating the ejecta deposits (fig. 14).

Structures

Primary and secondary structures within V–56 are 

described here; individual structural domains are described 

within the regional context.

Primary Structures

The primary structures form during the emplacement of the 

geologic units, and their characters may assist in defining the 

spatial limits of individual material units. The primary structures within V–56 are shields, channels, and lobate flow fronts 

with flow directions.

Shields

Shields are small (<1–15 km in diameter) circular to quasicircular features with dome, cone, shield, or flat-topped shapes 

that may or may not contain a central pit (Guest and others, 

1992; Addington, 2001) and are interpreted as small volcanic 

edifices (fig. 5). We mapped shields as two groups, one with <5 

km diameter and the other with >5 km. There are 5,058 shields 

in the <5 km category and 60 shields above 5 km diameter (fig. 

9). In V–56, the shields occur in association with the shield 

plains material.

Channels

Channels are narrow, generally about 1 km wide, steepsided, shallow at a scale of tens of meters, sinuous troughs 

morphologically similar to terrestrial fluvial channels (fig. 11), 

interpreted to form by channelized fluid flow (Baker and others, 

1992, 1997). We mapped 17 channels in V–56. The nature of 

the fluid is undefined, as is the type of erosion, whether mechanical or thermal, cutting downward from the surface or upward 

from depth (for example, Gregg and Greeley, 1993; Bussey and 

others, 1995; Lang and Hansen, 2006).
6

Lobate Flow Fronts

Lobate flow fronts are the lobate margins of discrete lava 

flows (Chapman, 1999). The boundary of the lobate plains and 

intra-tessera basin plains is defined by the lobate flow fronts, 

which are easily identified in the SAR image (fig. 12). These 

are both bright and dark, depending upon the nature of lava 

flows (either pahohoe or aa flows). Flow direction, which is not 

a primary structure but interpreted from primary structures (for 

example, channels, levees, and other flow constructs), is shown 

as an arrow pointing in the flow direction. 

Impact Crater Rim

The impact crater rim has been identified as a primary 

structure, because it formed during the emplacement of material units associated with the impact craters (fig. 14). The rim 

of a crater extends above the local surface, usually in a circular 

or elliptical pattern. The rim of a crater refers to the circular or 

elliptical ridge that raised above the pre-impact surface. In radar 

image, the rim appears in the form of a circular or elliptical 

ridge. 

Secondary Structures

Secondary structures form after emplacement of the material units (for example, the structures in the heavily deformed 

terrain materials) and record the effects of tectonic processes; 

they provide clues for the operative tectonic processes (collision, rifting, uplift). In addition, the distribution and character of 

secondary structures may also help in the delineation of material 

units (for example, the boundary of the tessera terrain materials), as well as establishing temporal relations between different 

material units.

Lineaments

Lineaments are characterized by long and linear tectonic 

features, which may be fractures or fault segments that cut 

across the underlying material units. The lineaments shown 

in V–56 are specific to the tessera terrain material unit (fig. 

3). There are 1,493 lineaments mapped in the tessera terrains 

of V–56. The lineaments appear as single straight lines or as 

double lines with a radar shadow juxtaposed to a radar-bright 

wall, indicating the presence of a trough or graben (for example, 

Head and others, 1991; Solomon and others, 1992; Grosfils and 

Head, 1994; Hansen and Willis, 1996). 

Fractures

Fractures are fine, sharply defined, continuous radar-bright 

lineaments (figs. 7, 8) that are typically observed in the lowlands and are commonly interpreted to be fractures (Squyres 

and others, 1992; Basilevsky and Head, 2000). If a fracture is 

associated with a volcanic eruptive center, it may represent the 

surface expression of a subsurface dike. About 4,698 fractures 

have been mapped in V–56, and these are largely concentrated 

along the large-scale extensional belts (fig. 2).

Faults

Faults are broad, sharply defined, continuous radar lineaments (fig. 15). The faults are principally singular scarps, 

with radar-looking scarps brightly illuminated. Faults occur in 

varying morphology, including straight, curved, and branching 

(for example, Stofen and others, 1993; Kumar, 2005). In V–56, 

about 137 faults have been mapped, and most of them are associated with the fracture belts. 

Grabens

Grabens are paired parallel dark and light lineaments that 

are separated by linear troughs (Stofan and others, 1993) (fig. 

7). Grabens are the conspicuous tectonic features in V–56; there 

are 4,021 grabens. The majority of them have been mapped 

along the large-scale extensional belts and coronae. Grabens 

are also common in other material/terrain units such as tessera, 

tessera-like terrain, and densely lineated terrains. Some grabens 

are asymmetric basins that appear similar to sigmoidal pullapart structures in strike-slip zones (fig. 16). In Hanghepiwi 

Chasma (fig. 17), the graben has a wide floor filled with lava 

flows. The boundaries of the chasma are ridges. On the west 

side, the ridges are affected by two sets of grabens: one set is 

oblique to the chasma boundary and the other is orthogonal. On 

the east side, the two sets tend to become parallel to the boundary. Around Eithinoha Corona, conjugate grabens and fractures 

are also present (fig. 13). Radially arranged grabens are also 

present in an astra-like structure, named the Loo-Wit Mons (fig. 

18). Grabens are also present in the tessera terrain but these are 

embayed by the surrounding plains material, which restricts 

their presence only to the tessera. Therefore, these are shown 

separately as tessera grabens.

Linear Ridges

Ridges have linear topographic relief with oppositely 

dipping slopes (Stofen and others, 1993). The radar-looking 

slope is illuminated and the brightness across the crest gradually changes to darkness (fig. 19). The linear ridges are straight 

to curvilinear and are often associated with the coronae, for 

example, Otygen Corona (fig. 8) and Okhin-Tengri Corona. 

However, the linear ridges have also been seen in some of the 

densely lineated terrains and in parts of the tessera-like terrains. 

A prominent linear ridge belt has been noticed in Vaidilute 

Rupes (fig. 19) and is subparallel to Hanghepiwi Chasma (fig. 

17) in the west. We mapped 834 linear ridges in V–56.

Wrinkle Ridges

Wrinkle ridges are sinuous ridges, but are less prominent 

compared to the linear ridges (McGill, 1993; Bilotti and Suppe, 

1999). These occur widely in plains in the Kaiwan Fluctus 
7

region (fig. 6), Aibarchin Planitia (fig. 12), and Mugazo Planitia. 

We mapped 450 wrinkle ridges in V–56.

Stratigraphic Relations

Contact relations of material units and secondary structures have been determined to infer the sequence of material 

emplacement and tectonic deformation. The materials that are in 

contact and not in contact have been grouped and superposition 

relations have been determined. The oldest known material units 

are the tessera terrain materials. The tightly spaced lineaments 

in the tessera (unit tt) are embayed by the surrounding plains 

materials (fig. 3). Unit tt is also in contact with unit tdl—the 

latter embays the former. Unit tt is cut by multiple orientations 

of lineaments, while unit tdl is characterized by unidirectional 

lineaments that are also present in the tessera. This suggests that 

unit tdl was emplaced after unit tt. Another material unit that 

shares some characteristics of the tessera is the tessera-like terrain material (unit tlt) in the northeastern quadrant of V–56 (fig. 

4). Units tt and tlt are widely separated and do not have contact 

relations. The presence of multiple generations of lineaments 

with an increased spacing in unit tlt would suggest either lower 

strain rates compared to those in unit tt or greater compressive 

or tensional strength of unit tlt materials. Hence, the age of 

unit tlt may be the same as unit tt or slightly younger. Unit tlt

is also in contact with unit tdl, and their relation is the same as 

that between units tt and tdl. These relations would mean that 

units tt, tlt, and tdl were emplaced during an intense tectonic 

process and that these materials were successively emplaced in 

a sequence of decreasing age. The heavily deformed materials 

also show evidence of younger tectonic deformation manifested 

in the form of chasma/chasmata belts (Chang-Xi, Sutkatyn, 

Kov-Ava, and Seo-Ne). These belts are deep, elongated, steepsided depressions (fig. 20). The chasmata belts were formed 

after the emplacement of units tt, tlt, and tdl but before the 

formation of the surrounding plains materials. 

The regional plains materials (units pwr, pr) show embayment relations with the heavily deformed terrain materials (fig. 

3) and, therefore, postdate the heavily deformed terrain material and predate the volcanogenic plains material. Contacts 

between units pr and pwr are not exposed and, therefore, their 

relations are uncertain. However, the wrinkle ridges in unit pwr

are absent in unit pr. If we assume that the wrinkle ridges in 

unit pwr were formed synchronously during a regional tectonic 

process (Basilevsky and Head, 2006), absence of wrinkle ridges 

in unit pr would indicate a younger age for unit pr. Even if the 

wrinke ridges were a product of a local process, then we would 

expect that the deformation should still affect the adjoining preexisting materials, but there is no evidence of the wrinkle ridges 

affecting unit pr near the exposures of unit pwr. 

After emplacement of the regional plains, the next generation of intense tectonic deformation began. For example, 

throughout V–56, unit pr has been affected by formation of four 

large-scale extensional belts and coronae structures (figs. 2, 7, 

8). Formation of coronae structures is also synchronous with 

the formation of large-scale extensional structures. This synchronous formation is observed through complex stratigraphic 

relations between the coronae and extensional belts. For 

example, in some places the corona structures cut across the 

regional extensional belts (fig. 21), while in other places the 

latter postdate the former (fig. 13). Sarpanitum, Eithinoha, and 

Quetzalpetlatl Coronae puncture the Derceto-Quetzalpetlatl 

belt, while the Otygen, Demvamvit, and Okhin-Tengri Coronae 

are cut by the Alpha-Lada belt. Other coronae (Dyamenyuo and 

Toyo-uke Coronae, Loo-wit and Kshumay Montes) puncture 

two other extensional belts that branch from Alpha-Lada belt, 

namely Geyaguga belt and Dyamenyuo belt (fig. 2). Clearly, the 

coronae and extensional belts were formed after the regional 

plains formation and before the volcanogenic plains material. It 

is worth mentioning here that a portion of Alpha-Lada extensional belt must have formed after the emplacement of Dinah 

impact crater (fig. 15) but before Pychik impact crater.

Volcanogenic plains are the most widely spread materials 

in V–56, as they constitute about 48 percent of the surface. The 

shields responsible for the production of units psh and pshc

are the most dominant volcanic primary structures observed in 

V–56 (fig. 9). It is uncertain whether the shields in V–56 are 

all of similar ages throughout V–56. However, the shield plains 

occurring in the heavily deformed materials (units tt, tlt, tdl) 

may have formed earlier. Unit pshc is present in most of the 

coronae that overlie unit pr and the tectonic structures present 

within them. Coronae also produced several lava flows that 

traveled several hundred kilometers across the regional plains. 

These lobate plains are abundant in Aibarchin Planitia, Mugazo 

Planitia, Astkhik Planum, and Kaiwan Fluctus areas. Contact 

relations show that the lava flows can be grouped into three 

units, pll, plm, and plu, successively from the oldest to the 

youngest (fig. 12). Materials comparable to the lobate plains 

are also present in the basins inside the tessera terrains. These 

intra-tessera basin materials are surrounded largely by unit tt

but to a lesser extent by units tdl and psh. The tectonic structures in the surrounding units (tt, tdl, psh) predate the intratessera basin plains material. Because the basin plains material 

does not have direct contact with the regional plains material, 

no stratigraphic comparisons can be made between them. Units 

itbl, itbm, and itbu were formed by volcanism within the tessera terrains (fig. 11). However, some of the lava flows in the 

basins are transported through channels from the lobate plains 

present outside the tessera terrain. For example, some of the 

upper unit of lobate plains material in Ngyandu Vallis flow 

along a channel to the intra-tessera basin region to form the 

units itbm and itbu (fig. 10). This suggests that the units itbm

and itbu can be correlated respectively with units plm and plu

of the Ngyandu Vallis. The relation between units itbl and pll

is unclear. Unit Itbl is invariably affected by a set of parallell 

fractures that disappear sharply along the boundary of units 

itbm and itbu (fig. 10), indicating the embayment of unit itbl by 

units itbm and itbu. Although unit itbl can be correlated with 

unit pll, unit itbl may be even older, because fractures in unit 

itbl are also common in units tt and tdl but are absent in unit pll. 

This uncertainty places the relative age of unit itbl over a much 

broader time frame and it may be older than that assigned for 

the unit pll.

Although a majority of deformational structures in the 

large-scale extensional structures and coronae were formed 
8

after the regional plains and much before the volcanogenic 

plains, a small number of fractures and grabens are also present 

in unit pshc and the lobate plains (fig. 13). Therefore, a weak 

tectonic activity continued during the emplacement of these 

plains units or later. In addition, some fractures and grabens 

were also formed locally in the regional plains after the formation of the corona-extensional belt, for example, in the region 

east of Otygen Corona. These fractures trend in two directions: 

east-northeast and northwest. They appear to represent the latest deformation in the plains and could probably be related to 

the terrain uplift. 

Impact craters are young geologic units in V–56 and are 

superimposed on units tt, pwr, pr, itbu, pll, and plm. Impact 

craters are absent in the youngest plains units, plu and itbu. 

Significantly, the craters in the older terrains tend to be simple 

craters with moderate to poor preservation. But, craters on the 

younger plains are complex structures with moderate to good 

preservation. Interestingly, in V–56, impact craters were also 

affected by tectonic structures. Tsects Chasma of Lada Terra 

extensional belt cuts across Dinah crater (fig. 15). These observations suggest that impact-cratering events may have occurred 

in V–56 over a long period of time, after the formation of tessera and some of the plains materials, although impacts could 

have occurred during the entire Venusian geologic history and 

may be continuing in the present.

Geologic History

The order in which the material and structural units were 

emplaced in V–56 provides insights into the sequence of geologic processes that formed the geologic history of this region. 

Geologic evolution of V–56 is divided into three periods: 

(1) formation of heavily deformed terrains, (2) formation of 

regional plains, large-scale extensional belts, and coronae, and 

(3) emplacement of volcanogenic plains. The processes making 

up the heavily deformed terrains (units tt, tlt, tdl) form the first 

and the earliest period of geologic activity in V–56. Tectonic 

features in these units suggest that the most vigorous geodynamic processes occurred in the earliest period. The observed 

ridges and grabens point to the repetitive occurrence of shortening and extensional processes that waned progressively over 

a period of time during the emplacement of units tlt and tdl. A 

minor volcanic activity in the form of shield eruptions and lava 

ponding occurred in the heavily deformed terrains after cessation of the major tectonic activity.

The second prominent period of geologic evolution 

involved the emplacement of regional plains materials, followed 

by the formation of wrinkle ridges, large-scale extensional belts, 

and coronae. Origin of the regional plains is unknown, because 

there are no associated primary volcanic structures within them. 

The plains emplacement event was followed by the second episode of intense tectonic activity. This tectonic episode involved 

the formation of large-scale extensional belts and corona (fig. 

2). A complex network of grabens, fractures, and faults was 

formed in a wide zone of intense tectonic activity that traversed 

along four belts, as shown in fig. 2. Chains of corona structures 

were also emplaced along these extensional belts. Tectonic fabric at the Hanghepiwi Chasma and near Okhin-Tengri Corona 

shows involvement of strike-slip motion in the generation of the 

extensional belts. The coexistence of the extensional belts and 

coronae requires a combination of thermal processes in the sublithospheric mantle and extensional tectonics in the lithosphere 

leading to the break-up of the lithosphere and volcanism. 

The third prominent period of geological evolution 

involved the emplacement of volcanogenic plains in association with the coronae emplacement. The shields are observed to 

have formed everywhere, most significantly around the coronae, 

and the lava flows that emanated from them formed the local 

material units. This period of shield volcanism was followed 

by significant volcanic eruptions around coronae that deposited large-scale lobate plains extending for several hundreds 

of kilometers covering almost a half of the total surface area 

of V–56. These volcanic plains are comparable to the large 

igneous provinces on Earth. Volcanic processes also occurred 

inside the tessera terrain, probably synchronously with the 

coronae volcanism, although some lava flows were transported 

from the exterior of the tessera materials to the interior basins. 

Local tectonic activities in some parts of the regional plains also 

occurred during the most recent period of geologic history; for 

example, more than six parallel fractures of several hundred 

kilometers length formed in Yenkhoboy Fossae, as did several 

tens of fractures and dikes in the region between Otygen and 

Ekhe-Burkhan Coronae. Impact events produced simple and 

complex craters in V–56. Outflow channels and deposits from 

the two largest craters (Flagstad and Marsh) were also observed, 

and their origin is consistent with the condensation of the ejecta 

plume producing these outflows (Sugita and Schultz, 2002), as 

these deposits were associated with the ejecta deposits. 

The most significant geologic processes that affected V–56 

and adjoining quadrangles are the formation of extensional belts 

and coronae and associated volcanism. Visible and Infrared 

Thermal Imaging Spectrometer (VIRTIS) of Venus Express 

has shown the Quetzalpetlatl and Otygen Coronae are associated with high thermal emissivity coinciding with some of the 

large lava flows (Helbert and others, 2008). The data indicate 

that these flows are young, probably hot lava flows (Ivanov and 

Head, 2010b). Magee and Head (1995) proposed the upwelling 

of deep mantle material as a possible source for these young 

basaltic lava flows. Therefore, these surface manifestations were 

the result of mantle upwelling (Magee and Head, 1994), operating at different spatial scales with chains of pronounced melting 

anomalies.

Summary

The geologic map of Lada Terra quadrangle (V–56) has 

been prepared at a scale of 1:5,000,000 using Magellan synthetic aperture radar images and ArcGIS. The map shows the 

distribution of various material units, primary and tectonic 

structures, and relative age relations between them. Material 

units are classified into (1) the heavily deformed materials 

such as tessera terrain, tessera-like terrain, and densely lineated 
9

terrain materials, (2) regional plains and wrinkle ridged plains 

materials, and (3) volcanogenic plains materials originated from 

the shields and the coronae. The older geologic units such as 

tessera, tessera-like terrain, and densely lineated plains record 

an older episode of tectonic processes that operated before 

the emplacement of regional plains and volcanic plains. The 

regional plains are transected by the large-scale extensional 

belts, coronae, and localized fractures. The extensional belts 

are composed of fractures, grabens, and strike-slip zones. 

Interestingly, the extensional belts are also the sites of largescale coronae formation, generating contacts that provide clear 

stratigraphic relations between these two units. The coronae are 

50–300 km diameter, tectonic, circular domed structures, often 

associated with several centers of volcanism. In many places, 

corona structures cut across the regional extensional belts, while 

in other places, the extensional belts deform and thus postdate 

the coronae. Lava flows emanating from the coronae travel 

several hundred kilometers across the regional plains. Impact 

craters are the youngest geologic units, except for one affected 

by the fractures. The geologic map provides clues to the history 

of geodynamic processes that occurred both on the surface and 

in the interior of Venus. Mantle upwelling on Venus appears 

to operate at different spatial scales with chains of pronounced 

melting anomalies and is responsible for the formation of 

most of the material units and structural features in Lada Terra 

quadrangle.

Acknowledgments 

Kumar acknowledges the BOYSCOST Fellowship 

awarded by the Department of Science and Technology 

(DST), Government of India; INDEX project of CSIR-NGRI; 

PLANEX (ISRO); Alexander Basilevsky, Mikhail Ivanov, 

Debra Hurwitz, Jay Dickson, Prabhat, Swarna Priya, and 

Rakesh Menga for productive discussions; and Director, NGRI, 

for permission to publish this map. Special thanks to Trent Hare 

at USGS for his help, which is gratefully appreciated. Technical 

reviews of McGowan and Roger Bannister and the suggestions 

from Ken Tanaka significantly improved the map. 

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Table 1. Morphology of impact craters in Lada Terra quadrangle (V–56), Venus.

Crater name Location (lat, long) Diameter 

(km) Structure Preservation1 Target material

Akosua 18.00, –58.54 5 Simple Weak Tessera terrain material, wrinkle 

ridged plains material

Berggolts 53.00, –63.46 28 Complex Good Wrinkle ridged plains material, lobate plains material middle unit

Caitlin 12.00, –65.25 12 Simple Weak Tessera terrain material

Danute 56.50, –63.50 13 Complex Moderate Lobate plains material middle unit

Dinah 37.06, –62.85 16 Simple Deformed by grabens, poor Regional plains material

Erxleben 39.46, –50.84 33 Complex Moderate Tessera-like terrain material, lobate 

plains material middle unit

Flagstad 18.85, –54.29 40 Complex Good, outflows in the ejecta Regional plains material

Guilbert 13.64, –57.96 25 Complex Moderate Regional plains material

Hsueh Tao 12.46, –52.96 13 Simple Weak

Tessera terrain material, regional 

plains material, lobate plains material 

middle unit

Kollado 53.36, –61.00 5 Simple Poor Lobate plains material middle unit

Marsh 46.62, –63.59 48 Complex Good, outflows in the ejecta Shield plains material

Pychik 33.77, –62.36 10 Simple Poor Regional plains material

Rand 59.56, –63.77 22 Complex Moderate Wrinkle ridged plains material

Tuyara 15.47, –62.89 12 Simple Poor Tessera terrain material, intra-tessera 

basin plains material middle unit

Von Siebold 36.71, –51.97 33 Complex Moderate Tessera-like terrain material, lobate 

plains material lower unit

1

The preservation state of impact craters includes ejecta, rim, and crater interior.