Geology of the Thaumasia region, Mars: plateau development, valley

origins, and magmatic evolution

by James M. Dohm, Kenneth L. Tanaka

Geologic features Geologic features of the Thaumasia regionof the Thaumasia region

HIGHLANDS AND INNER PLATEAUHIGHLANDS AND INNER PLATEAU

Scattered massifs and Scattered massifs and volcanoesvolcanoes

Mountain beltsMountain belts Numerous large impact Numerous large impact

craterscraters Successions of lava-flow Successions of lava-flow

fieldsfields Systems of rifts, narrow Systems of rifts, narrow

grabens, wrinkle ridges, grabens, wrinkle ridges, and folds and thrustsand folds and thrusts

EROSION OF THE OUTER EROSION OF THE OUTER MARGINMARGIN

Extensive valley Extensive valley networksnetworks

CanyonsCanyons TroughsTroughs Tilted, eroded rock Tilted, eroded rock

layers forming layers forming cuestascuestas

Geologic SettingGeologic Setting

Geologic SettingGeologic Setting

StratigraphyStratigraphy

StratigraphyStratigraphy Relative ages are based on a time-stratigraphic scale from Relative ages are based on a time-stratigraphic scale from

Tanka (1986) which reflects material ages and stratigraphic Tanka (1986) which reflects material ages and stratigraphic relationsrelations

This indicates 5 main stages of geologic activity (oldest to This indicates 5 main stages of geologic activity (oldest to youngest)youngest)– Stage 1: NoachianStage 1: Noachian– Stage 2: Late Noachian to Early HesperianStage 2: Late Noachian to Early Hesperian– Stage 3: Early HesperianStage 3: Early Hesperian– Stage 4: Late Hesperian to Early AmazonianStage 4: Late Hesperian to Early Amazonian– Stage 5: AmazonianStage 5: Amazonian

Stage 1:Stage 1:

NoachianNoachian The more rugged units formed during this The more rugged units formed during this

stagestage Complex modification due to cratering, Complex modification due to cratering,

tectonic deformation, erosional processes, and tectonic deformation, erosional processes, and volcanic and sedimentary burial has degraded volcanic and sedimentary burial has degraded or destroyed older craters (making it difficult or destroyed older craters (making it difficult to determine onset)to determine onset)

Stage 2:Stage 2:

Late Noachian to Early HesperianLate Noachian to Early Hesperian Some materials have been heavily modified by

folding or faulting and/or valley development during this stage

Rock materials from stage 1 & 2 cover more than half of the Thaumasia region

Stage 3:Stage 3:

Early HesperianEarly Hesperian Extensive rigid plains volcanism in Sinai

Planum and Corprates East (CE) as well as local valley formation in southern

Thaumasia Plateau

Stage 3 & 4:Stage 3 & 4:

Hesperian to Early AmazonianHesperian to Early Amazonian Extensive lava sheets were erupted from crest

and flanks of Syria Planum and Tharsis Montes (in NW)

40% rock from these stages

Stage 5:Stage 5:

AmazonianAmazonian relatively small outcrops of volcanic materials

and colluvial and eolian deposits = 3% of outcrop from region

Tectonic HistoryTectonic History The analysis of Thaumasia’s faults and grabens, rift systems

and wrinkle ridges indicate tectonic activity began and reached it’s peak during Noachian (stage 1) and declined during the Hesperian and Amazonian periods (stages 2-5)

Additionally, intense extensional and contractional deformation appears to have largely resulted from:

1. 1. Tharsis- and Syria-centered volcanotectonic activity (1-5)

2. 2. uplift and associated rifting of that plateau, including local centers of volcanotectonic activity (mainly 1 and 2)

3. 3. formation and tectonic relaxation of the Argyre impact basin (1 and 2)

4. Other. Tectonic deformation of region, such as compression due to rapid planetary cooling

Volcanic HistoryVolcanic History The Thaumasia region preserves some of the best

examples of early highland volcanoes and intermediate-age plateau lavas on Mars

Many of the prominent, isolated mountains that occur along or near faults and commonly exhibit summit depression and highly dissected flanks have been interpreted as ancient volcanoes

complex geomorphologies may indicate interbedded lava and pyroclastic deposits

Volcanic HistoryVolcanic History Mapped 14 volcanoes - using stratigraphic relations as well as

morphology

Formed throughout the Noachian and into Early Hesperian

STAGE 1 - 11 volcanoes

STAGE 2 - 3 volcanoes, and widespread volcanism continued to resurface local areas throughout the map area

STAGE 3 & 4 - Sheet lavas erupted from the crest and flanks of of Syria Planum and Arsia Mons (outside the study) and cover several provinces

STAGE 5 - Continued Tharsis volcanic activity resulted in lava flows through the Daedalia Planum province

Erosional HistoryErosional History they mapped and dated > 4000 branching and single valleys

branching or networked valleys strongly indicate water- or ice-based erosion

single, nonbranching valleys may also form by eolian, tectonic, and/or volcanic processes

Valleys tend to concentrate in areas of volcano flanks and near rift systems of the central part of the Thaumasia Highlands province and southern part of the Coprates province

STAGE 1 - valleys are obscure and discontinuous, probably due to later resurfacing

STAGE 1 & 2 - overall valley formation was most extensive

STAGE 3 & 4 - valleys tend to be more pristine and mostly occur in the map region

STAGE 5 - no stage 5 valleys occur on this map

Further Studies Further Studies

The Thaumasia region is a major, complex The Thaumasia region is a major, complex volcanotectonic province of Tharsis for which volcanotectonic province of Tharsis for which comprehensive reconstruction of geologic comprehensive reconstruction of geologic history has been lackinghistory has been lacking

This is an interpretive geologic history of the This is an interpretive geologic history of the Thaumasia region based on geologic mapping Thaumasia region based on geologic mapping and topical analysisand topical analysis

This detailed geologic study provides a basis This detailed geologic study provides a basis to address tectonic, magmatic, and to address tectonic, magmatic, and resurfacing issues in greater depthresurfacing issues in greater depth