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