Age dating MAPCIS (Massive Australian

Precambrian/Cambrian Impact Structure)

A multi-modal indirect approach

Daniel P. Connelly 2009You will find background at MAPCIS.net

or at the GSA northeastern meeting March 2009 uploaded files, MAPCIS the Case for a Massive Australian Precambrian/Cambrian Impact Structure

Post presentation comments are in green

Original Ring Discovery 2007

This discovery starts the search.The search leads to new discoveries.New discoveries propagate theories.

Discovery Vs Theory

D. P. Connelly 2009

~545 Ma

Impact ConstraintsAcraman Gosse Bluff 590Ma 142Ma 800km & 200km

from MAPCIS center

Rain over Gosse Bluff 2/2008

undisturbed

Ejecta from Acraman does not cover MAPCIS

Alice Springs Orogeny Constraint ~450Ma

Mutijulu Arkose,i Ayers RockMt. Currie Conglomerate

Deposited during Petermann orogeny

Uplifted during Alice Springs Orogeny

Basement consistent with age?

Neoproterozoic ridges Kangaroo IslandNeoproterozoic ridges Kangaroo Island

This map is used as an example of the many 1:250,000 Geology maps used to cross check basement ages by examining exposed outcrops.Although this 1954 map conforms with the 2008 GA Mafic Ultramafic map, there is considerable debate on the accuracy of these maps in this region.

MAFIC Events and MAPCIS Dating

29

29

MGr

1311

109

13

10

11

9

2626

16

16

A26G26

MGr Moorilyanna Graben ~550MaME29 Skipworth Event ~575ME 26 Gairdner Event ~825A26 Amata dyke swarmG26 Gairdner dyke swarmME16 Curramulka Event ~1590ME13 Woman in White Event ~1680ME 11 Lunch Creek Event ~1750ME10 Hart Event ~1780ME 9 Mount Hay Event ~1810Ma

Tasman Gap

Derived from

Basic plate tectonics: When multiple events are divided, look for the youngest event to estimate the date of division.

Musgrave = Grenville age zircons

Arenite

Feldspar local

ArkoseConglomerate

Grenville Age zircons

Worldwide Cambrian SS Enigma

P/C Boundary

Distal

Zircon age diagram of suspected post impact proximal ejecta deposits

Musgrave Provence = Impact CenterOver 120,000 Sq. Km

A. Camacho et Al. 2002

The enigma is solved, if one has a huge impact in the center of a Grenville Aged province. This is what appears to have happened.

Seven smaller impacts possibly

coeval withMAPCIS

A cross check of impact age databases found this grouping of possibly coeval impacts, that appears to be associated with the predicted impact trajectory noted in dark blue .

Foelsche ~545Ma and Bukalara SS

P.W. Haines &D.J. Rawlings 2001

After impact rapid burial

Now

Bukalara SS with shocked clasts blends into extensive regional unit.

Antrim Plateau Volcanics (Kalkarindji LIP) ~510-545MaCover unlithifiedBukalara SS

Infers a rapid sequence of impact, fill, and coverage by basalt.

MAPCIS Center Overview1. Trajectory Northeast to

Southwest2. Radial Transpression Ridges ?

Visible on 1:250, 000 Geology maps

3. PT Arcuate & Radial light blue

Neoproterozoic Winnall, Inindia & Pinyinna beds of Mt. Conner appear to be missing from MAPCIS Center.

From Ayers Rock 1:250,000 Geology Map 2002

Largest known Pseudotachylite deposits, similar to Vredefort and Sudbury impacts.

Mt. Frazer Radial Pseudotachylite

Edgoose CJ, Scrimgeour IR, Close DF 2003 Geology of the Musgrave Block, NT, NT Geological Survey Report 15 An example of PT not associated with a major fault.

Sampling Data from NT Geological Survey

There appears to be no attempt to date the pseudotachylite itself

Sample sites plotted on Google Earth

Mt. Frazer

Sample B549

Edgoose CJ, Scrimgeour IR, Close DF 2003 Geology of the Musgrave Block, NT, NT Geological Survey Report 15

Derived from

Sample B54930km North of Mann Range pseudotachylite

Notable that these zircons have a metamorphic peak at 561ma +- 11, and zircon 13 exhibits a mosaic pattern.

Mosaic patterns in zircons has been associated with shock metamorphism.

Cumulative probability diagram of biotite ages for entire Musgrave Provence

Camacho et al., 2002Inferred that all fault systems in the Musgrave Provence were activated during thethe Petermann Orogeny.

120,000 square Km moved here and portions were exhumed from 40km deep.

Camacho et al., 2002

Conclusions• 1. Precambrian Basement underlies all visible parts within the outer ring.• 2. No known Precambrian impacts within 600km radius. • 3. Ejecta from Acraman 590Ma does not overlay MAPCIS ejecta.• 4. Gosse Bluff 142Ma and Alice Springs Orogeny structures are undisturbed.• 5. Lower Cambrian layers, proximal and distal exhibit a Musgrave fingerprint.• 6. Neoproterozoic beds appear to be missing from impact center.• 7 . Moorilyanna Graben forms and the Tasman Gap opens syn-orgenic with

Petermann Orogeny• 8. Cambrian Bukalara SS fills and preserves Foelsche impact ~545mya.• 9. Mass extinction of Ediacarans in Australia occurs at the end of Precambrian.• 10. Dating of monazite and zircons nearest to pseudotachylite gives dates

close to 545mya.

MAPCIS probably occurred just before the Precambrian/ Cambrian Boundary. Further research is needed to refine this dating.