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A multi-modal indirect approach Daniel P. Connelly 2009

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1 A multi-modal indirect approach Daniel P. Connelly 2009
Post presentation comments are in green Age dating MAPCIS (Massive Australian Precambrian/Cambrian Impact Structure) A multi-modal indirect approach Daniel P. Connelly 2009 You will find background at or at the GSA northeastern meeting March 2009 uploaded files, MAPCIS the Case for a Massive Australian Precambrian/Cambrian Impact Structure

2 Original Ring Discovery 2007
Discoveries are tangible measurable and not up for debate. Theories are explanations based on discoveries and are very much debatable. Search moves from the general to specific, whether geographic area or age constraint. Discovery Vs Theory This discovery starts the search. The search leads to new discoveries. New discoveries propagate theories.

3 ~545 Ma D. P. Connelly 2009

4 Impact Constraints Acraman Gosse Bluff 590Ma 142Ma 800km & 200km from MAPCIS center
Ejecta from Acraman does not cover MAPCIS undisturbed Gosse Bluff near the center is undisturbed and Acraman ejecta is not found over MAPCIS ejecta. Rain over Gosse Bluff 2/2008

5 Alice Springs Orogeny Constraint ~450Ma
Deposited during Petermann orogeny Uplifted during Alice Springs Orogeny Mt. Currie Conglomerate Mutijulu Arkose,i Ayers Rock Deposited during Petermann Orogeny mya. Uplifted during Alice Springs Orogeny 450mya

6 Basement consistent with age?
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. Neoproterozoic ridges Kangaroo Island

7 MAFIC Events and MAPCIS Dating
Basic plate tectonics: When multiple events are divided, look for the youngest event to estimate the date of division. 13 29 11 10 MGr Moorilyanna Graben ~550Ma ME29 Skipworth Event ~575 ME 26 Gairdner Event ~825 A26 Amata dyke swarm G26 Gairdner dyke swarm ME16 Curramulka Event ~1590 ME13 Woman in White Event ~1680 ME 11 Lunch Creek Event ~1750 ME10 Hart Event ~1780 ME 9 Mount Hay Event ~1810Ma 9 Tasman Gap 26 MGr 16 9 A26 10 11 29 26 13 16 G26 Derived from

8 Musgrave = Grenville age zircons
Zircon age diagram of suspected post impact proximal ejecta deposits Worldwide Cambrian SS Enigma Arenite Distal Grenville Age zircons Feldspar local A. Camacho et Al Musgrave Provence = Impact Center Over 120,000 Sq. Km 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. Arkose Conglomerate P/C Boundary

9 Seven smaller impacts possibly coeval with MAPCIS
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 . All have evidence of a younger age constraint ~ at P/C boundary

10 Foelsche ~545Ma and Bukalara SS
Bukalara SS with shocked clasts blends into extensive regional unit. Antrim Plateau Volcanics (Kalkarindji LIP) ~ Ma Cover unlithified Bukalara SS After impact rapid burial Infers a rapid sequence of impact, fill, and coverage by basalt. Now P.W. Haines &D.J. Rawlings 2001

11 MAPCIS Center Overview
Trajectory Northeast to Southwest Radial Transpression Ridges ? Visible on 1:250, 000 Geology maps PT Arcuate & Radial light blue From Ayers Rock 1:250,000 Geology Map 2002 Largest known Pseudotachylite deposits, similar to Vredefort and Sudbury impacts. 1. Understand the locations shown on the next slide Neoproterozoic Winnall, Inindia & Pinyinna beds of Mt. Conner appear to be missing from MAPCIS Center.

12 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.

13 Sampling Data from NT Geological Survey
There appears to be no attempt to date the pseudotachylite itself

14 Sample sites plotted on Google Earth
Sample B549 Derived from Edgoose CJ, Scrimgeour IR, Close DF 2003 Geology of the Musgrave Block, NT, NT Geological Survey Report 15 Mt. Frazer

15 Sample B549 30km North of Mann Range pseudotachylite
Notable that these zircons have a metamorphic peak at 561ma , and zircon 13 exhibits a mosaic pattern. Mosaic patterns in zircons has been associated with shock metamorphism.

16 Cumulative probability diagram of biotite ages for entire Musgrave Provence
Camacho et al., 2002 Inferred that all fault systems in the Musgrave Provence were activated during the the Petermann Orogeny. 120,000 square Km moved here and portions were exhumed from 40km deep. Camacho All faults and shear zones were activated Camacho et al., 2002

17 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.



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