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Age dating MAPCIS (Massive Australian Precambrian/Cambrian Impact Structure) A multi-modal indirect approach Daniel P. Connelly 2009 You will find background.

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Presentation on theme: "Age dating MAPCIS (Massive Australian Precambrian/Cambrian Impact Structure) A multi-modal indirect approach Daniel P. Connelly 2009 You will find background."— Presentation transcript:

1 Age dating MAPCIS (Massive Australian Precambrian/Cambrian Impact Structure) A multi-modal indirect approach Daniel P. Connelly 2009 You 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

2 Original Ring Discovery 2007 This discovery starts the search. The search leads to new discoveries. New discoveries propagate theories. Discovery Vs Theory

3 D. P. Connelly 2009 ~545 Ma

4 Impact Constraints Acraman Gosse Bluff 590Ma 142Ma 800km & 200km from MAPCIS center Rain over Gosse Bluff 2/2008 undisturbed Ejecta from Acraman does not cover MAPCIS

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

6 Basement consistent with age? Neoproterozoic 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.

7 MAFIC Events and MAPCIS Dating 29 MGr A26 G26 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 Tasman Gap Derived from Basic plate tectonics: When multiple events are divided, look for the youngest event to estimate the date of division.

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

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.

10 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) ~ Ma Cover unlithified Bukalara SS Infers a rapid sequence of impact, fill, and coverage by basalt.

11 MAPCIS Center Overview 1.Trajectory Northeast to Southwest 2.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.

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

15 Sample B549 30km 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.

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 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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