Allan Ludman, John Aleinikoff, Bill Devlin

Slides:



Advertisements
Similar presentations
Geology of the Thaumasia region, Mars: plateau development, valley origins, and magmatic evolution by James M. Dohm, Kenneth L. Tanaka.
Advertisements

The first 80% of the History of Venus?. Some Geological Conclusions from Magellan Analysis -Volcanism and tectonism are the most abundant geological processes.
Lower Palaeozoic history of UK 1. Continental motions 2. Cambrian events 3. Ordovician events - The Grampian Orogeny 4. Ordovician and Silurian - The history.
Ch. 20 Sec. 2 Orogeny.
ISOSTASY Removal of material from the top will induce uplift at the surface. Removal of material from the bottom will produce subsidence. Thus, in the.
Exam Short answer questions Diagram interpretation Some multiple choice Material from discussion sections will be included Lab material will not be covered.
Tectonic History of Long Island Glenn Richard Stony Brook University Map from:
Crustal Deformation and Mountain Building
11.3 Mountains and Plates Mountains and Plates.
Mountain building & the evolution of continents
Environmental and Exploration Geophysics II tom.h.wilson Department of Geology and Geography West Virginia University Morgantown, WV.
The Basement & Supercontinents Florida: (Origins).
Regional geology and tectonic history of Wyoming Geological Field Techniques Course.
EARLY PALEOZOIC EVENTS CAMBRIAN PALEOGEOGRAPHY Development of a shallow epeiric or epicontinental sea Continent situated on the equator, so waters most.
Mountain building & the evolution of continents
Earth: Geologic Principles and History FIRST EDITIONCHERNICOFF/FOX/TANNER.
Phanerozoic Tectonic Evolution of the Chukotka-Arctic Alaska Block: Problems of the Rotational Model Boris A. Natal’in Istanbul Technical University.
By Alexandra Y, Logan, and Julia
Geology of Virginia Why? Pulls together what they already know: Rocks Plate Tectonics Wilson Cycles Geologic Structures Stratigraphic Principles/Sequence.
Magnetic Anomaly Map Including outline of island Magnetic Anomalies of Macquarie Island.
Harry Williams, Geomorphology1 TECTONIC REGIONS OF NORTH AMERICA The distribution of tectonic activity around continents (including North America) usually.
Part 1: The Vendian, Cambrian, and Early Ordovician Periods
Harry Williams, Historical Geology1 HISTORICAL GEOLOGY LECTURE 10. LATE PALEOZOIC GEOLOGY I. The Late Paleozoic (Devonian-Mississippian- Pennsylvanian-Permian)
North American Geological History. So what did we figure out about the East Coast so far? Proterozoic: suture zone, rifting Cambrian: passive margin Ordovician:
20.2. Continental Margins The line that divides the continental crust from the oceanic crust is not always obvious. Shorelines are not the true boundaries.
Rocks of different origins and ages occur in three fundamentally different geological provinces Mountain belts Cratons or shield areas Rift systems –Have.
Coastal Plain Appalachian Highlands Laurentian Upland Interior Plains Interior Highlands Rocky Mountain System Colorado Plateau Basin and Range Columbia.
Geology 1023 Cordillera and Appalachians. Orogenic (mobile) belts At the edges of continents Platform sequence that gets buckled by collision Also volcanism,
The Origin of Squam Lake: A Story of the Structural and Glacial Controls that Shaped this Iconic Lake by Erica Lehner.
Evolution of the Precambrian Rocks of Yellowstone National Park (YNP): Regional Overview David Mogk 1, Darrell Henry 2,Paul Mueller 3, and David Foster.
Geologic Sequencing: The order of geologic events
THE THEORY OF PLATE TECTONICS
The Paleozoic, Mesozoic, and Cenozoic Eras
Lecture Outlines Physical Geology, 14/e
Lecture Outlines Physical Geology, 10/e
Convergent Plate Boundaries
Continental Drift and the theory of Plate Tectonics
Stratigraphy.
FOR THE ADDITIONAL INFORMATION: MOUSE-OVER AND CLICK ON SCREEN
Lecture 30 Tectonics Chapter 15.1  15.7 Tectonic Movements
Mountain Building “Tectonic Forces at Work”
Scientific revolutions
The anatomy of continents
Oceans & Continents Unit 9.4.
SPATIAL VARIATION IN FOLD-AND-THRUST BELT STRUCTURAL GEOMETRY AND RESTORED SYN-TECTONIC LOADS: PENNSYLVANIA VALLEY AND RIDGE EVANS, Mark A., Department.
Pangaea Nearly 100 years ago, Alfred Wegener proposed that all the continents were once part of a supercontinent called Pangaea. Over time, Pangaea began.
The Global Detrital Zircon Database: An Update
DETRITAL ZIRCON RECORD
THE EVOLUTION OF OCEAN BASINS. 1. THE EVOLUTION OF OCEAN BASINS An individual ocean basin grows from: - An initial rift, reaches a maximum size, then.
LECTURE 9. EARLY PALEOZOIC GEOLOGY II.
NC Geological History.
Chapter 10: Plate Tectonics
Plate Tectonics Mountain Building.
After Wegner has published his book on the origin of continents and oceans in Scientists started to have interest in studying Wegner’s hypothesis.
Discovering Earth’s History
LECTURE 10. LATE PALEOZOIC GEOLOGY I.
Distribution of oceans and continents
HISTORY OF THE CONTINENTS
LECTURE 8. EARLY PALEOZOIC GEOLOGY I.
Cordillera and Appalachians
Sedimentary Basins related to Volcanic Arcs
Chapter 10.
How Old is Old? Geologic Time.
ALABAMA GEOLOGY.
Crust-Mantle Relationships
Place these notes into your Geology Notebooks.
Earth Part 3 G. Yannakoulias.
Timing the Geologic Record
Phil Thurston Laurentian University
Tectonic evolution of the Tien Shan revisited
Presentation transcript:

Allan Ludman, John Aleinikoff, Bill Devlin Interpreting detrital zircon provenance in the context of regional stratigraphic and tectonic models: an example from Late Ordovician–Early Devonian cover rocks on Ganderia, eastern Maine Allan Ludman, John Aleinikoff, Bill Devlin For those of you who spend most of your time in the lab, Henry Berry and I are demonstrating the lengths that Maine mappers will go to find outcrops from which you can date zircons.

NORTHERN APPALACHIAN TECTONIC FRAMEWORK Ganderia widens to the northeast from southern New England, reaching its greatest width in Maine and New Brunswick. We will look today at rocks from the heart of the Ganderia terrane in eastern and east central Maine [outlined here]. Hibbard et al., 2006

Ganderian rocks underlie nearly all of Maine and consist of NE-trending belts of Cambrian through late Middle Ordovician basement rocks, that are blanketed and separated by Late Ordovician through Early Devonian cover rocks. Our focus today is on detrital age spectra from the cover rocks of the Central Maine/Aroostook-Matapedia basin and Fredericton trough. If you thought from the first slide that we’re desperate for outcrops, the fossil age control situation is worse. In the entire area outlined here, there are three fossil localities and we turned to detrital zircons for some age constraints of broad swaths of turbidites of the Central Maine/Aroostook-Matapedia basin and Fredericton trough.

ATLANTIC GEOLOGY 54, 335–387 (2018) Ganderian rocks underlie nearly all of Maine and consist of NE-trending belts of Cambrian through late Middle Ordovician basement rocks, that are blanketed and separated by Late Ordovician through Early Devonian cover rocks. Our focus today is on detrital age spectra from the cover rocks of the Central Maine/Aroostook-Matapedia basin and Fredericton trough. If you thought from the first slide that we’re desperate for outcrops, the fossil age control situation is worse. In the entire area outlined here, there are three fossil localities and we turned to detrital zircons for some age constraints of broad swaths of turbidites of the Central Maine/Aroostook-Matapedia basin and Fredericton trough.

AGE CONSTRAINTS FOR UNFOSSILIFEROUS COVER ROCK UNITS 2. IMMEDIATE SEDIMENTARY PROVENANCE OF COVER ROCKS 3. ULTIMATE TECTONIC PROVENANCE OF GANDERIA We are also desperate for any information that could help constrain the ages of the rocks we do uncover, and the project that led to this talk was originally designed to do that. Complete results are available in Atlantic Geology. Today we highlight some unanticipated results from that study.

Central Maine/Aroostook-Matapedia basin Fredericton trough This shows the distribution of cover rock detrital zircon samples. We also dated detrital and volcanic zircons from the Miramichi and St. Croix basement belts, and a plutonic sample from the Pocomoonshine gabbro diorite. Complete results are reported in Atlantic Geology – today we will focus on three interpretations, two of which were unanticipated.

Correlation across the Central Maine basin and Fredericton trough This figure shows the inferred ages and correlation of Ganderian cover rocks across the Central Maine/Aroostook-Matapedia basin and Fredericton trough. The red lines identify units sampled in our study, none of which were fossiliferous at the time they were sampled. Palynomorphs now confirm the age ranges of the Flume Ridge and part of the Vassalboro Group.

ZIRCON AGE SPECTRA FOR COVER ROCKS One of the surprises was the presence of a young zircon population in most rocks of 430 -422 Ma, corresponding to Wenlock and Ludlow stages – just a few million years younger than the inferred ages of the rocks from which they were collected –as seen in the next slide.

COVER ROCK Youngest zircons Zircons very young for proposed age Zircons too young for proposed age F F F Although the zircon ages are in general consistent with the proposed stratigraphic ages, there are some issues. CLICK the youngest Hutchins Corner zircons are younger than the Llandovery age of the formation. This is not catastrophic as the Hutchins Corner and Mayflower Hill formations are nearly identical – although our sample had been assigned to the Hutchins Corner, it appears that it is Mayflower Hill. CLICK these zircons are just a few million years older than the units in which they are found, and this led to our first unexpected result.

AGE CONSTRAINTS FROM DETRITAL ZIRCONS Age spectra/youngest zircons are generally consistent with the previously interpreted ages of the cover rock units– no big problems, BUT It is unlikely that the youngest zircons, in at least the Flume Ridge Formation, would have had enough time to crystallize in an igneous rock, be exhumed, eroded, deposited, and incorporated in thousands of meters of sediments that were then lithified, folded, and intruded by the Pocomoonshine gabbro-diorite at ̴421.9 ± 2.4 Ma We therefore suggest that these zircons were not recycled from older rocks, but were instead, erupted with tephra during local early Silurian volcanic activity, e.g. the Eastport-Mascarene arc, and incorporated directly into the sediment At last year’s meeting, Sheila Seaman proposed that there had been “supervolcano eruptions” in the Coastal Maine magmatic province, and we suggest that this is the most likely source of the anomalously young zircons – although this is not the only possibility.

AGE CONSTRAINTS FOR COVER ROCK UNITS 2. IMMEDIATE SEDIMENTARY PROVENANCE OF COVER ROCKS 3. ULTIMATE TECTONIC PROVENANCE OF GANDERIA

Possible sources of Ganderian cover-rock sediment: Laurentia, Avalonia, and internal Ganderian “basement” Silurian paleogeography and Northern Appalachian tectonic models indicate three probable sources for the Ganderian cover-rock sediments: internal Ganderian sources, and external sources from Laurentia and Avalonia.

Those highlands are represented today by the Cambro-Ordovician belts. Clast provenance and lithofacies patterns confirm basement Ganderian sources for the cover rocks— highlands emergent during initiation of Late Ordovician sedimentation. Those highlands are represented today by the Cambro-Ordovician belts. After Ludman et al, 2017 Tremblay and Pinet, 2005, 2016 But were there also external contributions from Avalonia to the east and Laurentia to the west? There is abundant evidence for internal Ganderian sources. The basement belts in most of Maine were emergent immediately after late Middle Ordovician accretion of Ganderia to Laurentia, and unique basement lithologies are readily identified in the adjacent proximal facies. But several previous workers have cited both Laurentian and Avalonian provenance for cover rock units, and that is what we expected to find.

Initial thought: zircon ages suggest provenance from all three sources There are certainly zircon populations corresponding to frequently cited Laurentian and Avalonian ages, and this figure represents our first thoughts. However,

Eastport-Mascarene arc-trench system However, generally accepted tectonic models (e.g. Llamas and Hepburn, 2013) suggest that there would have been a significant, if not impenetrable, barrier to sediment transport from Avalon to the “east” Eastport-Mascarene arc-trench system Widely accepted tectonic models for the region suggest that it would have been difficult for Avalonian or Laurentian zircons to reach the depocenters that we studied.

…….and similarly from Laurentia to the west, where zircons would have had to negotiate the deep-water Central Maine basin with its islands and marginal highlands 1000 km not unlikely – twice the width of the Sea of Japan

HOW WIDE A BARRIER WAS THE DEEP-WATER CENTRAL MAINE BASIN? Minimum 50% shortening based on scant data from upright isoclinal folds (“conservative estimate” from Bradley et al, 2000) W > 300 – 400 Km. Ludman, 1969 Currently: 150 Km wide Add effects of early recumbent folds W > 500 – 600 Km ?? [Wider than the Sea of Japan] Osberg et al., 1985 1000 km not unlikely – twice the width of the Sea of Japan Include multiple early and late thrusts W ̴̴ ?? Km Tucker et al., 2001

Add shallow crustal blind thrusts Perhaps 2X the Sea of Japan?

IMMEDIATE SEDIMENTARY PROVENANCE CONCLUSIONS Cover rock detrital zircons were sourced internally, from Cambro-Ordovician rocks in Late Ordovician Ganderian basement highlands and from Silurian volcanic eruptions derived by melting of Ganderian crust. 2. The detrital zircon signature of basement and cover rocks is therefore the pristine “signature of Ganderia” – useful, perhaps, for workers elsewhere in the Northern Appalachians.

AGE CONSTRAINTS FOR COVER ROCK UNITS 2. IMMEDIATE SEDIMENTARY PROVENANCE OF COVER ROCKS 3. ULTIMATE TECTONIC PROVENANCE OF GANDERIA

Modified after Nance et al., 2008 Zircon age spectra compared with zircon-producing events in post-Rodinian plates Bradley, this meeting Modified after Nance et al., 2008