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Wikipedia Search Protection ring Article Talk Language Download PDF Watch Edit Several terms redirect here. For other uses, see Ring (disambiguation) and Ring 0 (disambiguation). Learn more This article includes a list of general references, but it lacks sufficient corresponding inline citations. (February 2015) In computer science, hierarchical protection domains,[1][2] often called protection rings, are mechanisms to protect data and functionality from faults (by improving fault tolerance)...
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Several terms redirect here. For other uses, see Ring (disambiguation) and Ring 0 (disambiguation).
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This article includes a list of general references, but it lacks sufficient corresponding inline citations. (February 2015)
In computer science, hierarchical protection domains,[1][2] often called protection rings, are mechanisms to protect data and functionality from faults (by improving fault tolerance) and malicious behavior (by providing computer security).


Privilege rings for the x86 available in protected mode
Computer operating systems provide different levels of access to resources. A protection ring is one of two or more hierarchical levels or layers of privilege within the architecture of a computer system. This is generally hardware-enforced by some CPU architectures that provide different CPU modes at the hardware or microcode level. Rings are arranged in a hierarchy from most privileged (most trusted, usually numbered zero) to least privileged (least trusted, usually with the highest ring number). On most operating systems, Ring 0 is the level with the most privileges and interacts most directly with the physical hardware such as certain CPU functionality (e.g. the control registers) and I/O controllers.

Special mechanisms are provided to allow an outer ring to access an inner ring's resources in a predefined manner, as opposed to allowing arbitrary usage. Correctly gating access between rings can improve security by preventing programs from one ring or privilege level from misusing resources intended for programs in another. For example, spyware running as a user program in Ring 3 should be prevented from turning on a web camera without informing the user, since hardware access should be a Ring 1 function reserved for device drivers. Programs such as web browsers running in higher numbered rings must request access to the network, a resource restricted to a lower numbered ring.

X86S, a recently published Intel architecture, has only ring 0 and ring 3. Ring 1 and 2 will be removed under X86S since modern OSes never utilize them.[3]

Implementations
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Multiple rings of protection were among the most revolutionary concepts introduced by the Multics operating system, a highly secure predecessor of today's Unix family of operating systems. The GE 645 mainframe computer did have some hardware access control, including the same two modes that the other GE-600 series machines had, and segment-level permissions in its memory management unit ("Appending Unit"), but that was not sufficient to provide full support for rings in hardware, so Multics supported them by trapping ring transitions in software;[4] its successor, the Honeywell 6180, implemented them in hardware, with support for eight rings;[5] Protection rings in Multics were separate from CPU modes; code in all rings other than ring 0, and some ring 0 code, ran in slave mode.[6]

However, most general-purpose systems use only two rings, even if the hardware they run on provides more CPU modes than that. For example, Windows 7 and Windows Server 2008 (and their predecessors) use only two rings, with ring 0 corresponding to kernel mode and ring 3 to user mode,[7] because earlier versions of Windows NT ran on processors that supported only two protection levels.[8]

Many modern CPU architectures (including the popular Intel x86 architecture) include some form of ring protection, although the Windows NT operating system, like Unix, does not fully utilize this feature. OS/2 does, to some extent, use three rings:[9] ring 0 for kernel code and device drivers, ring 2 for privileged code (user programs with I/O access permissions), and ring 3 for unprivileged code (nearly all user programs). Under DOS, the kernel, drivers and applications typically run on ring 3 (however, this is exclusive to the case where protected-mode drivers or DOS extenders are used; as a real-mode OS, the system runs with effectively no protection), whereas 386 memory managers such as EMM386 run at ring 0. In addition to this, DR-DOS' EMM386 3.xx can optionally run some modules (such as DPMS) on ring 1 instead. OpenVMS uses four modes called (in order of decreasing privileges) Kernel, Executive, Supervisor and User.

While x86 has 4 protection rings, it is more common for architectures to only have two. Even on x86, most operating systems only use ring 0 and 3.
A renewed interest in this design structure came with the proliferation of the Xen VMM software, ongoing discussion on monolithic vs. micro-kernels (particularly in Usenet newsgroups and Web forums), Microsoft's Ring-1 design structure as part of their NGSCB initiative, and hypervisors based on x86 virtualization such as Intel VT-x (formerly Vanderpool).

The original Multics system had eight rings, but many modern systems have fewer. The hardware remains aware of the current ring of the executing instruction thread at all times, with the help of a special machine register. In some systems, areas of virtual memory are instead assigned ring numbers in hardware. One example is the Data General Eclipse MV/8000, in which the top three bits of the program counter (PC) served as the ring register. Thus code executing with the virtual PC set to 0xE200000, for example, would automatically be in ring 7, and calling a subroutine in a different section of memory would automatically cause a ring transfer.

The hardware severely restricts the ways in which control can be passed from one ring to another, and also enforces restrictions on the types of memory access that can be performed across rings. Using x86 as an example, there is a special[clarification needed] gate structure which is referenced by the call instruction that transfers control in a secure way[clarification needed] towards predefined entry points in lower-level (more trusted) rings; this functions as a supervisor call in many operating systems that use the ring architecture. The hardware restrictions are designed to limit opportunities for accidental or malicious breaches of security. In addition, the most privileged ring may be given special capabilities (such as real memory addressing that bypasses the virtual memory hardware).

ARM version 7 architecture implements three privilege levels: application (PL0), operating system (PL1), and hypervisor (PL2). Unusually, level 0 (PL0) is the least-privileged level, while level 2 is the most-privileged level.[10] ARM version 8 implements four exception levels: application (EL0), operating system (EL1), hypervisor (EL2), and secure monitor / firmware (EL3), for AArch64[11]: D1-2454  and AArch32.[11]: G1-6013 

Ring protection can be combined with processor modes (master/kernel/privileged/supervisor mode versus slave/unprivileged/user mode) in some systems. Operating systems running on hardware supporting both may use both forms of protection or only one.

Effective use of ring architecture requires close cooperation between hardware and the operating system.[why?] Operating systems designed to work on multiple hardware platforms may make only limited use of rings if they are not present on every supported platform. Often the security model is simplified to "kernel" and "user" even if hardware provides finer granularity through rings.

Modes
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See also: Real mode and Protected mode
Supervisor mode
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In computer terms, supervisor mode is a hardware-mediated flag that can be changed by code running in system-level software. System-level tasks or threads may[a] have this flag set while they are running, whereas user-level applications will not. This flag determines whether it would be possible to execute machine code operations such as modifying registers for various descriptor tables, or performing operations such as disabling interrupts. The idea of having two different modes to operate in comes from "with more power comes more responsibility" – a program in supervisor mode is trusted never to fail, since a failure may cause the whole computer system to crash.

Supervisor mode is "an execution mode on some processors which enables execution of all instructions, including privileged instructions. It may also give access to a different address space, to memory management hardware and to other peripherals. This is the mode in which the operating system usually runs."[12]

In a monolithic kernel, the operating system runs in supervisor mode and the applications run in user mode. Other types of operating systems, like those with an exokernel or microkernel, do not necessarily share this behavior.

Some examples from the PC world:

Linux, macOS and Windows are three operating systems that use supervisor/user mode. To perform specialized functions, user mode code must perform a system call into supervisor mode or even to the kernel space where trusted code of the operating system will perform the needed task and return the execution back to the userspace. Additional code can be added into kernel space through the use of loadable kernel modules, but only by a user with the requisite permissions, as this code is not subject to the access control and safety limitations of user mode.
DOS (for as long as no 386 memory manager such as EMM386 is loaded), as well as other simple operating systems and many embedded devices run in supervisor mode permanently, meaning that drivers can be written directly as user programs.
Most processors have at least two different modes. The x86-processors have four different modes divided into four different rings. Programs that run in Ring 0 can do anything with the system, and code that runs in Ring 3 should be able to fail at any time without impact to the rest of the computer system. Ring 1 and Ring 2 are rarely used, but could be configured with different levels of access.

In most existing systems, switching from user mode to kernel mode has an associated high cost in performance. It has been measured, on the basic request getpid, to cost 1000–1500 cycles on most machines. Of these just around 100 are for the actual switch (70 from user to kernel space, and 40 back), the rest is "kernel overhead".[13][14] In the L3 microkernel, the minimization of this overhead reduced the overall cost to around 150 cycles.[13]

Maurice Wilkes wrote:[15]

... it eventually became clear that the hierarchical protection that rings provided did not closely match the requirements of the system programmer and gave little or no improvement on the simple system of having two modes only. Rings of protection lent themselves to efficient implementation in hardware, but there was little else to be said for them. [...] The attractiveness of fine-grained protection remained, even after it was seen that rings of protection did not provide the answer... This again proved a blind alley...

To gain performance and determinism, some systems place functions that would likely be viewed as application logic, rather than as device drivers, in kernel mode; security applications (access control, firewalls, etc.) and operating system monitors are cited as examples. At least one embedded database management system, eXtremeDB Kernel Mode, has been developed specifically for kernel mode deployment, to provide a local database for kernel-based application functions, and to eliminate the context switches that would otherwise occur when kernel functions interact with a database system running in user mode.[16]

Functions are also sometimes moved across rings in the other direction. The Linux kernel, for instance, injects into processes a vDSO section which contains functions that would normally require a system call, i.e. a ring transition. Instead of doing a syscall these functions use static data provided by the kernel. This avoids the need for a ring transition and so is more lightweight than a syscall. The function gettimeofday can be provided this way.

Hypervisor mode
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Recent CPUs from Intel and AMD offer x86 virtualization instructions for a hypervisor to control Ring 0 hardware access. Although they are mutually incompatible, both Intel VT-x (codenamed "Vanderpool") and AMD-V (codenamed "Pacifica") allow a guest operating system to run Ring 0 operations natively without affecting other guests or the host OS.

Before hardware-assisted virtualization, guest operating systems ran under ring 1. Any attempt that requires a higher privilege level to perform (ring 0) will produce an interrupt and then be handled using software, so called "Trap and Emulate".

To assist virtualization and reduce overhead caused by the reason above, VT-x and SVM allows the guest to run under Ring 0. VT-x introduces VMX Root/Non-root Operation: The hypervisor runs in VMX Root Operation mode, possessing the highest privilege. Guest OS runs in VMX Non-Root Operation mode, which allows them to operate at ring 0 without having actual hardware privileges. VMX non-root operation and VMX transitions are controlled by a data structure called a virtual-machine control.[17] VT-x allows the hypervisor and the guest OS to both run under ring 0, rendering "Trap and Emulate" obsolete, improving virtualization performance.

Privilege level
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Main article: Privilege (computing)
A privilege level in the x86 instruction set controls the access of the program currently running on the processor to resources such as memory regions, I/O ports, and special instructions. There are 4 privilege levels ranging from 0 which is the most privileged, to 3 which is least privileged. Most modern operating systems use level 0 for the kernel/executive, and use level 3 for application programs. Any resource available to level n is also available to levels 0 to n, so the privilege levels are rings. When a lesser privileged process tries to access a higher privileged process, a general protection fault exception is reported to the OS.

It is not necessary to use all four privilege levels. Current operating systems with wide market share including Microsoft Windows, macOS, Linux, iOS and Android mostly use a paging mechanism with only one bit to specify the privilege level as either Supervisor or User (U/S Bit). Windows NT uses the two-level system.[18] The real mode programs in 8086 are executed at level 0 (highest privilege level) whereas virtual mode in 8086 executes all programs at level 3.[19]

Potential future uses for the multiple privilege levels supported by the x86 ISA family include containerization and virtual machines. A host operating system kernel could use instructions with full privilege access (kernel mode), whereas applications running on the guest OS in a virtual machine or container could use the lowest level of privileges in user mode. The virtual machine and guest OS kernel could themselves use an intermediate level of instruction privilege to invoke and virtualize kernel-mode operations such as system calls from the point of view of the guest operating system.[20]

IOPL
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The IOPL (I/O Privilege level) flag is a flag found on all IA-32 compatible x86 CPUs. It occupies bits 12 and 13 in the FLAGS register. In protected mode and long mode, it shows the I/O privilege level of the current program or task. The Current Privilege Level (CPL) (CPL0, CPL1, CPL2, CPL3) of the task or program must be less than or equal to the IOPL in order for the task or program to access I/O ports.

The IOPL can be changed using POPF(D) and IRET(D) only when the current privilege level is Ring 0.

Besides IOPL, the I/O Port Permissions in the TSS also take part in determining the ability of a task to access an I/O port.

Miscellaneous
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In x86 systems, the x86 hardware virtualization (VT-x and SVM) is referred as "ring −1", the System Management Mode is referred as "ring −2", the Intel Management Engine and AMD Platform Security Processor are sometimes referred as "ring −3".[21]

Use of hardware features
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Many CPU hardware architectures provide far more flexibility than is exploited by the operating systems that they normally run. Proper use of complex CPU modes requires very close cooperation between the operating system and the CPU, and thus tends to tie the OS to the CPU architecture. When the OS and the CPU are specifically designed for each other, this is not a problem (although some hardware features may still be left unexploited), but when the OS is designed to be compatible with multiple, different CPU architectures, a large part of the CPU mode features may be ignored by the OS. For example, the reason Windows uses only two levels (ring 0 and ring 3) is that some hardware architectures that were supported in the past (such as PowerPC or MIPS) implemented only two privilege levels.[7]

Multics was an operating system designed specifically for a special CPU architecture (which in turn was designed specifically for Multics), and it took full advantage of the CPU modes available to it. However, it was an exception to the rule. Today, this high degree of interoperation between the OS and the hardware is not often cost-effective, despite the potential advantages for security and stability.

Ultimately, the purpose of distinct operating modes for the CPU is to provide hardware protection against accidental or deliberate corruption of the system environment (and corresponding breaches of system security) by software. Only "trusted" portions of system software are allowed to execute in the unrestricted environment of kernel mode, and then, in paradigmatic designs, only when absolutely necessary. All other software executes in one or more user modes. If a processor generates a fault or exception condition in a user mode, in most cases system stability is unaffected; if a processor generates a fault or exception condition in kernel mode, most operating systems will halt the system with an unrecoverable error. When a hierarchy of modes exists (ring-based security), faults and exceptions at one privilege level may destabilize only the higher-numbered privilege levels. Thus, a fault in Ring 0 (the kernel mode with the highest privilege) will crash the entire system, but a fault in Ring 2 will only affect Rings 3 and beyond and Ring 2 itself, at most.

Transitions between modes are at the discretion of the executing thread when the transition is from a level of high privilege to one of low privilege (as from kernel to user modes), but transitions from lower to higher levels of privilege can take place only through secure, hardware-controlled "gates" that are traversed by executing special instructions or when external interrupts are received.

Microkernel operating systems attempt to minimize the amount of code running in privileged mode, for purposes of security and elegance, but ultimately sacrificing performance.

See also
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Call gate (Intel)
Memory segmentation
Protected mode – available on x86-compatible 80286 CPUs and newer
IOPL (CONFIG.SYS directive) – an OS/2 directive to run DLL code at ring 2 instead of at ring 3
Segment descriptor
Supervisor Call instruction
System Management Mode (SMM)
Principle of least privilege
Notes
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E.g., In IBM OS/360 through z/OS, some system tasks run in problem state key 0.
References
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Karger, Paul A.; Herbert, Andrew J. (1984). An Augmented Capability Architecture to Support Lattice Security and Traceability of Access. 1984 IEEE Symposium on Security and Privacy. p. 2. doi:10.1109/SP.1984.10001. ISBN 0-8186-0532-4. S2CID 14788823.
Binder, W. (2001). "Design and implementation of the J-SEAL2 mobile agent kernel". Proceedings 2001 Symposium on Applications and the Internet. pp. 35–42. doi:10.1109/SAINT.2001.905166. ISBN 0-7695-0942-8. S2CID 11066378.
"Envisioning a Simplified Intel Architecture for the Future". Intel. Retrieved 28 May 2024.
"A Hardware Architecture for Implementing Protection Rings". Communications of the ACM. 15 (3). March 1972. Retrieved 27 September 2012.
"Multics Glossary - ring". Retrieved 27 September 2012.
The Multics Virtual Memory, part 2 (PDF). Honeywell Information Systems. June 1972. pp. 160–161.
Russinovich, Mark E.; David A. Solomon (2005). Microsoft Windows Internals (4 ed.). Microsoft Press. pp. 16. ISBN 978-0-7356-1917-3.
Russinovich, Mark (2012). Windows Internals Part 1 (6th ed.). Redmond, Washington: Microsoft Press. p. 17. ISBN 978-0-7356-4873-9. The reason Windows uses only two levels is that some hardware architectures that were supported in the past (such as Compaq Alpha and Silicon Graphics MIPS) implemented only two privilege levels.
"Presentation Device Driver Reference for OS/2 – 5. Introduction to OS/2 Presentation Drivers". Archived from the original on 15 June 2015. Retrieved 13 June 2015.
ARM Architecture Reference Manual ARMv7-A and ARMv7-R edition. Arm Ltd. p. B1-1136.
Arm Architecture Reference Manual Armv8, for A-profile architecture. Arm Ltd.
"supervisor mode". FOLDOC. 15 February 1995.
Jochen Liedtke (December 1995). "On µ-Kernel Construction". Proc. 15th ACM Symposium on Operating System Principles (SOSP).
Ousterhout, J. K. (1990). Why aren't operating systems getting faster as fast as hardware?. Usenix Summer Conference A. naheim, CA. pp. 247–256.
Maurice Wilkes (April 1994). "Operating systems in a changing world". ACM SIGOPS Operating Systems Review. 28 (2): 9–21. doi:10.1145/198153.198154. ISSN 0163-5980. S2CID 254134.
Gorine, Andrei; Krivolapov, Alexander (May 2008). "Kernel Mode Databases: A DBMS Technology For High-Performance Applications". Dr. Dobb's Journal.
Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 3C (PDF). Intel Cooperation (published September 2016). 2016. pp. 1–3.
Russinovich, Mark E.; Solomon, David A. (2005). Microsoft Windows Internals (4th ed.). Microsoft Press. p. 16. ISBN 978-0-7356-1917-3.
Sunil Mathur. Microprocessor 8086: Architecture, Programming and Interfacing (Eastern Economy ed.). PHI Learning.
Anderson, Thomas; Dahlin, Michael (21 August 2014). "2.2". Operating Systems: Principles and Practice (2nd ed.). Recursive Books. ISBN 978-0985673529.
De Gelas, Johan. "Hardware Virtualization: the Nuts and Bolts". AnandTech. Retrieved 13 March 2021.
Intel 80386 Programmer's Reference
Further reading
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David T. Rogers (June 2003). A framework for dynamic subversion (PDF) (MSc). Naval Postgraduate School. hdl:10945/919.
William J. Caelli (2002). "Relearning "Trusted Systems" in an Age of NIIP: Lessons from the Past for the Future". Archived from the original (PDF) on 20 April 2015.
Haruna R. Isa; William R. Shockley; Cynthia E. Irvine (May 1999). "A Multi-threading Architecture for Multilevel Secure Transaction Processing" (PDF). Proceedings of the 1999 IEEE Symposium on Security and Privacy. Oakland, CA. pp. 166–179. hdl:10945/7198.
Ivan Kelly (8 May 2006). "Porting MINIX to Xen" (PDF). Archived from the original (PDF) on 27 August 2006.
Paul Barham; Boris Dragovic; Keir Fraser; Steven Hand; Tim Harris; Alex Ho; Rolf Neugebauer; Ian Pratt; Andrew Warfield (2003). "Xen and the Art of Virtualization" (PDF).
Marcus Peinado; Yuqun Chen; Paul England; John Manferdelli. "NGSCB: A Trusted Open System" (PDF). Archived from the original (PDF) on 4 March 2005.
Michael D. Schroeder; Jerome H. Saltzer (1972). "A Hardware Architecture for Implementing Protection Rings".
"Intel Architecture Software Developer's Manual Volume 3: System Programming (Order Number 243192)" (PDF). Chapter 4 "Protection"; section 4.5 "Privilege levels". Archived from the original (PDF) on 19 February 2009.
Tzi-cker Chiueh; Ganesh Venkitachalam; Prashant Pradhan (December 1999). "Integrating segmentation and paging protection for safe, efficient and transparent software extensions". Proceedings of the seventeenth ACM symposium on Operating systems principles. Section 3: Protection hardware features in Intel X86 architecture; subsection 3.1 Protection checks. doi:10.1145/319151.319161. ISBN 1581131402. S2CID 9456119.
Takahiro Shinagawa; Kenji Kono; Takashi Masuda (17 May 2000). "Exploiting Segmentation Mechanism for Protecting Against Malicious Mobile Code" (PDF). Chapter 3 Implementation; section 3.2.1 Ring Protection. Archived from the original (PDF) on 10 August 2017. Retrieved 2 April 2018.
Boebert, William Earl; R. Kain (1985). A Practical Alternative to Hierarchical Integrity Policies. 8th National Computer Security Conference.
Gorine, Andrei; Krivolapov, Alexander (May 2008). "Kernel Mode Databases: A DBMS technology for high-performance applications". Dr. Dobb's Journal.
Last edited 2 months ago by Imeriki al-Shimoni
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Operating modes for central processing unit
Call gate (Intel)
Mechanism in Intel's x86 architecture for changing the privilege level
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{{short description|Hotspot partly responsible for volcanic activity forming the Iceland Plateau and island}}
{{short description|Hotspot partly responsible for volcanic activity forming the Iceland Plateau and island}}
{{use dmy dates|cs1-dates=ly|date=December 2020}}
{{use dmy dates|cs1-dates=ly|date=December 2020}}
Line 200: Line 24:
It is believed that a [[mantle plume]] underlies Iceland, of which the hotspot is thought to be the surface expression, and that the presence of the plume enhances the volcanism already caused by plate separation. Additionally, flood basalts on the [[continental margin]]s of [[Greenland]] and [[Norway]], the oblique orientation of the [[Reykjanes Ridge]] segments to their spreading direction, and the enhanced igneous crustal thickness found along the southern [[Aegir Ridge|Aegir]] and [[Kolbeinsey Ridge|Kolbeinsey]] ridges may be results of interaction between the plume and the [[Mid-Atlantic Ridge]].<ref name=":0">{{Cite journal|last1 = Howell|first1 = Samuel M.|last2 = Ito|first2 = Garrett|last3 = Breivik|first3 = Asbjørn J.|last4 = Rai|first4 = Abhishek|last5 = Mjelde|first5 = Rolf|last6 = Hanan|first6 = Barry|last7 = Sayit|first7 = Kaan|last8 = Vogt|first8 = Peter|date = 2014-04-15|title = The origin of the asymmetry in the Iceland hotspot along the Mid-Atlantic Ridge from continental breakup to present-day|journal = Earth and Planetary Science Letters|volume = 392|pages = 143–153|doi = 10.1016/j.epsl.2014.02.020|bibcode = 2014E&PSL.392..143H|hdl = 10125/41133|hdl-access = free}}</ref> The plume stem is believed to be quite narrow, perhaps {{cvt|100|km}} across and extending down to at least {{cvt|400|&ndash;|650|km}} beneath the Earth's surface, and possibly down to the [[Core–mantle boundary|core-mantle boundary]], while the plume head may be greater than {{cvt|1000|km}} in diameter.<ref name=":0" /><ref>{{Cite journal|last1 = Dordevic|first1 = Mladen|last2 = Georgen|first2 = Jennifer|date = 2016-01-01|title = Dynamics of plume–triple junction interaction: Results from a series of three-dimensional numerical models and implications for the formation of oceanic plateaus|journal = Journal of Geophysical Research: Solid Earth|volume = 121|issue = 3|language = en|pages = 2014JB011869|doi = 10.1002/2014JB011869|issn = 2169-9356|bibcode = 2016JGRB..121.1316D|url = https://digitalcommons.odu.edu/cgi/viewcontent.cgi?article=1220&context=oeas_fac_pubs|doi-access = free}}</ref>
It is believed that a [[mantle plume]] underlies Iceland, of which the hotspot is thought to be the surface expression, and that the presence of the plume enhances the volcanism already caused by plate separation. Additionally, flood basalts on the [[continental margin]]s of [[Greenland]] and [[Norway]], the oblique orientation of the [[Reykjanes Ridge]] segments to their spreading direction, and the enhanced igneous crustal thickness found along the southern [[Aegir Ridge|Aegir]] and [[Kolbeinsey Ridge|Kolbeinsey]] ridges may be results of interaction between the plume and the [[Mid-Atlantic Ridge]].<ref name=":0">{{Cite journal|last1 = Howell|first1 = Samuel M.|last2 = Ito|first2 = Garrett|last3 = Breivik|first3 = Asbjørn J.|last4 = Rai|first4 = Abhishek|last5 = Mjelde|first5 = Rolf|last6 = Hanan|first6 = Barry|last7 = Sayit|first7 = Kaan|last8 = Vogt|first8 = Peter|date = 2014-04-15|title = The origin of the asymmetry in the Iceland hotspot along the Mid-Atlantic Ridge from continental breakup to present-day|journal = Earth and Planetary Science Letters|volume = 392|pages = 143–153|doi = 10.1016/j.epsl.2014.02.020|bibcode = 2014E&PSL.392..143H|hdl = 10125/41133|hdl-access = free}}</ref> The plume stem is believed to be quite narrow, perhaps {{cvt|100|km}} across and extending down to at least {{cvt|400|&ndash;|650|km}} beneath the Earth's surface, and possibly down to the [[Core–mantle boundary|core-mantle boundary]], while the plume head may be greater than {{cvt|1000|km}} in diameter.<ref name=":0" /><ref>{{Cite journal|last1 = Dordevic|first1 = Mladen|last2 = Georgen|first2 = Jennifer|date = 2016-01-01|title = Dynamics of plume–triple junction interaction: Results from a series of three-dimensional numerical models and implications for the formation of oceanic plateaus|journal = Journal of Geophysical Research: Solid Earth|volume = 121|issue = 3|language = en|pages = 2014JB011869|doi = 10.1002/2014JB011869|issn = 2169-9356|bibcode = 2016JGRB..121.1316D|url = https://digitalcommons.odu.edu/cgi/viewcontent.cgi?article=1220&context=oeas_fac_pubs|doi-access = free}}</ref>


It is suggested that the lack of a time-progressive track of seamounts is due to the location of the plume beneath the thick Greenland [[craton]] for ~ 15 {{abbr|Myr|million years}} after continental breakup,<ref>{{Cite journal|last1 = Mihalffy|first1 = Peter|last2 = Steinberger|first2 = Bernhard|last3 = Schmeling|first3 = Harro|date = 2008-02-01|title = The effect of the large-scale mantle flow field on the Iceland hotspot track|journal = Tectonophysics|series = Plate movement and crustal processes in and around Iceland|volume = 447|issue = 1–4|pages = 5–18|doi = 10.1016/j.tecto.2006.12.012|bibcode = 2008Tectp.447....5M}}</ref> and the later entrenchment of the plume material into the northern Mid-Atlantic Ridge following its formation.<ref name=":0" />
It is suggested that the lack of a time-progressive track of seamounts is due to the location of the plume beneath the thick Greenland [[craton]] (Laurentia) for ~ 15 {{abbr|Myr|million years}} after continental breakup,<ref>{{Cite journal|last1 = Mihalffy|first1 = Peter|last2 = Steinberger|first2 = Bernhard|last3 = Schmeling|first3 = Harro|date = 2008-02-01|title = The effect of the large-scale mantle flow field on the Iceland hotspot track|journal = Tectonophysics|series = Plate movement and crustal processes in and around Iceland|volume = 447|issue = 1–4|pages = 5–18|doi = 10.1016/j.tecto.2006.12.012|bibcode = 2008Tectp.447....5M}}</ref> and the later entrenchment of the plume material into the northern Mid-Atlantic Ridge following its formation.<ref name=":0" />


====Geological history====
====Geological history====
According to the [[mantle plume|plume]] model, the source of [[Volcanism of Iceland|Icelandic volcanism]] lies deep beneath the center of the island. The earliest volcanic rocks attributed to the plume are found on both sides of the Atlantic. Their ages have been determined to lie between 64 and 58 million years.<ref name=Ruedas2007>{{cite book|chapter =Iceland: The current picture of a ridge-centred mantle plume|year =2007|first1 =Thomas|last1 =Ruedas|first2 =Gabriele|last2 =Marquart|first3=Harro|last3 =Schmeling|doi =10.1007/978-3-540-68046-8_3|title =Mantle Plumes: A multidisciplinary approach|pages =71–126|publisher =Springer|editor-first1 =Joachim R. R.|editor-last1= Ritter|editor-first2 =Ulrich R.|editor-last2 =Christensen|url =https://www.researchgate.net/publication/264942825|isbn=9783540680451}}</ref>{{rp|pp=73-74}} This coincides with the opening of the north Atlantic in the late [[Paleocene]] and early [[Eocene]], which has led to suggestions that the arrival of the plume was linked to, and has perhaps contributed to, the breakup of the<ref>
According to the [[mantle plume|plume]] model, the source of [[Volcanism of Iceland|Icelandic volcanism]] lies deep beneath the center of the island. The earliest volcanic rocks attributed to the plume are found on both sides of the Atlantic. Their ages have been determined to lie between 64 and 58 million years.<ref name=Ruedas2007>{{cite book|chapter =Iceland: The current picture of a ridge-centred mantle plume|year =2007|first1 =Thomas|last1 =Ruedas|first2 =Gabriele|last2 =Marquart|first3=Harro|last3 =Schmeling|doi =10.1007/978-3-540-68046-8_3|title =Mantle Plumes: A multidisciplinary approach|pages =71–126|publisher =Springer|editor-first1 =Joachim R. R.|editor-last1= Ritter|editor-first2 =Ulrich R.|editor-last2 =Christensen|url =https://www.researchgate.net/publication/264942825|isbn=9783540680451}}</ref>{{rp|pp=73-74}} This coincides with the opening of the north Atlantic in the late [[Paleocene]] and early [[Eocene]], which has led to suggestions that the arrival of the plume was linked to, and has perhaps contributed to, the breakup of<ref>
{{cite journal
{{cite journal
|last1=White |first1=R.
|last1=White |first1=R.
Line 213: Line 37:
|bibcode=1989JGR....94.7685W
|bibcode=1989JGR....94.7685W
|doi=10.1029/JB094iB06p07685
|doi=10.1029/JB094iB06p07685
}}</ref> North Atlantic continent. In the framework of the plume hypothesis, the volcanism was caused by the flow of hot plume material initially beneath thick continental lithosphere and then beneath the lithosphere of the growing ocean basin as rifting proceeded. The exact position of the plume at that time is a matter of disagreement between scientists,<ref>
}}</ref> [[Laurasia]]. In the framework of the plume hypothesis, the volcanism was caused by the flow of hot plume material initially beneath thick continental lithosphere and then beneath the lithosphere of the growing ocean basin as rifting proceeded. The exact position of the plume at that time is a matter of disagreement between scientists,<ref>
{{cite journal
{{cite journal
|last1=Lawver |first1=L. A.
|last1=Lawver |first1=L. A.
Line 470: Line 294:
===Bibliography===
===Bibliography===
*{{cite book|chapter =Iceland: The current picture of a ridge-centred mantle plume|year =2007|first1 =Thomas|last1 =Ruedas|first2 =Gabriele|last2 =Marquart|first3=Harro|last3 =Schmeling|doi =10.1007/978-3-540-68046-8_3|title =Mantle Plumes: A multidisciplinary approach|pages =71–126|publisher =Springer|editor-first1 =Joachim R. R.|editor-last1= Ritter|editor-first2 =Ulrich R.|editor-last2 =Christensen|url =https://www.researchgate.net/publication/264942825|isbn=9783540680451}}
*{{cite book|chapter =Iceland: The current picture of a ridge-centred mantle plume|year =2007|first1 =Thomas|last1 =Ruedas|first2 =Gabriele|last2 =Marquart|first3=Harro|last3 =Schmeling|doi =10.1007/978-3-540-68046-8_3|title =Mantle Plumes: A multidisciplinary approach|pages =71–126|publisher =Springer|editor-first1 =Joachim R. R.|editor-last1= Ritter|editor-first2 =Ulrich R.|editor-last2 =Christensen|url =https://www.researchgate.net/publication/264942825|isbn=9783540680451}}
*{{cite journal |last1=Allen |first1=R. M. |last2=Nolet |first2=G. |last3=Morgan |first3=W. J. |year=1999 |title=The thin hot plume beneath Iceland |journal=Geophysical Journal International |volume=137 |issue=1 |pages=51–63 |doi=10.1046/j.1365-246x.1999.00753.x |bibcode = 1999GeoJI.137...51A |display-authors=etal|citeseerx=10.1.1.412.695 |s2cid=14740389 }}
*{{cite journal |last1=Allen |first1=R. M. |last2=Nolet |first2=G. |last3=Morgan |first3=W. J. |year=1999 |title=The thin hot plume beneath Iceland |journal=Geophysical Journal International |volume=137 |issue=1 |pages=51–63 |doi=10.1046/j.1365-246x.1999.00753.x |doi-access=free |bibcode = 1999GeoJI.137...51A |display-authors=etal|citeseerx=10.1.1.412.695 |s2cid=14740389 }}
*{{cite journal |author-link=Gillian Foulger |last1=Foulger |first1=G. R. |author-link2=Don L. Anderson |last2=Anderson |first2=D. L. |year=2005 |title=A cool model for the Iceland hotspot |journal=Journal of Volcanology and Geothermal Research |volume=141 |issue=1–2 |pages=1–22 |doi=10.1016/j.jvolgeores.2004.10.007 |bibcode = 2005JVGR..141....1F }}
*{{cite journal |author-link=Gillian Foulger |last1=Foulger |first1=G. R. |author-link2=Don L. Anderson |last2=Anderson |first2=D. L. |year=2005 |title=A cool model for the Iceland hotspot |journal=Journal of Volcanology and Geothermal Research |volume=141 |issue=1–2 |pages=1–22 |doi=10.1016/j.jvolgeores.2004.10.007 |bibcode = 2005JVGR..141....1F }}
* {{cite book |last1=Morgan |first1=W. Jason |author-link1=W. Jason Morgan |last2=Morgan |first2=Jason Phipps |chapter=Plate velocities in hotspot reference frame: electronic supplement |year=2009 |title=Plates, Plumes, and Planetary Processes (P<sup>4</sup>) |editor1-last=Foulger |editor1-first=Gillian R. |editor2-last=Jurdy |editor2-first=Donna M. |chapter-url=http://www.mantleplumes.org/P%5E4/P%5E4Chapters/MorganP4ElectronicSupp1.pdf |url=http://www.mantleplumes.org/P%5E4/P%5E4.html}}
* {{cite book |last1=Morgan |first1=W. Jason |author-link1=W. Jason Morgan |last2=Morgan |first2=Jason Phipps |chapter=Plate velocities in hotspot reference frame: electronic supplement |year=2009 |title=Plates, Plumes, and Planetary Processes (P<sup>4</sup>) |editor1-last=Foulger |editor1-first=Gillian R. |editor2-last=Jurdy |editor2-first=Donna M. |chapter-url=http://www.mantleplumes.org/P%5E4/P%5E4Chapters/MorganP4ElectronicSupp1.pdf |url=http://www.mantleplumes.org/P%5E4/P%5E4.html}}

Latest revision as of 18:52, 6 October 2024

Eruption at Krafla, 1984
Active volcanic areas and systems in Iceland

The Iceland hotspot is a hotspot which is partly responsible for the high volcanic activity which has formed the Iceland Plateau and the island of Iceland. It contributes to understanding the geological deformation of Iceland.

Iceland is one of the most active volcanic regions in the world, with eruptions occurring on average roughly every three years (in the 20th and 21st century until 2010 there were 45 volcanic eruptions on and around Iceland).[1] About a third of the basaltic lavas erupted in recorded history have been produced by Icelandic eruptions. Notable eruptions have included that of Eldgjá, a fissure of Katla, in 934 (the world's largest basaltic eruption ever witnessed), Laki in 1783 (the world's second largest),[2] and several eruptions beneath ice caps, which have generated devastating glacial bursts, most recently in 2010 after the eruption of Eyjafjallajökull.

Iceland's location astride the Mid-Atlantic Ridge, where the Eurasian and North American Plates are moving apart, is partly responsible for this intense volcanic activity, but an additional cause is necessary to explain why Iceland is a substantial island while the rest of the ridge mostly consists of seamounts, with peaks below sea level.

As well as being a region of higher temperature than the surrounding mantle, the hotspot is believed to have a higher concentration of water. The presence of water in magma reduces the melting temperature, which may also play a role in enhancing Icelandic volcanism.

Theories of causation

[edit]

There is an ongoing discussion about whether the hotspot is caused by a deep mantle plume or originates at a much shallower depth.[3] Recently, seismic tomography studies have found seismic wave speed anomalies under Iceland, consistent with a hot conduit 100 km (62 mi) across that extends to the lower mantle.[4]

Foulger et al. believe the Icelandic plume reaches only to the mantle transition layer and can therefore not come from the same source as Hawaii.[5] Bijwaard and Spakman, however, believe the Icelandic plume does reach to the mantle, and therefore comes from the same source as Hawaii.[6] While the Hawaiian island chain and the Emperor Seamounts show a clear time-progressive volcanic track caused by the movement of the Pacific Plate over the Hawaiian hotspot, no such track can be seen at Iceland.

It is proposed that the line from Grímsvötn volcano to Surtsey shows the movement of the Eurasian Plate, and the line from Grímsvötn volcano to the Reykjanes volcanic belt shows the movement of the North American Plate.[7]

Mantle plume theory

[edit]

The Iceland plume is a postulated upwelling of anomalously hot rock in the Earth's mantle beneath Iceland. Its origin is thought to lie deep in the mantle, perhaps at the boundary between the core and the mantle at about 2,880 km (1,790 mi) depth. Opinions differ as to whether seismic studies have imaged such a structure.[8] In this framework, the volcanism of Iceland is attributed to this plume, according to the theory of W. Jason Morgan.[9]

It is believed that a mantle plume underlies Iceland, of which the hotspot is thought to be the surface expression, and that the presence of the plume enhances the volcanism already caused by plate separation. Additionally, flood basalts on the continental margins of Greenland and Norway, the oblique orientation of the Reykjanes Ridge segments to their spreading direction, and the enhanced igneous crustal thickness found along the southern Aegir and Kolbeinsey ridges may be results of interaction between the plume and the Mid-Atlantic Ridge.[10] The plume stem is believed to be quite narrow, perhaps 100 km (62 mi) across and extending down to at least 400–650 km (250–400 mi) beneath the Earth's surface, and possibly down to the core-mantle boundary, while the plume head may be greater than 1,000 km (620 mi) in diameter.[10][11]

It is suggested that the lack of a time-progressive track of seamounts is due to the location of the plume beneath the thick Greenland craton (Laurentia) for ~ 15 Myr after continental breakup,[12] and the later entrenchment of the plume material into the northern Mid-Atlantic Ridge following its formation.[10]

Geological history

[edit]

According to the plume model, the source of Icelandic volcanism lies deep beneath the center of the island. The earliest volcanic rocks attributed to the plume are found on both sides of the Atlantic. Their ages have been determined to lie between 64 and 58 million years.[13]: 73–74  This coincides with the opening of the north Atlantic in the late Paleocene and early Eocene, which has led to suggestions that the arrival of the plume was linked to, and has perhaps contributed to, the breakup of[14] Laurasia. In the framework of the plume hypothesis, the volcanism was caused by the flow of hot plume material initially beneath thick continental lithosphere and then beneath the lithosphere of the growing ocean basin as rifting proceeded. The exact position of the plume at that time is a matter of disagreement between scientists,[15] as is whether the plume is thought to have ascended from the deep mantle only at that time or whether it is much older and also responsible for the old volcanism in northern Greenland, on Ellesmere Island, and at Alpha Ridge in the Arctic.[16]

As the northern Atlantic opened to the east of Greenland during the Eocene, North America and Eurasia drifted apart; the Mid-Atlantic Ridge formed as an oceanic spreading center and a part of the submarine volcanic system of mid-oceanic ridges.[17] The initial plume head may have been several thousand kilometers in diameter, and it erupted volcanic rocks on both sides of the present ocean basin to produce the North Atlantic Igneous Province.[13]: 74  Upon further opening of the ocean and plate drift, the plume and the mid-Atlantic Ridge are postulated to have approached one another, and finally met. The excess magmatism that accompanied the transition from flood volcanism on Greenland, Ireland and Norway to present-day Icelandic activity was the result of ascent of the hot mantle source beneath progressively thinning lithosphere, according to the plume model, or a postulated unusually productive part of the mid-ocean ridge system.[18] Some geologists have suggested that the Iceland plume could have been responsible for the Paleogene uplift of the Scandinavian Mountains by producing changes in the density of the lithosphere and asthenosphere during the opening of the North Atlantic.[19] To the south the Paleogene uplift of the English chalklands that resulted in the formation of the Sub-Paleogene surface has also been attributed to the Iceland plume.[20]

An extinct ridge exists in western Iceland, leading to the theory that the plume has shifted east with time. The oldest crust of Iceland is more than 20 million years old and was formed at an old oceanic spreading center in the Westfjords (Vestfirðir) region.[13]: 74  The westward movement of the plates and the ridge above the plume and the strong thermal anomaly of the latter caused this old spreading center to cease 15 million years ago and lead to the formation of a new one in the area of today's peninsulas Skagi and Snæfellsnes; in the latter there is still some activity in the form of the Snæfellsjökull volcano. The spreading center, and hence the main activity, shifted eastward again 9 to 7 million years ago and formed the current volcanic zones in the south–west (Reykjanes, Hofsjökull) and north–east (Tjörnes). Presently, a slow decrease of the activity in the north–east takes place, while the volcanic zone in the south–east (Katla, Vatnajökull), which was initiated 3 million years ago, develops.[21] The reorganisation of the plate boundaries in Iceland has also been attributed to microplate tectonics,[18] and an independent Hreppar microplate exists.

Topography/bathymetry of the north Atlantic around Iceland

Challenges to the plume model

[edit]

The weak visibility of the postulated plume in tomographic images of the lower mantle and the geochemical evidence for eclogite in the mantle source have led to the theory that Iceland is not underlain by a mantle plume at all, but that the volcanism there results from processes related to plate tectonics and is restricted to the upper mantle.[22][3]

Subducted ocean plate

[edit]

According to one of those models, a large chunk of the subducted plate of a former ocean has survived in the uppermost mantle for several hundred million years, and its oceanic crust now causes excessive melt generation and the observed volcanism.[18] This model, however, is not backed by dynamical calculations, nor is it exclusively required by the data, and it also leaves unanswered questions concerning the dynamical and chemical stability of such a body over that long period or the thermal effect of such massive melting.

Upper mantle convection

[edit]

Another model proposes that the upwelling in the Iceland region is driven by lateral temperature gradients between the suboceanic mantle and the neighbouring Greenland craton and therefore also restricted to the upper 200–300 km (120–190 mi) of the mantle.[23] However, this convection mechanism is probably not strong enough under the conditions prevailing in the north Atlantic, with respect to the spreading rate, and it does not offer a simple explanation for the observed geoid anomaly.

Geophysical and geochemical observations

[edit]

Information about the structure of Earth's deep interior can be acquired only indirectly by geophysical and geochemical methods. For the investigation of postulated plumes, gravimetric, geoid and in particular seismological methods along with geochemical analyses of erupted lavas have proven especially useful. Numerical models of the geodynamical processes attempt to merge these observations into a consistent general picture.

Seismology

[edit]

An important method for imaging large-scale structures in Earth's interior is seismic tomography, by which the area under consideration is "illuminated" from all sides with seismic waves from earthquakes from as many different directions as possible; these waves are recorded with a network of seismometers. The size of the network is crucial for the extent of the region which can be imaged reliably. For the investigation of the Iceland Plume, both global and regional tomography have been used; in the former, the whole mantle is imaged at relatively low resolution using data from stations all over the world, whereas in the latter, a denser network only on Iceland images the mantle down to 400–450 km (250–280 mi) depth with higher resolution.

Regional studies from the 1990s and 2000s show that there is a low seismic-wave-speed anomaly beneath Iceland, but opinion is divided as to whether it continues deeper than the mantle transition zone at roughly 600 km (370 mi) depth.[17][24][25] The velocities of seismic waves are reduced by up to 3% (P waves) and more than 4% (S waves), respectively. These values are consistent with a small percentage of partial melt, a high magnesium content of the mantle, or elevated temperature. It is not possible to unambiguously separate out which effect causes the observed velocity reduction.

Geochemistry

[edit]

Numerous studies have addressed the geochemical signature of the lavas present on Iceland and in the north Atlantic. The resulting picture is consistent in several important respects. For instance, it is not contested that the source of the volcanism in the mantle is chemically and petrologically heterogeneous: it contains not only peridotite, the principal mantle rock type, but also eclogite, a rock type that originates from the basalt in subducted slabs and is more easily fusible than peridotite.[26][27] The origin of the latter is assumed to be metamorphosed, very old oceanic crust which sank into the mantle several hundreds of millions of years ago during the subduction of an ocean, then upwelled from deep within the mantle.

Studies using the major and trace-element compositions of Icelandic volcanics showed that the source of present-day volcanism was about 100 °C (212 °F) greater than that of the source of mid-ocean ridge basalts.[28]

The variations in the concentrations of trace elements such as helium, lead, strontium, neodymium, and others show clearly that Iceland is compositionally distinct from the rest of the north Atlantic. An example of this is seen in the ratio of helium-3 (3He) to helium-4 (4He) isotopes. The ratio of helium-3 and helium-4 is a marker that indicates the origin of the mantle involved in eruptions. Helium-3 is captured during planetary accretion, thus is associated with relatively deeper or lower mantle. Helium-4 is created from the decay of uranium and thorium parent isotopes. A low ratio of 3He to 4He is strongly correlated with mid ocean ridge eruptions due to its shallow source of mantle, while high ratios of 3He to 4He are correlated with ocean island basalts due to its deeper source of mantle. Both high and low ratios of 3He to 4He are found on Iceland. High ratios are associated with the western portion of the island, while lower ratios are associated with the eastern part of the island.[29] These ratio trends correlate well with geophysical anomalies, and the decrease of this and other geochemical signatures with increasing distance from Iceland. Combined, they indicate that the extent of the compositional anomaly reaches about 1,500 km (930 mi) along the Reykjanes Ridge and at least 300 km (190 mi) along the Kolbeinsey Ridge. Depending on which elements are considered and how large the area covered is, one can identify up to six different mantle components, which are not all present in any single location.

Furthermore, some studies show that the amount of water dissolved in mantle minerals is two to six times higher in the Iceland region than in undisturbed parts of the mid-oceanic ridges, where it is regarded to lie at about 150 parts per million.[30][31] The presence of such a large amount of water in the source of the lavas would tend to lower its melting point and make it more productive for a given temperature. It would also produce the higher melt temperatures found, than typical of mid-ocean ridge basalts.[13]: 106 

Gravimetry/Geoid

[edit]

The north Atlantic is characterized by strong, large-scale anomalies of the gravity field and the geoid. The geoid rises up to 70 m (230 ft) above the geodetic reference ellipsoid in an approximately circular area with a diameter of several hundred kilometers. In the context of the plume hypothesis, this has been explained by the dynamic effect of the upwelling plume which bulges up the surface of the Earth.[32] Furthermore, the plume and the thickened crust cause a positive gravity anomaly of about 60 mGal (=0.0006 m/s²) (free-air).

Free-air gravity anomalies in the north Atlantic around Iceland. For better representation the color scale was limited to anomalies up to +80 mGal (+0.8 mm/s²).

Geodynamics

[edit]

Since the mid-1990s several attempts have been made to explain the observations with numerical geodynamical models of mantle convection. The purpose of these calculations was, among other things, to resolve the paradox that a broad plume with a relatively low temperature anomaly is in better agreement with the observed crustal thickness, topography, and gravity than a thin, hot plume, which has been invoked to explain the seismological and geochemical observations.[33][34] The most recent models prefer a plume that is 180–200 °C (356–392 °F) hotter than the surrounding mantle and has a stem with a radius of about 100 km (62 mi).[13]: 71  Such temperatures have not yet been confirmed by petrology, however.

Magma Transportation Under Iceland

[edit]

Understanding how magma is transported from great depths near the Moho discontinuity to the surface has implications for understanding the mechanics of magma movement under Iceland. A study on the Borgarhraun basalt flow helped to constrain the velocity of magma transport from great depths to the surface.[35] Geothermal barometry and statistical analysis of aluminium within olivine crystals allowed the researchers to determine the depth that these crystals were formed in and how long it took them to reach the surface. In this case, the magma was originally at a depth of 24 km (15 mi). The resulting velocity of the magma ascension was calculated to be 0.02-0.1 m/s so that magma takes a mean of 10 days to reach the surface of Iceland from the Moho discontinuity which is faster than previously thought.[35]

See also

[edit]

References

[edit]

Notes

[edit]
  1. ^ "Hversu mörg eldgos hafa verið á Íslandi síðustu fimmtíu árin?". Vísindavefurinn (in Icelandic).
  2. ^ Bindeman, Ilya; Gurenko, Andrey; Sigmarsson, Olgeir; Chaussidon, Marc (1 September 2008). "Oxygen isotope heterogeneity and disequilibria of olivine crystals in large volume Holocene basalts from Iceland: Evidence for magmatic digestion and erosion of Pleistocene hyaloclastites". Geochimica et Cosmochimica Acta. 72 (17): 4397–4420. Bibcode:2008GeCoA..72.4397B. doi:10.1016/j.gca.2008.06.010.
  3. ^ a b Foulger, G. R. (8 February 2005). "Iceland & the North Atlantic Igneous Province". MantlePlumes.org. Retrieved 2008-03-22.
  4. ^ Rickers, Florian; Fichtner, Andreas; Trampert, Jeannot (1 April 2013). "The Iceland–Jan Mayen plume system and its impact on mantle dynamics in the North Atlantic region: Evidence from full-waveform inversion". Earth and Planetary Science Letters. 367: 39–51. Bibcode:2013E&PSL.367...39R. doi:10.1016/j.epsl.2013.02.022. hdl:20.500.11850/77780.
  5. ^ Foulger, G. R.; Pritchard, M. J.; Julian, B. R.; Evans, J. R. (1 September 2000). "The seismic anomaly beneath Iceland extends down to the mantle transition zone and no deeper". academic.oup.com. pp. F1 – F5.
  6. ^ Bijwaard, Harmen; Spakman, Wim (15 March 1999). "Tomographic evidence for a narrow whole mantle plume below Iceland". Earth and Planetary Science Letters. 166 (3–4): 121–126. Bibcode:1999E&PSL.166..121B. doi:10.1016/S0012-821X(99)00004-7.
  7. ^ Morgan, W. Jason; Morgan, Jason Phipps (2009). "Plate velocities in hotspot reference frame: electronic supplement" (PDF). In Foulger, Gillian R.; Jurdy, Donna M. (eds.). Plates, Plumes, and Planetary Processes (P4).
  8. ^ Ritsema, J.; Van Heijst, H. J.; Woodhouse, J. H. (1999). "Complex shear wave velocity structure imaged beneath Africa and Iceland". Science. 286 (5446): 1925–1928. doi:10.1126/science.286.5446.1925. PMID 10583949. S2CID 46160705.
  9. ^ Morgan, W. J. (1971). "Convection Plumes in the Lower Mantle". Nature. 230 (5288): 42–43. Bibcode:1971Natur.230...42M. doi:10.1038/230042a0. S2CID 4145715.
  10. ^ a b c Howell, Samuel M.; Ito, Garrett; Breivik, Asbjørn J.; Rai, Abhishek; Mjelde, Rolf; Hanan, Barry; Sayit, Kaan; Vogt, Peter (15 April 2014). "The origin of the asymmetry in the Iceland hotspot along the Mid-Atlantic Ridge from continental breakup to present-day". Earth and Planetary Science Letters. 392: 143–153. Bibcode:2014E&PSL.392..143H. doi:10.1016/j.epsl.2014.02.020. hdl:10125/41133.
  11. ^ Dordevic, Mladen; Georgen, Jennifer (1 January 2016). "Dynamics of plume–triple junction interaction: Results from a series of three-dimensional numerical models and implications for the formation of oceanic plateaus". Journal of Geophysical Research: Solid Earth. 121 (3): 2014JB011869. Bibcode:2016JGRB..121.1316D. doi:10.1002/2014JB011869. ISSN 2169-9356.
  12. ^ Mihalffy, Peter; Steinberger, Bernhard; Schmeling, Harro (1 February 2008). "The effect of the large-scale mantle flow field on the Iceland hotspot track". Tectonophysics. Plate movement and crustal processes in and around Iceland. 447 (1–4): 5–18. Bibcode:2008Tectp.447....5M. doi:10.1016/j.tecto.2006.12.012.
  13. ^ a b c d e Ruedas, Thomas; Marquart, Gabriele; Schmeling, Harro (2007). "Iceland: The current picture of a ridge-centred mantle plume". In Ritter, Joachim R. R.; Christensen, Ulrich R. (eds.). Mantle Plumes: A multidisciplinary approach. Springer. pp. 71–126. doi:10.1007/978-3-540-68046-8_3. ISBN 9783540680451.
  14. ^ White, R.; McKenzie, D. (1989). "Magmatism at rift zones: The generation of volcanic continental margins and flood basalts". Journal of Geophysical Research: Solid Earth. 94 (B6): 7685. Bibcode:1989JGR....94.7685W. doi:10.1029/JB094iB06p07685.
  15. ^ Lawver, L. A.; Muller, R. D. (1994). "Iceland hotspot track". Geology. 22 (4): 311–314. Bibcode:1994Geo....22..311L. doi:10.1130/0091-7613(1994)022<0311:IHT>2.3.CO;2.
  16. ^ Forsyth, D. A.; Morel-A-L'Huissier, P.; Asudeh, I.; Green, A. G. (1986). "Alpha Ridge and iceland-products of the same plume?". Journal of Geodynamics. 6 (1–4): 197–214. Bibcode:1986JGeo....6..197F. doi:10.1016/0264-3707(86)90039-6.
  17. ^ a b Wolfe, C. J.; Bjarnason, I. Th.; VanDecar, J. C.; Solomon, S. C. (1997). "Seismic structure of the Iceland mantle plume". Nature. 385 (6613): 245–247. Bibcode:1997Natur.385..245W. doi:10.1038/385245a0. S2CID 4353383.
  18. ^ a b c Foulger, G. R.; Anderson, D. L. (2005). "A cool model for the Iceland hotspot". Journal of Volcanology and Geothermal Research. 141 (1–2): 1–22. Bibcode:2005JVGR..141....1F. doi:10.1016/j.jvolgeores.2004.10.007.
  19. ^ Nielsen, S. B.; et al. (2002). "Paleocene initiation of Cenozoic uplift in Norway". In Doré, A. G.; Cartwright, J. A.; Stoker, M. S.; Turner, J. P.; White, N. (eds.). Exhumation of the North Atlantic Margin: Timing, Mechanisms and Implications for Petroleum Exploration. Geological Society, London, Special Publications. Vol. 196. Geological Society of London. pp. 103–116. Bibcode:2002GSLSP.196...45N. doi:10.1144/GSL.SP.2002.196.01.04. S2CID 128675048.
  20. ^ Gale, Andrew S.; Lovell, Bryan (2018). "Proceedings of the Geologists' Association". The Cretaceous–Paleogene Unconformity in England: Uplift and Erosion Related to the Iceland Mantle Plume. 129 (3): 421–435. doi:10.1016/j.pgeola.2017.04.002. S2CID 133817989.
  21. ^ Sæmundsson, K. (1979). "Outline of the geology of Iceland" (PDF). Jökull. 29: 7–28. doi:10.33799/jokull1979.29.007. S2CID 257227875.
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Bibliography

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64°24′00″N 17°18′00″W / 64.4000°N 17.3000°W / 64.4000; -17.3000

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