My whole startup disk has gone blank
Granted that gparted didn't erase/secure erase data (overwriting important parts of your disk with zeros or arbitrary data) you probably can recreate the old standard GUID partition table which follows a fixed Apple scheme. gparted or similar gpt partitioning executables usually only modify the first and last 34 blocks (512 B) or 6 blocks (4096 B) of a disk. 

The fast approach below won't work, if you've modified the disk previously (e.g installed Windows, resized the main volume and added a second partition). It only works with the "vanilla" OS X install partition scheme.

Recreating the old GUID partition table should restore the previous volume(s). Here is a related answer: HFS+ invalid number of allocation blocks.

The standard Apple GUID partition scheme looks like that:

                0           1         PMBR
                1           1         Pri GPT header
                2          32         Pri GPT table
               34           6         
               40      409600      1  GPT part - C12A7328-F81F-11D2-BA4B-00A0C93EC93B
           409640  part2-size      2  GPT part - partition type
part2-size+409640     1269536      3  GPT part - 426F6F74-0000-11AA-AA11-00306543ECAC
    total_size-40           7         
    total_size-33          32         Sec GPT table
     total_size-1           1         Sec GPT header


Here total-size is the total size of the disk in 512 B-blocks. part2-size usually is total-size - 1679216 in 512 B-blocks.

The partition type of the second partition is either 53746F72-6167-11AA-AA11-00306543ECAC (CoreStorage) or 48465300-0000-11AA-AA11-00306543ECAC (HFS+).

Newer systems on SSDs preferably have a CoreStorage- and older systems on HDDs an HFS+-type main partition.

Preparation:


Detach any external drive
Restart to Internet Recovery Mode by pressing alt cmd R at startup. 

The prerequisites are the latest firmware update installed, either ethernet or WLAN (WPA/WPA2) and a router with DHCP activated.
On a 50 Mbps-line it takes about 4 min (presenting a small animated globe) to boot into a recovery netboot image which usually is loaded from an Apple/Akamai server.

I recommend ethernet because it's more reliable. If you are restricted to WIFI and the boot process fails, just restart your Mac until you succeed booting.

Alternatively you may start from a bootable installer thumb drive (preferably Yosemite or El Capitan) or a thumb drive containing a full system (preferably Yosemite or El Capitan). If you boot to a full system and login as admin you have to prepend sudo to execute some commands like gpt ... or newfs_hfs ...!


Remove the an old/wrong MBR/GUID partition table


Enter diskutil list and gpt -r show /dev/diskX (with x=0,1,2,3 etc) to get an overview. Usually the internal disk has the disk identifier disk0. Below I assume your internal disk is disk0.
Enter gpt destroy /dev/disk0 to remove any current GUID pt.
Enter gpt create -f /dev/disk0 to create a new empty GPT partition table and replace any MBR by an PMBR.


Restore previous partitions


EFI:

gpt add -b 40 -i 1 -s 409600 -t C12A7328-F81F-11D2-BA4B-00A0C93EC93B /dev/disk0

Recovery partition:

Now do the math: the start block $sbrecovery of the Recovery HD is total-size - 1269576. $sbrecovery has to be dividable by 8!

gpt add -b $sbrecovery -i 3 -s 1269536 -t C12A7328-F81F-11D2-BA4B-00A0C93EC93B /dev/disk0

Main volume

Do the math again: the size of the volume $mainvolumesize is total-size - 1679216. $mainvolumesize has to be divisible by 8! Your main volume may either be a CoreStorage or a HFS+-type partition. Here I assume it's the first one: 

gpt add -b 409640 -i 2 -s $mainvolumesize -t 53746F72-6167-11AA-AA11-00306543ECAC /dev/disk0

Now check if diskutil list finds a CoreStorage volume:

diskutil cs list


If the GUUID partition table is properly restored and your main partition was a CoreStorage volume you should get an output similar to this one:

  CoreStorage logical volume groups (1 found)
|
+-- Logical Volume Group A629E051-D7B0-4B8C-A803-074F62704636
    =========================================================
    Name:         System
    Status:       Online
    Size:         53946696192 B (53.9 GB)
    Free Space:   16777216 B (16.8 MB)
    |
    +-&lt; Physical Volume 90C09FC0-4215-4871-901B-70E2C9C7D464
    |   ----------------------------------------------------
    |   Index:    0
    |   Disk:     disk0s2
    |   Status:   Online
    |   Size:     53946696192 B (53.9 GB)
    |
    +-&gt; Logical Volume Family F6962E38-50E4-4458-BFE6-CF2E179352F5
        ----------------------------------------------------------
        Encryption Status:       Unlocked
        Encryption Type:         None
        Conversion Status:       NoConversion
        Conversion Direction:    -none-
        Has Encrypted Extents:   No
        Fully Secure:            No
        Passphrase Required:     No
        |
        +-&gt; Logical Volume BD36C73D-860D-4DC6-B125-AD624F448B88
            ---------------------------------------------------
            Disk:                  disk2
            Status:                Online
            Size (Total):          53496696192 B (53.5 GB)
            Conversion Progress:   -none-
            Revertible:            Yes (no decryption required)
            LV Name:               System
            Volume Name:           System
            Content Hint:          Apple_HFS

verify the CoreStorage volume with

diskutil verifyVolume diskX 


(in the above CoreStorage example diskX is disk2 - check (Disk of Logical Volume), your diskX probably is disk14 or disk15)


If you get an error or no output your main volume either is a HFS+-type partition or the boundaries of the partition are wrong. 


Then try the following and remove the CoreStorage-type partition and create an HFS+-type partition instead:

gpt remove -i 2 /dev/disk0
gpt add -b 409640 -i 2 -s $mainvolumesize -t 48465300-0000-11AA-AA11-00306543ECAC /dev/disk0

Verify the volume:

diskutil verifyVolume /dev/disk0s2





If you run into problems or get strange errors please post a comment to the answer!